A near-Earth object that astronomers believed was an asteroid for nearly three decades has been unmasked as a faint, active comet, revealing a case of cosmic mistaken identity that could help improve planetary defense.

The object, known since its discovery in 1998 as 1998 SH2, appeared to be an ordinary asteroid. It follows a 4.5-year orbit around the sun and showed no obvious signs of cometary activity, such as the glowing coma or tail produced when sunlight vaporizes surface ice.

However, during a close pass about 2 million miles (3 million kilometers) from Earth in August 2025, researchers using NASA's Deep Space Network planetary radar system noticed something unexpected: The object wasn't where orbital predictions said it should be, according to a statement from the space agency. That discrepancy prompted scientists to take a closer look, and what they found surprised them.

Using decades of precision optical astrometry — measurements of the object's position against background stars — researchers found that gravity alone couldn't explain its irregular motion. Instead, they detected tiny nongravitational forces consistent with jets of gas escaping from the object's surface as hidden ice warmed in sunlight.

"After we measured the nongravitational perturbations affecting the motion of 1998 SH2 and recognized they weren't compatible with the object being an asteroid, we suspected the object could be an active comet," Davide Farnocchia, lead author of the study and navigation engineer with NASA's Center for Near-Earth Object Studies at the Jet Propulsion Laboratory, said in the statement.

To test the idea, the team observed the object with the European Southern Observatory's Very Large Telescope in Chile and the Canada-France-Hawaii Telescope atop Mauna Kea. The observations revealed a faint but unmistakable comet tail, confirming the object's true identity.

The discovery earned 1998 SH2 a second designation: P/1998 SH2, officially recognizing it as a comet. Beyond solving the mystery, the finding has important implications for planetary defense.

Unlike rocky asteroids, comets can subtly change course as gas escaping from their surfaces acts like tiny thrusters. Identifying those nongravitational forces allows scientists to more accurately predict an object's future orbit and assess any potential impact risk.

"This work shows the importance of continuously tracking near-Earth objects," Farnocchia said in the statement. "Because of outgassing, the motion of comets is more significantly perturbed than that of asteroids.

"Detecting these perturbations can be an important diagnostic tool for planetary defense that will help understand which objects may be comets rather than asteroids, how their orbits evolve, and how that influences their Earth impact risks."

The study also suggests that 1998 SH2 may not be unique. The researchers noted that analyzing the motions of near-Earth objects with increasingly precise astrometry could reveal more hidden comets that have long been classified as asteroids because they lack obvious tails or glowing comas.

As astronomers continue to monitor the growing population of near-Earth objects, subtle orbital changes may prove just as revealing as spectacular comet tails, uncovering more examples of cosmic mistaken identity while helping scientists better understand which objects pose potential threats to Earth.

Their findings were published July 10 in the journal Nature Astronomy.

More evidence that the interstellar comet 3I/ATLAS is much older than our solar system has come to light, along with clues that it formed on the outskirts of the protoplanetary disk belonging to its parent star long ago.

Earlier this year, researchers led by Martin Cordiner of NASA's Goddard Space Flight Center revealed that data from the James Webb Space Telescope (JWST) suggested that 3I/ATLAS is between 10 and 12 billion years old, based on the ratios of its carbon and deuterium isotopes. This would make it more than twice the age of our 4.6-billion-year-old solar system. Now, new results from the Ultraviolet and Visual Echelle Spectrograph (UVES) on the European Southern Observatory's Very Large Telescope support the JWST observations of carbon isotopes, and also introduce measurements of nitrogen isotopes that arrive at very interesting conclusions.

Isotopes are versions of atomic elements with different numbers of neutrons. For example, carbon-12 contains six protons and six neutrons, while carbon-13 contains six protons and seven neutrons. Meanwhile nitrogen-14 has seven protons and neutrons each, while nitrogen-15 has seven protons and eight neutrons.

These isotopes can form through subtly different processes, at different times and in different locations in the galaxy. The ratio of these isotopes in the gases released by comet 3I/ATLAS into its coma and tail as it neared the sun and grew warmer can therefore tell us much about its origin and history.

Consequently, interstellar objects such as 3I/ATLAS "are sort of fossils from a planetary formation process that happened very far away, but we get the chance to study from much closer," said astronomer Cyrielle Opitom of the University of Edinburgh in a statement.

Opitom led the team who got the chance to observe 3I/ATLAS with the VLT. They found that the ratio of carbon-12 to carbon-13 is higher than is found in comets in our solar system or indeed in the local interstellar medium. Carbon-13 is produced in greater abundances than carbon-12 over time, typically in red giant stars, so for there to be far more carbon-12 than carbon-13 tells us that 3I/ATLAS was born long ago before carbon-13 had a chance to build in abundance across the galaxy. This finding supports the JWST carbon isotope measurements.

Additionally Opitom's team, which was co-led by Jean Manfroid and Damien Hutsemékers of the University of Liège in Belgium, measured a ratio of nitrogen-14 to nitrogen-15 in 3I/ATLAS that is more than twice as large as the value measured in comets native to our solar system. In fact, the ratio is typical of that found on the outer edge of planet-forming discs around young stars, implying 3I/ATLAS formed a long way out from its parent star, perhaps in the equivalent of its Kuiper belt.

"Unlike comets from our solar system, this interstellar visitor carries unusually high carbon and nitrogen isotopic ratios," said team-member Aravind Krishnakumar, who is also of the University of Liège.

The results give us clues to how 3I/ATLAS found itself wandering the space lanes alone for billions of years. Models indicate that migrating giant planets can kick small bodies into interstellar space, but the location of 3I/ATLAS's birth far from that planetary action means that it is quite possible instead that it was snatched from its parent star by the gravity of a passing star and was subsequently hurled into deep space.

The JWST had also previously shown that 3I/ATLAS is rich in carbon monoxide and carbon dioxide relative to water, and also contains unexpectedly high abundances of nickel and iron and a very high abundance of methanol relative to hydrogen cyanide – all of which tells us that 3I/ATLAS formed in an environment with conditions and chemistry notably alien to our own solar system.

Unfortunately similar measurements were not possible with the other two known interstellar objects – 1I/'Oumuamua was not seen to outgas, while 2I/Borisov was too faint. However, 3I/ATLAS is a tantalizing indication that studies of more interstellar objects caught entering our solar system will be able to teach us about planet-forming conditions across both space and time in our Milky Way galaxy.

"3I/ATLAS is a really exciting opportunity to probe the composition of another planetary system, one that formed long before our Sun and solar system even existed," concluded Rosemary Dorsey, an astronomer from the University of Helsinki in Finland.

The findings were published on July 6 in the journal Nature Astronomy.

NASA's James Webb Space Telescope is finding clues that are leading scientists closer to understanding the origins of the interstellar comet 3I/ATLAS.

What is it?

Comet 3I/ATLAS captured the world's attention when it was discovered nearly a year ago on July 1, 2025. The comet was first spotted by the Asteroid Terrestrial-impact Last Alert System (ATLAS), and is only the third interstellar object every discovered.

The comet swooped through our solar system, passing by Earth at a far (and safe) distance on its tour of our cosmic neighborhood. It is on a long trajectory that will take it out of our solar system, never to return.

In observations from the James Webb Space Telescope, scientists were able to look in the direction the comet as it began moving away from the sun in December of last year. While in close proximity to our star, the sun's heat warmed the comet, making it extra bright and easy to observe.

With this view, astronomers were able to calculate some of the ratios of the chemicals present in the comet. This further highlighted that the object is from out of our solar system, as they found ratios of carbon and heavy hydrogen not found in comets in our solar system.

Researchers described their results in a new paper published June 22 in the journal Nature.

Why is it incredible?

Being only the third interstellar object ever found, people were excited about 3I/ATLAS. They were so excited, in fact, that conspiracies about the object sprouted up quickly. Due to it being from outside of our solar system, some claimed that the comet could be some sort of alien spaceship, similar to the initial suspicions about the interstellar object 'Oumuamua found years earlier.

But with new information coming in from space telescopes, and astronomers eager to understand this object better, these clues are leading us closer and closer to the true origins of this strange comet.

Methane has been seen spewing from comet 3I/ATLAS, marking the first time that the gas has been identified on an interstellar object. The amount of methane, relative to water, is also larger than is typically seen in comets from our solar system, further highlighting how different this interstellar visitor is than objects from our own cosmic neighborhood.

The James Webb Space Telescope (JWST) initially observed the interstellar comet with its Mid-Infrared Instrument (MIRI) on Dec. 15-16 2025, when 3I/ATLAS was 205 million miles (330 million kilometers or 2.20 astronomical units) from the sun. However, there was a problem with two of the observations, which failed to acquire a guide-star in order for the telescope to point accurately. This meant that those two observations had to be repeated later, on Dec. 27, when 3I/ATLAS was 236 million miles (380 million km or 2.54 AU) from the sun.

As it happened, these repeat observations turned out to be quite fortuitous.

Both sets of observations came less than two months after 3I/ATLAS had reached perihelion – its closest point to the sun – on Oct. 29, 2025. The extra heating from the sun had warmed the comet’s surface, increasing the amount of outgassing from the comet, but the level of outgassing was beginning to decrease as the comet moved away.

MIRI detected water vapor streaming at large distances from the comet's nucleus as icy grains in the coma (the gaseous ‘atmosphere’ surrounding the comet’s solid nucleus) vaporized.

However, this is where the observations on the Dec. 27 came into play: JWST noted that the production of water vapor had dropped sharply between Dec. 16 and 27, indicating that solar heating was fading and more water-ice was staying frozen, especially since by then 3I/ATLAS had crossed the 'snow line', which is the distance from the sun beyond which temperatures are low enough for water vapor to freeze to ice.

"The water-ice line in the solar system is located around 2.5AU, and as 3I ATLAS approached those heliocentric distances … water production from the coldest regions of 3I’s surface and coma was starting to shut down," wrote the research team, led by Caltech's Matthew Belyakov, in their science paper. "Meanwhile, because of their much lower vapor pressures, carbon dioxide and methane are expected to have remained fully activated."

JWST also detected carbon-dioxide gas and even nickel vapor, matching previous observations and confirming that 3I/ATLAS has a surprisingly large abundance of carbon dioxide relative to water vapor.

Most intriguing, though, was the detection of methane for the first time. Though not a rare gas, it hadn’t been detected on either of the previous two interstellar objects seen to pass through the solar system, and only became apparent on 3I/ATLAS after perihelion.

The reason for its delayed appearance is probably because the methane is buried deeper into the cometary nucleus and it took time for the Sun’s heat to reach those depths and warm the methane enough for it to sublimate and burst out. Once upon a time the comet probably did have methane closer to, or even on, the surface, but it was lost to space long ago.

"This could imply that 3I previously underwent a period of significant heating within its natal planetary system prior to its ejection into the cold interstellar medium that depleted the methane in the outermost layers," wrote the researchers. "Consequently, the surviving reservoir of primordial methane-ice resides at depth and was only fully activated after the thermal wave induced by 3I’s perihelion passage propagated into the interior."

They also point out that the delayed production of methane is mirrored by a similar delayed production of carbon monoxide outgassing, which became notable in December by undergoing a 40-fold increase relative to carbon dioxide.

Another fascinating facet is that, like carbon dioxide, methane also has a surprisingly high abundance relative to water on 3I/ATLAS.

Yet while the ratio of methane and carbon dioxide to water seems unusually high for our solar system, it could be quite ordinary for the star system in which 3I/ATLAS formed, possibly as long ago as 11–12 billion years. Those ratios indicate that 3I/ATLAS must have formed in a somewhat different environment compared to the one in which the comets native to our solar system formed, with different physical conditions and a different chemistry.

These findings illustrate the importance of studying interstellar objects, in that they give us a view into other planet-forming environments that we wouldn't otherwise get. In turn, these insights can provide comparisons that can teach us more about how our own solar system and Earth formed.

The results were reported in The Astrophysical Journal Letters.

Sorry, true believers: It appears the interstellar comet 3I/ATLAS is indeed just a comet.

Radio astronomers recently hunted for "technosignatures" coming from 3I/ATLAS, which is just the third confirmed interstellar object ever seen in our solar system. As expected, that search came up empty — but it still gathered valuable data, the scientists said.

"The results from 3I/ATLAS show how realistic it is to detect a signal with the technology we have today," study co-author Valeria Garcia Lopez, of Furman University in South Carolina, said in a statement Wednesday (June 3). "That is why it is important to keep searching for technosignatures, even from objects we might not expect to have signals."

3I/ATLAS was first seen on July 1, 2025 by the Deep Random Survey remote telescope in Chile, which is part of the ATLAS (Asteroid Terrestrial-impact Last Alert System) project.

That explains "ATLAS" in the object's name. "3I" indicates that it's the third known interstellar interloper, after 1I/'Oumuamua and 2I/Borisov, which were discovered zooming through our neck of the cosmic woods in 2017 and 2019, respectively.

Telescope observations strongly suggest all three of these visitors are natural objects — namely, comets that were born in other solar systems and subsequently booted into interstellar space, likely via gravitational interactions.

However, it's still worth studying such bodies in detail, according to lead author Sofia Sheikh, who's based at the SETI (Search for Extraterrestrial Intelligence) Institute in California.

"Eventually, our own Voyager spacecraft will be extraterrestrial artifacts in other stellar systems," Sheikh said in the same statement. "Given that, it is important that we understand the natural distribution of interstellar objects so that we will be able to identify any anomalies that could one day be signs of an artificial interstellar object."

There's also the possibility, however remote, that one or more of these interstellar objects could actually be the product of alien intelligence. Indeed, that hypothesis has been advanced to explain 'Oumuamua's perceived weirdness.

So Sheikh and her team studied 3I/ATLAS using the SETI Institute's Allen Telescope Array, a network of radio dishes at the Hat Creek Radio Observatory in Northern California, not long after the comet's discovery. They collected more than seven hours of observations, looking for "narrowband" radio signals — emissions that aren't produced by any known natural phenomenon.

The researchers identified nearly 74 million such signals, which they then culled to about 200 after eliminating human interference and filtering out artifacts caused by 3I/ATLAS' movement. They were then able to explain away those final 200 as well, as signals generated here on Earth or by orbiting satellites.

The new study, which was published online Wednesday in The Astronomical Journal, "sets new constraints reinforcing that 3I/ATLAS is a natural object," SETI Institute officials wrote in the same statement.

"The observations place upper limits on the power of any radio transmitter on or near 3I/ATLAS, ruling out signals stronger than about 10-110 watts, approximately the power of a household appliance, over the detected frequencies," they added.

It turns out interstellar comet 3I/ATLAS was almost called 3I/Rubin, after researchers found that the giant survey telescope coincidentally spotted this visitor from the stars over a week before it was officially discovered.

3I/ATLAS was officially identified on July 1, 2025 by the Asteroid Terrestrial-impact Last Alert System (ATLAS), which is a network of robotic telescopes in Hawaii, Chile and South Africa. But ten days before, the Vera C. Rubin Observatory, which is also in Chile, began its science validation phase ahead of entering full operation later that year. The science validation phase was designed to calibrate the 27.6-foot (8.4-meter) telescope and its instruments, to ensure that they were working correctly.

Curious as to whether Rubin had seen 3I/ATLAS before its official discovery date, a team led by Colin Orion Chandler of the University of Washington went sifting through the data from Rubin's commissioning phase. Lo and behold, they found that Rubin had imaged 3I/ATLAS on its very first night of taking practice images, on June 20, ten days before ATLAS spotted it.

It wasn't an easy task. Today Rubin has a very well planned out routine — called a 'pipeline' — for taking data and processing it for astronomers, but back during the validation phase the pipeline was not in operation. This meant that Chandler and his team had to devise their own custom pipeline to access the data.

Chandler estimates that if Rubin had begun its science validation phase a few weeks earlier, its data-handling pipelines might have been up and running in time to snag 3I/ATLAS before July 1.

The researchers found that Rubin proceeded to image the interstellar comet a further nine times between June 21 and July 2, and several more times between July 2 and July 20. The images clearly show that 3I/ATLAS was active even before ATLAS detected it, with an obvious coma — a cloud of dust and gas around the head of a comet that is liberated from the comet's surface when it heats up as it nears the sun.

Rubin is designed to find up to 10,000 new comets over the 10-year lifetime of its initial Legacy Survey of Space and Time, and Rubin's early detection of 3I/ATLAS bodes well for estimates that it could find, on average, one interstellar comet passing through our solar system each year. So while 3I/ATLAS doesn't bear Rubin's name, it's a good bet that future interstellar comets will.

Jupiter probes team up

Meanwhile, 3I/ATLAS hasn't left our solar system yet, and new information is still being revealed by spacecraft that have been keeping an eye on it. Observations by spacecraft came in particularly useful when the comet was hidden behind the sun from our point of view in October 2025, which coincided with perihelion (closest approach to the sun) when then comet was expected to be most active.

Scientists at the South-west Research Institute (SwRI) who lead the Ultraviolet Spectrograph (UVS) instruments on the European Space Agency's JUICE mission and NASA's Europa Clipper, both currently on their way to Jupiter, have revealed that the two spacecraft made joint observations of 3I/ATLAS in late 2025.

"As the comet passed between JUICE and Europa Clipper, we were able to informally coordinate observations between the two spacecraft," said SwRI's Kurt Retherford in a statement.

JUICE had a view of the interstellar comet's dayside, while Europa Clipper saw its nightside, allowing researchers to see the same gas emissions from two different directions.

The joint observations by the UVS instrument on each spacecraft detected hydrogen, oxygen and carbon that were produced when molecular gases escaping 3I/ATLAS's nucleus interacted with ultraviolet light from the sun, which broke the molecules apart into their component atoms. The abundance of carbon was higher than is typical for comets native to our solar system, which confirms James Webb Space Telescope observations that found excess carbon dioxide on 3I/ATLAS.

"By studying the ratio of water-ice and dry ice [i.e. carbon-dioxide ice], we can compare the composition of this interstellar comet to comets native to our solar system," said SwRI's Philippa Molyneux. "This helps us understand if the solar system where 3I/ATLAS formed is similar to ours or different."

These findings add to the bounty of data on 3I/ATLAS already gathered by multiple space missions and ground-based observations. We know that the nucleus of 3I/ATLAS is about a kilometer (0.6 miles) wide, and its high velocity of 140,000 mph (61 kilometers per second) suggests that it is probably at least seven billion years old and possibly up to 12 billion years old, and has experienced many encounters with other stars that have boosted its velocity.

The analysis of Rubin's observations of the comet were published on April 20 in The Astrophysical Journal Letters.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), scientists have discovered that the interstellar invader comet 3I/ATLAS formed in a much colder region of the Milky Way than our solar system.

The discovery came about when scientists made the first-ever measurement of so-called semi-heavy water (or deuterated water) for an object that originated beyond the solar system. Deuterated water refers to water in which one hydrogen atom is replaced with deuterium, a heavy hydrogen isotope that has an atomic nucleus composed of one proton and one neutron. ALMA's measurements of deuterated water revealed that 3I/ATLAS contains around 30 times as much semi-heavy water as is found in comets that originate in the solar system.

The findings indicate that 3I/ATLAS, just the third interstellar object discovered passing through the solar system, formed in a much more frigid region of space compared to our planetary backyard.

"Our new observations show that the conditions that led to the formation of our solar system are much different from how planetary systems evolved in different parts of our galaxy," team leader Luis E. Salazar Manzano at the University of Michigan said in a statement.

Manzano and colleagues studied 3I/ATLAS as it reached its closest point to the sun, a feat made possible by the ability of ALMA's 66 radio antennas to point toward the sun, something optical telescopes can't do because of the glare of sunlight.

An interstellar snowball

The high water content of comets in the solar system means that they are often referred to as "dirty snowballs." This water contains a record of the chemistry of the environment in which the comets formed at the time of their birth, which for comets in our solar system was around 4.6 billion years ago, when planets were also forming around the infant sun.

Comets don't just contain ordinary water composed of two hydrogen atoms with nuclei composed of just one proton bonded to an oxygen atom  — they also contain molecules of deuterated water. In the comets of the solar system, one molecule of deuterated water exists for every 10,000 molecules of ordinary water, but the ratio of semi-heavy water to water is 30 times greater for 3I/ATLAS than this. This is, in turn, 40 times greater than the same ratio in the oceans of Earth.

This elevated ratio points to 3I/ATLAS having formed in an exceptionally cold and chemically distinct environment somewhere else in the Milky Way.

"The chemical processes that lead to the enhancement of deuterated water are really sensitive to temperature and usually require environments colder than about 30 Kelvin, or about minus 406 degrees Fahrenheit [207 degrees Celsius]," Manzano said.

The ratio acts as a record of the chemical environment of 3I/ATLAS' home system, having remained intact throughout the interstellar invader's long journey to the solar system. The ratio is also an important one because abundances of deuterium and hydrogen throughout the universe are thought to have been set during the Big Bang itself.

"Each interstellar comet brings a little bit of its history, its fossils, from elsewhere," team member Teresa Paneque-Carreño of the University of Michigan said. "We don't know exactly where, but with instruments like ALMA, we can begin to understand the conditions of that place and compare them to our own."

The team's research was published on Thursday (April 23) in the journal Nature Astronomy.

The interstellar comet 3I/ATLAS' chemistry was changing as it made its close approach to the sun last fall, a new study has found.

3I/ATLAS is fascinating to scientists because it is just the third object ever found passing through our solar system that was born around another star. Thus, it offers an opportunity to investigate the raw materials that existed in other star systems as they were forming planets, asteroids and comets.

In the new study, researchers observed 3I/ATLAS using the Subaru Telescope, an 8.2-meter optical-infrared telescope located near the summit of Maunakea, Hawaii, on Jan. 7, 2026.

"By applying the observational and analytical techniques we have developed through studies of solar system comets to interstellar objects, we can now directly compare comets hailing from both inside and outside the solar system and explore differences in their composition and evolution," team leader Yoshiharu Shinnaka, of the Koyama Space Science Institute in Japan, said in a statement.

By studying the colors of 3I/ATLAS' coma, the bubble of gas that surrounds comets regardless of their origins, Shinnaka and colleagues estimated the ratio of carbon dioxide to water around the interstellar invader.

They discovered that this ratio had changed since 3I/ATLAS made its close approach to the sun on Oct. 29, 2025.

This discovery didn't just suggest that the chemistry of 3I/ATLAS is changing, however. It also provided hints about the internal structure of this interstellar object.

That is because a comet's coma forms from gas that escapes from its frozen core when it passes close to the sun, and solar radiation causes solid ice to immediately change into gas, a process called sublimation.

The change in coma chemistry observed by the team implies that the internal chemistry of 3I/ATLAS differs from its external chemistry.

"With the full-scale operation of survey telescopes in the coming years, many more interstellar objects are expected to be discovered," Shinnaka said. "Through studies of such objects, we hope to gain a deeper understanding of how planetesimals and planets formed in a wide variety of stellar systems, including our own solar system."

The team's research is set to appear in the Astronomical Journal on April 22. A peer-reviewed version appears on the paper repository site arXiv.

The interstellar invader comet 3I/ATLAS is spraying enough water into space to fill 70 Olympic swimming pools each day. The discovery gives scientists a remarkable opportunity to study the elements present during the formation of planets around other stars, potentially much older than the sun.

The discovery was made by the European Space Agency (ESA) mission Jupiter Icy Moons Explorer (Juice), which is currently heading towards Jupiter and its icy moons. JUICE observed 3I/ATLAS, which is just the third object found passing through the solar system from beyond its boundaries, in November, 2025, using its MAJIS (Moons And Jupiter Imaging Spectrometer) and JANUS (Jovis, Amorum ac Natorum Undique Scrutator) instruments.

Like comets native to the solar system, 3I/ATLAS began expelling material when it passed close to the sun, with solar radiation heating its icy heart, causing solid ice to transform immediately into gas, a process called sublimation. As this gas makes its explosive escape, it forms the coma and tail that are characteristic of comets. This is accompanied by a brightening of the comet, but 3I/ATLAS brightened even more than expected.

During its observations, MAJIS identified infrared emissions from water vapor and carbon dioxide molecules. These are known as "volatiles" because they evaporate easily.

"Repeated detections of water vapor and carbon dioxide by MAJIS indicate that volatile ices buried beneath the surface were actively released into space shortly after perihelion passage," team member Giuseppe Piccioni of the National Institute for Astrophysics (INAF) said in a statement. "From the data collected, we estimated an outflow from the comet's nucleus of about two tons per second, equivalent to approximately 70 Olympic swimming pools of water vapor ejected into space every day.

"The MAJIS data will allow us to better understand the activity of this comet after perihelion and the physical and chemical properties of the materials formed around another star billions of years ago."

The JUICE observations of 3I/ATLAS were more extraordinary because they were unplanned, only occurring to the team after the discovery of 3I/ATLAS on July 1, 2025. The observations were challenging due to the short periods of time JUICE had to spot 3I/ATLAS and how faint the interstellar comet's emissions were.

These observations were followed by a prolonged wait, with the data only reaching Earth in February 2026.

"We waited a long time, but it was truly worth it," team member Pasquale Palumbo, an INAF researcher and principal investigator of JANUS, said. "The wonderful images collected reveal for the first time the comet's intense activity right around perihelion. 3I/ATLAS showed an extended coma, a tail, and various morphological structures, such as rays, jets, and filaments. The data collected will allow us to study the morphological structures, light intensity, and evolution of the comet's coma and tail on short and medium timescales.

"We are very pleased with the performance JANUS has provided us; it is an excellent preview of what it will be able to do when it operates around Jupiter and its icy moons, the final destination of the JUICE mission."

Comet-hunting often means going it alone. In the quiet dark of a sleeping house, I slip out of bed well before dawn, careful not to wake anyone, and make my way up the creaking stairs into the loft.

At the top, I ease open the door and reach for the window. The latch clicks, the frame shifts — and suddenly a rush of cold air floods in. It's enough to wake me instantly. I pull on a winter coat, shut the door behind me to keep the warmth below, and lean out into the stillness.

I'm expecting clouds — I always expect clouds — but this morning the sky is clear. Finally! Stars hang in the darkness, but the eastern horizon is beginning to glow — a soft, growing light that signals the sun's rise. Somewhere in that narrowing window between night and day is my target: a faint, ancient visitor, visible only briefly before sunrise.

Before me is a suite of gear assembled the night before — a manual camera with a telephoto lens on a tripod, a smart telescope and, now around my neck, a pair of 10x50 binoculars. I begin to scan, using the brighter stars as guides, having memorized a star chart showing exactly where the comet is this morning. My view is framed by rooftops and chimneys. Then, just above the horizon, it appears in my field of view — a dim, diffuse smudge, almost ghostly against the brightening sky.

"Got it," I whisper, to no one but myself. I resist the temptation to say hello to the comet. After all, it's just a big snowball.

Are you ready for the arrival of Comet C/2025 R3 (PanSTARRS)? Hunting a dawn comet is a race against daylight — one that begins in the stillness of early morning and ends in the glow of dawn. For those willing to make the effort, the reward is a fleeting glimpse of a relic from the solar system's edge, revealed in the quietest moments of the day.

What to expect from comet PanSTARRS

No one ever quite knows what a newly arrived comet will do. When the PanSTARRS survey in Hawaii discovered it in September 2025, it was just another faint point of light. Like almost all comets, it's a one-off opportunity for anyone alive today.

Right now, the comet is hovering just below magnitude +6, according to the Comet Observation database, so already technically on the edge of naked-eye visibility under very dark night skies.

As it approaches perihelion on April 19-20, it is expected to brighten rapidly — potentially reaching magnitude +3 — making it a relatively easy binocular object and possibly visible to the unaided eye in excellent conditions. Even if it reaches naked-eye brightness, binoculars will give a much better view.

However, there's a geometrical catch. As the comet brightens, it also moves closer to the sun in the sky, it's lower on the horizon, and it's fighting against the brighter twilight. That means its peak brightness may coincide with its most difficult observing conditions.

When and where to look for comet Pan-STARRS

From mid-northern latitudes, the best chance to see comet C/2025 R3 (PanSTARRS) will be about 90 minutes before sunrise, when it will be low in the eastern sky. What you're looking for is subtle: a soft, diffuse coma, possibly with the beginnings of a tail. At present, the comet shows little tail in small optics, but that could change quickly as solar heating intensifies.

The key window is April 10-20, when the comet is brightening but not yet too deeply embedded in the sun's glare. After perihelion, it becomes increasingly difficult — and eventually impossible — to see from the Northern Hemisphere. "If you want to catch the comet, your best chance is over the next week or so as the comet brightens, but it remains observable in a relatively dark sky," says Nick James, head of the comet section at the British Astronomical Association. "You will need to get up early, a couple of hours before sunrise, and have a good, low, eastern horizon."

By contrast, Southern Hemisphere observers will have the advantage later in April and into May, when the comet moves away from the sun in their skies and becomes better placed after perihelion.

How I'm planning to see comet PanSTARRS

Preparation and clear skies are everything. The night before, I'll look at the weather forecast and use planetarium software — Stellarium, Starry Night or a stargazing app like Sky Tonight or Sky Guide — to pinpoint the comet's exact position relative to the stars in the Great Square. As twilight takes hold, there's no time to search blindly — you need to know exactly where to look.

Binoculars will be my primary tool, sweeping slowly along the horizon. A 10x50 pair strikes the right balance between field of view and light-gathering power.

For imaging, I'll use a tripod-mounted camera with a 200–400mm lens, experimenting with ISO 1600–6400 and short exposures. Shooting in RAW is essential — faint comet detail often emerges only later. I'll have a smart telescope nearby, too, to automatically lock on to the comet and stack image after image.

Is imaging just as important as seeing the comet with your own eyes? Absolutely. There's a strong possibility that the comet will look better in photographs than it does visually — especially before a tail develops in the days around perihelion.

Comet PanSTARRS: key dates and highlights

The best plan for observers in the Northern Hemisphere is to get up at least 90 minutes before sunrise whenever clear weather is forecast between now and around April 19. The sooner you do that, the higher the comet will be, but the longer you wait, the brighter it may be — and the more daylight you'll need to battle. It's all a balance! However, a few mornings in April stand out as particularly rewarding opportunities to find Comet C/2025 R3 (PanSTARRS).

• April 14: A 12%-lit waning crescent moon appears nearby, with Mercury becoming visible before sunrise.
• April 18: Comet PanSTARRS is within about 2 degrees of galaxy NGC 7814, a distant edge-on spiral. A new moon the previous day will make this date and those on either side the sweet spot.
• April 19: Comet PanSTARRS exits the Great Square region, appearing about 2 degrees from bright star Algenib.

Asterism of the week: Great Square of Pegasus

If you know the famous asterism, the Great Square of Pegasus, by heart already, you'll know exactly where it is. If you don't, it's easy to find because its corners are marked by four stars of roughly equal brightness — Scheat, Alpheratz, Markab and Algenib. From April 13-19, the comet will travel across the bottom of the Great Square, from just above the bright stars Markab to just above Algenib, before it moves into Pisces.

Comet PanSTARRS may get brighter, but it will also get harder to see and will, in any case, get drowned by dawn. My advice? Go find it on the next clear morning — and aim to get it in your sights at least once before April 19.

The solar system has one less comet.

The much-heralded Comet MAPS, proclaimed by some as "The Great Easter Comet," met its end this past Saturday (April 4). The comet apparently underwent a cataclysmic fragmentation just hours before it was to make its closest approach — called perihelion — to the sun. Such was not completely unexpected, for Comet MAPS was a Kreutz sungrazer, a type of comet that comes literally within a hairbreadth of the sun. They may all have evolved from the breakup of a usually large comet's close approach to the sun, perhaps a millennium ago. From this progenitor, countless fragments of different sizes have been circling the sun in similar orbits.

Most of these fragments have themselves shattered into several pieces following their own solar rendezvous. In a few cases, these broken comets have escaped total annihilation by sweeping back out into the depths of space; survival is primarily dependent on how large the comet nucleus is. Kreutz comets on the order of a few miles or more in diameter, such as the Great Comets of 1843, 1882 and Ikeya-Seki of 1965, put on spectacular displays and managed to avoid total annihilation.

But this was not to be for Comet MAPS.

Much smaller than originally thought

Initially, when discovered in January, it was arbitrarily assumed that Comet MAPS might be rather large, as most Kreutz comets go. Indeed, many such comets have escaped detection on their way toward the sun until only some days or at most several weeks before perihelion. But Comet MAPS was found nearly four months before it arrived in the vicinity of the sun. No Kreutz comet had ever been detected so far out in space.

But it had since been determined that the initial sightings were due more to improved technology in picking up very faint objects as opposed to this being a large comet. Indeed, when it was first sighted on Jan. 13 using the 11-inch f/2.2 Schmidt telescope with a CCD camera at the AMACS1 Observatory at San Pedro de Atacama, Chile, the comet was exceedingly faint: magnitude +18 or about 12,000 times dimmer than the faintest sky objects at the threshold of a normal person's eyesight.

More recently, utilizing images taken with the James Webb Space Telescope, researchers suggested that the nucleus of Comet MAPS was, in fact, unusually small: only about 0.2 miles (0.4 kilometers) in diameter. Since the comet was destined to pass only about 100,000 miles (160,000 km) above the sun's surface at around 14 hours UTC (10 a.m. EDT) on Saturday, the odds did not look good for Comet MAPS to survive its close brush with the sun.

Poor prospects for endurance

In a Space.com article published on March 31, we suggested that the comet could likely either completely disintegrate on its way to the sun, or, if it somehow survived, disintegration would come later, leaving only a trail of dusty debris in its wake, producing a display similar to the Great Southern Comet of 1887 (described as "The Headless Wonder") or Comet Lovejoy of 2011.

As it turned out, the former option was how Comet MAPS met its ultimate fate.

Comet's date with destiny

On Saturday, all eyes were monitoring the comet's progress using the Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO) C2 and C3 cameras, as well as the Compact Coronagraph (CCOR) on the GOES 19 satellite. All showed Comet MAPS rapidly approaching the sun — at perihelion, the comet would be racing along a hairpin curve at a maximum of 300 miles (500 km) per second.

Sometime between 07 and 09 hours UTC, the comet noticeably brightened, reaching a magnitude of approximately -1 (nearly as bright as Sirius, the brightest star). This may have signaled a major disruptive event for the comet nucleus. By 11:36 UTC, the comet on LASCO imagery appeared as an elongated streak with no head.

During the few hours surrounding the time of the comet's closest approach to the sun, the comet was hidden behind the occulting disk, which also blocks the direct light of the sun. Observers anxiously awaited the comet's reappearance but saw nothing. Then, at around 22 hours UTC, the remains of the comet appeared as a sort of "blob" of material at 2-3 o'clock (if the occulting disk were imagined as the face of a clock).

No show this week

In short, MAPS went in, but only a cloud of debris came out: Obviously, sometime between 12 hours and 22 hours UT (8 a.m. and 6 p.m. EDT), the nucleus of Comet MAPS completely shattered, leaving behind in its wake an immense cloud of dust, which has since rapidly dissipated. As such, there will be nothing for skywatchers to see in the western evening sky this week. Hopes for a spectacularly bright comet or even a conspicuous narrow appendage of light (the tail) have been taken away this week in the wake of the comet's destruction.

What happened?

It's easy to understand how this celestial wanderer met its end. Having spent much of the last 18 centuries out beyond the known limits of our solar system, Comet MAPs was literally "soaking up the cold." Temperatures out there are likely to be within a few degrees of absolute zero: −459.67 °F ( −273.15 °C).

Suddenly, the comet finds itself hurtling headlong toward the sun and its nucleus begins heating up very rapidly. On the outside, temperatures begin climbing to above 3,000° F (5,000° C), though on the inside it's still frigidly cold. In addition to the sun's intense heat, it was also likely subjected to tremendous solar gravitation and tidal forces.

Question: What happens when you pour very hot tea into a very cold glass?

That's probably what happened to Comet MAPS. Simply a matter of too much stress on its relatively tiny nucleus, combined with dramatic temperature differences inside and out, sadly led to the comet's extinction.

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, Sky and Telescope, The Old Farmer's Almanac and other publications.

The interstellar comet that recently dominated headlines, 3I/ATLAS, could be between 10 and 12 billion years old, a new assessment of the comet's isotopic composition has shown. This so-called "invader" in our solar system is only the third object on record to enter our cosmic neighborhood from beyond.

If these new age estimates of the comet are true, they would suggest 3I/ATLAS was born within a few billion years of the birth of the Milky Way.

When it was discovered in 2025, 3I/ATLAS was speeding in at 36 miles (58 kilometers) per second relative to the sun. It is the fastest comet ever seen, vastly exceeding the velocities of its predecessors 1I/'Oumuamua and 2I/Borisov. And according to theory, the faster an interstellar object is travelling, the older it must be because it must have experienced multiple space-object encounters and gravitational slingshots with other stars that would accelerate it to a high velocity.

So, based on the comet's velocity, astronomers Aster Taylor and Darryl Seligman of the University of Michigan and Michigan State University, respectively, determined 3I/ATLAS has a "kinematic" age somewhere between 3 billion and 11 billion years old. That's a large range with substantial uncertainty — but now, a new study led by NASA Goddard's Martin Cordiner has come out in favor of the older end of that range, based on the comet's isotopic composition.

From studies with the James Webb Space Telescope's Near-Infrared Spectrometer (NIRSpec), Cordiner and his team measured both the ratio of carbon-12 to carbon-13 in 3I/ATLAS and also how enriched 3I/ATLAS's water is with the molecule deuterium, which is one of two stable isotopes of hydrogen. Both these properties are important tools for deducing the age and origin of the comet.

Isotopes are atoms of the same element that have the same number of protons but differing numbers of neutrons. Carbon-12 is the regular form of carbon, with 6 protons and 6 neutrons. Carbon-13 is the isotope, with 6 protons and 7 neutrons. Deuterium has one proton and one neutron (as opposed to your regular old hydrogen, which has one proton and no neutrons).

The carbon isotopes are found on 3I/ATLAS in compounds such as carbon monoxide and carbon dioxide, and even organic molecules such as methanol, formaldehyde and methane.

NIRSpec found that 3I/ATLAS contains far more carbon-12 relative to carbon-13 than anything seen in our solar system, or indeed even in nearby planet-forming disks around other stars, or local molecular clouds. This tells us that 3I/ATLAS ain't from around here, at least.

Carbon-13 becomes enriched over time within the interstellar medium and the molecular clouds that form stars. A low abundance of carbon-13 relative to carbon-12 therefore indicates that 3I/ATLAS must have formed a long time ago — before carbon-13 was able to build up to modern-day levels.

We can turn to models of galactic evolution to hazard an estimate as to exactly how long ago that was.

After the Milky Way formed about 13 billion years ago, it underwent a starburst: a huge bout of star formation. Many of these stars quickly evolved into red giants before casting adrift their outer layers and forming a planetary nebula while leaving behind their hot, inert core, which is what we call a white dwarf.

When in a close binary system with another star, a white dwarf can steal so much material that it ignites a thermonuclear explosion on its surface. We call this a nova, and such events are prodigious producers of carbon-13. A rapid burst of nova explosions is expected to have therefore occurred during the first four billion years of the Milky Way's history. For 3I/ATLAS to contain such a low ratio of carbon-13 relative to carbon-12, yet still contain some heavy elements, it must have formed in the middle of all this, before the carbon-13 abundance had a chance to build up in the galaxy.

This would actually place 3I/ATLAS's age as 10–12 billion years old.

The enrichment of deuterium in 3I/ATLAS also tells us about the interstellar comet's origins. Deuterium can replace one or both of the ordinary hydrogen atoms in water, which is what scientists mean by deuterium enrichment. The enrichment of deuterium in 3I/ATLAS's water has a D/H ratio that is an order of magnitude greater than in typical comets that formed in our solar system.

This degree of enrichment takes place in certain environments. Water-ice can become enriched in deuterium at temperatures less than 30 degrees above absolute zero (30 kelvin/–243 degrees Celsius/–405 degrees Fahrenheit), which is typical of interstellar clouds, and in an environment relatively poor in heavy elements, which points back to a formation early in the history of our galaxy.

Comets form alongside planets, so if these findings are correct, then 3I/ATLAS may very well be a relic of one of the earliest planetary systems in the galaxy. Can 3I/ATLAS tell us anything about these early planets that it formed alongside?

Comets, being icy objects, are thought to form in the more distant reaches of planet-forming disks, away from the heat of their young star that would otherwise vaporize ices. The boundary in a planet-forming disk between where water exists as a vapor or liquid, and where it exists as ice, is called the snow line.

"We believe that cometary materials in general are representative of the building blocks of planets outside the water snow-line in the protoplanetary disk," Cordiner told Space.com. "So the same is probably true of interstellar comets, and they provide unique insights into what extrasolar planets could be formed from."

Scientists are still building up a complete picture of 3I/ATLAS' chemical inventory, but there are a few things they can say at this stage.

"2I/Borisov and 3I/ATLAS both show a relatively carbon-rich composition compared to solar system comets," Cordiner said. "At the very least, this implies the abundant presence of carbon in the originating planetary system. 3I/ATLAS is also very water-rich."

The presence of deuterium, and various carbon and oxygen compounds, is indicative of a fairly complex chemistry that took place on icy dust grains from which 3I/ATLAS' planetary system likely formed, telling us that organic molecules and water were important components of planets even that early in the universe's history.

However, 3I/ATLAS' true point of origin remains a mystery, and likely always will. Tracing its path back more than 10 million years becomes difficult if not impossible, because of gravitational interactions between 3I/ATLAS and the stars that it passes close to, which perturb its trajectory.

However, the knowledge of its age narrows things down a little bit.

The Milky Way's disk is split into two parts — a narrow, 1,000-light-year-deep disk where most of our galaxy's star-formation now takes place (and where our sun was born), which is located inside a more diffuse and deeper thick disk (about 3,000 light-years deep). Observations of stars in the thick disk by the European Space Agency's Gaia mission suggest the thick disk began forming 13 billion years ago, whereas the thin disk is thought to be much younger, forming about 9 billion years ago. If these ages are correct, then 3I/ATLAS may have come from a thick-disk star.

"That seems more probable the older [3I/ATLAS] is," said Cordiner.

Indeed, 3I/ATLAS is so ancient that the star system that produced it may not even exist any longer. Is 3I/ATLAS truly a relic from a lost era of planet formation?

The findings are currently awaiting peer review, but are available via a pre-print.

The Hubble Space Telescope has witnessed a spinning comet slow its own rotation and then start spinning in the opposite direction, in the first observation of its kind demonstrating that comets can be even more dynamic than we thought.

Comet 41P/Tuttle–Giacobini–Kresák is a Jupiter-family comet, meaning that it is a short-period comet (orbiting the sun every 5.4 years) that has come in from the Kuiper Belt before being snagged by Jupiter's gravity.

41P's last close approach to the sun — known as perihelion — was in September 2022, but it was the previous close approach in 2017 that was observed by the Hubble Space Telescope, as well as several other telescopes including NASA's space-based Neil Gehrels Swift Observatory and the four-meter (13 foot) Lowell Discovery Telescope in Arizona.

However, Hubble's observations weren't analyzed until David Jewitt, a planetary scientist at the University of California, Los Angeles, found the data in the Mikulski Archive for Space Telescopes, named after former U.S. Democratic senator Barbara Mikulski, who has been a staunch supporter of NASA.

Hubble's data, when combined with that of Swift and the Lowell Discovery Telescope, revealed something very odd about the comet. When Swift observed the comet in May 2017, it was spinning once every 46 to 60 hours, about three times slower than it had been in March 2017 when the Lowell Discovery Telescope observed it. That in itself was intriguing, but the Hubble observations deepened the intrigue as they showed that, by December 2017, the comet's spin had sped up again, and now had a period of about 14 hours. What had happened to reignite the comet's dizzying rotation?

Jewitt thinks that outgassing from the surface of the comet, which heated up during its perihelion passage that brings it about as close to the sun as Earth, is the cause. This heating prompted volatile gases close to the surface to expand and burst out in jets, carrying comet dust with them.

"Jets of gas streaming off the surface can act like small thrusters," said Jewitt in a statement. "If those jets are unevenly distributed, they can dramatically change how a comet, especially a small one, rotates."

The comet's nucleus is just 0.6 miles (1 kilometer) across, which is too small for even Hubble to resolve, but its speed of rotation can be measured from its light curve: How the light of the comet’s elongated nucleus changes as it rotates and alternates between showing us its longer and shorter sides. Because the comet's nucleus is fairly small, it leaves it susceptible to torques, or twisting forces, produced by the jets. However, it was not possible to infer the direction of that rotation, whether it was clockwise or counterclockwise, from the observations.

Jewitt was further able to infer that the rotation, regardless of which direction it was initially, had reversed. The jets countered the comet's initial rotation, which caused the initial slow-down seen between the Lowell Discovery and Swift observations. Those jets then continued working against the rotation and eventually reversed it and spun the comet up fast the other way, which explains Hubble's observations.

"It's like pushing a merry-go-round," said Jewitt. "If it’s turning in one direction, and then you push against that, you can slow it and reverse it."

It is uncommon to see a comet change so abruptly, and if we go back to Hubble's observations of the comet in 2001, we can see that its overall activity when at perihelion has decreased since then by approximately an order of magnitude. Perhaps repeated perihelions — the comet is thought to have been in its current orbit for about 1,500 years — might be beginning to exhaust its supply of volatile ices. Or, perhaps the dust liberated by the jets is falling back onto the comet, covering those ices in an insulating layer that prevents the ices from being heated by the sun and sublimating as quickly.

However, Jewitt is skeptical that 41P/Tuttle–Giacobini–Kresák will last much longer. If the changes in its spin proceed apace, then gradually it is going to render the comet unstable and the fast rotation will lead to centrifugal forces that spin the comet apart.

"I expect this nucleus will very quickly self-destruct," said Jewitt.

The findings were published on March 26 in The Astronomical Journal.

NASA's Hubble Space Telescope has captured a rare cosmic moment: a comet breaking apart in real time.

During its routine imaging of the universe, the space telescope spotted an unexpected object called C/2025 K1 (ATLAS), or comet K1 for short. Remarkably, Hubble's observations revealed that the comet's nucleus was actively fragmenting, according to a statement from NASA.

"Sometimes the best science happens by accident," John Noonan, co-author of the study and physics professor at Auburn University, said in the statement. "This comet [was] observed because our original comet was not viewable due to some new technical constraints after we won our proposal. We had to find a new target — and right when we observed it, it happened to break apart, which is the slimmest of slim chances."

Comets are icy, rocky objects from the outer solar system that heat up as they approach the sun, releasing gas and dust to form a glowing coma and tail. They can also break apart when solar heating and gravitational forces overwhelm their fragile structure.

Astronomers observed K1 over three consecutive days, from Nov. 8 through Nov. 10, 2025, and found that it had already begun breaking apart before Hubble turned its gaze toward it. The telescope caught the comet splitting into at least four pieces, each surrounded by its own coma. One fragment appeared to split again during the observations, suggesting the process was still unfolding.

Researchers estimate the breakup began roughly a week earlier, likely triggered by the comet's close approach to the sun, known as perihelion, when heating and stress are at their peak.

K1 was discovered in May 2025 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey and is a long-period comet from the distant Oort Cloud, a vast reservoir of icy bodies at the edge of the solar system. These objects are considered relics of the early solar system, preserving material largely unchanged for billions of years. Before fragmenting, K1 was likely a bit larger than an average comet, measuring about 5 miles (8 kilometers) across, according to the statement.

Comets like K1 are often described as "dirty snowballs," made of ice, dust and rock loosely bound together. As they near the sun, ices sublimate into gas, creating jets that can push outward on the nucleus. Combined with internal weaknesses and gravitational stress, these forces can cause the comet to fracture.

But K1's breakup revealed an additional mystery. Ground-based observers did not see the comet brighten immediately after it fragmented, as might be expected when fresh ice is exposed. Instead, there was a delay between the breakup and visible outbursts.

Scientists think this may be because a comet's brightness comes mainly from sunlight reflecting off dust, not ice. Newly exposed ice may first need to develop a thin dust layer that can then be blown off, or heat may need to build beneath the surface before releasing an expanding cloud of dust, according to the statement.

"Never before has Hubble caught a fragmenting comet this close to when it actually fell apart. Most of the time, it's a few weeks to a month later. And in this case, we were able to see it just days after," Noonan said in the statement.

"This is telling us something very important about the physics of what's happening at the comet's surface. We may be seeing the timescale it takes to form a substantial dust layer that can then be ejected by the gas."

Watching a comet disintegrate in real time is extremely rare, as these events are unpredictable and often too faint to observe in detail. Hubble's high-resolution images allowed scientists to track the fragments as they drifted apart, offering an unusually clear view of the process. As those fragments continue to separate and fade, K1 is offering a rare and fleeting window into how some of the solar system's oldest objects evolve.

Their findings were published Feb. 6 in the journal Icarus.

Astronomers studying the interstellar visitor 3I/ATLAS have discovered the comet is unusually rich in alcohol — a chemical clue that could reveal how planets and icy bodies form around other stars.

Using the powerful radio antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, researchers detected extremely strong signals of methanol (CH3OH), a simple alcohol molecule, in the comet's expanding cloud of gas.

As 3I/ATLAS approached the sun and sunlight warmed its icy surface, it released gas and dust, forming a glowing halo — or coma — around its core, which allowed ALMA to analyze the comet's chemical composition in detail.

The measurements show that methanol is far more abundant, relative to hydrogen cyanide, than astronomers typically see in comets from our own solar system. That chemical imbalance suggests 3I/ATLAS likely formed in a planetary system with very different physical conditions — such as colder temperatures and/or a different chemical inventory — than the one that produced our own comets, according to a statement from the National Radio Astronomy Observatory (NRAO).

"Observing 3I/ATLAS is like taking a fingerprint from another solar system," Nathan Roth, lead author of the study and a professor at American University, said in the statement. "The details reveal what it's made of, and it's bursting with methanol in a way we just don't usually see in comets in our own solar system."

Methanol — which is used for industrial purposes here on Earth, in contrast to the drinkable ethanol — isn't rare in space. It forms on the surfaces of icy dust grains in interstellar clouds and is commonly incorporated into comets during planet formation. But the amount detected in 3I/ATLAS appears unusually high compared with the ratios seen in solar system comets, making the object a valuable chemical "fingerprint" from another planetary system.

Discovered in July 2025 by the Asteroid Terrestrial-impact Last Alert System, 3I/ATLAS is only the third known object confirmed to have entered the solar system from interstellar space. The first was 'Oumuamua, spotted in 2017, followed in 2019 by 2I/Borisov, which displayed a more traditional comet-like appearance.

Since 3I/ATLAS' discovery, telescopes around the world — including the Hubble Space Telescope and the James Webb Space Telescope — have been monitoring the comet as it travels through the inner solar system. Images show a diffuse coma and faint dust tail created as sunlight heats the comet's ices, releasing gas and dust into space.

Those outflows also help explain another phenomenon observed around the comet: a vast cloud of gas glowing in X-rays as charged particles from the solar wind slam into material escaping from the nucleus. The ALMA observations further revealed that hydrogen cyanide mostly streams directly from the comet's nucleus, while methanol is released both from the nucleus and from icy grains in the coma acting like miniature comets — the first time such detailed outgassing behavior has been mapped in an interstellar object, according to the statement.

The arrival of a new interstellar object has also fueled speculation online, including suggestions that 3I/ATLAS could be artificial in origin. But the growing body of evidence — including its comet-like tail, gas jets and molecular composition — strongly indicates that the object is a natural icy body.

For astronomers, that's the real excitement. Objects like 3I/ATLAS act as messengers from other planetary systems, preserving the chemical conditions present where they formed billions of years ago — and offering rare opportunities to study the building blocks of distant worlds without ever leaving our own solar system.

The new study has been submitted for publication and is currently available as a preprint on arXiv.

A newly discovered comet could put on a dazzling show in the coming weeks and if it survives a fiery brush with the sun, it might even become an 'Easter comet' visible in early April.

Comet C/2026 A1 (MAPS) was discovered photographically on Jan. 13 at the AMACS1 observatory in San Pedro de Atacama, Chile, by four French astronomers. The group runs a dedicated near- Earth asteroid search program called MAPS, an acronym based on their last names — Alain Maury, Georges Attard, Daniel Parrott, and Florian Signoret.

At the time of its discovery, Comet MAPS was located 191 million miles (308 million kilometers) from the sun, shining in the constellation of Columba the Dove. It was an 18th-magnitude object, meaning it was exceedingly faint and far beyond the reach of most amateur telescopes.

Since then, the comet has brightened some 600-fold to magnitude 11, bright enough to be readily detected in amateur telescopes of 8 to 10-inch aperture. It will likely ramp up in brightness in the coming days and weeks as it races toward an extreme rendezvous with the sun on April 4.

Why it's exciting

What makes this potentially exciting is that Comet MAPS has been identified as a Kreutz sungrazer. Some of the brightest comets in history were members of the Kreutz group. Examples include the Great Comets of 1843 and 1882, and Comet Ikeya-Seki of 1965. The most recent Kreutz comet that put on a fine showing was Comet Lovejoy in December 2011.

Comet MAPS will arrive at its perihelion — its closest approach to our star — at around 10 a.m. EDT (1400 GMT) on April 4.

At that moment, the comet will pass just 99,000 miles (159,300 km) from the solar photosphere. Since it will be passing through the sun's intensely hot corona, where temperatures can reach about 2 million degrees Fahrenheit (1.1 million degrees Celsius), there is a possibility that the comet may not survive, likely being either completely consumed by the extreme heat or torn apart by the sun's massive gravitational tidal forces.

But Lovejoy's predicted path does not take it directly into the sun. To escape such a fate, the comet must move incredibly fast. Around the time of its closest approach, the comet will whip around the sun on a hairpin-like curve at a speed of over 1 million miles per hour.

Daytime visibility?

On his Visual Comets in the Future webpage, Seiichi Yoshida of Japan has Comet MAPS peaking near magnitude -5 at perihelion, which would make it about as bright as Venus.

Around that time, the comet will be passing just to the immediate left of the sun, possibly tempting some to try and see it as a speck of light by blocking out the dazzling disk of the sun with their thumb or outstretched hand.

However, as in the case of watching a partial solar eclipse, there are inherent dangers in attempting to sight a comet so close to the sun. Viewing the comet itself poses no danger, but potential danger lies in staring at the sun, whose infrared rays can burn the retina of the eye and cause irreparable damage, all without causing any pain. It should be emphasized that neither sunglasses, telescopes, nor binoculars will protect against the type of eye damage that could ultimately result in blindness when a person, however briefly, looks directly into the sun's rays.

The safest way to watch

By far the safest way to watch the comet's close brush with the sun is to view it on your computer screen courtesy of the Solar and Heliospheric Observatory ("SOHO"). Astronomers hope to get spectacular views of the comet by utilizing SOHO's LASCO (Large Angle and Spectrometric Coronagraph Experiment) C3 camera and accessing either near-live images or videos that span the past 24 hours.

Back in October 2024, the public was captivated when SOHO captured Comet Tsuchinshan-ATLAS sweeping closely past the sun. Since it was launched in 1995, literally thousands of otherwise unknown comets have been first detected in SOHO imagery, generating competition among a handful of armchair astronomers. To date, SOHO officials have reported more than 5,000 comet discoveries using that spacecraft's LASCO C3 imagery.

Comet MAPS will be within range of the LASCO C3 imagery from April 2 at 8:00 a.m. EDT (12:00 GMT) through April 6 at 1:00 a.m. EDT (05:00 UTC). During a roughly four-hour timespan centered on the time of perihelion, the comet will appear to pass behind the sun as seen from our earthly perspective, then rapidly swing around and cross in front of the sun.

Scientists think it's possible for a spacecraft to gain enough velocity to catch up with iconic interstellar comet 3I/ATLAS, which is currently speeding away from us, by firing its booster rockets during a very close approach to the sun.

If this mission could launch in 2035, the researchers say, it could at minimum catch up with 3I/ATLAS by 2085 at a distance of 732 astronomical units (AU) from the sun. In other words, that's 732 times farther from the sun than Earth is, which is 68 billion miles (109 billion kilometers). For comparison, our most distant active space probe, Voyager 1, is currently only 170 AU from the sun after almost the same flight-time as the proposed mission to 3I/ATLAS.

To cross such huge distances so quickly, the mission would take advantage of something called the Oberth effect, named after the Austro–Hungarian rocket scientist Hermann Oberth (who later became a nationalized German and worked for the Nazis). Oberth first proposed the concept in 1929 in his book "Wege zur Raumschiffahrt" (meaning "Ways to Space Travel").

The idea is that as an orbiting spacecraft falls into a gravitational field produced by a planet or, in this case, the sun, the spacecraft accelerates. At periapsis – the spacecraft's closest point to the gravitating body — it fires its engines to gain even greater velocity. The Oberth effect describes how doing this when at higher velocities produces a greater change in velocity — what rocket scientists refer to as "delta-V" – and the highest velocities attainable are at periapsis.

"Pretty much every launch uses the Oberth effect," T. Marshall Eubanks, a former NASA scientist who is now chief scientist at Space Initiatives Inc. and an author of a new paper describing this mission to 3I/ATLAS, told Space.com. "It's why for example missions such as Artemis 2 do their translunar injection burns at perigee, not apogee. That's an Oberth maneuver. However, I cannot find a record of a straight-out Oberth maneuver of the type we propose, which is a major rocket burn at closest approach in a flyby."

As the most massive body in the solar system, the sun is the best place to take advantage of the Oberth effect. But that means getting close — really close.

To achieve a delta-V of at least 5.1 miles (8.4 kilometers) per second, which you can think of as the work required to accelerate a spacecraft onto a new trajectory, the mission would have to perform a solar Oberth maneuver (SOM) at a distance of 3.2 solar radii from the center of the sun. The radius of the sun is 432,450 miles (696,000 kilometers).

Three solar radii equals about 0.015 AU.

Getting this close to the sun, which would be deep inside the solar corona, is not impossible. When NASA's Parker Solar Probe made its closest approach to the sun in 2023, it came within 0.04AU (3.7 million miles/6.1 million km). Even though this isn't quite as close to the sun as the proposed 3I/ATLAS interceptor would get, it gives an indication of what would be in store: Parker Solar Probe experienced temperatures of 2,500–2,600 degrees Fahrenheit (1,370–1,400 degrees Celsius).

Still, Parker Solar Probe's heat shield protected it. Adam Hibberd, who is a member of the Initiative for Interstellar Studies and lead author of the research, cites the example of a 2015 design study from the Keck Institute of Space Studies for an interstellar mission that would take advantage of the risky maneuver. The heat shield in the Keck study was a carbon-composite, like the one on Parker Solar Probe, but with added layers of aerogel to further insulate from the sun's searing heat.

"In principle, a similar heat shield could be used for the mission to 3I/ATLAS," Hibberd told Space.com.

The solar Oberth maneuver would accelerate the 3I/ATLAS interceptor so much it would become the fastest spacecraft ever, "by a good measure," said Eubanks.

Hibberd is a software engineer by trade and creator of the Optimum Interplanetary Trajectory Software, which he utilized for this study to determine when would be the most efficient time to launch, given the relevant positions of the Earth, the sun, Jupiter and 3I/ATLAS. He found that 2035 provided the optimum trajectory.

The idea is to first fly out to Jupiter, and use Jupiter's gravity to slow the spacecraft enough that it is then able to loop back around and fall towards the sun. Though this sounds counterintuitive, it's necessary. Any spacecraft launched from Earth already possesses Earth's orbital motion of 18.6 miles (30 kilometers) and at this velocity a spacecraft heading towards the sun would be moving too fast and end up being flung around the sun on a wide orbit rather than get close.

So, the spacecraft needs to shed velocity first. Parker Solar Probe used seven flybys of Venus over seven years to achieve this. Since 3I/ATLAS is racing away from us at 38 miles (61 kilometers) per second, any mission to it doesn't have time to make multiple Venus flybys, so the 3I/ATLAS interceptor would race out to Jupiter on a journey taking about a year, before heading back towards the sun.

Hibberd, Eubanks and their co-author Andreas Hein of the University of Luxembourg calculate that the spacecraft could have a mass of about 1,100 pounds (500 kilograms), which is about the same as NASA's New Horizons mission to Pluto. The mass of the heat shield would have to be deducted from this 500 kilograms – on Parker Solar Probe the heat shield is 160 pounds (73 kilograms).

Separate to this payload would be two or three solid-rocket boosters needed to provide the immense thrust needed at perihelion for the solar Oberth maneuver. The team suggests that several Starship Block 3s (featuring nine Raptor 3 engines) attached to the spacecraft in low Earth orbit before it departs on its mission would be sufficient.

How quickly the mission would reach 3I/ATLAS would depend on the delta-V provided during the solar Oberth maneuver. A delta-V of 5.19 miles per second (8.36 kilometers per second) would enable a fly-by of 3I/ATLAS after a flight duration of 50 years. If we don’t want to wait that long, then if it is possible to get the delta-V up to 6.43 miles per second (10.36 kilometers per second), the rendezvous would take place in just 30 years. This is not impossible — NASA's Dawn spacecraft to the Asteroid Belt achieved a delta-V of 6.84 miles per second (11 kilometers per second) after separating from its booster rocket.

Because both 3I/ATLAS and the spacecraft would be moving so fast, only a flyby would be possible, rather than entering orbit around the interstellar interloper. This however begs the question, why bother chasing 3I/ATLAS down? Especially as astronomers expect the Rubin Observatory, which has now begun science operations in Chile, to find on average one interstellar comet per year — a big increase on the three that have been identified so far. Very soon there should be plenty of easier targets to reach.

"We'll just have to see," said Eubanks. "Maybe after, say, 10 interstellar objects have been found, 3I will seem commonplace and it won't seem worthwhile to mount an expedition to chase it. But then again, maybe it will seem different and unusual and there will be such a desire."

3I/ATLAS was well-characterized by astronomers as it passed through last year, and if he had the choice, Hibberd would prefer to see a mission to 1I/'Oumuamua, which was a more puzzling object, instead. In fact, Hibberd has already developed a mission plan for an 'Oumuamua interceptor called Project Lyra, but feels that the chance to catch it has now slipped away.

Indeed, if we have a mission ready to go, then if we can spot an interstellar comet early enough, more conventional means of reaching it should suffice. This is a viewpoint that was supported by a study from scientists at the South-west Research Institute in 2025.

"For future interstellar objects, a solar Oberth maneuver should be avoided if possible, since it is designed to catch a specific interstellar object 'after the bird has flown' and it is heading away from the sun," said Hibberd. “There are better mission architectures, using a probe already in orbit in space, which would intercept an interstellar object around perihelion in much less time, rendering an Oberth unnecessary."

The European Space Agency's Comet Interceptor mission, set for launch either in late 2028 or early 2029, is just such a mission. It will wait at the L2 Lagrange point for a suitable target, either a new long-period comet from the Oort Cloud or an interstellar comet, before being dispatched to rendezvous with it. So, there is a fair chance we'll have a spacecraft investigating an interstellar comet in the next 10 years.

"I feel quite confident that when we develop the ability to reach these interstellar objects, there will be a strong desire to directly explore at least some of them," said Eubanks.

That doesn't mean that the mission profile of a spacecraft taking advantage of a solar Oberth maneuver needs to be discarded. A spacecraft could swing past the Sun to gather speed to head out to explore the outer solar system beyond Neptune.

"Any trans-Neptunian object would be a pretty easy target, and the exploration of those has hardly begun," said Eubanks.

Additionally, if the theorized Planet Nine is discovered, then it would be so far away, with estimates ranging from 290 AU to 800 AU; a mission to it would likely have no choice but to make use of a solar Oberth maneuver if it wants to get there anytime soon. The maneuver could even be used to send a telescope out to 550 AU from the sun, which is the distance at which the sun's gravitational field creates a gravitational lens that can be used as a telescope far more powerful than any built so far.

For the time being, 3I/ATLAS continues to speed away from us. Regardless of whether anyone gives chase or not, the development of spacecraft trajectories utilizing solar Oberth maneuvers means that the outermost reaches of our solar system may not be as inaccessible to us as we had feared after all.

Hibberd, Eubanks and Hein's research is available as a pre-print on arXiv.

The fate of a comet that was predicted to pass close to Earth remains a mystery five years after its dramatic breakup in the inner solar system — but some astronomers think a part of it might still be out there.

In early 2020, astronomers discovered the icy traveler, known as C/2019 Y4 ATLAS, and predicted it might provide a night-sky spectacle that would liven up everyone's COVID-19 pandemic lockdown: a comet visible with the unaided eye as it passed within 23 million miles (37.5 million kilometers) of the sun, or about one quarter of the distance at which Earth orbits our star. But then the comet broke into dozens of pieces, leaving would-be observers hanging — and leaving astronomers wondering whether there could still be anything substantial left of our ill-fated icy visitor.

A team of astronomers led by Salvatore A. Cordova Quijano of Boston University hoped to answer that question by scanning the autumn 2020 skies. And according to their recent paper in The Astronomical Journal, there may be a half-kilometer-wide chunk of the comet still in orbit, swinging back outward toward the cold darkness of the outer solar system.

The lost comet's remains could still be out there

Cordova Quijano and co-authors Quanzhi Ye and Michael S. P. Kelley scanned the skies in August and October of 2020, searching for any sign of the comet's remnants, to no avail. Observations with the Lowell Discovery Telescope (a 4.3-meter telescope in Arizona) and nightly images from the Zwicky Transient Facility (which makes a wide-view scan of the northern sky every two nights, looking for changing or short-lived objects like comets and supernovas) turned up nothing. But that doesn't mean there's nothing left of C/2019 Y4; it might just mean that what's left is smaller than the smallest fragment these telescopes would have been able to see, which comes out to about half a kilometer wide.

Besides solving an intriguing astronomical mystery, this new study of C/2019 Y4 offers some clues about what happens when comets break apart in the intense heat near the sun, as well as a chance to study the millennia-long decline of an ancient comet family (C/2019 Y4 might be a fragment of a larger comet which broke up thousands of years ago, according to a 2021 study).

"The uncertain fate of C/2019 Y4 raises an intriguing question," the astronomers wrote in the study. "How many presumably disrupted comets have really completely disrupted, and could any of them have actually survived with a reduced, inactive nucleus?"

In the case of C/2019 Y4, the answer to that second question may be yes: it's possible that a fragment of comet, less than half a kilometer wide, could still be tracing its larger parent's long path around the sun.

A dramatic backstory

Comet C/2019 Y4 ATLAS was just a faint smudge of light in the distance when astronomers with the Asteroid Terrestrial-impact Last Alert System first spotted it in December 2019. The comet started getting brighter very quickly in early 2020 as it flew toward the inner solar system, and astronomers excitedly predicted that it could be visible with the unaided eye by the time it made its closest pass to Earth in late May.

And then, like the rest of us, C/2019 Y4 suddenly fell apart in late April 2020.

In the aftermath, astronomers used the Hubble Space Telescope and other observatories around the world to track a couple of dozen pieces of the shattered comet, in what appeared to be grouped in four main clusters of icy debris. But one of those clusters later turned out to be a glitch in the data, and another only lasted for a few days before completely dissipating. That left two more debris clusters, dubbed fragment A and fragment B.

Astronomers' last glimpse of any piece of C/2019 Y4's icy debris was on June 8, 2020, in images from NASA's STEREO spacecraft, nine days after the comet's closest approach to the sun. At the time, the comet's nucleus definitely looked "completely disrupted," Cordova Quijano and colleagues wrote. The lingering question is what happened to the nucleus after those observations.

By now, Fragment A is probably nothing but a slowly-spreading cloud of gas and maybe some dust grains. Within the first three days after the breakup, the chunks of former comet nucleus that made up fragment A seemed to lose about 70% of their mass (because, again, ice sublimates, and smaller chunks tend to sublimate faster than big ones).

Just before perihelion, in late May 2020, the biggest chunk of fragment B was about 0.75 miles, or 1.2 kilometers wide. By the time of Cordova Quijano and colleagues' observations in late August and mid-October 2020, it was clear that "fragment B had undergone further major disintegration," but it's still not clear exactly how much. Cordova Quijano and co-authors couldn't spot any trace of fragment B in their Lowell or Zwicky data, which could mean there's nothing left — or that the remaining fragment is less than half a kilometer wide.

"We cannot conclude from the available data whether any sizable fragments still exist," they wrote. "Observed disintegration events have produced long-lasting fragments as small as 0.3 kilometers diameter, which is smaller than our detection limit."

How to catch the next one

For astronomers, C/2019 Y4's dramatic breakup offered a rare chance to watch a comet disintegrate. So far, they've only gotten to observe this dramatic phenomenon a handful of times: three confirmed and four only suspected. Of those four, astronomers have no real idea what happened after the breakup — like whether any large chunks survived long enough to make it out of the hot inner solar system — and according to Cordova Quijano and his colleagues, that's mostly because of a lack of follow-up observations to confirm the comets' fates.

The researchers wrote that about two or three months after each comet passed "behind" the sun from our viewpoint, then emerged again, it should have been easier for telescopes to see. This would have been a perfect time to look for surviving fragments — or their absence. Such observations would have confirmed the comets' demise and also shed light on whether smaller pieces of their shattered nuclei would keep orbiting the sun as mini-comets.

"For C/2019 Y4, a deep search right after the solar conjunction (such as immediately following the initial shallower search in early August of 2020) could have conclusively determined the state of the remnant," they wrote in their recent paper. "Similarly, dedicated deep searches would be helpful in closing cases like the other three comets and would provide insights into comet disruption dynamics."

It's a little too late to do that for C/20129 Y4, but the study offers a heads-up to astronomers to be prepared for these kinds of observations the next time a comet falls apart on its way through the inner solar system.

Imagine a visitor from beyond our cosmic neighborhood. Not just from the next street over, but from an entirely different star system, a place we can only dream of reaching.

These ancient wanderers, like comet 3I/ATLAS, are cosmic time capsules. They carry the elemental fingerprints of other stellar nurseries, offering a rare glimpse into the primordial ingredients that built worlds far, far away. Humanity wants to know the universal recipe for planet formation, and these interstellar objects are the closest we get to a direct taste.

A recent study reveals something truly special about 3I/ATLAS. Astronomers got an unprecedented chance to track the precise evolution of atomic nickel and iron emissions, both before and after this comet's Oct. 30 closest approach to the sun. This kind of detailed observation is incredibly rare. It is a big step in understanding how other planets might form. We are learning how the raw stuff of the universe gets put together in distant stellar systems, and this comet gave us a front-row seat. It is a unique window into the building blocks of alien worlds, and it is helping us map out the cosmic origins of everything, including ourselves.

The ability to track atomic nickel (Ni) and iron (Fe) emissions in a comet, both before and after it swings by its star, is a big deal. For comets born in our own solar system, this kind of comprehensive dataset is almost unheard of. Only one solar system comet, C/2002 V1 (NEAT), has given us anything comparable. So, for an interstellar comet like 3I/ATLAS to provide such rich information, it is like hitting the cosmic jackpot.

Why do these specific metals matter so much? Nickel and iron are heavy elements. They are fundamental building blocks for rocky planets. Seeing their abundance and how they behave in an object from another star system tells us a lot about the "primordial metallicity" of that system.

Think of it as checking the ingredients list of a cake that came from a bakery on another planet. We want to know what flour, sugar and spices they use. These Ni and Fe measurements offer a promising pathway to explore the foundational elemental makeup of other planetary systems. This lets us compare their cosmic recipe with our own, asking if all star systems use the same basic set of ingredients to whip up planets. We are essentially trying to understand if the universe has a standard pantry for making worlds.

Now, the universe rarely makes things simple for us. While 3I/ATLAS gave us this fantastic data, its behavior after passing the sun threw a bit of a curveball. The comet's post-perihelion observations, particularly the chemistry it exhibited, looked surprisingly similar to objects from our own solar system. We saw detections of methanol, ethane, and dark dust in new SPHEREx analyses, which are common in our local comets. This similarity means that the comet's outer layers, the ones we could observe, had been significantly processed by the sun's radiation. It is like trying to guess what a raw ingredient tastes like after it has been thoroughly cooked and seasoned.

But new research shows that 3I/ATLAS does not directly expose the pristine material from which it originally formed. The outer layers we observed are not the untouched, deep-space stuff. They are the sun-baked crust. This complicates our quest to directly read the "primordial metallicity" from its surface. It means we cannot just look at the emissions and declare, "Aha, this is exactly what their star system is made of." We have to account for the sun's influence, which adds another layer to the cosmic detective work.

This twist — that 3I/ATLAS' outer layers have been baked by the sun — does not derail our mission. It just makes the science more interesting. Astronomers are clever. They will find ways to peel back those layers, to understand the processing, and to infer the original composition from the altered signals.

This work, even with its complexities, helps us dissect the metallic fingerprints of these cosmic wanderers. It is a crucial step in decoding the universal recipe for planet formation. We are connecting the story of our own solar system, with its familiar planets and ingredients, to the vast, unknown origins of worlds across the Milky Way galaxy. Every piece of data, every observation, helps us build a more complete picture. We are searching for the foundational ingredients that shape worlds, from the smallest asteroid to the largest gas giant. Ultimately, this quest is about more than just comets and metals. It is about understanding our own cosmic origins and our place in the vast, sprawling cosmos. These interstellar visitors are not just rocks and ice; they are messengers, carrying tales of distant stellar nurseries, helping us write the grand narrative of how the universe builds worlds.

So, even with the sun's interference, 3I/ATLAS delivered a treasure trove of data. It showed us that, even when a cosmic messenger gets a little singed on its journey, it still carries invaluable information. The precise tracking of nickel and iron, before and after the comet's solar encounter, remains an unprecedented feat. We now have a deeper understanding of how these interstellar comets evolve under stellar radiation. More importantly, we have a new, albeit complex, pathway to explore the primordial metallicity of other planetary systems. The journey to decode the universe's recipe for planet formation is long, but every interstellar visitor brings us closer. They are the original cosmic explorers, and by studying their metallic whispers, we are learning the secrets of worlds we may never see directly. It is a humbling and exciting prospect, connecting our tiny corner of the galaxy to the grand, elemental story of star systems far beyond our own.

New infrared observations reveal the rare interstellar visitor comet 3I/ATLAS dramatically brightening during its farewell tour of the solar system.

NASA's SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer) space telescope captured views in December 2025 of the comet releasing a surge of gas, dust and complex molecules two months after the object's closest approach to the sun — a surprising outburst that's giving scientists their clearest chemical look yet at material formed around another star, according to a statement from NASA.

The SPHEREx images were taken as the comet was already heading back out of the inner solar system. Instead of fading quietly into the dark, 3I/ATLAS flared with activity, developing a glowing coma rich in water vapor, carbon dioxide and organic compounds. Observations also show a pear-shaped dust tail, created by rocky material being ejected as the comet's activity increases.

"Comet 3I/ATLAS was full-on erupting into space in December 2025, after its close flyby of the sun, causing it to significantly brighten," Carey Lisse, lead author of the study, said in the statement. "Even water ice was quickly sublimating into gas in interplanetary space."

Discovered in July 2025 by the ATLAS asteroid survey, 3I/ATLAS is only the third confirmed interstellar object ever spotted passing through our solar system, following 1I/'Oumuamua in 2017 and 2I/Borisov detected in 2019. Unlike its predecessors, however, 3I/ATLAS put on an extended chemical show that SPHEREx was uniquely equipped to observe.

SPHEREx studies the universe in infrared light, allowing scientists to identify not just dust, but also a detailed mix of molecules streaming off the comet — including water ice, carbon dioxide, methane, methanol and cyanide, which are substances that serve as key ingredients in planetary formation.

While comets typically become most active near perihelion, when solar heat causes surface ices to vaporize, the SPHEREx data shows that 3I/ATLAS intensified well after that point. This suggests sunlight slowly penetrated beneath the comet's surface before triggering a delayed release of buried, ancient ices, according to the statement.

"Since comets consist of about one-third bulk water ice, it was releasing an abundance of new, carbon-rich material that had remained locked in ice deep below the surface," Lisse said in the statement. "We are now seeing the usual range of early solar system materials, including organic molecules, soot, and rock dust, that are typically emitted by a comet."

Because 3I/ATLAS originated beyond our solar system, its chemistry offers a rare chance to compare our local comets with icy bodies formed around other stars. The similarities and differences could help scientists determine whether the raw materials for planets and potentially life are common throughout the Milky Way.

"The comet has spent ages traversing interstellar space, being bombarded by highly energetic cosmic rays, and has likely formed a crust that's been processed by that radiation," Phil Korngut, co-author of the study, said in the statement. "But now that the sun's energy has had time to penetrate deep into the comet, the pristine ices below the surface are warming up and erupting, releasing a cocktail of chemicals that haven't been exposed to space for billions of years."

Their findings were published February 2026 in the journal Research Notes of the AAS.

A new comet approaching the sun has caught the attention of astronomers, primarily because of its lineage. It appears to belong to a group of comets that in some cases have briefly become outstandingly bright objects.

About sixty-six comet groups have been tentatively identified, of which there are fifteen that can be regarded as well-established and have been designated by letters from A to Q ("I" and "J" designations were not used). The members of the "M" group have a special name. In his 1997 book "Comet of the Century" (Springer-Verlag New York Inc.) popular astronomy author Fred Schaaf writes that "The very mention of this name sends chills of awe down the spines of comet observers." They are the Kreutz sungrazers.

Our new comet is catalogued as C/2026 A1 (MAPS) and was discovered on Jan. 13 at the AMACS1 observatory in San Pedro de Atacama, Chile. Here, an independent asteroid discovery program has been established using small wide-field telescopes, CMOS cameras (cameras that use a sensor that converts light into electrical signals to create digital images), as well as synthetic tracking technology. The acronym "MAPS" evolved from the initials of the four surnames of astronomers who led the program, Alain Maury, Georges Attard, Daniel Parrott and Florian Signoret.

The new object was found using an 11-inch (0.28 meter) f/2.2 Schmidt telescope with a CCD camera. When first sighted, it was located at 191 million miles (308 million km) from the sun; shining in the constellation of Colomba the Dove at a magnitude of +17.8, meaning it was exceedingly faint.

Once enough observations were collected, including a pre-discovery image that was taken in December 2025, an orbit was determined that showed that Comet MAPS was a member of the Kreutz comet family. This discovery was unprecedented in this aspect: no inbound Kreutz comet has ever been discovered so far from the sun, with such a long lead time — 11.5 weeks — before reaching its closest point to the sun (perihelion). The previous record was held by the brilliant comet C/1965 S1 (Ikeya–Seki) at only 33 days before perihelion. This does not necessarily mean that Comet MAPS is also going to be brilliant, but before we start making any considerations, let's take a closer look at other Kreutz family members.

Comet fragments

Apparently, all the members of this group of comets were pieces of a single giant comet, which had fragmented in the distant past. The source of the group may have been the Great Comet of 371 BC, described by the Greek historians Ephorus, Aristotle and Seneca. It apparently came very close to the sun and might have even split into two pieces.

In February 1106, a very bright comet appeared, described in many Chinese, Japanese, Korean and European chronicles. It may have been related to the comet of 371 BC and is believed to have ultimately fractured into numerous fragments. It now appears quite probable that these fragments have themselves broken up repeatedly as they've orbited the sun, resulting in orbital periods ranging from about 500 to 900 years or more.

The German astronomer Heinrich Carl Friedrich Kreutz (1854 –1907) studied many comets that came within a hairbreadth of the surface of the sun, and noted that several had very similar orbits, which apparently were produced, he surmised, when a very large sun-grazing comet fragmented many hundreds of years previously. In honor of his extensive work, the members of this group are referred to as Kreutz sungrazers.

Two of these sungrazers, (in 1843 and 1882) not only developed very long tails but also achieved the rare distinction of having been bright enough to be seen in broad daylight with the unaided eye. Many years later, Dr. Brian G. Marsden (1937-2010), a highly regarded specialist in celestial mechanics and astrometry, considered that almost all the comets belonging to the Kreutz group separated from one of two comets that appeared around 1100 AD. One of these might very well have been the comet of 1106.

How many?

We know today that there are literally thousands of Kreutz sungrazers. Beginning in 1979, orbiting space observatories such as SOLWIND and the Solar Maximum Mission satellite began to detect sungrazing comets using instruments called coronagraphs. A coronagraph is designed to look at the solar atmosphere by blocking out the bright disk of the sun. Tiny sungrazing comets, which normally would be too faint and too near to the glare of the sun, can be picked up using a coronagraph.

In fact, sungrazers continue to be routinely being discovered using the Large Angle Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) satellite. Over 5,000 SOHO comet discoveries have been made by amateurs using SOHO images on the internet, and SOHO comet hunters come from all over the world. Over 3,500 SOHO comets have been identified as Kreutz sungrazers. Most are probably just a few meters across; none have survived their sweep around the sun.

But that also doesn't necessarily mean that we will never see another large, bright comet moving in the same orbit. Indeed, Kreutz comets are like trains of all sizes moving along the same railroad track while passing our station (Earth) in space. And like impatient commuters we can only watch and wonder what awaits us up the track!

Comets belonging to the Kreutz group include the Great Comets of 1668, 1843, 1882 and Ikeya-Seki in 1965. All were very bright objects, sporting long tails. They all had relatively large nuclei, probably measuring several miles or more in diameter.

But just when will another large and spectacular member of the Kreutz group, like Ikeya-Seki, appear? No one can say for sure. The last Kreutz Sungrazer to become bright was Comet Lovejoy in December 2011, and yet, that comet disintegrated shortly after perihelion.

So now we are looking at Comet MAPS. The big question now is: Will it sizzle and become bright and spectacular, or will it fizzle and remain faint and possibly even disintegrate when it sweeps around the sun?

How bright? Opinions differ

Comet MAPS is expected to arrive at perihelion early on April 4, passing a mere 99,600 miles (160,200 km) above the solar surface (photosphere). To survive such an exceedingly close approach, the comet needs to travel along what equates to a hairpin turn around the sun at speeds measuring over 2 million miles (3 million km) per hour! Even at such extreme velocities, the comet will be subjected to temperatures of thousands of degrees Fahrenheit, and might end up being completely vaporized or torn apart by massive tidal forces if it's not very large, perhaps leaving only a tail in its wake. One of the best examples of this was the Great Southern Comet of 1887, which is known in some astronomical annals as the "headless wonder."

Astronomer Daniel Green at the Central Bureau for Astronomical Telegrams, believes Comet MAPS will suffer a similar fate, noting on Circular 5658: "The faint absolute magnitude of C/2026 A1 (MAPS) does not bode well for the comet's survival past perihelion." But Czech astronomer and veteran comet observer Jakub Černý disagrees. In a recent post on Facebook's ICQ Comet Observations Group Forum page, he notes that Kreutz comets are an "extremely special case from many points of view, and it is difficult to apply many general rules to these objects. The most probable scenario is that this is a mid-size Kreutz comet, possibly larger than Comet Lovejoy, and that it may survive perihelion passage or even the entire return, resulting in a bright naked-eye comet, potentially with or without a distinct head ('headless wonder' appearance)."

So, when will we know?

It appears that we will need several more weeks to determine whether Comet MAPS is developing into a potentially bright object or will remain small and dim. By early March, we should have a much better idea as to how it will perform. If it does develop into an eye-catching naked-eye comet, it would grace our evening sky during the second week of April, low in the west shortly after sunset.

Of course, if that happens, Space.com will provide all the details on how, where and when you might see it for yourself. Keep your fingers crossed and stay tuned!

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, Sky and Telescope, The Old Farmer's Almanac and other publications.

A comet was caught falling apart on camera, using a powerful telescope in Hawaii.

Comet C/2025 K1 (ATLAS) crumbled in high-resolution footage captured by the Gemini North telescope atop Mauna Kea in Hawaii. Glowing pieces of the comet are visible in the 8.1-meter diameter optical/infrared telescope, which is part of a twin pair of telescopes at the International Gemini Observatory.

New imagery of the comet released Thursday (Jan. 29) shows pieces tumbling apart in separate pictures obtained Nov. 11 and Dec. 6. The National Science Foundation-funded work complements a number of other observations by professionals and amateurs late last year.

The comet, which was a loosely held collection of ice and dust, swooped around the sun in October and made its closest approach on Oct. 8. The strong solar gravity and the pressure of the solar wind, or constant stream of particles streaming off our sun, fragmented the comet into several chunks.

For example, astronomer Gianluca Masi, of the Virtual Telescope Project in Italy, imaged the breaking-apart comet in early November using a Celestron C14 Schmidt-Cassegrain telescope on a Paramount ME robotic mount. The images appeared to show "three fragments of the original nucleus and possibly a fourth one," Masi wrote in a statement accompanying the images.

Astronomers at the Asiago Observatory in Italy also previously showed the comet in two fragments, separated by roughly 1,200 miles (2,000 km), on Nov. 11. They used a 1.82-meter Copernicus telescope to achieve the work.

C/2025 K1 (ATLAS), as the name implies, was found in May 2025 using the Asteroid Terrestrial-impact Last Alert System. It is a solar system comet that likely was formed in the Oort Cloud, which is a large group of icy bodies past the orbit of Neptune. There may be billions of comets like C/2025 K1 (ATLAS) there, which may orbit the sun at a distance for eons until a gravitational "kick" sends them towards the inner solar system.

These long-period comets are especially prized by astronomers studying the early solar system, since Oort Cloud members are more pristine than regular, recurring visitors like Halley's Comet originating closer to the sun.

Want to see these visitors from the outer solar system for yourself? Skywatchers hoping to capture their own views of distant solar system comets should check out our roundups of the best smart telescopes, cameras and lenses for astrophotography, along with our guide on how to view and photograph comets.

Editor's Note: If you would like to share your own comet photos with Space.com's readers, then please send your photo(s), comments, and your name and location to spacephotos@space.com.

NASA's planet-hunting TESS spacecraft recently caught a view of a very different kind of cosmic object: interstellar comet 3I/ATLAS.

During a special observation run from Jan. 15 to Jan. 22, the Transiting Exoplanet Survey Satellite (TESS) repeatedly observed comet 3I/ATLAS as it headed out of our solar system. With its wide field of view, TESS recorded the comet as a bright, fast-moving dot dragging a faint tail across a crowded starfield.

Using data from some of earlier January observations, Daniel Muthukrishna of the Massachusetts Institute of Technology (MIT) compiled the images into a 28-hour video that shows comet 3I/ATLAS's trajectory. Unfortunately, TESS' observations were interrupted when the spacecraft entered "safe mode" after experiencing an issue with its solar panels, so the video includes a time jump from Jan. 15 to Jan. 18.

Scientists like Muthukrishna hope to use the dataset to study the comet's activity and rotation, clues that reveal how vigorously it's shedding dust and gas and how quickly the comet's core spins.

TESS measurements put comet 3I/ATLAS's brightness at about 11.5 in apparent magnitude, roughly 100 times fainter than what we can see with the naked eye, but accessible using telescopes.

NASA's TESS mission was designed to find exoplanets via the transit method, in which a faraway star dims slightly when a planet in its system passes in front of it. But TESS' wide field of view and consistent monitoring also make it useful for detecting and tracking closer objects, including comets and asteroids, for longer stretches of time.

This capability helped astronomers spot comet 3I/ATLAS before they even knew it was there. TESS happened to observe a comet in May 2025, two months before 3I/ATLAS was discovered. By looking back through all the data and compiling multiple observations, astronomers could filter out the interstellar visitor through the noise and track its movements. While unfortunately this doesn't tell us where the comet originated, it does give us other key details.

The January TESS observations are now publicly available and can be found on the the Mikulski Archive for Space Telescopes. It's within these precious hours that astronomers may find repeating patterns of brightness that reveal further secrets about our brief interstellar visitor.

For the first time, NASA's James Webb Space Telescope has seen a young star forge crystals in blazing heat and hurl them to the icy outskirts of its planet-forming disk, which could help explain the evolution of comets at the edge of our solar system.

The protostar, called EC 53, lies about 1,300 light-years from Earth and is surrounded by a disk of gas and dust where planets and other bodies are taking shape. Using the Mid-Infrared Instrument on the James Webb Space Telescope, astronomers mapped where crystalline silicates form and how they travel outward.

Webb pinpointed the inner disk — roughly where Earth and the inner planets would have formed in our solar system — as the birthplace of these crystals. Powerful winds from the star's disk act like a cosmic conveyor belt, propelling the crystals into the frigid outer disk, where comets may eventually form, according to a statement from NASA.

"EC 53's layered outflows may lift up these newly formed crystalline silicates and transfer them outward, like they're on a cosmic highway," Jeong‑Eun Lee, lead author of a new study reporting the results, said in the statement. "Webb not only showed us exactly which types of silicates are in the dust near the star, but also where they are both before and during a burst."

EC 53 experiences bursts roughly every 18 months, rapidly accreting material and sending some back into space as jets and winds. It's during these energetic 100-day-long episodes that the star forges silicate crystals — minerals that should only form in hot environments — and catapults them outward, seeding the outer disk with the ingredients that icy comets carry today.

Astronomers have long detected crystalline silicates in comets and other stars' disks, but the connection between their fiery origins and cold resting places was unclear — until now. Webb's detailed spectra and spatial mapping provide the first direct evidence linking formation and transport.

"We've effectively shown how the star creates and distributes these superfine particles, which are each significantly smaller than a grain of sand," Joel Green, co-author of the study, said in the statement.

The study highlights just how dynamic young planetary systems are and how stars actively reshape their surroundings. Observing protoplanetary disks like EC 53 can offer new insights on the building blocks of planets and comets scattered across space.

Their findings were published Jan. 21 in the journal Nature.

Solar system comet C/2024 E1 (Wierzchos) makes its closest approach to the sun today (Jan. 20) during an event known as perihelion, when it will pass a little over half the Earth-sun distance from our parent star, causing it to brighten significantly.

Comet Wierzchos makes its closest flyby at 1:24 p.m.EST (1824 GMT) on Jan. 20, passing the sun at a distance of 52.6 million miles (84.6 million km).

At perihelion, a combination of proximity and the increase in solar radiation is expected to boost the comet's visibility. Heat from the sun vaporizes ice material in the comet's solid nucleus, releasing masses of gas and dust that forms a reflective cocoon, or coma, around the nucleus. Charged particles streaming outward from the sun sweep this material into the comet's characteristic tail.

The comet is expected to reach a peak brightness, or magnitude, of around +8.1 in the days following perihelion, according to the Comet Observation Database (COBS) run by the Crni Vrh Observatory in Slovenia (the lower the number, the brighter the object in the night sky). That puts C/2024 E1 (Wierzchos) beyond naked-eye visibility, which allows us to see objects down to a magnitude of approximately +6.5 under dark sky conditions. However, the comet should be visible with the aid of a small backyard telescope, assuming that you're in the right part of the world to see it.

By mid-January, comet Wierzchos will be traveling through the stars of the southerly constellation Microscopium and will be lost from sight below the horizon during the nighttime hours for stargazers in the U.S.

Northern Hemisphere observers will get another chance to see C/2024 E1 (Wierzchos) in the weeks following its close approach to Earth on Feb. 17, when it will pass a little over 93 million miles (1 Astronomical Unit) from our Blue Marble. During this event, known as perigee, the comet will appear low on the southwestern horizon at sunset for stargazers in the U.S. with an estimated magnitude of +8.9. C/2024 E1 (Wierzchos)'s brightness will continue to recede as it rises higher in the evening sky in the following weeks, as it travels away from the warming influence of the sun.

C/2024 E1 (Wierzchos) was discovered in March 2024 by astronomers analyzing data collected by the Catalina Sky Survey — a NASA-funded project at the University of Arizona, which continuously scans the night sky for potentially hazardous near-Earth objects.

The wandering body is thought to have originated from the shell of icy material that surrounds the solar system known as the Oort Cloud and was first spotted as it raced sunward at a distance of 8 AU. It has since been observed by the James Webb Space Telescope, which recorded a distinct lack of carbon monoxide (CO) in its light fingerprint, suggesting that the element may have been lost prior to being expelled by giant inner solar system planets shortly after its formation.

Photographers hoping to capture the silent majesty of wandering comets should read our guide to photographing comets with a DSLR, while those looking to update their equipment would do well to read our roundups of the top cameras and lenses for astrophotography.

Editor's Note: If you would like to share your comet images with Space.com's readers, then please send your photo(s), comments, and your name and location to spacephotos@space.com.

Editor's Note: This article was corrected on Feb. 6 to reflect a lack of carbon monoxide in JWST observations of C/2024 E1 (Wierzchos).

Tune in today (Jan. 16) to bid farewell to interstellar comet 3I/ATLAS, courtesy of a livestream from the Virtual Telescope Project featuring live views of the enigmatic visitor as it continues its one-way journey out of our solar system.

Friday's livestream will begin at 5 p.m. EST (2100 GMT), with views of 3I/ATLAS being provided by a 14-inch Schmidt-Cassegrain robotic telescope located at the organization's facility in Manciano, Italy, weather permitting.

"This is a very precious opportunity to personally see, in real-time, the interstellar comet 3I/ATLAS, one of the most important discoveries of the last decade," said Virtual Telescope Project founder Gianluca Masi in a recent post on the website.

3I/ATLAS was discovered on July 1, 2025 and was quickly confirmed to be just the third interstellar object to visit our solar system based on an analysis of its trajectory, which proved that it was not gravitationally bound to our parent star. The alien comet made its closest approach to the sun on Oct. 29 during an event called perihelion, prior to which it had brightened more than had been expected by scientists.

The comet was hidden from view in the weeks surrounding perihelion, as it passed on the far side of the sun relative to Earth. 3I/ATLAS later made its closest approach to our Blue Marble on Dec. 19, when it passed 168 million miles (270 million kilometers) from our planet. Its next milestone will involve a much closer pass of Jupiter in March later this year, when it will buzz the gas giant at a distance of approximately 33.4 million miles (53.7 million km).

Following this final planetary flyby, 3I/ATLAS will embark on a silent journey lasting several thousand years as it coasts beyond the orbit of the outermost icy planets, before careening through the icy shell of the Oort cloud to return to the cold embrace of interstellar space.

"Greenland 2: Migration," the long-awaited sequel to 2020's cosmic disaster film, "Greenland," is set to arrive in theaters on January 9, 2026. This time it's fortified with a beefier $90 million budget and more harrowing survival action for the Garrity family, as they venture forth from the diminishing safety of their apocalypse bunker five years after the events of the first film.

Lionsgate and STX Films' new launch trailer has just hit the internet, and it's a nerve-jangling barrage of oceanic calamities, gun-toting militant factions, vertigo-inducing ladder crawls across bottomless chasms, electrifying radiation storms, and intense familial bonding moments.

Director Ric Roman Waugh is back in the director's chair, operating from an engaging story from "Greenland's" original screenwriter Chris Sparling, alongside Kandahar’s Mitchell LaFortune. Butler and Baccarin return to offer up yet more excellent performances in this second installment, portraying John and Allison Garrity, as does Roman Griffin Davis as their young son, Nathan.

The trio makes the decision to break away from the Greenland shelter and head south towards France and the location of the Clarke interstellar comet crater. This spot has been rumored to be a far safer zone where society is attempting to rebuild without the lethal radioactive clouds and barrage of cometary fragments still raining down upon the Earth. But it's going to be a perilous path indeed that might see many casualties along the route.

"Greenland 2: Migration's" remaining cast members include Amber Rose Revah, Sophie Thompson, Trond Fausa Aurvåg, and William Abadie. Ric Roman Waugh and Gerard Butler were aboard the follow-up project as producers in collaboration with "John Wick" franchise producer Basil Iwanyk, alongside Alan Siegel, Sebastien Raybaud, John Zois, and Brendon Boyea.

Stay tuned for our exclusive interview with Gerard Butler for the film's official release on Jan. 9! In the meantime, you can also watch the first movie on HBO Max.

After the excitement of three visible comets in 2025, another may put on a show in late April 2026. However, although the comet, known as C/2025 R3 (PanSTARRS), could become bright enough to be seen with the naked eye, it could just as easily remain visible only through binoculars and telescopes.

In the wake of Comets C/2025 A6 (Lemmon) and C/2025 R2 (SWAN) in October, Comet R3 (PanSTARRS) is due to reach perihelion — its closest point to the sun — on April 20, 2026. On that date, this icy visitor to the inner solar system will come within 47.4 million miles (76.3 million kilometers) of the sun.

That's between the orbits of Mercury and Venus, or between 29 million and 67 million miles (47 million to 108 million kilometers), on average. On April 27, Comet C/2025 R3 (PanSTARRS) will be at its closest point to Earth — within 44 million miles (70.8 million km) — and so will probably be at its brightest.

Comet C/2025 R3 (PanSTARRS) distance and brightness

The brightness of comets is notoriously unpredictable. Although Comet C/2025 R3 (PanSTARRS) could prove to be the brightest comet of 2026, it's not known how bright it will get. Some predict it could reach magnitude 8, which is about the same brightness as Neptune — too faint to be seen with the naked eye but easy to spot in binoculars or a small telescope. Others predict Comet C/2025 R3 could reach a brightness of magnitude 2.5. That's comparable to the brightest stars in the famous W-shaped constellation Cassiopeia, which is easily visible with unaided eyes in a dark sky.

Comet R3's prospects of becoming a bright, easy-to-see nighttime object may be enhanced by a phenomenon called forward scattering. Because this comet will move between Earth and the sun, its tail will reflect and scatter a lot of sunlight in the direction of Earth — and into the eyes of observers — in late April 2026.

When and where to see Comet C/2025 R3 (PanSTARRS)

Comet C/2025 R3 (PanSTARRS) will be at its best in the predawn sky in late April, as seen from the Northern Hemisphere, and after sunset in early May for viewers in the Southern Hemisphere. It will reach perihelion in the constellation Pisces, just beneath the Great Square of Pegasus.

When Comet R3 (PanSTARRS) brightens in the night sky, there will likely be some interference from moonlight, but darkness will prevail close to perihelion. A new moon on April 17, 2026, bodes well for the comet's post-sunset perihelion on April 20. But at its closest point to Earth on April 27, it will likely be lost in the sun's glare.

Around April 13-15, the comet will be within the Great Square of Pegasus, around 15 degrees above the eastern horizon, an hour before sunrise, as viewed from mid-northern latitudes. There will be a close to a waning crescent moon for a few mornings.

Discovery of Comet C/2025 R3 (PanSTARRS)

Comet C/2025 R3 (PanSTARRS) was discovered on Sept. 8, 2025, by Pan-STARRS, a pair of 1.8-meter (5.9 feet) reflector telescopes atop Haleakalā volcano in Hawaii. Pan-STARRS constantly takes wide images of the sky, and then software compares them with older images, flagging anything that moves. Follow-up observations using the 3.6-meter (11.8 feet) Canada-France-Hawaii Telescope at Mauna Kea, Hawaii, on Sept. 17 helped astronomers calculate the comet's path.

A cluster of comets

After a few barren years in the wake of Comet C/2020 F3 (NEOWISE), six notable comets made their mark in 2024 and 2025. First, there was the "Devil Comet" 12P/Pons-Brooks" (also dubbed the "Mother of Dragons" comet) in April 2024. Then came Comet C/2023 A3 (Tsuchinshan-ATLAS) in October 2024 and the bright C/2024 G3 (ATLAS), the "New Year comet," which put on a great show for viewers in the Southern Hemisphere in January 2025. It was followed in mid-October by Comet C/2025 A6 (Lemmon), which reached the cusp of naked-eye visibility and, to a lesser extent, Comet C/2025 R2 (SWAN).

That's not to mention 3I/ATLAS, only the third interstellar object ever to visit the solar system, after 'Oumuamua in 2017 and 2I/Borisov in 2019. 3I/ATLAS came closest to the sun on Oct. 29 during its trip through the solar system and then rapidly brightened, baffling scientists.

Will Comet C/2025 R3 (PanSTARRS) become a "great comet" in 2026? Only time will tell.

It may be on its way away from Earth and heading out of the solar system, but interstellar invader comet 3I/ATLAS still has some surprises for researchers.

New research reveals that jet structures in the sun-facing "anti-tail" of this comet, estimated in some observations to stretch up to 620,000 miles (1 million kilometers), were wobbling every 7 hours and 45 minutes as 3I/ATLAS approached the sun. Of course, comets are famous for their tails and haloes, comprised of gas and dust that is blown from their nucleus as radiation from the sun heats them. However, these tails generally face away from the sun and the influx of solar radiation. A rare anti-tail is a cometary tail that points toward the sun, rather than away from it.

3I/ATLAS is only the third object known to have entered our solar system from around another star. The first was the cigar-shaped space-rock 'Oumuamua, discovered passing through the solar system in Oct. 2017, and the second was the first interstellar comet 2I/Borisov, spotted in our solar system in August 2019. Though rare, scientists have seen comets originating in the solar system display a sun-facing anti-tail before, and wobbling jets have been observed in these anti-tails. However, this is the first time that such an "outgassing" has been observed from an interstellar comet.

"Characterizing jets in 3I thus represents a rare opportunity to investigate the physical behavior of a pristine body formed in another planetary system," the researchers behind this discovery wrote in a paper published on the paper repository site arXiv.

The team discovered the wobbling jets in the coma of 3I/ATLAS after observing the comet across 37 nights between July 2 and Sept. 5, 2025, with the Two-meter Twin Telescope (TTT), a robotic facility located at the Teide Observatory in Tenerife, Canary Islands.

These observations allowed the researchers to track how the comet's coma evolved from a sun-facing fan of dust before August, to a pronounced antisolar tail. They attribute this transformation to the increasing influence of solar radiation on dust with the coma as 3I/ATLAS headed toward a close approach to the sun on Oct. 30, 2025, when it came to within around 130 million miles (210 million km) of our star.

The jet structure appeared within the anti-tail of 3I/ATLAS on 7 nights between Aug. 3 and Aug. 29, and its wobble or precessional motion implied to the team that the icy heart of this interstellar invader is rotating around once every 15 hours and 30 minutes. This is a shorter rotational period for 3I/ATLAS than has previously been estimated.

3I/ATLAS made its closest approach to Earth on Dec.19, coming to within around 168 million miles (270 million kilometers). Since then, the interstellar interloper has been making its way to the outer solar system. Like 'Oumuamua and 2I/Borisov before it, the comet is expected to eventually leave the solar system for good.However, as this research demonstrates, 3I/ATLAS may soon be gone, but thanks to its impact on science, it is unlikely to be forgotten.

2025 has seen stargazers look on in awe as a trio of magnificent comets barreled headlong into the inner solar system to survive a close brush with the sun, only to emerge to race back out into the blackness of space, never to be seen again.

Of these comets — the interstellar invader 3I/ATLAS, C/2025 A6 (Lemmon) and C/2025 R2 (SWAN) — not all survived their trial by solar radiation intact, while others drew the attention of a global audience thanks in part to their scientific significance and in some cases, the disinformation that swirled around them.

Join us as we look back at six of the most memorable cometary highlights of 2025, featuring stunning astrophotography, the unexpected advance of an interstellar invader and the dramatic demise of an icy visitor from the Oort Cloud.

5 incredible moments that made 2025 the year of the comet

1. Enter interstellar comet 3I/ATLAS

Comet 3I/ATLAS was discovered on July 1, 2025, by the NASA-funded ATLAS telescope in Rio Hurtado, Chile and was quickly confirmed to be just the third interstellar visitor to our solar system, after 1I'Oumuamua and 2I/Borisov.

Its exotic nature quickly seized the interest of the scientific community and the imagination of the public while simultaneously sending the conspiracy-peddling community into a frenzy, some of whom claimed that 3I/ATLAS was an alien spacecraft that had voyaged to the heliosphere for reasons unknown.

Follow-up observations confirmed 3I/ATLAS to be the brightest and potentially the largest interstellar object discovered to date, measuring up to 3.5 miles (5.6 kilometers) in diameter, based on observations from the Hubble Space Telescope, according to NASA.

2. When the cosmos gives you Lemmon, make astrophotography

If 3I/ATLAS was the most scientifically riveting of the cometary trio, C/2026 A6 (Lemmon) was arguably the most dynamic and photogenic. Comet Lemmon was discovered on Jan. 3 earlier this year and swiftly became a popular target among the astrophotography community, as it brightened from +21.5 to naked eye visibility around its close approach to the sun —known as perihelion — on Nov. 8.

Astrophotographers kept C/2026 A6 (Lemmon) firmly locked in their field of view throughout its journey, capturing each stage of its dramatic evolution. As it approached the sun, the increase in heat radiation caused icy matter in the comet's central nucleus to sublimate into gas, dragging dust particles with it.

The resulting cloud of cometary debris was then snatched up by the charged particles pouring out from the sun — called the solar wind — giving rise to a spectacular tail.

Astronomer Gianluca Masi captured a rare shot of the cosmic wanderer, when a glowing meteor tail in Earth's upper atmosphere appeared to wrap itself around Comet Lemmon's distant tail as it passed through the constellation Serpens on Oct. 24, creating a "a pure perspective miracle".

3. Comet SWAN dives through the Eagle Nebula

While Comet Lemmon's complex tail snagged the attention of astrophotographers worldwide, others took aim at the solar system wanderer C/2025 R2 (SWAN), which put on a magnificent show on Oct. 17, as it passed in front of the Eagle Nebula in the constellation Serpens.

Daniele Gasparri captured a striking view of C/2025 R2 (SWAN)'s vivid green coma as it hung in the pristine skies above the Atacama Desert in Chile, with the vast emission nebula serving as a jaw-dropping backdrop for the cometary body.

The pillars of creation, vast columns of interstellar dust and gas shaped by the radiation of nearby stars and made famous by the Hubble Space Telescope, can be seen nestled in the glowing heart of the vast nebula, to the left of the comet's glowing central nucleus.

4. Comet 3I/ATLAS reaches perihelion

Oct. 30 marked the climax of interstellar traveller 3I/ATLAS's headlong charge into the inner solar system, as it made its closest approach to the sun, passing 125 million miles (202 million km) from our parent star at the point of perihelion.

The event occurred just as 3I/ATLAS flew behind the sun from the perspective of Earth, robbing some of humanity's most powerful observatories of the chance to analyze the comet's chemical composition as it reached a peak of activity. Thankfully, perihelion was observed from elsewhere in the solar system by a flotilla of spacecraft orbiting Mars and travelling through interplanetary space.

3I/ATLAS finally emerged intact from behind the glare of the sun to become visible to Earthbound astronomers and skywatchers in early November, though it remained too dim to spot with the naked eye.

NASA subsequently held a press conference on Nov. 19 following the re-opening of the federal government, where it revealed several new images of the interstellar invader that documented its glowing central nucleus, sun-facing jet and growing tail. Conspiracy theorists were left somewhat broken-hearted by NASA Associate Administrator Amit Kshatriya, who noted, "It looks and behaves like a comet, and all evidence points to it being a comet", as opposed to the technologically advanced spaceship suggested by others.

5. K1 ATLAS breakup

One of the most dramatic cometary moments of 2025 occurred on the night of Nov. 11, when astronomers tracked the solar system comet C/2025 K1 (ATLAS) as its central nucleus broke into three massive pieces, following its close pass of the sun on Oct. 8.

The comet may have crumbled during its first visit to the inner solar system from the shell of icy material which surrounds its outer edge, known as the Oort Cloud.

The increase in heat radiation experienced during perihelion may have created a violent and sudden outflow of material from the nucleus, which could have undermined its structure, leading to the fracturing seen on Nov. 11, according to Elena Mazzotta Epifani of the Italian National Institute for Astrophysics.

Editor's Note: If you would like to share your astrophotography with Space.com's readers, then please send your photo(s), comments, and your name and location to spacephotos@space.com.

On Friday (Dec. 19), the interstellar invader, comet 3I/ATLAS, made its closest approach to Earth, coming to within 168 million miles (270 million kilometers) of our planet at 1 a.m. EST (0600 GMT).

Following this close approach and the opportunity it offers to investigate this interloper from beyond the solar system, 3I/ATLAS will begin to move back out to the outer regions of the solar system, before leaving altogether to continue its voyage through the Milky Way.

3I/ATLAS is just the third body discovered passing through the solar system from interstellar space, its predecessors being 1I/'Oumuamua in 2017 and comet 2I/Borisov in 2019. As such, 3I/ATLAS has been offering scientists the unique opportunity to study the raw materials that came together to form comets, asteroids, and planets orbiting stars other than the sun.

First spotted by NASA's Asteroid Terrestrial-impact Last Alert System (ATLAS) on July 1, 2025, with its trajectory indicating its origin lies elsewhere in the Milky Way.

In fact, its path through space suggests that this interstellar comet comes from a region of our galaxy that is much older than the 4.6 billion-year-old solar system.

The water-rich comet seems to originate from the Milky Way's "thick disk" of stars, rather than the thin stellar disk of which the sun is a member. The thick disk formed earlier than the thin disk, meaning 3I/ATLAS could be up to 7 billion years old.

"All non-interstellar comets, such as Halley's comet, formed at the same time as our solar system, so they are up to 4.5 billion years old," University of Oxford astronomer Matthew Hopkins said in a statement back in July. "But interstellar visitors have the potential to be far older, and of those known about so far, our statistical method suggests that 3I/ATLAS is very likely to be the oldest comet we have ever seen."

During its time within the solar system, 3I/ATLAS has continued to surprise astronomers. As it began to make its closest approach to the sun, or its perihelion, on Oct. 29, the comet brightened more than scientists had expected.

Comets tend to brighten as they approach our star due to solar radiation heating their icy cores and causing solid ice to transform straight into vapor, which erupts from the comet, growing its halo or "coma" and its characteristic glowing tail.

Quite why 3I/ATLAS brightened more than expected as observed by STEREO-A and STEREO-B, the twin spacecraft that make up Solar Terrestrial Relations Observatory (STEREO), the sun observing Solar and Heliospheric Observatory (SOHO), and the weather satellite GOES-19, is still unknown.

"The reason for 3I’s rapid brightening, which far exceeds the brightening rate of most Oort cloud comets at similar r [radial distance], remains unclear," the scientists behind the research, Qicheng Zhang of Lowell Observatory in Flagstaff, Arizona, and Karl Battams, an astrophysicist at the Naval Research Laboratory (NRL) in Washington DC, wrote in a paper discussing the observation published on the research repository site arXiv.

Though 3I/ATLAS is now in the final stage of its occupation of the solar system, the data collected from it will likely inform scientists for some time to come, continuing to paint a more intricate picture of the Milky Way beyond the solar system.

Using NASA’s Eyes on the Solar System interactive app, you can track comet 3I/ATLAS through the solar system and see where it’s headed next.

It came from outer space. Interstellar space, to be precise. From somewhere beyond the influence of our sun, possibly from one of our Milky Way galaxy's most ancient stars, one that formed long before our own sun and solar system. We may never know for sure.

Interstellar comet 3I/ATLAS was discovered on July 1, 2025, by the NASA-funded ATLAS survey (Asteroid Terrestrial-impact Last Alert System) in Chile, a network of telescopes that scans the entire sky multiple times each night looking for moving objects that might pose a threat to Earth. Within hours, astronomers around the world were thrilled by the discovery: the object appeared to be the third-known interstellar object to pass through our solar system, behind 1I/'Oumuamua in 2017 and 2I/Borisov in 2019.

Such visitors offer astronomers a rare opportunity to study objects that may be unlike anything found in our own cosmic neck of the woods. But within months, observations from some of Earth's most powerful telescopes as well as multiple spacecraft and observatories in orbit revealed 3I/ATLAS to in fact be much like comets from our own solar system: it appears to have an icy nucleus surrounded by a coma, a bright cloud of gas and dust that sublimates away from the nucleus as the comet approaches the sun and warms up.

Nevertheless, in what may be indicative of the post-truth age and influencer-dominated media landscape we now live in, a feeding frenzy of sensationalism and misinformation sprang up around the comet throughout the latter half of 2025. Claims that 3I/ATLAS might be an alien spacecraft or some form of extraterrestrial probe spread rapidly throughout social media within weeks of its discovery.

Cable news channels caught on. Kim Kardashian published a viral request on X imploring acting NASA administrator Sean Duffy to spill the "tea" on the object. Even members of the U.S. Congress got interested, writing letters to implore NASA to release whatever data it may have on the comet.

How, or why, did this interstellar comet generate such mainstream interest and capture the public imagination throughout 2025? Where did all of the sensational claims come from?

"It all came during the shutdown"

For one, it came down to timing.

Qicheng Zhang, a postdoctoral fellow at the Lowell Observatory in Arizona and author of a study of the comet's brightness as it approached the sun earlier this year, said that because 3I/ATLAS was discovered months before its closest approaches to the sun and Earth (unlike the previous two interstellar objects), there was much more of an opportunity for misinformation to spread.

"That seems to have given it a whole lot of extra time for conspiracy theorists to run wild and drum up attention before their unsubstantiated predictions are disproven to the extent they can ever be and people lose interest," Zhang told Space.com.

Another aspect of the timing of the comet's discovery centered on the fact that the U.S. government was shut down from Oct. 1 to Nov. 12 as Congress deliberated over funding appropriations for the 2026 fiscal year. During that time, many NASA operations were paused, including most public affairs agencies that would normally issue press releases and answer questions from the media and the public.

But during that time, the comet was also racing through the solar system. On Oct. 2, NASA's Mars Reconnaissance Orbiter took images of 3I/ATLAS with its HiRISE camera, which, given the instrument's resolution, were thought to be the best opportunity astronomers had to nail down an estimate of the comet's size.

In the vacuum of any official information from NASA, unofficial theories flourished, particularly ones that accused the space agency of using the shutdown to hide the "true" nature of the comet, said Larry Denneau of the University of Hawaii, who discovered 3I/ATLAS.

"Unfortunately, it all came during the shutdown," Denneau told Space.com. "And so that created its own complications, because the folks out there, who, you know, are conspiracy bent, thought NASA was trying to hide something."

In fact, when asked about why the comet became such a mainstream topic throughout 2025, most of the sources Space.com spoke to had one singular answer: the Frank B. Baird, Jr. Professor of Science at Harvard University, Avi Loeb, who served as the chair of Harvard's astronomy department from 2011 to 2020.

"The public laps it up"

In July, just weeks after the comet's discovery, Loeb published a non-peer-reviewed paper on the open source repository arXiv, arguing that the comet's characteristics suggest it might actually be alien technology. Loeb later wrote that images of 3I/ATLAS were "held hostage for bureaucratic reasons at NASA" during the shutdown.

The claims spread like wildfire, and within weeks, the comet was dominating headlines and social media feeds. But many astronomers were baffled by the attention 3I/ATLAS was receiving.

"It doesn't help that we have a Harvard professor who's out there, you know, saying that this thing could be an alien spacecraft or this doing all of this weird stuff," Denneau told Space.com. "That's a whole thing in itself. Why is Avi Loeb doing that? It's kind of a mystery to some of us in the field," Denneau added.

Mick West, a science writer who has published books on how to debunk sensational claims, echoed the comet's discoverer. "It's because of Avi Loeb," West told Space.com. "His unremitting push, combined with the gravitas of his Harvard professorship, makes it an easy sensational story for the media. He has many technical critics who point out (with the math) that it's almost certainly just a comet.

"But that's boring, so the media goes with 'Harvard astrophysicist says alien probe' and the public laps it up."

Space.com reached out to Loeb to ask why he thought the comet captured so much public interest throughout the year.

"My explanation for the viral interest in 3I/ATLAS involves its anomalies, as listed in my essay," Loeb said via email. "My essays received more than 5 million views over the month of November, and my interview on the Joe Rogan Experience received more than 7 million views for the same reason."

Loeb previously wrote that "seeking scientific data is key to learning the truth" in a blog post criticizing NASA for not releasing its data on 3I/ATLAS during the government shutdown. "By staying curious and humble while collecting clues in this detective story, science brings us together. When egos get in the way, politics and social media set us apart."

"Not too much is unusual there"

As more imagery and observations of 3I/ATLAS continue to be made, scientists aren't focused on these anomalies, but instead say the comet appears to be just that: a normal comet.

"You kind of know the signatures that you're looking for; we were quick to be able to say, 'Yep, it definitely behaves like a comet,'" Nicky Fox, associate administrator of NASA's Science Mission Directorate, said during a Nov. 19 press briefing during which the agency released imagery of 3I/ATLAS. "We certainly haven't seen any technosignatures or anything from it that would lead us to believe it was anything other than a comet."

Other astronomers have said the same. "We can see how much of each particular gas the comet is emitting and compare it to the gas coming out of solar system comets," Zhang said in a Lowell Observatory statement this month. "And so far, those ratios fall within the fairly typical range that we're seeing for solar system comets. So, not too much is unusual there."

Likewise, a new study published in Research Notes of the AAS based on observations by two different interplanetary spacecraft, NASA's Psyche spacecraft and Europe's Mars Trace Gas Orbiter, was able to calculate the non-gravitational acceleration 3I/ATLAS exhibited as it approached the sun caused by gases escaping its frozen shell. It found that 3I/ATLAS behaves as scientists expect a comet should.

"The results are pretty typical of ordinary comets, and certainly not record-breaking," lead author T. Marshall Eubanks told SpaceWeather.

But in a blog post in November 2025, Loeb criticized the "violent insistence of comet experts" that argued the acceleration was caused by this ordinary outgassing, "rather than thrusters on a spacecraft."

"Always an uphill battle"

The mainstream interest in 3I/ATLAS appears to have waned, but Earth-based telescopes and space-based observatories continue to study the comet.

Scientists working with the Gemini North telescope in Hawaii captured new images of the comet just after its close pass with the sun in late November.

Two European X-ray observatories, XMM-Newton and XRISM (a joint project with the Japanese space agency JAXA), recently captured images of the comet, revealing X-rays streaming out for nearly 250,000 miles (400,000 kilometers) around 3I/ATLAS's nucleus.

But as more data continues to be collected about the comet, it's unlikely these observations will make the types of headlines that 3I/ATLAS generated earlier in the year. The possibility of alien visitors from afar is far easier to understand than photometric analyses of cometary outgassing, and for decades, science fiction has encouraged us to keep our eyes to the skies not for conducting routine science, but in the search for signs of intelligent life out there in the vacuum of space.

Unfortunately, it truly appears that what made 3I/ATLAS such a popular topic throughout 2025 is the fact that one scientist with an impressive list of credentials made claims of possible alien technology, claims that landed him on television and podcasts, but that clouded the real, hard science being done to learn about the third-known object to fly through the solar system from another star.

"The misinformation is much easier to produce and much harder to squash, and so it's just always an uphill battle," Denneau told Space.com. "But you know, we're all doing what we can do right?"

For the first time ever, astronomers have captured two distinct X-ray views of an interstellar comet, providing an unprecedented glimpse into the interplay between a visitor from beyond our solar system and solar wind.

Interstellar comet 3I/ATLAS, the third confirmed object known to have originated outside our solar system, has now been imaged in X-ray light by both the European Space Agency's (ESA) XMM-Newton observatory and the X-Ray Imaging and Spectroscopy Mission (XRISM) led by the Japanese space agency JAXA in partnership with NASA and ESA. These X-ray observations allow scientists to detect and study gases that other instruments can't easily spot, according to a statement from ESA.

Comets shine in visible light when sunlight reflects off dust and gas escaping their icy core, while X-ray light tells a very different story. In space, the interaction between fast-moving charged particles from the sun — also known as solar wind — and a comet's surrounding gas cloud produces X-ray emissions. Detecting that glow lets scientists trace where and how these interactions occur and what kinds of gases are present at levels that optical telescopes might miss.

While NASA's James Webb Telescope and other instruments have already spotted abundant water vapor, carbon monoxide and carbon dioxide in 3I/ATLAS's coma, X-ray observations are uniquely sensitive to lighter gases such as hydrogen and nitrogen that are otherwise hard to detect.

The first X-ray observation of 3I/ATLAS was made by the XRISM space telescope, which observed the comet for 17 hours between Nov. 26 and 28. The resulting image was captured using XRISM's soft X-ray telescope, Xtend, whose field of view spans roughly 1.2 million square miles (3 million square kilometers), revealing X-ray emission extending about 250,000 miles (400,000 kilometers) from the comet's nucleus — evidence that the comet's gas is being energized by the solar wind, according to a statement from ESA releasing the image.

The XRISM data also carry spectral signatures of elements such as carbon, nitrogen and oxygen, which helps scientists begin to disentangle the mix of particles released from the comet's nucleus and how they interact with the high-energy environment near the sun, ESA officials said in the statement.

Shortly after, ESA's XMM-Newton X-ray observatory studied 3I/ATLAS for about 20 hours on Dec. 3, when the comet was roughly 175–177 million miles (282–285 million km) from the spacecraft. The image was captured using the telescope's most sensitive X-ray instrument, the European Photon Imaging Camera (EPIC)-pn, revealing a distinct X-ray glow (shown in red) surrounded by fainter gradients. These features mark regions where the solar wind is interacting with gas streaming off the comet, according to a statement from ESA releasing the image.

"3I/ATLAS presents a new opportunity to study an interstellar object, and observations in X-ray light will complement other observations to help scientists figure out what it is made of," ESA officials said in the statement.

Together, X-ray, optical, infrared and radio observations are offering fresh insights into 3I/ATLAS as it makes its rare journey through the inner solar system, with its upcoming closest approach to Earth expected around Dec. 19.

Interstellar comet 3I/ATLAS made its closest approach to Earth early on Friday, Dec. 19. While it didn't come close enough to pose any risk to our planet, astronomers have calculated the precise moment when the comet reached its minimum distance to us.

According to the orbital calculations from NASA's Jet Propulsion Laboratory (JPL) Horizons system, comet 3I/ATLAS was closest to Earth at 1 a.m. EST (0600 GMT) on Dec. 19. At that time, the comet was about 1.8 astronomical units away — roughly 168 million miles (270 million kilometers — or nearly twice the average distance between Earth and the sun.

Discovered on July 1, by NASA-funded ATLAS telescopes in Chile, 3I/ATLAS is only the third known interstellar object ever detected passing through our solar system, following 'Oumuamua in 2017 and 2I/Borisov in 2019.

While comet 3I/ATLAS will remain far too distant and faint to become a naked-eye spectacle as it passes Earth, its flyby is scientifically valuable because interstellar objects are so rare. Studying 3I/ATLAS near its closest approach provides astronomers with their best opportunity to examine material formed around another star, offering a fleeting glimpse into planetary systems beyond our own.

Skywatchers can also follow along with the flyby live online Dec.19-20 on Space.com courtesy of the Virtual Telescope Project. The livestream will begin at 11 p.m. EST on Dec. 19 (0400 GMT on Dec. 20), offering viewers a chance to see the interstellar visitor as it makes its closest approach to Earth, weather permitting.

Follow along with the latest 3I/ATLAS news with our live blog.

Editor's note: This article was updated at 1:30 a.m. EST (0630 GMT) to reflect the close approach that occurred as expected at 1:00 a.m. (0600 GMT) Dec. 19, 2025.

Eager skywatchers will soon have front-row seats to a rare cosmic encounter as interstellar comet 3I/ATLAS makes its closest approach to Earth, and you can watch it happen live online tonight!

The Virtual Telescope Project will host a free livestream starting at 11 p.m. EST on Dec. 19 (0400 GMT on Dec. 20), sharing real-time telescope views of comet 3I/ATLAS captured by its robotic observatories in Manciano, Italy, weather permitting.

Comet 3I/ATLAS made its closest approach to Earth at 1 a.m. EST (0600 GMT) on Dec. 19. At that time, it was about 1.8 astronomical units away — roughly 168 million miles (270 million kilometers), nearly twice the average distance between Earth and the sun.

Discovered in July 2025 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey, 3I/ATLAS quickly captured the attention of both scientists and the public. It is only the third confirmed interstellar object ever detected passing through our solar system, following 1I/'Oumuamua in 2017 and 2I/Borisov in 2019. Researchers are especially interested in its composition and behavior, which could offer rare clues about how planetary systems form around other stars.

The comet is too faint to be seen with the naked eye and will be challenging even for small backyard telescopes. Under dark skies, observers with a telescope of 8 inches or larger may be able to spot it as a faint, fuzzy patch of light. If you're unable to look for the comet in person, you can sit back, relax and enjoy the view from the comfort of your own home via the livestream.

Editor's note: This article was updated Dec. 18 at 11 p.m. EST to notify readers that the livestream of interstellar comet 3I/ATLAS by the Virtual Telescope Project has been postponed one day due to rain at the observing site. It is now scheduled for Friday, Dec. 19, at 11 p.m. EST (0400 GMT).

The interstellar comet 3I/ATLAS made its closest approach to Earth today (Dec. 19, 2025). Here's the latest news you need to know.

• Comet 3I/ATLAS will approach within 168 million miles (270 million kilometers) of Earth when it makes its close flyby on Dec. 19.
• You can watch comet 3I/ATLAS's flyby live online in a free webcast.
• Who discovered comet 3I/ATLAS? We talked to the scientist behind the find

Latest Comet 3I/ATLAS news

Comet 3I/ATLAS has last hurrah this week

Good morning, Space Fans! As of today, we are T-2 days until the interstellar comet 3I/ATLAS makes its closest approach to Earth and then we'll have to say our goodbyes.

Whether or not you're in Team Comet or Team "Could It Be A Spaceship?" 3I/ATLAS has dominated the comet conversation since its discovery on July 1 by the ATLAS telescope in Chile. On Friday, Dec. 19, 2025, the comet will be at its closest to Earth at a range of roughly 168 million miles (270 million kilometers) before heading out of our solar system for good.

Over the next two days, we'll chronicle comet 3I/ATLAS's Earth flyby, and revisit its passage through our solar system — and its legacy.

Read our full preview of the comet's Earth flyby.

Comet 3I/ATLAS: An early Christmas gift for scientists

When 3I/ATLAS is closest to Earth on Dec. 19, all the features that we are looking for will be easier to detect with our telescopes and it has scientists as eager as kids on Christmas.

Comet 3I/ATLAS is the third large interstellar visitor (an asteroid or a comet) known to have passed through our solar system from beyond our solar system. By studying it closely, astronomers hope to learn more about other celestial objects through telescope observations.

"It has since been careening through the interstellar medium of the Milky Way galaxy for billions of years," Darryl Z. Seligman, an assistant professor of physics and astronomy at Michigan State University, wrote in an op-ed. "And we get front-row seats to watch as it gets close to our sun, for what is almost surely the first time it has ever gotten close to a star".

Read the full op-ed on the comet's Earth flyby here.

Who discovered Comet 3I/ATLAS?

If you've been as captivated as us here at Space.com by comet 3I/ATLAS's trip through the solar system, you might find yourself wondering exactly how it was discovered. So did we, which is why our own Kenna Hughes-Castleberry took it upon herself to find out  —  and the result was eye-opening!

What seemed like a normal July night ended up making history when astronomer Larry Denneau at the University of Hawaii's Institute for Astronomy discovered a new moving object while scrolling through data from ATLAS — the Asteroid Terrestrial-impact Last Alert System."I was the person reviewing at the time that 3I popped out of the pipeline," Denneau told Space.com "And at the time, it looked like a completely garden variety new Near Earth Object."

Read the full story behind the discovery of comet 3I/ATLAS here.

How to watch the comet 3I/ATLAS Earth flyby

The interstellar comet 3I/ATLAS will make its closest pass by Earth on Dec. 19, and you'll be able to watch its approach live online, but you'll need to tune a bit earlier than you'd think.

Astrophysicist Gianluca Masi of the Virtual Telescope Project will host a free livestream of comet 3I/ATLAS on Thursday, Dec. 18, at 11 p.m. EST Dec. 18 (0400 GMT on Dec. 19), weather permitting. You can watch the livestream here on Space.com.

Masi's livestream will run through comet 3I/ATLAS's closest approach at 1 a.m. EST (0600 GMT), but will depend on good weather from his telescope's observing site.

The comet is too faint to be seen with the naked eye and will be challenging even for small backyard telescopes. Under dark skies, observers with a telescope of 8 inches or larger may be able to spot it as a faint, fuzzy patch of light. Read how to watch the comet 3I/ATLAS flyby live online.

How far is Comet 3I/ATLAS from Earth right now?

As of 12 p.m. ET today (Dec. 17), Comet 3I/ATLAS is about 166.9 million miles (268.6 million kilometers) from the Earth and closing, ahead of its closest approach on Dec. 19.

You can track comet 3I/ATLAS yourself with the help of NASA's Eyes On The Solar System webpage, which has a "Distance Tool" that allows you to calculate the separation between the comet and any other solar system object included in the simulation.

Not the first interstellar comet

As its name suggests, comet 3I/ATLAS is not the first interstellar object known to come from beyond our solar system. To date, there have been three in total (hence the "3I" in the name, it stands for "3 Interstellar").

Comet 3I/ATLAS's discovery in 2025 followed the discovery of the first interstellar object, 1I/'Oumuamua, in 2017. Two years later, another object was spotted. That one was called comet 2I/Borisov in 2019. Both 'Oumuamua and 2I/Borisov spent months passing through the solar system, only to leave us behind for the void of interstellar space.

The same fate awaits 3I/ATLAS, so we should enjoy the comet while it's with us.

Is comet 3I/ATLAS really a comet?

You've probably heard all the theories: It's really an alien spaceship. It's changed direction. It spat out a tiny spacecraft.

Well, NASA recently made it official: Comet 3I/ATLAS is just what it looks like - a comet from beyond our solar system. In late November, NASA held a televised press conference to put the comet 3I/ATLAS rumours to bed.

"It looks and behaves like a comet, and all evidence points to it being a comet. But this one came from outside the solar system, which makes it fascinating, exciting and scientifically very important," NASA Associate Administrator Amit Kshatriya told reporters during the press briefing.

Here's the full story on NASA's take on comet 3I/ATLAS.

Good night, for now.

Good evening, Space Fans. We're wrapping up today's T-2 day countdown to the comet 3I/ATLAS flyby of Earth, but we'll be back tomorrow with another series of stories and a look back at the comet's legacy.

Tune in then!

Comet 3I/ATLAS is less than 1 day away from Earth flyby

Good morning, space fans! We are officially T-1 day away from the closest approach to Earth of comet 3I/ATLAS, with the flyby set for early Friday, Dec. 19.

We're keeping a close eye on the comet's progress and as of this posting, comet 3I/ATLAS is about 166.8 million miles (268.5 million kilometers) from Earth and closing. But there's no need to worry about the comet's approach.

At its closest point, comet 3I/ATLAS will be about 168 million miles (270 million kilometers) away. After that, it will get farther and farther with each passing minute until it's off to visit some other solar system.

We've got a great set of comet stories for you today, so check back here for the latest on 3I/ATLAS as we get closer to its Earth flyby.

How comet 3I/ATLAS captured our hearts with mystery

We'll admit it: We would love it if the interstellar comet 3I/ATLAS really was an alien spaceship, but at the end of the day, it's still a comet. Yet that does not mean 3I/ATLAS isn't still completely amazing; otherwise, we wouldn't have covered the comet's passage through our solar system as we've done over the last six months.

Why not read up on the four key things that NASA revealed about the comet in a long-awaited briefing following the reopening of the U.S. government in November? At the event, NASA Associate Administrator Amit Kshatriya explained "we very much want to find signs of life in our universe," before re-iterating, "but 3I/ATLAS is a comet".

Full article: 4 key things NASA just revealed about the interstellar comet 3I/ATLAS.

Interstellar comet 3I/ATLAS just revealed its secret wobble

Astronomers have spotted the first-ever wobbling jet from an interstellar comet and it is changing how we understand visitors from beyond our solar system.

Using the Two-meter Twin Telescope at Tenerife's Teide Observatory, researchers detected a faint jet of gas and dust blasting from 3I/ATLAS, slowly wobbling as the comet rotates. Crucially, that rhythmic motion confirms that 3I/ATLAS spins once every 14-17 hours, making it the first interstellar comet with a directly measured rotation period tied to visible activity on its surface.

What surprised scientists most is how familiar the behavior looks. Despite forming around another star, 3I/ATLAS behaves much like comets born closer to home. Scientists describe it as an "extraordinarily normal interstellar comet," complete with sunlight-driven jets.

The findings of this study are published in the journal Astronomy & Astrophysics.

Spacecraft reveal 3I/ATLAS's X-ray signature

Scientists are working hard to collect valuable data on 3I/ATLAS's spectral fingerprint before it disappears from our skies for good, in an attempt to shed light on the composition of the distant star system where it was born.

The European Space Agency's XMM-Newton observatory and the Japanese space agency-led X-Ray Imaging and Spectroscopy Mission (XRISM) revealed a vast 250,000 mile (400,000 kilometer) X-ray glow extending from the comet's nucleus. An analysis of this X-ray light, emitted by gasses interacting with the solar wind, will help scientists understand how the comet is being influenced by the high-energy environment surrounding our star after its marathon voyage through interstellar space.

Read the full story here: Scientists detect X-ray glow from interstellar comet 3I/ATLAS extending 250,000 miles into space.

How fast is interstellar comet 3I/ATLAS going?

Having made its closest approach to the sun on Oct. 30, comet 3I/ATLAS is now on its way back out of the solar system, charging away from our parent star at a breathtaking speed of 144.1 thousand miles per hour (231.9 thousand kilometers per hour) as it heads towards interstellar space.

The ancient interloper is already well beyond the orbit of Mars ahead of its closest pass of Earth on Dec. 19. Its next planetary rendezvous will be with Jupiter in March next year, when it will pass 36 million miles (58 million kilometers) from the gas giant, before continuing on an incident-free course to exit the heliosphere.

What time is comet 3I/ATLAS's closest Earth approach?

If you're hoping to try and watch comet 3I/ATLAS's closest approach to Earth live online, it would help to know exactly when to tune in. But don't worry, space fans, we've got you covered.

As Space.com's Daisy Dobrijevic reports, comet 3I/ATLAS closest point to Earth will occur at 1 a.m. EST (0600 GMT) as it zips past our planet at a whopping 144.1 thousand mph (231.9 thousand kph). At the time, it will be 168 million miles (270 million km) from Earth.

You'll be able to watch the flyby live online starting at 11 p.m. EST (0400 GMT), courtesy of the Virtual Telescope Project. Comet 3I/ATLAS is too far from Earth to see with the unaided eye, and you'd need a large telescope to try and spot it, so the livestream may be one of our last public looks at the interstellar visitor as it passes by.

How you can track interstellar comet 3I/ATLAS

You may not be able to see 3I/ATLAS with your own eyes or most telescopes, but there are multiple ways you can track it from home.In fact, there are four different ways you can track the interstellar comet right now, according to our skywatching writer Anthony Wood.

The coolest way to track comet 3I/ATLAS is through NASA's Eyes on the Solar System website, which allows you to follow the comet's progress in a very accessible format by creating a 3D model based on real-life observations. You can see that feature below as well, right now.

But there are other ways. The Comet Observation Database allows you to track the comet's brightness over time based on observations from amateur astronomers. A smartphone astronomy app (I like to use SkySafari) can also allow you to pinpoint where comet 3I/ATLAS is in the sky, even if we can't see it with the naked eye.

Finally, there is the Virtual Telescope Project run by astrophycisit Gianluca Masi, which will offer a livestream of comet 3I/ATLAS during its closest approach. That livestream begins at 11 p.m. ET (0400 GMT) and will run through the closest approach at 1 a.m. ET (0600 GMT), weather permitting.Happy comet hunting!

NASA's Europa Clipper sees comet 3I/ATLAS!

It may look like only a pale blue blob, but this is definitely the interstellar comet 3I/ATLAS.

This image was taken by NASA's Europa Clipper spacecraft, which is on its way to the Jupiter moon Europa, and publicly unveiled to the world today (Dec. 18), just one day before the comet's closest approach to Earth on Dec. 19.

The Europa Clipper spacecraft used its Ultraviolet Spectrograph (UVS) developed by the Southwest Research Institute (SwRI) to observe comet 3I/ATLAS on Nov. 6 at a time when it could not be seen properly from telescopes on Earth and spacecraft orbiting Mars. At the time, Europa Clipper was about 103 million miles (164 million kilometers) away from the comet.

"We’re excited that this opportunity to view another target on the way to Jupiter was completely unexpected,” SwRi's Kurt Retherford, principal investigator for Europa-UVS, said in a statement. "Our observations have allowed for a unique and nuanced view of the comet."

The Europa Clipper image looks sunward towards comet 3I/ATLAS, revealing its twin tails from behind, as well as a glimpse at the comet's head-like coma and surronding cloud of gas. The UVS instrument found signs of oxygen, hydrogen and dust-related features, "supporting the preponderance of data indicating that comet 3I/ATLAS underwent a period of high outgassing activity during the period just after its closest approach to the Sun," SWRI reported.

NASA launched Europa Clipper toward Jupiter in 2024. It should arrive at Jupiter in 2030 to begin orbiting the icy moon Europa.

3I/ATLAS close Earth flyby: What to know tonight

Okay, space fans, it's nearly make or break time for the close Earth flyby of the interstellar comet 3I/ATLAS.

In case you're just joining us, we are now just hours away from the closest approach to Earth by the interstellar comet 3I/ATLAS. We've been offering live coverage over the last two days for the flyby, with a series of stories and guides online, including how to watch the flyby in a livestream, different ways to track the comet and more. But it all goes down tonight. Comet 3I/ATLAS will make its closest approach to Earth at 1 a.m. EST (0600 GMT) tonight, when it will come within 168 million miles (270 million km) of our planet. That's about 1.8 astronomical units, or nearly twice as far from Earth as our own planet is away from the sun. So there's no danger of an impact to Earth.

Scientists around the world have been tracking the interstellar comet to understand how it differs from the comets and dust we see in our own solar system.

Comet 3I/ATLAS is the third known interstellar comet after 2017's 1I/'Oumuamua and 2019's 2I/Borisov. It was discovered on July 1, 2025 and made its closest approach to the sun in October. Now it is looping outward to exit the solar system. Once it's gone, it will be gone forever.

See you at 11 pm ET for comet 3I/ATLAS's Earth approach!

Okay, space fans, we're going to pause our updates for interstellar comet 3I/ATLAS for a few hours as we await the final countdown to its 1 a.m. EST (0600 GMT) approach to Earth. Thanks for joining us today.

We'll be back at 11 p.m. EST (0400 GMT) with the start of the livestream coverage of the comet from the Virtual Telescope Project by Gianluca Masi of Ceccano, Italy. PLEASE NOTE: The livestream is weather dependent. If the skies are cloudy over Ceccano, the livestream could be delayed or canceled. But we're hoping for good weather. See you at 11 p.m. ET, space fans.

Good night!

2 hours to Comet 3I/ATLAS flyby: Livestream postponed

The interstellar comet 3I/ATLAS is now less than 2 hours away from its closest approach to Earth.

We were expecting to begin sharing a livestream of the comet as seen by astrophysicist Gianluca Masi with the Virtual Telescope Project in Ceccano, Italy. However, Masi reports that rain over his observing site is thwarting observations.

"Because of rain, this event has been postponed," Masi wrote in an update.

The livestream has been rescheduled for Friday night, Dec. 19, at 11 p.m. EST (0400 GMT).

Meanwhile, comet 3I/ATLAS continues on its course by Earth.

As of 11 p.m. ET tonight, it was 166.8 milion miles (286.5 million km) from Earth and traveling at about 148,600 mies per hour (239,200 km/h), according to NASA's Eyes On The Solar System.

1 hour until comet 3I/ATLAS is closest to Earth

We are now one hour away and counting until the closest approach to Earth by comet 3I/ATLAS, the interstellar comet from beyond our solar system.

As of 12:08 a.m. EST (0500 GMT), the comet is beyond the orbit of Mars, as it is about 166.8 milion miles (286.5 million km) from Earth, according to NASA's Eyes On The Solar System site.

Comet 3I/ATLAS's closest poitn to Earth will come at abotu 1 a.m. EST (0600 GMT).

Did you see it? Interstellar comet 3I/ATLAS has just zoomed past Earth!

Good morning space fans!

Interstellar comet 3I/ATLAS made its closest approach to Earth moments ago, passing within 168 million miles (270 million km) of our planet. The icy visitor will now continue its journey through the outer solar system, passing Jupiter in early 2026, crossing the orbits of Saturn, Uranus and Neptune by 2028 and then head out to interstellar space, never to return.

As some of you may be aware, the comet livestream hosted by Gianluca Masi with the Virtual Telescope Project has been postponed until 11 p.m. EST Friday night, Dec. 19 (0400 GMT on Dec. 20), weather permitting. Join us later today to catch a glimpse of 3I/ATLAS before it's gone forever!

Stay tuned today as we continue to bring you the latest Comet 3/I ATLAS news and bid farewell to our icy visitor.

Farewell, 3I/ATLAS!

Our interstellar visitor has officially passed its closest approach to Earth and is now heading back out toward the outer solar system — and eventually beyond.

On Dec. 19, comet 3I/ATLAS came within about 168 million miles of our planet, giving scientists a rare chance to study material from beyond our solar system before it begins its long journey back into the Milky Way.

If you want to know what happens next, why this object is so special, you can read our wrap story here.

Why did comet 3I/ATLAS go viral in 2025?

Earth is in the rear-view mirror now for comet 3I/ATLAS after its closest approach to our planet today, but as we say farewell to the interstellar visitor, I have to be honest: I will not miss the "Is it a spaceship?" questions that bombarded me over the last six months. (Most recently at a company holiday party!)

But the widespread reach of that question - "Is comet 3I/ATLAS really a spaceship?" - really got us wondering, especially after NASA came out in November and outright said no, it was a comet.

So, to honor 3I/ATLAS's place in our collective hearts, managing editor Brett Tingley went out to find out why comet 3I/ATLAS seemed to go more viral than its predecessors. The answer, it seems, comes down to timing.

Read Brett's full story on How the interstellar comet 3I/ATLAS went from routine to viral in 2025.

Final Comet 3I/ATLAS

Hi, space fans, while the interstellar comet 3I/ATLAS is headed away from Earth, there is still another chance to see it tonight.

At 11 p.m. EST (0400 GMT) the Virtual Telescope Project by Gianluca Masi of Ceccano, Italy. will hold a free livestream that will run through 1 a.m. EST (0600 GMT). PLEASE NOTE: The livestream is weather dependent. If the skies are cloudy over Ceccano, the livestream could be delayed or canceled. But we're hoping for good weather.

Thank you for joining us on this awesome week of comet 3I/ATLAS's approach, and we look forward to the next interstellar visitor!

Good night!

What seemed to be just a normal evening on July 1, 2025 for Larry Denneau, senior software engineer and astronomer at the University of Hawaii's Institute for Astronomy began the same way hundreds of nights before it had: with data quietly rolling in from telescopes scanning the night sky.

Denneau is part of the team behind ATLAS — short for Asteroid Terrestrial-impact Last Alert System — a network of wide-field telescopes that repeatedly images huge swaths of sky to catch anything that moves, particularly near-Earth asteroids. The system snaps the same patch of sky four times in quick succession to create a short motion path, or "tracklet" that shows possible movement, then uses reference images where the sky is still to subtract out any stars and galaxies, leaving behind moving points that could be asteroids, comets, or something else. Candidates that survive these automated filters are sent to a human reviewer to verify they're real and ready to be catalogued by the Minor Planets Center.

That July evening, one of those survivors landed in front of Denneau. When 3I/ATLAS first showed up in the ATLAS software, it didn’t look special at all. "I was the person reviewing at the time that 3I popped out of the pipeline," Denneau told Space.com "And at the time, it looked like a completely garden variety new Near Earth Object." So Denneau did as the software he designed recommended he do. He clicked "submit."

When the discovery of a new interstellar object lit up astronomers' inboxes around the world, Larry Denneau was nowhere near his email.

He was up in the mountains at Mauna Loa, high on Hawaii's Big Island, servicing a telescope. For an entire day, he was effectively offline, while excitement quietly built around a strange object moving across the solar system.

When he finally got back that night, reality hit all at once.

"I was oblivious to them until we got back that night," he said. "And my inbox was completely exploded with all of this stuff […] At that point, we're thinking about where is it, how fast is it going? Within a day, because this object is so interesting, there are hundreds of observations from different telescopes all confirming the orbit."

The object was classified by the Minor Planets Center as 3I/ATLAS, only the third-known interstellar visitor ever observed passing through our solar system, following 1I/'Oumuamua's discovery in 2017 and 2I/Borisov's in 2019. Unlike typical asteroids or comets, interstellar objects are not gravitationally bound to the sun; they originate around other stars and are briefly visible to us only as they pass through our solar system.

To find these objects, software like the type ATLAS uses looks for any moving objects, just points of light shifting against a background of stars.

"What comes out of our pipeline are really positions," Denneau said. "Things that look like stars that are moving across the background."

At that stage, a human still has to make the call. Someone has to look at the data and decide whether it's real.

"So, yeah," Denneau said, "I'm literally the person who clicked the button and submitted the discovery observations for this object."

Only later did the oddities become clear, especially in the models showing from where 3I/ATLAS might have been moving. As Denneau explained, "Folks with follow-up telescopes go to these places in the sky and they'll see the thing moving in the direction that it’s supposed to be moving. And they'll send in the observations and then Minor Planet Center and the Jet Propulsion Laboratory (JPL) in Pasadena, at the same time, will fit the observations to the orbit and try to compute what the orbit should be."

These follow-up observations and models showed that the object's orbit didn’t behave like anything bound to the sun.

"All of the orbit fits turned out to be really poor," Denneau said. "They didn’t look like the solar system — they had this funny trajectory that said it's going really fast. It's not bound to the sun."

That's when it became obvious: this was something from outside our solar system entirely.

"I was getting asked by JPL, do we have any earlier possible observations that can confirm the trajectory and stuff?" He added. "So we scrambled to try to find some more observations from previous nights."

Where engineer meets astronomer

Denneau doesn't fit the traditional mold of an astronomer. He didn't start his career studying stars or planets — he started with code.

"I'm sort of a non-traditional astronomer," he said. "I started out my career in engineering, mostly computer programming, and so my degree is in EE actually, and not in physics or astronomy." Denneau eventually did receive a Ph.D. in astrophysics from Queen's University Belfast, but continued to use his software skills to shape his career.

After moving to Hawaii and working as the software architect for the asteroid detection pipeline on the Pan-STARRS telescope project, Denneau became deeply involved in building the software systems that modern sky surveys depend on. He eventually joined ATLAS, a NASA-funded project designed to scan the sky every night for near-Earth asteroids. From Denneau's perspective, astronomy depends on a mix of hardware and software.

"We built some telescopes," Denneau said, "but after the telescopes are built, it's really a software project." It would be that software project, one that Denneau helped develop, that would eventually capture images of an interstellar comet.

Each night, ATLAS telescopes take thousands of images of the sky. Because the system uses wide-field lenses, it can cover an area of the sky more than 100 full moons at once. This adds up to an area the size of nearly the entire visible sky every 24 hours, repeatedly revisiting the same regions to look for motion. Those images are automatically transferred, processed, compared and filtered by custom software designed to find anything that moves, especially asteroids close to Earth.

"We have automated software that controls the telescopes, copies the data to Honolulu and then searches these images […] for things that are moving," Denneau explained. That volume is intense as "four or five telescopes combined take a good fraction of a terabyte of data every night," he added. "We're a multi-petabyte project at this point. And so that's the kind of stuff that, as a computer person, keeps me awake, because it’s a lot of data to keep secure and backed up."

That’s why, for Denneau, studying the stars is more of a software project as opposed to a hardware project, as the system has to ingest, clean, subtract, detect, match and archive, all while helping to filter out false positives that could waste other astronomers’ time chasing ghosts.

"We're really sensitive to not wanting to put false things on the confirmation page," Denneau said. "Because other telescopes will spend precious telescope time chasing something that's not real."

ATLAS aims for near-perfect reliability before sending out an alert. "We want to be like 99-point-something-percent reliable on that front," he added.

Detecting other moving objects

Not only was Denneau the person who initially detected 3I/ATLAs using his software, but just months earlier, he'd also been the one on duty for another discovery: near-Earth asteroid YR4.

As with most ATLAS detections, YR4 first appeared as a faint moving point pulled out of the background. Denneau checked the detections and confirmed that they were real before sending the data to the Minor Planets Center. The building-sized YR4 was initially thought to only have slim chances of hitting Earth on Dec. 22, 2032. However, with more study from astronomers, NASA concluded that YR4 actually poses no significant impact threat at all.

Why 3I/ATLAS was hard to detect

Unlike YR4, finding earlier observations of 3I/ATLAS to model where it might have come from was easier said than done. During its July 1, 2025 detection, the interstellar object happened to be moving through a particularly crowded part of the sky, packed with stars from the Milky Way. That made detection much harder.

ATLAS requires four clean detections to officially flag a new object. Until 3I/ATLAS moved into a less cluttered region of the sky, it stayed hidden in the noise, which is most likely why it wasn't detected sooner.

"When there's so many stars in the background, sometimes an asteroid goes right on top of a star," Denneau explained. "And so you only get three out. Because it was in the Milky Way, we had to kind of wait for it to get to a less dense part of the sky, for our pipeline to automatically admit it. And so we got it a week later than we actually first thought." Once 3I/ATLAS did move to a less dense area, the software worked exactly as designed, and even dug up earlier, "precovery" observations that helped confirm its unusual orbit.

Since its initial classification, 3I/ATLAS's popularity has spilled from the astronomy community into headlines and social media feeds. Interstellar visitors are still so rare that each one captures the public imagination and 3I/ATLAS is no exception. Each of these objects offers a fleeting, invaluable glimpse of material formed around another star.

And in this case, that glimpse began not with a dramatic telescope view, but with software, data, and one person clicking a button at exactly the right time.

"Every day I still love coming to work and working on astronomy," Denneau said. "It's just super fun."

Could the Star of Bethlehem, which guided the 'three wise men' to the infant Jesus in the Christian Bible, have been a comet that came as close to the Earth as the moon?

That's the remarkable hypothesis from Mark Matney, a planetary scientist in NASA's Orbital Debris Program Office by day and a self-declared Christmas junkie. "I love Christmas," Matney told Space.com. "I love Christmas music, I love Christmas decorations — I love the whole thing!"

It was this love of Christmas, expressed in a festive show at the planetarium that Matney worked at when he was in college, that inspired his interest in the Star of Bethlehem. A passage in the Bible's Book of Matthew describes how the star went before the wise men — known as 'magi', who were probably astrologers looking for signs in the sky — and stood over Bethlehem. The planetarium show suggested that no known astronomical event behaves in this bizarre way, but rather than accept that, Matney saw it as a challenge. "I remember sitting there and thinking, I can think of one thing that can behave that way," he recalled.

For Matney, there are three ways to look at the story of the Star of Bethlehem. One, which is how those of a religious leaning might see it, is as a miraculous, divine event, the archangel Gabriel shining the way towards the baby Jesus.

Another, more cynical, view is to believe the whole story to be a myth, at best perhaps a misrepresentation or embellishment. If the Star of Bethlehem was either of these two things, then there's no point in looking for a scientific explanation.

On the other hand, the third way of looking at it is as a real astronomical event. Over the years, astronomers have suggested everything from a conjunction of Jupiter and Saturn to a supernova and, yes, a comet.

The problem with all previous astronomical explanations, says Matney, is that "objects in the sky, whether it be the sun, moon, planets, ordinary stars or normal comets, rise in the east and set in the west, they don't go before you and hover over a location."

However, Matney realized that if an object came close enough, at just the right time, moving in just the right direction at just the right speed through the sky, then it could appear to do these things.

"I came up with the idea of temporary geosynchronous motion," said Matney. "It has to be just right, but in principle it can happen."

The Chinese comet of 5 BCE

Matney filed his idea away in the back of his brain, until later when he learned that Chinese astrologers (astronomers and astrologers back then were synonymous) had seen a bright comet in 5 BCE, which is believed to be the year that Jesus was born.

The recorded observations of the comet are not sufficient to chart its exact orbit, but instead its measured positions in the sky could belong to a range of possible orbits. By running numerical simulations describing all these possible orbits, Matney found a subset of orbits that would have brought the comet close to Earth, and one possible orbit where it would have been close as Earth's moon.

Matney isn't saying that the comet definitely came that close — it's just one of a number of possible orbits the comet could have had. Had it done so, however, it could be a tantalizing explanation for the Star of Bethlehem, explaining a great many things.

The Christmas festivities tell us that Jesus was born on Dec. 25, but theologians and historians aren't actually sure of his birth date. However, the Chinese comet was discovered in mid-March, 5 BCE and, in the possible orbit flagged as being of interest to the Star of Bethlehem story, it would have reached its closest point to Earth on June 8 that year.

This doesn't necessarily mean that Jesus was born in June either; it's also not clear how long after Jesus' birth the magi were said to have visited him. We do know that when Herod later learned of Jesus' birth, he ordered all infant boys under the age of two to be killed, adding more uncertainty to when Jesus was born.

Unusual behavior at the comet's closest approach

Regardless, the comet would have continued along its orbit unperturbed by what was happening on Earth. In the possible orbit of interest discovered by Matney, the comet's closest approach to Earth would have been at a distance of 241,685 miles (388,954 kilometers). This would have been closer to Earth than any other comet in recorded history, so close that Earth itself would have been encased in the comet's coma, its expansive halo of dust around its icy nucleus.

As the comet neared its closest approach, its direction of origin would have meant that its motion in the sky began to accelerate eastwards, not westwards, fast enough to begin to counter Earth's rotation in the opposite direction. Between 10 a.m. and 11:30 a.m. on the morning of June 8, as seen from the Jerusalem/Bethlehem area, this motion would have given the comet the illusion of remaining still in the daytime sky, as bright as the full moon and appearing to be above Bethlehem from the point of view of the magi.

Afterwards, the comet would have resumed westward motion on an orbit that would have seen it skim the sun's corona. We call such comets 'sungrazers' and the close encounter with the sun would have probably resulted in the comet breaking up and being destroyed.

That the comet would have been visible during the daytime, in its guise as the Star of Bethlehem, even solves a minor mystery of the Christmas story, according to Matney.

"All the Christmas cards have the magi on camels at night, but during those times people typically did not travel at night," he said, citing hazards such as unlit paths and the danger from robbers. "So the fact that this comet would have been visible in broad daylight makes sense to me, as they were more likely to have travelled during the day."

Comets, omens and history

If Matney is right, why doesn't the Book of Matthew refer to a comet rather than a star? To the ancients, everything in the celestial sky barring the sun and the moon was a star. Planets were 'wandering stars', while comets were 'hairy stars' or 'broom stars' to the Chinese. And while comets are often seen as portents of doom, Matney explains that it's not as simple as that.

"Comet omens of that period are nuanced, but they were often omens of great change," said Matney. Often, it really depended on your point of view. Herod was very interested in the duration that the star was in the sky, and he would of course have seen the comet as a bad omen.

It seems that the Chinese were also influenced by the comet's presence in the sky. Although there's no record in their annals of the comet growing so bright as to rival the moon in the daytime sky, the comet seems to have affected the astrological reckoning surrounding the emperor of that time, Emperor Ai of the Han dynasty.

"The Chinese had periods in the Emperor's reign, and I'm not 100% sure of this, but according to my Chinese colleague, the Chinese temporarily changed the dating of these periods in part because of the comet," said Matney. "So it was enough that it got their attention."

Even so, it does seem like it would require a remarkable set of coincidences for the comet to have been the Star of Bethlehem, by being in the right direction, at the right time, moving at the right speed and at the right distance — a Goldilocks comet, if you will.

"It is a very unusual set of parameters," conceded Matney. "It had to come at the right time so that the right longitude could see it. Twelve hours sooner and it would have been on the other side of the world. But even though it is a highly unlikely set of circumstances, it's not out of the question. After all, every comet's orbit is a unique set of parameters."

Despite how rare it is for comets to come as close to the Earth as our moon — if Matney is right, this is the only comet in the past 2030 years — we have seen in the past decade that it is possible for a comet to sail close to a planet. In 2014, comet C/2013 A1 (Siding Spring) passed within 140,000 kilometers (87,000 miles) of Mars.

Searching for more evidence

Such a close approach could have physically left its mark on Earth. As the comet's dusty coma would have swept across our planet, there would have been one heck of a meteor shower with its radiant in the constellation of Capricornus, the Sea Goat, and some of that cometary dust would have drifted through the atmosphere and settled onto Earth, finding its way into sediment, just waiting to be found as a thin geological layer.

"There might be something in the ice cores, a sudden jump in cometary or meteoritic dust," said Matney. "I did look for something like that but didn't find anything obvious. Maybe someone who studies ice cores for a living can take a better look."

Another problem with Matney's hypothesis is that other than the short section in the Book of Matthew, which is believed to have been written after 70 AD, the only other source of information regarding the comet and its possible link with the Star of Bethlehem is the Chinese observations of the comet. If anyone else did see the star, they didn't leave any records — or at least, no records that have survived across the millennia since. Still, Matney is hopeful that something else might yet turn up.

"The weakest link in my story is that we don't have other records, which is why I'm still on the lookout for some untapped historical or archaeological source that might provide more clues," he said.

Matney is not claiming his hypothesis to be the final solution to the mystery of the Star of Bethlehem. "I have no proof that the comet came that close, I just show that it could have," he said. "Unless we can turn over more records from the first century AD that can help us pinpoint the comet's orbit, it will stay in the realm of speculation."

We might never know what the Star of Bethlehem was, or even if there was a star at all. Matney's motivation was just to show that no matter how rare it might be, there is an astronomical event that in principle could behave like the Star of Bethlehem is reported to have behaved.

It's ironic; were a comet to come that close today, there'd probably be panic about it possibly crashing into Earth, but a little over 2,000 years ago, it might have been seen as the rise of a new king, the birth of a savior and the dawn of a new religion.

Matney's research into the Star of Bethlehem and the comet hypothesis was published on Dec. 3 in the Journal of the British Astronomical Association.

Interstellar comet 3I/ATLAS will make its closest approach to Earth on Friday, Dec. 19, marking a key moment in the journey of one of the rarest visitors ever observed in our solar system.

Discovered on July 1 by the NASA-funded ATLAS telescopes in Chile, 3I/ATLAS is only the third confirmed interstellar object known to have passed through our cosmic neighborhood, following 1I/'Oumuamua in 2017 and comet 2I/Borisov in 2019. Its trajectory shows that it originated from beyond our solar system and will eventually travel back into interstellar space.

During its closest approach, the comet will come no nearer than about 1.8 astronomical units from Earth — roughly 168 million miles (270 million kilometers) — nearly twice the average Earth-sun distance, according to the European Space Agency (ESA). Comet 3I/ATLAS poses no danger to Earth or any other planets as it passes through the inner solar system.

While the comet will keep a safe distance from Earth, the flyby still holds significance for researchers. By observing 3I/ATLAS near its closest approach, astronomers will have an opportunity to study the dust and gases released from its icy nucleus as the comet is warmed by the sun, offering a rare insight into how comets and planetary material form around other stars.

In recent months, multiple space agencies and observatories have turned their attention to this interstellar visitor. Just last week, new images captured by the Hubble Space Telescope and JUICE Jupiter probe were released, showing the fleeting traveller racing through the inner solar system.

Follow along online

You can also follow the close approach of 3I/ATLAS online in a free livestream hosted by Gianluca Masi at the Virtual Telescope Project. The livestream will begin at 11 p.m. EST on Dec. 18 (0400 GMT on Dec. 19), weather permitting.

Follow along with the latest 3I/ATLAS news with our live blog!

Darryl Z. Seligman is an Assistant Professor of Physics and Astronomy at Michigan State University.

Comet 3I/ATLAS is the third large interstellar visitor that we have ever discovered —- an asteroid or comet that originated outside of our solar system and was discovered passing through. Astronomers can glean information about celestial bodies by observing the light reflected off them with telescopes. When 3I/ATLAS is closest to the Earth, all the features that we are looking for will be easier to detect with our telescopes.

This interstellar vagabond presumably formed in a protoplanetary disk of gas and dust swirling around another star, the sites of active planet formation. Most likely, 3I/ATLAS was ejected by a close gravitational slingshot off a giant exoplanet. It has since been careening through the interstellar medium of the Milky Way galaxy for billions of years. And we get front-row seats to watch as it gets close to our sun, for what is almost surely the first time it has ever gotten close to a star.

On Dec. 19, just six days before Christmas, this erratic wanderer will be the closest to Earth that it will ever be over the lifetime of the entire universe. You'll be able to get a glimpse of it up close with a small telescope or very powerful binoculars. This close approach also offers astronomers our best opportunity to look up close and learn about how planet formation in exoplanetary systems is similar or different to how it unfolded in our solar system.

In the past seven years, we have discovered three members of an entirely new population of celestial bodies: interstellar objects. These objects have hyperbolic orbits, as opposed to the bound circular or elliptical orbits of everything native to the solar system. That's how we know that they come from elsewhere: they come and leave and never return. All we get is a fleeting look into the lifetime of these objects, and the measurements we take during their brief passage through our solar system could provide critical clues into our understanding of planet formation throughout the galaxy.

We know that the solar system ejected a huge amount of material into the Milky Way galaxy in the form of interstellar comets. Our best computer simulations have shown that, in order to reproduce the structure of the solar system that we see today, there was most likely a violent period during which the giant planets Jupiter, Uranus, Saturn, and Neptune migrated, flinging material into the Kuiper Belt and the Oort Cloud. During that process, we probably liberated about 30 Earth masses of 3I/ATLAS-sized comets into the interstellar medium.

In the last 30 years, we have discovered that planets are surprisingly common around other stars. It is therefore not surprising that other planetary systems should also have ejected comets into the Milky Way galaxy. The first known interstellar object, 1I/'Oumuamua, was discovered in 2017. Two years later, we discovered 2I/Borisov, which displayed a prominent cometary tail, and its composition was much different than those of solar system comets. Our telescopic observations revealed that it contains more carbon monoxide than water. Most solar system comets are comprised of a lot more water than any other type of ice.

The ices we see in a comet can tell us something about the conditions in which they formed. For example, water freezes at cold temperatures. The farther away from the sun a comet forms, the colder it is. Therefore, the fact that comets in our solar system have water as their main ice tells us that they mostly formed around where Jupiter is now, about five times more distant than the Earth. Carbon monoxide and carbon dioxide freeze at much colder temperatures than water. Therefore, 2I/Borisov's carbon monoxide tells us that it probably formed at a much farther distance from its star than the typical comets left in our solar system.

Astronomers had been looking for interstellar objects unsuccessfully for six years until we spotted 3I/ATLAS this July. And 3I/ATLAS has been well worth the wait. We have been monitoring it since we discovered it, and our early observations with facilities like the James Webb Space Telescope have revealed that it is enriched in carbon dioxide. This is probably telling us that, like 2I/Borisov, 3I/ATLAS formed much farther out in its progenitor star system than our solar system comets did.

Mere days before Christmas 3I/ATLAS will be at its closest approach to the Earth. This is exciting for everyone, because anyone can go see 3I/ATLAS with a powerful amateur telescope. And for us astronomers, all these critical ice features are easier to detect the closer 3I/ATLAS is to Earth.

These observations might be telling us that comet formation occurs in much farther regions than we previously thought possible based on our inferences from the solar system. In that way, the solar system would be somewhat unique. Alternatively, it's possible that we also produced such distant comets, but all of them were subsequently ejected. And then maybe the solar system is not so unique after all. Either way, 3I/ATLAS is giving us a new window to put our solar system into its cosmic context this Christmas.

Two flagship spacecraft captured striking new images of Interstellar comet 3I/ATLAS, including a surprisingly sharp snapshot from a camera never meant for scientific imaging.

Discovered on July 1 by the NASA-funded ATLAS telescope in Chile, 3I/ATLAS is only the third confirmed visitor from another solar system, following 1I/'Oumuamua in 2017 and comet 2I/Borisov in 2019.

In November, both the European Space Agency's Jupiter-bound JUICE spacecraft and the Hubble Space Telescope captured new views of the fleeting traveler as it raced through the inner solar system, providing valuable clues about the chemistry and dynamics of bodies born around other stars, scientists say.

On Nov. 2, JUICE pointed five of its science instruments at 3I/ATLAS during a planned campaign to study the comet's activity and composition. That high-resolution data won't reach Earth until February 2026, however. The spacecraft is currently using its main high-gain antenna as a heat shield to protect itself from the sun, according to an ESA statement.

"Our JUICE team couldn't wait that long," ESA wrote. Eager for a sneak peek, engineers used the spacecraft's smaller, slower antenna to trickle home just one-quarter of a single frame from JUICE's Navigation Camera (NavCam), a low-resolution imager designed not for science but for navigating JUICE around Jupiter's icy moons after its 2031 arrival.

The resulting grainy teaser reveals the comet's bright nucleus surrounded by a glowing coma of gas and dust. If you look closely, a faint tail stretches upward. That is the comet's plasma tail, created when sunlight ionizes gas released from its warming surface and the solar wind sweeps those charged particles away from the sun, according to ESA.

If you squint harder, you might also spot a subtler dust tail drifting down and to the left. Recent observations show this dust shows slightly atypical properties, hinting that its grain sizes differ from those of local comets, NASA revealed at a news briefing last month.

The snapshot was taken on Nov. 2, just two days before JUICE's closest approach to 3I/ATLAS, when the spacecraft passed about 41 million miles (66 million kilometers) from the comet. Because JUICE observed the comet just after its closest approach to the sun, on Oct. 30, mission scientists expect the full dataset to reveal even more vigorous, sun-driven activity.

Just weeks after JUICE captured its preview, the Hubble Space Telescope turned its Wide Field Camera 3 back toward 3I/ATLAS for a second round of observations on Nov. 30. The comet was then about 178 million miles (286 million kilometers) from Earth and racing across the background stars. Hubble tracked the comet's motion, causing the stars to smear into thin streaks in the image, a second ESA statement read.

Hubble first imaged 3I/ATLAS in July, shortly after its discovery, revealing a teardrop-shaped cocoon of dust streaming from the comet's icy nucleus. The new observations show a bright central core similarly wrapped in a glow of dust, confirming continued activity.

A recent coordinated NASA-led campaign, which drew on dozens of spacecraft and telescopes from Earth orbit to Mars and beyond, hints at unusual chemistry in the comet’s dust, including a higher-than-normal carbon-dioxide–to–water ratio and gas unusually rich in nickel relative to iron. Both findings may point to formation conditions unlike those in our own solar system, NASA scientists said at a November news briefing.

At the briefing, scientists also said 3I/ATLAS has probably spent a very long time drifting through interstellar space. Its incoming speed suggests it may have been born in an ancient planetary system, possibly one that predates our own.

That "gives me goosebumps to think about, frankly," said Tom Statler, the lead scientist at NASA for solar system small bodies.

At the same briefing, Nicky Fox, the associate administrator of NASA's Science Mission Directorate, stressed that 3I/ATLAS poses no threat to Earth. The comet will come no closer than 170 million miles (270 million kilometers) to our planet and will not pass near any planets as it exits the solar system, including when it crosses Jupiter's orbit in spring 2026.

The objects in our solar system, Fox said, "will be just fine."

Comets are famous for making brief, dramatic appearances in our skies, but one icy wanderer just received an unprecedented level of attention from one of NASA's newest spacecraft.

For nearly 40 days, NASA's PUNCH mission imaged the recently-discovered Comet C/2025 R2 (SWAN) every four minutes as it drifted through the inner solar system. That near-continuous stare "may be the longest any comet has been tracked" with such a frequency, according to a recent NASA announcement.

"Other comets have been tracked at once-per-day cadence for years," Craig DeForest, the principal investigator for the PUNCH mission at the Southwest Research Institute in Colorado, said in the statement. "What's new here is the few-minute cadence of observation."

The video above stitches together hundreds of PUNCH images taken from Aug. 25 to Oct. 2, showing the comet gliding between two bright objects — Mars at the top and the star Spica in the constellation of Virgo at the bottom. Because the images were not fully processed before being combined, boundaries between individual snaps remain visible as thin black seams, the statement read.

Comet C/2025 R2 (SWAN) was first spotted in September by Ukrainian amateur astronomer Vladimir Bezugly, who noticed the icy visitor a bright blob close to the sun while scanning publicly available images from the sun-watching Solar and Heliospheric Observatory (SOHO). Just a day after its discovery, the comet reached perihelion, its closest point to the sun, passing at a distance of 46.74 million miles (75.20 million km) of our star.

Early images had revealed the comet’s bluish-green coma, created as the sun's heat vaporized the comet's ices in a process called sublimation. Gas and dust released were swept backward by the solar wind, forming the glowing tail captured in various images. By mid-September, the coma had taken on an unusual triangular "hammerhead" shape, a distortion astronomers often link to a fragmenting nucleus, as outgassing from multiple pieces can stretch a normally round coma into a lopsided form.

At the same time, Comet C/2025 R2 (SWAN) happened to share the same swath of sky with the now-famous interstellar visitor 3I/ATLAS. In the PUNCH time-lapse below, 3I/ATLAS appears briefly near the end of the sequence, zipping left to right beneath SWAN.

As Comet C/2025 R2 (SWAN) moves leftward in the images, its tail is pushed in the same direction by the solar wind, making the comet appear to drift "backward," the NASA statement noted.

Comet tails act as natural tracers of the solar wind, a continuous stream of charged particles flowing outward from the sun and shaping the space environment throughout the solar system.

"Watching the sun's effects from multiple vantage points — and with different types of instruments — is what gives us a complete picture of the space environment," Gina DiBraccio, a heliophysicist and acting director of the Solar System Exploration Division at NASA's Goddard Space Flight Center in Maryland, said in the same statement.

"We use these same tools to track and analyze how space weather impacts our astronauts, our spacecraft, and our technology here on Earth."

In late October, the comet made its closest approach to Earth at 25.10 million miles (40.38 million km), putting it on the cusp of naked-eye visibility and easily within reach of binoculars and small telescopes.

It was 4 a.m. on Nov. 25 at the top of Hawaii's dormant Maunakea volcano. The process to view the comet took less time than expected.

On the main screen, the subject at hand, interstellar comet 3I/ATLAS was a small, fuzzy blob drifting through a crowded field of stars. On another, its light had been stretched into a barcode of rainbow lines, some brighter than others, each corresponding to a different gas boiling off the object's nucleus.

"This is some prime-time science happening in real-time right now," said Bryce Bolin, principal investigator of a study on the interstellar comet, as he greeted a global audience logged into the online skywatching session. The session was hosted by Shadow the Scientists, an organization that directly connects experts and non-experts through virtual seminars like this recent one, and the Gemini North Telescope, one half of the international Gemini Observatory.

What we were really watching on the control room's screen, though, wasn't just a comet. It was a time capsule: a chunk of ice and rock that may be older than the sun, now on its out of our solar system after accidentally passing by on its cosmic voyage through the universe. It even managed to get a close pass by our star, the sparkling orb it has spent most of its existence watching from afar.

And this wasn't the International Gemini Observatory's first date with 3I/ATLAS.

Back in August, while the comet was still diving toward the sun, Chile's Gemini South telescope, the other half of the international observatory, captured pre-perihelion spectra and images as its tail "switched on" and began to grow. Those data showed a distinctly comet-like object with a bright coma and jets of gas dominated by carbon dioxide and cyanogen — a contrast to the water-rich behavior seen in most solar system comets.

By late October, 3I/ATLAS had whipped through perihelion, or its closest spot to our solar system's sun, at about 130,000 miles per hour (roughly 209,000 kilometers per hour), then disappeared behind the sun from Earth's point of view. This journey was captured by many telescopes and spacecraft, from the Mars Reconnaissance Orbiter to even the Perseverance rover. Unfortunately, though, with the Gemini Observatory being on Earth, it didn't catch the show.

But now, in November, I watched from my laptop as 3I/ATLAS climbed into northern skies as Hawaii's Gemini North Telescope took over.

"This is our first observation from Gemini since it reappeared behind the sun," explained scientist Brian Lemaux. "We're under active observations right now, which is what Shadow the Scientists is all about. this is not a show. We're actually trying to analyze and understand the data. The comet is very dynamic," he added. In other words, its brightness and spectral features had changed since the Gemini South run.

Before Gemini North ever pointed at 3I/ATLAS, we watched the calibration dance.

On screen, Lemaux showed a spectrum: bright, vertical lines corresponding to known elements used to nail down the wavelength scale to see the interstellar comet more accurately. "All these vertical lines are different chemical species of known origin that we can use to calibrate the observation," he said.

They followed that with flat fields — uniformly illuminated frames to correct for imperfections in the instrument — and a carefully chosen "solar analog" star. Because the comet mostly reflects sunlight, they needed to divide that sunlight out to isolate the comet's own emissions.

"The telescope optics are imperfect. The atmosphere is a problem from the ground. Our instruments, despite being very awesome, are not perfect either," Lemaux said. "We want to not care about any of that. We want to get to the intrinsic nature of any source that we observe."

Only once those pieces were in place did they move to the main act: a long-slit spectrum across the coma, followed by an integral field unit (IFU) observation — essentially a tiny 3D data cube giving a spectrum at every point in a small image of the comet.

Last time, at Gemini South, that combination of data delivered a surprise. "We saw this big plume of what turned out to be cyanogen gas," Bolin recalled, "and it extended out from the comet to very large scales."

Now, post-perihelion, the team was looking for how that structure had changed, how the aging of the coma after closest approach could show up in its chemistry and shape.

How old is 3I/ATLAS?

During a lull between exposures, someone in the webinar chat asked a deceptively simple question: How long does it take this comet to go around the galaxy?

"The galactic orbital period of 3I/ATLAS is about 250 million years," Bolin replied. (That's roughly the time it takes the sun to complete one lap around the Milky Way.) "It's probably not its first rodeo," he added. In extragalactic astronomy, he joked, 100 million years is considered "instantaneous" by experts.

That throwaway answer anchors a much deeper story about 3I/ATLAS's age.

Two groups of researchers tackled the problem by treating 3I/ATLAS the way we treat stars: comparing its velocity to the known relationship between age and random motion in the galaxy.

A study by scientists Aster Taylor of the University of Michigan and Darryl Seligman of Michigan State University calculated a "kinematic age" from 3I/ATLAS's excess speed of about 36 miles per second (58 kilometers per second) relative to the sun. Their result: the interstellar comet is likely 3 billion to 11 billion years old, assuming interstellar objects and stars follow the same age–velocity relation.

A different study by scientist Matthew Hopkins at the University of Oxford and colleagues, used a model that focused on the Milky Way's thick disk, a population of older, dynamically "hotter" stars, to infer a likely age of the interstellar comet at between about 7.6 billion and 14 billion years.

Both lines of evidence point the same way: 3I/ATLAS is almost certainly older than our 4.6-billion-year-old sun, and may be among the oldest comets we've ever seen.

In our seminar, Bolin later showed a visualization of 3I/ATLAS's orbit around the galaxy — no neat ellipse, but rather a looping, spiraling path distorted by encounters with gas clouds, spiral arms and dark matter.

"These aren't simple ellipses anymore," he said.

An asteroid around the sun has a closed elliptical orbit; an interstellar comet in the Milky Way doesn't. The galaxy's "very inhomogeneous clumps of matter," as Bolin described, constantly tug on the interstellar comet, making it nearly impossible to back-trace 3I/ATLAS to a specific parent star.

In other words, 3I/ATLAS has been wandering so long that it has lost its return address.

Imaging this ancient comet

As the Hawaiian sky crept toward dawn, the spectral work wound down. The Gemini North team cycled through four filters to look at the interstellar comet.

The comet brightened and faded slightly from image to image as different parts of its spectrum came into view.

"These images are not just pretty," Bolin emphasized. They're being used to pin down 3I/ATLAS's exact position on the sky with exquisite precision.

When the last images came in, Shadow the Scientists staffer Jameeka Marshall reminded the audience that all the data would be public immediately: "There's zero 'proprietary time' associated with the data … anybody that's interested can take these data, reduce the data and make them in a scientifically viable form using the tools that we have here at the Gemini Observatory."

Outside the control room, sunrise threatened the image quality. Inside, the comet on the screen looked unchanged: a fuzzy blot of light with a tail barely hinted at against the brightening sky.

Hidden in those frames and spectra is the biography of a traveler that has been aging in interstellar space since long before Earth formed; a relic from an early, metal-poor corner of the galaxy, briefly caught in our telescopes on its way past.

For a few hours on Maunakea — and for a few months in 2025 through 2026 as observatories worldwide tracked it — comet 3I/ATLAS has given us something astonishingly rare: a direct look at the debris of someone (or something) else's planetary system, eroded by billions of years.

But not erased.

Since the interstellar comet 3I/ATLAS was discovered this past July — just the third confirmed object to arrive from another star — astronomers have been closely following its passage through our solar system.

As the icy visitor brightened on its coast toward the sun, the public narrative brightened too, with online rumors casting it as a possible alien spacecraft during the recent 43-day-long government shutdown when NASA could not comment on the object or release new images. Last week, with the shutdown over, NASA held a long-awaited briefing in which it shared observations and early analysis from more than 20 missions across the solar system, assembling the most complete picture yet of this rare visitor — and made one point immediately clear: 3I/ATLAS is of natural origin, not an example of alien technology.

"We very much want to find signs of life in the universe," NASA Associate Administrator Amit Kshatriya said during the briefing. "But 3I/ATLAS is a comet."

Discovered on July 1 by the NASA-funded ATLAS telescope in Chile, 3I/ATLAS offers a rare chance to study material forged around another star, scientists say. Early findings suggest the object is carrying chemical clues from a distant, unknown planetary system that's likely older than our own.

Here are four key things the agency revealed about the interstellar visitor.

1) 'This object is a comet'

In July, about two weeks after 3I/ATLAS was discovered, a trio of researchers, including Harvard astrophysicist Avi Loeb, posted a non-peer-reviewed preprint arguing that the comet's characteristics hint at disguised, possibly hostile alien technology. The claim echoed earlier speculation made about the first-known interstellar object, 'Oumuamua, and quickly gained traction online.

It picked up further momentum after SpaceX CEO Elon Musk suggested on a podcast that something beyond gravity could be influencing the comet's motion, and by Kim Kardashian's viral request on X asking NASA Acting Administrator Sean Duffy to spill the "tea" on the object.

During last week's NASA briefing, Kshatriya wasted no time addressing the speculation. "This object is a comet," he said at the outset. "It looks and behaves like a comet, and all evidence points to it being a comet."

Nicky Fox, the associate administrator of NASA's Science Mission Directorate, added that none of NASA's observations show any technosignatures "or anything from it that would lead us to believe it was anything other than a comet."

She also stressed that scientists are confident 3I/ATLAS poses no threat to Earth, as it will come no closer than 170 million miles (270 million kilometers) to our planet. It will also not come close to any other planets during its passage, including when it passes the orbit of Jupiter in Spring 2026. The objects in our solar system, Fox said, "will be just fine."

2) A solar system-wide watchtower

From the moment of its discovery, scientists knew from 3I/ATLAS' trajectory that it sat on the opposite side of the sun from Earth, making ground-based observations difficult. To compensate, NASA convened a coordinated planning session in August, bringing together teams from more than 20 missions to mount a fleet-wide campaign to track the interstellar comet. In the end, dozens of spacecraft from Earth orbit to Mars and beyond worked in concert, each with a different vantage point.

Tom Statler, the lead scientist at NASA for solar system small bodies, likened the effort to watching a baseball game from different seats around the stadium, with both flagship telescopes and smaller spacecraft trying to follow the same fast-moving target.

"Everybody has got a camera and they're trying to get a picture of the ball," he said. "Nobody has the perfect view, and everybody has a different camera."

Mars happened to be on the favorable side of the sun. In early October, NASA's Mars Reconnaissance Orbiter captured images of 3I/ATLAS as a fuzzy white ball, revealing its dust-and-ice coma, from about 90 million miles (145 million km) away. Around the same time, the MAVEN orbiter detected the comet from 20 million miles (32 million km) through ultraviolet "science wiggles" that picked up signatures of hydrogen gas released as sunlight vaporized the comet's water ice, said Statler. Combined with data from the Swift telescope and the James Webb Space Telescope (JWST), scientists were able to estimate the comet's water production rate, a key clue to its formation history.

Other spacecraft offered snapshots from farther out. In September, NASA's Psyche asteroid mission imaged the comet as a faint blob from 33 million miles (53 million km) away. A week later, the Lucy mission, en route to study Jupiter's Trojan asteroids, observed the coma and tail from the opposite direction, helping researchers reconstruct the 3D structure of the dust. Even the NASA-European Space Agency SOHO (Solar and Heliospheric Observatory), managed to detect the faint object in mid-October despite expectations that it would be too dim to register, scientists shared during the briefing.

Additional assets contributed further pieces of the puzzle. The Hubble Space Telescope, shortly after its 35th anniversary earlier this year, observed the comet from 277 million miles (446 million km) away, revealing a pear-shaped coma and narrowing the possible size of the nucleus to between 1,400 feet (427 meters) and 3.5 miles (5.6 km). JWST provided the first infrared look at an interstellar object since its launch, detecting an unusually high ratio of carbon dioxide to water ice, well above what's typical for comets born in our own solar system. That information suggests that 3I/ATLAS's ices may have been shaped by harsher radiation environments around an older star, scientists said.

"This is a snapshot of where we are very early in the scientific process," Statler said.

3) A rare window into distant, older star systems

Scientists say that 3I/ATLAS has likely been traveling through interstellar space for a long time. Based on how fast it was moving upon entering the solar system, Statler said the circumstantial evidence points to the comet originating in a very old planetary system, possibly one older than our own.

That "gives me goosebumps to think about, frankly," he said, noting that 3I/ATLAS may reveal insights into cosmic history that predates the formation of both Earth and the sun.

"It is a new window into the makeups and histories of other solar systems," he said.

4) Intriguing chemical clues

So far, 3I/ATLAS has behaved exactly as a comet should as it warms near the sun, shedding water and carbon dioxide, but with some intriguing twists. Scientists have detected a higher-than-usual ratio of carbon dioxide to water compared with typical solar system comets, as well as gas unusually rich in nickel relative to iron. Both findings are scientifically compelling and worth further investigation, researchers said.

The dust around the comet also shows slightly atypical properties, suggesting its grain sizes differ from those of local comets. One especially curious behavior was the dust was initially blown toward the sunward side before solar radiation gradually pushed it back, a longer and less common sequence than scientists usually observe in homegrown comets.

"We're still learning even about what questions we still need to ask," said Statler. "And this, of course, is the scientific process in action."

Ever since the famous "interstellar invader" comet 3I/ATLAS was discovered in our solar system earlier this year, scientists have been enamored with its existence and the serendipity that brought it here — including experts at NASA. As such, the agency has been working to point several of its spaceborne instruments at the peculiar subject, which, incredibly, is only the third interstellar object on record to enter our corner of the cosmos.

Indeed, on Wednesday (Nov. 19), NASA released brand-new images of comet 3I/ATLAS collected by quite a few spacecraft — including the James Webb Space Telescope, the Mars Reconnaissance Orbiter, the Perseverance Mars rover and the Lucy asteroid-studying probe, to name a few. In total, an impressive 15 different agency space missions are confirmed to have their eyes peeled for new data about the interstellar visitor.

"We've even pushed our scientific instruments beyond their normal capabilities, beyond the things that they were designed to achieve, to allow us to capture this amazing glimpse at this interstellar traveler," Nicky Fox, associate administrator of NASA's Science Mission Directorate, said during a press briefing on Wednesday.

The new images, which we'll discuss below, add to a growing set of footage we have of the object. For instance, we already have some striking stills, such as this composite showing it blasting a jet toward the sun, and this image capturing its growing tail.

And, first and foremost, NASA officials confirmed that comet 3I/ATLAS is actually a comet. In other words, no, it is not an alien spaceship, as many rumors across the internet suggest.

"It looks and behaves like a comet, and all evidence points to it being a comet. But this one came from outside the solar system, which makes it fascinating, exciting and scientifically very important," NASA Associate Administrator Amit Kshatriya said during the press briefing.

"You kind of know the signatures that you're looking for; we were quick to be able to say, 'Yep, it definitely behaves like a comet,'" Fox said. "We certainly haven't seen any technosignatures or anything from it that would lead us to believe it was anything other than a comet."

But comet 3I/ATLAS doesn't need to be an alien spaceship to be unique — it's still an ancient alien comet.

"It's a rare opportunity to compare ancient dust from a distant solar system to that from our own," Shawn Domagal-Goldman, acting director of NASA's Astrophysics Division, said during the briefing.

New interstellar data

The first image NASA officials highlighted during the briefing was one taken by the closest spacecraft the agency had to the comet: the Mars Reconnaissance Orbiter (MRO). MRO used its HiRISE camera to capture comet 3I/ATLAS on Oct. 2 while the object was about 19 million miles (31 million kilometers) away.

"You can see the comet 3I/ATLAS looks like a fuzzy white ball," Kshatriya said. "That ball is a cloud of dust and ice called the coma, which is shed by the comet as it continues its trajectory towards the sun."

Next up, analyzing the view from the current fan favorite and big dog space observatory, the James Webb Space Telescope (JWST), combined with data from the SPHEREx space telescope, has revealed more information than visual imagery of comet 3I/ATLAS could hope to impart. This is because the specialty of JWST and SPHEREx is scanning the cosmos in infrared light, which is invisible to the human eye but rich in things like compositional and thermal data. "We detected an abundance of carbon dioxide gas in the comet's coma and in the bright cloud of gas and dust surrounding that comet as it approaches the sun," Domagal-Goldman said.

The infrared data also revealed the presence of water ice alongside carbon dioxide in the comet's nucleus.

"It does the same thing comets do — it evaporates carbon dioxide gas; it evaporates water," Tom Statler, NASA lead scientist for solar system small bodies, said during the briefing. "But it's evaporating more carbon dioxide compared to water — so that's a very interesting thing."

One thing is for certain: It's pretty good that we have so much imagery of comet 3I/ATLAS because of the immense rarity of its passing through our solar system. Understanding the dynamics and composition of such distant cosmic objects can help us decode what the environments are like around other stars. What materials are present? What conditions might give rise to comets like 3I/ATLAS? Already, we're finding 3I/ATLAS to be rather special.

"It's going to look different because it didn't come from our solar system, and that's what makes it so magical," Fox said.

And, on the note of the JWST, this instrument will probably be the last of our spacecraft fleet to lay eyes on comet 3I/ATLAS as the object leaves our vicinity. This is because JWST is built to look deeper into the universe than ever before, so it should be able to pick up a signal even after other probes lose the target.

Comet 3I/ATLAS has also previously exhibited a few surprises compositionally in this vein, such as with its strikingly rapid brightening during its closest approach to the sun on Oct. 29. There also appeared to be a glowing nickel vapor in the gas surrounding 3I/ATLAS while the comet was considerably farther from the sun. This was weird because, at that distance from our star, "vapor" isn't likely to be spewing off an object. It's thought to be far too cold there for this to happen.

Statler said during the briefing that, though we know comets emit nickel and iron, 3I/ATLAS is putting out more nickel than iron, for some reason: "That's really interesting, really remarkable, and something to be studied in the future."

During the briefing, it became clear why it's important to have so many different spacecraft capture images and data about comet 3I/ATLAS. Not only is it beneficial to combine different instruments' data, as we saw with SPHEREx and the JWST, but it's really all about the angles when imaging something as dynamic as an object shooting through the vastness of space.

"Comet 3I/ATLAS has come through on a trajectory in the opposite direction and has arrived at its closest point to the sun when the Earth was on the wrong side for us to conveniently observe," Statler said. "But Mars was on the correct side of the sun, and our Mars assets were able to observe the comet, and also several of our other spacecraft were on the correct side of the sun."

Spacecraft tag-team

NASA's Psyche asteroid mission, which is currently headed toward the metal-rich space rock 16 Psyche, acquired four broadband images of the comet over the course of eight hours on Sept. 8 and Sept. 9 while the comet was about 33 million miles (53 million km) from the spacecraft.

The following week, the Lucy spacecraft on its way to study the Trojan asteroids of Jupiter observed the comet from the opposite direction, while about 40 million miles (64 million km) away. It caught the comet's coma, halo of gas and even its tail.

"You do not get these views unless you have spacecraft farther from the sun than the comet is so that you can see it backlit. We could not get this view from the vantage point of the Earth," Statler said.

Mars spacecraft also got an opportunity to view comet 3I/ATLAS as the object passed within 20 million miles (32 million km) of the Red Planet at the beginning of October. That's when MRO viewed it, and it appears that NASA's MAVEN (Mars Atmosphere and Volatile Evolution) orbiter did as well.

And it doesn't end there. The European Space Agency (ESA) and NASA have a project called the Solar and Heliospheric Observatory (SOHO), which imaged 3I/ATLAS from Oct. 15 to Oct. 16 after it had passed Mars from about 222 million miles (357 million km) away, and NASA's Parker Solar Probe got a glimpse as well — a glimpse scientists can't wait to parse out.

"NASA assets that are gathering observations of 3I/ATLAS include Hubble, the James Webb Space Telescope, TESS, Swift, SPHEREx, Perseverance Mars rover, Mars Reconnaissance Orbiter, Maven, Europa Clipper, Lucy, Psyche, my personal favorite Parker Solar Probe, PUNCH, STEREO and NASA's SOHO mission," Fox said to sum it up.

"The answers will come later on. We are still at this phase, very much in the state where we're figuring out what are even the right questions to ask about interstellar objects," Statler said.

For instance, scientists are still zeroing in on the comet's previous and predicted path. In fact, Europe's ExoMars Trace Gas Orbiter spacecraft orbiting the Red Planet observed 3I/ATLAS between Oct. 1 and Oct. 7. That's when the comet passed pretty close to Mars. Thanks to this, scientists managed to glean a highly accurate prediction of the comet's trajectory, and they say this knowledge could help bolster our planetary defense skills so we can refine strategies to protect Earth someday from a space object headed our way.

There's still a lot more to be learned about comet 3I/ATLAS — for example, scientists can't even confirm yet what its size is. The range right now is between a couple of thousand feet to a couple of miles in diameter, and the fact it's so obscured by dust makes it difficult to resolve the object's shape. The most interesting thing, though, perhaps concerns its birthplace.

"It would be fabulous if we could trace back the incoming trajectory into the solar system and trace that back and figure out where it came from," Statler said. "But things are not quite so simple."

As Stalter explained, the sun and all the other stars in our galaxy are in orbit around the center of the galaxy, meaning we can assume 3I/ATLAS has been in interstellar space for a very long time.

"We can't say this for sure, but the likelihood is it came from a solar system older than our own solar system itself, which gives me goosebumps to think about," he said.

A comet discovered earlier this year continues to break apart after its close brush with the sun this month.

Astronomer Gianluca Masi of the Virtual Telescope Project captured breathtaking imagery of solar system comet C/2025 K1 (ATLAS) as its central icy core, or nucleus, appears to have broken into multiple pieces after being warmed by the sun. The comet made its closest approach to the sun on Oct. 8, and astronomers captured images following the solar flyby that appear to show it dramatically breaking apart.

These most recent images seem to confirm that, as multiple distinct fragments can be seen. The images appear to show "three fragments of the original nucleus and possibly a fourth one," Masi wrote in a statement accompanying the images.

Masi captured the images over the past week using a Celestron C14 Schmidt-Cassegrain telescope on a Paramount ME robotic mount, with a SBIG ST-10XME CCD self-guiding camera. The images consist of seven different 60-second exposures captured without any filters.

He made those exposures on five separate nights between Nov. 11 and 18 Nov. 18, and stacked them together to make an animation that depicts the motion of the fragments relative to one another:

Based on one of the images, Masi suspects the comet may have actually broken into a fourth fragment.

Astronomers at the Asiago Observatory in Italy captured the comet on Nov. 11 with the 1.82-meter Copernicus telescope, which appeared to reveal that, at that point, the comet had broken into two distinct fragments separated by about 1,200 miles (2,000 kilometers).

But even then, astronomers suspected "the presence of a third, smaller and fainter fragment to the left of the pair," Mazzotta Epifani wrote in a statement published to the Italian National Institute for Astrophysics website (translation by Google).

Like many comets, C/2025 K1 (ATLAS) is believed to have come from the Oort cloud, a distant spherical bubble of small icy bodies that surrounds our solar system at the farthest reaches of our sun's neighborhood. Many long-period comets (those that only rarely pass through the inner solar system) originate from the Oort cloud, which is thought to contain billions of small icy objects like comets (though some Oort cloud bodies are so large they qualify as dwarf planets).

Want to see these visitors from the outer solar system for yourself? Skywatchers hoping to capture their own views of distant solar system comets should check out our roundups of the best smart telescopes, cameras and lenses for astrophotography, along with our guide on how to view and photograph comets.

Editor's Note: If you would like to share your comet photos with Space.com's readers, then please send your photo(s), comments, and your name and location to spacephotos@space.com.

The path of comet 3I/ATLAS through the solar system has been predicted with an accuracy 10 times greater than previous estimates, thanks to images taken by a European Space Agency spacecraft orbiting Mars. Though 3I/ATLAS poses no threat of striking Earth, the breakthrough could have important implications for defending Earth against other comets and asteroids someday.

The ExoMars Trace Gas Orbiter (TGO) spacecraft observed 3I/ATLAS between Oct. 1 and Oct. 7 as it passed relatively close to Mars, with the comet's closest approach bringing it to within 18 million miles (29 million kilometers) of the Red Planet on Oct. 3. Up until September, calculations of the location and trajectory of 3I/ATLAS relied on observations made by Earth-based telescopes. Scientists did expect a modest improvement in the accuracy of locating 3I/ATLAS with the addition of Mars-based data, but this addition actually yielded a tenfold improvement.

"The Mars probe got about 10 times closer to 3I/ATLAS than telescopes on Earth, and it observed the comet from a new viewing angle," the European Space Agency (ESA) wrote in a statement. "The triangulation of its data with data from Earth helped to make the comet’s predicted path much more accurate. Because 3I/ATLAS is passing through our solar system fast, traveling with speeds up to 155,000 miles per hour (250,000 kilometers per hour), it will soon vanish into interstellar space, never to return. The improved trajectory allows astronomers to aim their instruments with confidence, enabling more detailed science of the third interstellar object ever detected."

To image 3I/ATLAS, ExoMars TGO turned one of its instruments, CaSIS (Colour and Stereo Surface Imaging System), which usually surveys the surface of the Red Planet in high resolution, toward the stars. The planetary defense team at ESA's Near-Earth Object Coordination Center accounted for the location of the ESA spacecraft around Mars to ensure it captured footage of 3I/ATLAS.

This special consideration was necessary because observations of comet/asteroid trajectories are usually made using observatories in a fixed location, such as by Earth-based telescopes, or from orbit around Earth, such as the James Webb Space Telescope (JWST).

Accounting for ExoMARS TRO's special location, exact position around Mars, and the speed at which it orbits the Red Planet, the planetary defense team, with aid from ESA flight dynamics and science and instrument teams, was able to use data from the spacecraft to calculate the future locations of 3I/ATLAS, or its "ephemeris."

The data collected by ExoMars TRO represents the first time that astrometric data, or measurements of the position of a celestial object, have been collected and submitted to the Minor Planet Center (MPC) by a spacecraft orbiting another planet. The MPC is a hub of asteroid and comet observations from a range of observations, radar stations, and spacecraft.

That is a big deal for planetary defense.

"ESA routinely monitors near-Earth asteroids and comets, calculating orbits to provide warnings if required," the space agency wrote. "As this 'rehearsal' with 3I/ATLAS shows, it can be useful to triangulate data from Earth with observations from a second location in space. A spacecraft may also happen to be closer to an object, adding even more value."

This isn't the last time that 3I/ATLAS will be observed by a distant spacecraft, either. The interstellar comet is currently being sped by JUICE (Jupiter Icy Moons Explorer), which is bound for the Jovian system. Catching 3I/ATLAS immediately after its closest approach to the sun, JUICE is likely to get the best view of 3I/ATLAS during the interstellar comet's active phase as radiation from the sun is causing it to expel material.

However, because this spacecraft is currently on the other side of the sun from Earth, the JUICE observations of 3I/ATLAS won't be available to scientists until Feb. 2026.

A stunning new image of interstellar comet 3I/ATLAS (C/2025 N1 ATLAS) reveals the cosmic visitor's ion tail has grown dramatically longer and more structured — a sign of intensifying activity as it continues its journey through the inner solar system.

The image, captured by the Virtual Telescope Project at 11:31 p.m. EDT on Nov. 10 (0431 GMT on Nov. 11), is composed of 18 separate 120-second exposures, remotely taken by robotic telescopes located in Manciano, Italy. Despite the comet being just 14 degrees above the eastern horizon and a bright 61% moon shining about 70 degrees away, a sharply defined, luminous ion tail is seen.

"Exploiting the unusual good weather of this season, we imaged the interstellar comet 3I/ATLAS (C/2025 N1 ATLAS) again, recording a much more developed ion tail," Gianluca Masi, Virtual Telescope Project founder and astronomer, said in a post sharing the new image. "Looking at the picture, we see how the ion tail of 3I/ATLAS is clearly showing better and better."

An ion tail forms when the sun's ultraviolet radiation strips electrons from gas molecules released by the comet, turning them into charged ions. These ions are then swept away by the solar wind — a constant stream of charged particles flowing outward from the sun — creating a long, often bluish tail that always points directly away from the sun regardless of the comet's direction of travel. This tail differs from the dust tail, which tends to appear yellowish-white and curves gently along the comet's orbital path.

In the new image, the comet's bright core is surrounded by a compact coma and a sharply defined ion tail stretching roughly 0.7 degrees across the sky. A faint anti-tail — a feature caused by the observer's perspective as dust trails along the comet's orbit — can also be seen extending in the opposite direction. The image shows a clear increase in activity compared to earlier observations, suggesting that 3I/ATLAS is venting gas and dust more vigorously as it reacts to solar heating.

3I/ATLAS is only the third confirmed interstellar object ever detected, following 1I/'Oumuamua in 2017 and 2I/Borisov in 2019. Unlike its predecessors, this visitor from another star system is bright enough to be studied in detail by ground-based telescopes, offering astronomers a rare opportunity to observe how an interstellar comet behaves under the influence of our sun.

The growing length and brightness of the tail suggest increasing sublimation of volatile materials — likely including carbon dioxide and dust — that are then swept into space by the solar wind. Early data suggest that 3I/ATLAS may contain a high fraction of carbon dioxide ice, offering potential clues to the conditions in the distant planetary system where it formed, as well as valuable insight on how comets evolve beyond our solar neighborhood.

The Virtual Telescope Project will continue to monitor 3I/ATLAS as it travels through the inner solar system. You can check out past images of the comet taken since it was first detected in July of this year.

Comets of this type aren't everyday sightings. The opportunity to observe objects that might have orbital periods measured in thousands of years is fleeting. So when Comet Lemmon recently appeared in the night sky, eager skywatchers looked up to observe it move across the heavens.

What is it?

Comet Lemmon, or C/2025 A6, was discovered by the Arizona-based Mount Lemmon Survey, which observed it as an almost asteroid‐like object; it was later re-classified as a comet once coma and tail features became evident.

Comets are often described as "dirty snowballs" — icy bodies laced with dust and rock — from the fringes of the solar system. When they approach the sun, they heat up, releasing gas and dust that form the coma (the glowing cloud around the nucleus) and the tail(s) that stream away from them. Studying these phenomena gives insight into primordial solar system material.

In recent years, improved survey telescopes (like those used in the Mount Lemmon Survey) and more frequent astrophotography mean we're discovering and documenting more comets than ever. Yet, large and bright comets visible even to the unaided eye remain uncommon.

Where is it?

This photograph was taken near Pedraforca mountain in the Bergueda region in Spain.

Why is it amazing?

The image provides more than just a beautiful view; it records a moment of active sublimation: dust and gas escaping the nucleus due to solar heating. The color of a comet's coma often indicates what gases may be fluorescing under solar UV radiation, offering clues to the icy body's composition. Capturing the tail and coma structure helps astronomers model the dust production rate, tail shape and size, and how the comet is interacting with the solar wind and radiation pressure.

Want to learn more?

You can learn more about astrophotography and Comet Lemmon.

Comet 3I/ATLAS continues to captivate the public. The comet is only the third known interstellar visitor to our solar system, and has been repeatedly surprising astronomers as it flies through our cosmic neighborhood.

3I/ATLAS was first discovered in July. It made its closest pass to the sun on Oct. 30, and three sun-facing spacecraft collected images of the wanderer as it zoomed past our star. This imagery revealed that 3I/ATLAS underwent a "rapid brightening" that exceeds what is observed in most comets at similar distances to the sun. In a pre-print study of that imagery published on arXiv, scientists wrote that this new data shows 3I/ATLAS is "distinctly bluer than the sun" in contrast to "earlier observations showing the comet's dust to be red." Numerous media outlets jumped at the chance to declare the comet had "changed color" multiple times and, of course, said it happened for mysterious reasons.

But according to one of the scientists behind this new study, that's incorrect. "We don't have any evidence for the gas coma changing colors," Qicheng Zhang, a postdoctoral fellow at the Lowell Observatory in Arizona and one of the authors of the study, told Space.com by email. "Our result just showed that the gas coma is likely still around and contributing substantially to the overall brightness," Zhang added.

Comets are sometimes referred to as "dirty snowballs" due the fact that their icy solid cores, or nuclei, are made of frozen gases containing bits of rock and dust. As comets approach the sun, these frozen gases turn from solids back into a gaseous state, creating bright haloes of gas known as "comas" that give comets a fuzzy appearance. A coma can also form a long, bright tail as the solar wind pushes these gases away from the comet's nucleus.

Zhang said that, technically, comet 3I/ATLAS has only appeared to "change color" a single time  —  when its coma became bright as the comet ejected gases while warming up in the sun's heat earlier this year. This was far before reports started emerging about the interstellar visitor's supposed newsworthy "color change."

"As far as we know, the comet just 'changed color' once when its gas coma first became visible/bright, and it's still like that now (only brighter)," Zhang said.

"However, this was already beginning to happen by early September before it got too close to the sun in the sky, as there are numerous photos from amateur astronomers from around then already showing that the comet has a blue/green gas coma."

The comet has been the target of quite a bit of misinformation and extreme speculation, including conspiracy theories that allege it is actually an alien spacecraft and that the U.S. government is using the current government shutdown to conceal evidence of its true nature.

But such extreme circumstances aren't necessary to have this object be as fascinating as it is. Its serendipitous pass through our corner of the cosmos offers us a rare peek into what conditions might be like outside the solar system.

Numerous ground-based telescopes have captured images of the comet, even consumer-grade telescopes as small as 6 inches, and so have the Hubble Space Telescope, Europe's ExoMars Trace Gas Orbiter and China's Tianwen 1 Mars probe.

NASA's Mars Reconnaissance Orbiter was due to capture imagery of the comet as it passed by the Red Planet around Oct. 3, but due to NASA's operations being largely on hold due the shutdown, no imagery has been released from that flyby.

Comet 3I/ATLAS will make its closest approach to Earth on Dec. 19, when it will pass us at a distance of some 167 million miles (270 million km).