Clouds formed from vaporized rock could create the ultimate thermal insulation on one of the most common types of exoplanets discovered so far — the sub-Neptunes — raising temperatures so high that these worlds' solid surfaces melt and turn into oceans of magma.

"This work takes us one step closer to answering the question of what these mysterious worlds are made from," said astronomer Luis Welbanks, of Arizona State University, in a statement.

Sub-Neptunes are planets larger than Earth but smaller than Neptune. They are especially mysterious since we do not have a world of this type in our solar system. They are thought to contain a rocky core surrounded by a deep atmosphere, but not much else is known about their composition and structure. Their atmosphere could be hydrogen-rich like Jupiter's, or it could be abundant with water vapor and carbon-based organic molecules. In some cases, they might even be habitable under the hycean world paradigm, wherein a thick hydrogen atmosphere encases a global ocean of liquid water.

The James Webb Space Telescope (JWST) is busy probing the atmosphere of several sub-Neptunes to try and learn more about their bulk composition because their atmosphere should be representative of what such planets are made from, but results so far have been inconclusive.

Atmospheres of sub-Neptunes are deep and dense, meaning crushing pressures close to the boundary between the atmosphere and the solid body of the world can turn minerals into vapor that forms clouds. These minerals include aluminium oxide, iron, magnesium silicate, manganese sulfide, potassium chloride, sodium sulfide and zinc sulfide.

Using detailed computer simulations, a team led by Sagnick Mukherjee of Arizona State University explored what effect these clouds could have on both the surface and atmosphere of a sub-Neptune.

They showed that when these mineral clouds form deep down, they act as efficient insulating blankets that trap heat (and lots of it) leaking out from the core of the planet.

"Among the sub-Neptunes currently being studied with JWST, we were amazed to find that cloud-driven heating can raise the temperature at the planet's atmosphere–interior boundary by roughly over 1,400 to 2,600 degrees Celsius [2,550–4,712 degrees Fahrenheit]," said Mukherjee.

At the same time, because heat is being prevented from escaping, the upper atmosphere cools noticeably.

With all that heat retained close to the surface, the rock begins to melt.

"For some of the planets we modeled, that extra heat is enough to melt the planet's surface, creating a magma ocean," said team-member Matthew Nixon of Arizona State University.

These potential magma planets include GJ 1214b, which orbits a red dwarf star 48 light-years away. At one time it was thought to be a cool water-world, but JWST's discovery in 2025 of metallic vapors and carbon-dioxide haze in GJ 1214b's atmosphere rule this out, and now it seems that its surface, undetectable beneath the thick atmosphere, could be completely molten.

However, the presence of magma oceans opens up possibilities for more complex atmospheric chemistry. Gas seeps out of the magma and diffuses into the atmosphere, in theory enriching it in oxygen, silicon hydride and silicon monoxide, while going the other way the magma absorbs ammonia, methane and water vapor from the atmosphere. In other words, the atmosphere becomes enriched by material from underground, while also becoming depleted in some gases that astronomers would expect to see in greater abundance.

This means that JWST's attempts to learn about the bulk composition of a sub-Neptune exoplanet from the spectrum of its atmosphere could be skewed by this exchange of gases between a magma ocean and the atmosphere. The extra heating deep down will also impact the future of these sub-Neptune planets, since the extra heat will keep their lower atmosphere bloated and prevent the planet from contracting over billions of years.

If the findings are correct, they could place a huge obstacle on sub-Neptunes being habitable. Even if the boundary between the atmosphere and solid body of the planet isn't hot enough to form magma, it would still render the surface too hot to support liquid water or life.

The findings were published on July 8 in Astrophysical Journal Letters.

Neptune's moon Nereid might be the only satellite surviving from the planet's original system, researchers report in a new study.

This goes against the previous theory, which has long suggested that Nereid is actually an object captured from the Kuiper Belt, the ring of icy bodies beyond Neptune's orbit. In the early history of the outer solar system, it was chaos. Neptune's gravity is thought to have captured its largest moon, Triton, from the vast disk of the Kuiper Belt, which is home to countless small bodies, including a number of dwarf planets. This capture wreaked havoc on the Neptune system and, until now, it's been thought that the planet's third-largest moon, Nereid, was also an object captured from the Kuiper Belt. But a new paper begs to differ.

Nereid, it turns out, isn't a captured object like the other large moons of Neptune. In fact, it's likely that Nereid is actually an original moon of Neptune that happened to survive the tumult of the system capturing Triton, researchers suggest in a new study using data from NASA's James Webb Space Telescope. "Nereid is a huge outlier," lead author Matthew Belyakov, of the California Institute of Technology in Pasadena, told Space.com.

Uncovering a mystery

The Nereid-came-from-the-Kuiper-Belt theory prevailed for so many years because the moon has an irregular and eccentric orbit but is still an intact object, which is rare in moons that are original to the systems in which they orbit.

Original moons like this are so rare because, if an object like Triton is pulled into the system by gravity, the other objects orbiting that planet are typically destroyed or scattered by the event. So it was thought that Nereid couldn't be original, as it couldn't have survived such an encounter.

But the skepticism around the real origins of this moon began all the way back in 1949, when the moon was first discovered by astronomer Gerard Kuiper, the namesake of the Kuiper Belt.

In his discovery paper, Kuiper wrote, "There is some reason to hope that this object may become a clue to the unusual cosmogonic problem presented by the Neptune system, and as such is of more than routine interest."

To find the true nature of this moon, the team took a two-part approach: making observations with JWST and performing simulations of the dynamics of Neptune and its moons in the system's early years. With just over 10 minutes of observations with JWST, the team was able to collect enough data to show that the moon is very much unlike known Kuiper Belt objects (KBOs).

In comparing the moon to KBOs, they found that Nereid is much richer in water ice, is much brighter and reflective, and is also bluer than those objects. Also, volatile organics are common on KBOs, but the team did not find them on Nereid.

These observations with JWST highlighted just how different Nereid is from KBOs, making a fairly strong case that the object didn't come from the Kuiper Belt and is instead an original satellite of Neptune. But to add evidence to this theory, the team took things a step further, creating simulations of the Neptune system in its early years when Triton was first captured.

In these simulations, the team was able to show how Triton being captured into the Neptune system actually knocked Nereid into its current, highly eccentric orbit.

These new findings paint the history of this planetary system in a whole new light. Instead of a system of objects accumulated after Triton's chaotic entry, we have this incredible tale of Nereid's survival.

With this mystery beginning in 1949, today in 2026 we may finally have some answers.

"It takes a long time to do science," Belyakov said. JWST "has a finite lifetime," he added. "If we're not funding scientists to research during James Webb's lifetime, then maybe in decades to come we won't have the data that we would have had otherwise. So this study would not have been possible to any other point other than now."

This work was described in a study published May 20 in the journal Science Advances.

Could Uranus and Neptune be full of rocks? One new study thinks so.

Uranus and Neptune are two planets that have historically been classified and thought of as "ice giants," orbiting far out in the freezing edges of our solar system. But it's possible that our understanding of these planets' makeup could be totally off, and their atmospheres could be full of rocks, researchers suggest in a new study.

"We found out that both Uranus and Neptune have their outer shells made mostly of rocks (and hydrogen and helium gas)," study author Yamila Miguel of the Netherlands Institute for Space Research told Space.com. This "goes against the common belief that they are ice-giant planets."

These two planets both have inner rocky cores surrounded by icy mantles enveloped by a thick atmosphere that has been thought to contain hydrogen, helium and methane gases as well as silicate clouds. In some high pressure areas, the gaseous atmosphere becomes fluid — but the results of this study suggest these atmospheres could also be littered with rocks.

This research team was inspired to take a closer look at Neptune and Uranus thanks to recent research which has suggested that objects in the trans-Neptunian region, an icy region beyond Neptune, are more rocky than icy. Previous studies have suggested objects like Pluto, comets, and Kuiper belt bodies indeed have rocky atmospheres, the new study's researchers explained. "We thought, if those objects are made mostly of rocks, maybe Uranus and Neptune [are] as well?" Miguel said.

To get to their conclusions, the researchers modeled the composition of both Uranus and Neptune, simulating the planets' envelopes (combined inner and outer atmosphere), mantles and cores. Based on conditions like temperature throughout each planet's atmospheric envelopes, the team found the conditions would cause silicate clouds in certain areas of these atmospheres to condense into rocky material.

So, while Uranus and Neptune are known as ice giants, orbiting far from our sun in the outer reaches of the solar system, they're rockier than you might expect an "ice" planet to be, at least according to this study.

While "they might have quite some ice in their interiors," Miguel said, "they are definitely not completely icy as we used to believe."

Miguel asserts that these new findings could even warrant a conversation about re-classifying these planets. "We should indeed change their classification so as not to be misleading," they suggest. "Rather than 'icy' or 'rocky,' we should simply call them minor giants or something like that."

To be clear, this new study isn't a definitive new classification of these planetary giants. However, it does raise interesting questions about their makeup: Could their atmospheres really be full of rocks? Are there other major aspects of their composition that we haven't yet uncovered? What other mysteries lie in the cold, far corners of our cosmic neighborhood?

This work was described in a study published May 5 in the journal Astronomy & Astrophysics.

Look to the eastern sky in the hour preceding dawn on May 14 to catch a rare sight, as the moon, Saturn and Mars form a cosmic triangle in the glow of the rising sun, while the ice giant Neptune lurks unseen nearby.

The 8%-lit waning crescent moon will sit low on the eastern horizon as dawn's glow creeps into the sky. Saturn will appear as a bright star-like object to the moon's lower right, while the reddish glow of Mars shines lower still to the left of the pair.

Neptune will also be present roughly 10 degrees to the right of the thin lunar crescent — roughly the width of a clenched fist held at arm's length against the sky — but will be far too dim to spot with the unaided eye.

Mars, Saturn and the moon will all be less than 20 degrees above the horizon at sunrise, so be sure to find a location with a clear view to the east to see them before they're swallowed in the golden light of dawn.

While the cosmic trio will make for a spectacular naked eye target, we advise against any attempt to view them with a telescope owing to their proximity to the rising sun. Remember, pointing a telescope or binoculars at the sun can result in permanent and immediate loss of sight.

In the coming nights, Earth's satellite will disappear from the predawn sky ahead of its new moon phase on May 16, while Mars and Saturn subtly drift away from one another among the stars of the constellation Pisces.

Be sure to read our roundups of the best lenses and cameras for astrophotography to ensure that you're ready to capture the next big planetary rendezvous, along with our beginner's guide to imaging the night sky.

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

Jupiter, Saturn, Venus, Neptune, Uranus and Mercury are staring in a "planetary parade" this week, but your ability to actually spot them will depend on preparation, equipment and, as always, a spot of luck with the weather.

Most of this week's naked-eye planetary action will take place low in the western sky, which is where the aforementioned preparation comes in. Be sure to stake out a raised location with a clear view of the horizon well ahead of time — you can use a smartphone stargazing app to figure out exactly where the planets will be in your local environment, so there's no need to guess.

Do so, and you'll be granted a rare, if challenging opportunity to spot Mercury shining 10 degrees — roughly the width of your clenched fist held at arm's length — above the late winter skyline, with Venus close to its left, floundering in the glow of the setting sun. Saturn, meanwhile, will glow less than 10 degrees to the upper left of Venus, with a distant cousin lurking nearby, but more on that later.

Mercury and Venus will follow the sun out of sight roughly an hour after sunset, briefly becoming more visible as the sky darkens and they grow closer to the horizon. Jupiter, meanwhile, will shine high in the eastern sky, with the waxing gibbous moon below, obscuring the stars of the constellation Cancer with its reflected light.

The next two planets will need a little added magnification to spot — and even then, you'll have the odds stacked against you.

The ice giant Neptune will be positioned two degrees to the right of Saturn, but will be too dim to spot with the unaided eye. Under dark skies, a telescope with an aperture of 8 inches (200 millimeters) or more can reveal its tiny bluish disk. However its position low on the horizon and close to the glare of our parent star will make it a challenge to spot on the nights surrounding Feb. 28. As always the utmost care must be taken to ensure that the sun is firmly below the horizon before pointing telescopic equipment in its general direction.

Uranus, meanwhile, can be found by sweeping your scope across the patch of sky 5 degrees below the Pleiades open star cluster, to the right of the "V" formation of stars in the constellation Taurus in the hours following sunset. Again, those new to the night sky may want to use a smartphone astronomy app, which makes use of augmented reality technology to help you pinpoint everything from constellations and planets to galaxies and meteor shower radiants.

Award-winning night sky photographer Josh Dury grappled with the sheer scope of the scene along with the glow of the setting sun and other challenges to capture a gorgeous long exposure view of the planetary parade earlier this week as it brightened the sky over the south of England.

For more, check out our handy guide on the equipment needed to see and photograph the planets. If you're into photography, then why not also read our roundups of the best cameras and lenses for capturing the night sky?

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

Look to the western horizon at sunset on Feb. 20 to witness an incredible sight, as three planets shine below the slender crescent of the waxing moon, with Jupiter glowing high overhead in the winter sky.

The upturned sickle-shape of the 18%-lit moon will appear 40 degrees above the horizon as the sun sets, with a string of bright "evening stars" representing Venus, Mercury and Saturn arrayed beneath, fighting for attention in the glow of the setting sun.

Saturn will be positioned 15 degrees directly below the crescent moon, with Mercury less than 10 degrees— roughly the width of your clenched fist held at arm's length — to its lower right. Mercury is currently in prime viewing position, having just passed its point of greatest eastern elongation on Feb. 19, when it was at its furthest from the sun in Earth's sky in its current evening apparition.

Find a spot with a clear view to the west for a chance to see Venus shining directly below Mercury, less than 10 degrees above the horizon at sunset. Neptune will also be present less than 1 degree — approximately the width of your little finger — to the right of Saturn, though it'll be too dim to spot with the naked eye.

Neptune is so distant that the blue spec of its disk can only be seen with the aid of an 8-inch telescope, but utmost care must be taken to ensure that the sun is well below the horizon before pointing any telescopic equipment in its direction.

Uranus, meanwhile, will be five degrees below the Pleiades on Feb. 20 and while technically just bright enough to spot with the naked eye from a dark sky location, the planet will also benefit from the magnifying power of a telescope to spot its tiny aqua disk.

Jupiter dominates the sky this time of year and can be found high in the east at sunset, glowing with the bright stars Castor and Pollux in the constellation Gemini. A 6-inch telescope will reveal details in the cloud bands lining its surface, along with its four largest moons, Io, Ganymede, Europa and Callisto.

The lunar crescent will also make for a fascinating telescopic target, just three days out from its new moon phase on Feb. 17. Look out for the dark forms of Mare Crisium and Mare Fecunditatis darkening the sunlit wedge of Earth's satellite, which formed when ancient lava flows flooded networks of impact craters before hardening many millions of years ago.

Next, sweep your telescope across the line separating night from day on the lunar surface — known as the terminator — to spot a myriad of shadowed impact craters scarring the lunar surface.

Want to explore the planets of the solar system for yourself? Then be sure to read our roundup of the best telescopes available in 2026. If you're into photography you'll want to peruse our picks of the best cameras and lenses for capturing the night sky.

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

Want to know when each planet will be at its best or when you can catch eye-catching planetary pairings in 2026?

This guide breaks down the major planetary events of the year, from conjunctions to oppositions to close planet-star encounters.

Related: Night sky tonight live blog

Mercury

Mercury, the smallest of the planets visible to the naked eye, appears as an evening star in the western sky, setting about an hour after the sun. As a morning star, it rises about an hour before the sun in the eastern sky. To view the planet, a clear, unobstructed view of the horizon is essential. Mercury usually appears as a bright "star" with a yellowish or ochre tint.

Visibility windows in 2026

• Evenings: Feb. 5–26; June 1–22; Sept. 28–Oct. 19
• Mornings: March 27– April 17; July 26– Aug. 16; Nov. 13– Dec. 4

When will it be at its best?

• Evening: Feb. 5–26
• Morning: Nov. 13– Dec. 4

On the evening of Feb. 18, about 30 minutes after sunset, Mercury will sit just 1 degree above a slender waxing crescent moon low in the west-southwest.

Venus

Venus, with its nearly circular orbit and a diameter only 400 miles (640 kilometers) smaller than Earth's, shines with a brilliant, steady silvery light.

Visibility windows in 2026

• Evenings: March 8– Oct. 14
• Mornings: Nov. 3– Dec. 31

When will it be at its best?

Venus reaches greatest brilliancy in the evening sky on Sept. 19 and in the morning sky on Nov. 29. In late September through mid-October, and again through most of November, Venus will show a striking crescent phase in telescopes and steady binoculars.

Notable conjunctions:

• March 8: Venus passes 1 degree to the upper right of Saturn.
• June 9: Venus passes 1.6 degrees to the upper right of Jupiter — a brilliant sight in the west-northwest 45 minutes after sunset.
• Nov. 7 (morning): Shortly before sunrise, look low to the east-southeast for Venus, a crescent moon, and the star Spica, all fitting within 2.5 degrees.

Mars

Mars, long associated with Ares, the Greek god of war, shines like a star with a yellowish-orange hue and can vary considerably in brightness.

Visibility in 2026

• Mornings: March 18- Dec. 31

When will it be at its best?

This is an "off" year for Mars. The planet begins 2026 lost in the sun's glare and reaches solar conjunction on Jan. 9, sitting on the far side of the solar system about 223 million miles from Earth.

Mars begins to reappear in the third week of March, rising before sunrise among the faint stars of Aquarius. It moves into Taurus for the first half of summer, shining only around magnitude +1.3.

Sky highlights:

• Sept. 25: Castor and Pollux point directly toward Mars.
• Oct. 11: Mars passes through the Beehive Cluster in Cancer — an attractive sight in binoculars.
• Nov. 26: Mars passes 1.7 degrees above Regulus in Leo, creating a dramatic color contrast.
• By late December, Mars brightens to magnitude –0.1 and will rival Arcturus in both color and brightness.
• Feb. 19, 2027: Mars reaches its next opposition, so it steadily approaches Earth late in 2026.

Notable conjunctions:

• April 20: Mars aligns closely with Saturn and Mercury.
• July 4: Mars passes just 0.1 degree south of Uranus, offering a superb guidepost for locating Uranus.
• Nov. 16: Mars passes 1.2 degrees to the upper left of Jupiter.

Jupiter

Jupiter, the giant planet with a diameter about 11 times bigger than Earth's, shines with a bright silver-white luster.

Visibility windows in 2026

• Mornings: Jan. 1–9; Aug. 19– Dec. 31
• Evenings: Jan. 10–July 7

Jupiter reaches opposition on Jan. 10 and shines brightest from Jan. 1–22 at magnitude –2.7 in Gemini. It enters Cancer on June 22 and Leo on Sept. 24, where it remains through year's end.

On June 9, Jupiter pairs with Venus in a stunning "double planet" display low in the west-northwest at dusk.

Oct. 6 lunar occultation

On the morning of Oct. 6, observers across most of North America (excluding the far West) and northern Cuba will witness a spectacular lunar occultation of Jupiter. A waning crescent moon will slide directly in front of Jupiter, hiding it for up to an hour depending on location. Jupiter disappears behind the bright limb and reemerges dramatically from the moon's dark side.

Saturn

Saturn shines as a yellowish-white "star" of moderate brightness. Its famous rings, invisible to the naked eye, turned edge-on in 2025 and were nearly impossible to see for weeks. They are now slowly opening up again.

Constellation path in 2026:

• Starts in Aquarius (to Jan. 14)
• Enters Pisces (Jan. 14– April 8)
• Moves through Cetus (April 9– June 2)
• Back into Pisces (June 3–Sept 4)
• Back into Cetus (from Sept. 5 onward)

Visibility windows in 2026

• Evenings: Jan. 1–March 8; Oct. 4–Dec. 31
• Mornings: April 12– Oct. 3

Saturn reaches opposition on Oct. 4 and is brightest Sept. 24–Oct. 9.

Notable conjunctions:

• Feb. 15: Saturn sits less than 1 degree from Neptune, though Neptune is much fainter.
• Apr. 20: Saturn aligns with Mars and Mercury.

Uranus

Uranus can be glimpsed with the naked eye under very dark skies by keen-eyed observers. At magnitude +5.6, it is easily found with binoculars; small telescopes show a tiny greenish disk.

Uranus spends all of 2026 in Taurus.

Visibility windows in 2026

• Evenings: Jan. 1–May 5; Nov. 25– Dec. 31
• Mornings: June 9–Nov. 24

Uranus reaches opposition on Nov. 25 and is brightest Oct. 24–Dec. 30.

On July 4, Uranus sits only 0.1 degree north of Mars, making Mars an ideal pointer to the seventh planet. Mars will outshine Uranus by a factor of about 158.

Neptune

Neptune remains in Pisces throughout 2026. At magnitude +7.8, it is visible only in binoculars or a telescope and appears bluish-gray.

Visibility windows in 2026

• Evenings: Jan. 1–March 6; Sept. 25–Dec. 31
• Mornings: April. 8– Sept. 24

Neptune reaches opposition on Sept. 25 and is brightest July 28–Nov. 24.

On Feb. 15, Neptune lies less than 1 degree to the upper right of Saturn, though Neptune is only about 1/525 as bright.

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 and other publications.

Look to the southeastern horizon in the hours following sunset on Nov. 29 — you'll be able to see the moon shine close to the gas giant Saturn as Neptune lurks unseen nearby.

The waxing gibbous moon will appear half-lit on the night of Nov. 29, just one day on from its first quarter phase, as it glows with reflected sunlight beneath the stars of the constellation Pisces. Saturn will appear as a bright "evening star" shining less than 5 degrees — roughly the equivalent to the width of your clenched fist held at arm's length — to the lower right of the gas giant.

Nights surrounding the moon's first quarter phase present a superb opportunity to explore the lunar surface as the line separating night from day — known as the terminator — sweeps across the lunar surface, throwing craters and mountain ranges into sharp relief. As such, the moon will appear particularly spectacular through the eyepiece of a backyard telescope with an aperture of around 6-inches, which will reveal stunning detail in the tortured surface of Earth's ancient companion.

Saturn will make for a striking sight for both naked eye and telescopic observations on the night of Nov. 29. An 8-inch (200 mm) telescope will help reveal the horizontal bands lining the cloud surface of the gas giant, though its iconic ring system is currently positioned almost edge-on to Earth, making it appear as little more than a thin line bisecting the planet through the eyepiece of a scope.

The night of Nov. 29 will also see Saturn end its "retrograde" westward movement through the stars of Pisces, after which it will begin to track an eastward path through the sky, according to in-the-sky. Planetary retrograde motion occurs in the weeks and months following opposition, when Earth's tighter orbit around the sun causes it to "overtake" more distant worlds, briefly making it appear as if they are moving "backward" in the night sky.

Neptune will also lurk unseen roughly 2 degrees below the moon on the night of Nov. 29, though it will be far too dim to spot with the unaided eye. Under ideal conditions a telescope with an aperture of 8-inches or more may reveal the presence of the planet as a tiny blue dot against the blackness of space. However, the light of the nearby waxing moon could make spotting the distant world more challenging than usual on Nov. 29.

Want to explore the lunar maria and ancient craters of the moon for yourself? Then be sure to check out our roundup of the best telescopes for observing the night sky in 2025.

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

Saturn isn't the only planet in our solar system with a ring system. While Saturn's rings are the most dramatic, the three other gas giants — Jupiter, Neptune, and Uranus — each have a ring system as well. But the fun doesn't stop there. Astronomers have also spotted rings around smaller celestial bodies: dwarf planets Haumea and Quaoar, as well as centaur Chariklo.

Now, 2060 Chiron, better known as just Chiron, is the latest celestial body to join the party. In analyzing observations of Chiron taken by Brazil's Pico dos Dias Observatory in 2023, astronomers have just spotted four rings plus diffuse material around this icy centaur, which was first sighted in 1977.

Centaurs are a class of celestial objects that are a cross between comets and asteroids, located between Jupiter and Neptune. Chiron, which orbits the sun between Saturn and Uranus, is composed of rock, water ice, and organic compounds, and it's approximately 125 miles (200 kilometers) in diameter.

Its rings — thought to be made of water ice and rocky material, potentially from a collision between Chiron and another celestial body — circle the centaur at approximately 170 miles (273 km), 202 miles (325 km), 272 miles (438 km) and 870 miles (1,400 km) from its center. The distant fourth ring, researchers note, might not ultimately be stable enough to be considered a ring, so further observations are necessary.

What's special about Chiron's rings is that they're still forming; this marks the first time astronomers have ever seen a ring system under formation. By comparing the 2023 observations to previous ones from 2022, 2018, and 2011, researchers determined that the ring system has been evolving rapidly.

"It is an evolving system that will help us understand the dynamical mechanisms governing the creation of rings and satellites around small bodies, with potential implications for various types of disk dynamics in the universe," astronomer Braga Ribas of the Federal University of Technology-Parana and the Interinstitutional Laboratory of e-Astronomy in Brazil, who co-authored a study on the research, told Reuters.

The team's research was published in the Astrophysical Journal Letters on October 14, 2025.

Astronomers have long called Uranus and Neptune the "ice giants" because models suggested that these outer planets' interiors are largely made of mixtures of water, ammonia and other ices — compounds that freeze easily in deep space. But new research reveals that we actually know very little about what's going on inside these planets, causing researchers to propose that Uranus and Neptune be called "rocky giants" instead.

The problem with Uranus and Neptune is that we have extremely little data available to us. Unlike Jupiter and Saturn, both of which have received dedicated missions like the Cassini probe and the Juno spacecraft, the outer planets have not received any visitors since the Voyager 2 flybys more than 30 years ago.

So, to build an understanding of these planets' interiors, we must rely on a variety of indirect clues, like their magnetic fields, observations of surface atmosphere features, and subtle changes in the orbits of their moons. For decades, models of solar system formation dictated that the outer realms of the solar system were dominated by molecules like water and ammonia ice. So naturally, those compounds would make up the bulk of Uranus and Neptune, hence their "ice giant" moniker.

But a new pre-print study accepted for publication in the journal Astronomy and Astrophysics took a completely different approach. Instead of trying to build a physical model of planetary interiors from possibly flawed and biased assumptions, the authors generated a series of random models of the interior contents of Uranus and Neptune. Then, they compared those random models to a host of observational data and built a database of all models compatible with observations.

The models yielded a few expected results. Each planet is less than a quarter hydrogen and helium, which matches predictions from solar system formation models and the observed densities of the planets. The models also created layers of electrically conductive material, which can explain the magnetic fields of Uranus and Neptune.

But this agnostic approach did yield one major surprise: We may not have any idea what the interiors of Uranus and Neptune are really like.

For example, the rock-to-water ratio for Uranus varies widely, anywhere from a low of 0.04, meaning the planet is almost entirely water, to as much as 3.92, which is the complete opposite. Neptune is slightly better understood, but it could still have anywhere from as much as five times as much water as rock up to twice as much rock as water.

If that's the case, then "ice giants" may be the wrong name for these planets. Most of their bulk could be in the form of rock, potentially giving them more rocky material than even Jupiter or Saturn, even though Neptune and Uranus are much smaller than those two gas giants.

If this idea holds up, it could challenge existing models of solar system formation, as we would have to figure out a way to get enough rocky material into the outer solar system to let it accumulate onto these planets.

Only a dedicated mission to Uranus or Neptune could resolve these issues, as we need high-quality data from an orbiter to fully understand what's going on.

Named after the Roman god of the sea, Neptune is a world of powerful storms, deep mysteries, and breathtaking beauty.

Neptune may be distant, but it's anything but quiet. With the fastest winds in the solar system — reaching up to 1,500 miles per hour — it's a planet of swirling chaos beneath a calm blue exterior.

The planet also sports faint rings made of dust and ice, adding to its mysterious allure. This quiz will dive into Neptune's entourage and the strange dynamics of its outer world.

Whether you're a space enthusiast, a trivia lover, or just curious about the coldest corners of our solar system, this Neptune quiz is your chance to explore the unknown.

Try it out below and see how well you score!

Think you know your way around the solar system?

From the scorching surface of Mercury to the icy edges of Neptune, our planetary neighborhood is full of wonders. The order of the planets isn't just trivia—it tells a story about temperature, composition, and even the possibility of life. Understanding the planets' sequence helps us grasp how the solar system formed and how it functions today.

In this quiz, you'll be challenged to put the eight planets in their correct order from the Sun.

Whether you're a seasoned space explorer or just dipping your toes into astronomy, it's time to test your cosmic knowledge!

Try it out below and see how well you score!

Astronomers have found that a weird space rock at the edge of the solar system is locked in a rhythmic dance with Neptune.

The object, designated 2020 VN40, is part of a family of distant solar system objects called trans-Neptunian objects (TNOs). 2020 VN40 is the first object discovered that orbits the sun once for every ten orbits Neptune makes. Considering that one Neptunian year lasts 164.8 Earth years, that means 2020 VN40 has one heck of a long year, lasting around 1,648 years or 19,776 months on Earth!

The team behind this research thinks that 2020 VN40's ponderous orbital dance with Neptune may have come about when it was temporarily snared by the gravity of the ice giant planet. Thus, this discovery could help researchers better understand the dynamics of bodies at the edge of the solar system.

"This is a big step in understanding the outer solar system," team leader Rosemary Pike from the Center for Astrophysics | Harvard & Smithsonian said in a statement. "It shows that even very distant regions influenced by Neptune can contain objects, and it gives us new clues about how the solar system evolved."

The orbital rhythm of 2020 VN40 was discovered in data from the Large inclination Distant Objects (LiDO) survey. LiDO uses the Canada-France-Hawaii Telescope with backup from the Gemini Observatory and the Walter Baade Telescope to search the outer solar system for weird objects.

In particular, LiDO specializes in hunting TNOs with orbits that take them far above and below the orbital plane of Earth around the sun. These are regions of the solar system that have thus far only been sparsely explored by astronomers.

"It has been fascinating to learn how many small bodies in the solar system exist on these very large, very tilted orbits," LiDO team member and University of Regina researcher Samantha Lawler said.

The highly tilted path of 2020 VN40 finds it at an average distance from the sun equivalent to 140 times the distance between Earth and our star.

However, the most interesting element of the orbit of 2020 VN40 is its resonance with the orbit of Neptune. Other bodies rhythmically aligned with Neptune make their closest approaches to the sun, their perihelion, when Neptune is at its greatest distance from our star, or its aphelion.

Defying this trend, 2020 VN40 is at perihelion when Neptune is also close to the sun. That's if one were looking at it from above the solar system, with the tilt of 2020 VN40 meaning that this TNO and Neptune are not actually close together; the TNO is actually far below the solar system.

This also separates 2020 VN40 from other resonant TNOs, which tend to stay within the plane of the solar system when they make close approaches to the sun.

"This new motion is like finding a hidden rhythm in a song we thought we knew," team member and University of California Santa Cruz scientist Ruth Murray-Clay said. "It could change how we think about the way distant objects move."

Revealing the orbital strangeness of 2020 VN40 suggests that solar system objects with highly tilted orbits can adopt novel and unexpected types of movement.

The hunt is now on for more bodies like 2020 VN40, with the newly operating Vera C. Rubin Observatory set to play a key role in this investigation.

"This is just the beginning," team member and Planetary Science Institute researcher Kathryn Volk said. "We're opening a new window into the solar system's past."

The 2020 VN40 results were published on July 7 in The Planetary Science Journal.

Heads up stargazers! The moon will rise close to Saturn and the ice giant Neptune in the eastern sky on the night of July 15, close enough to be seen together in a pair of binoculars!

Saturn will rise above the eastern horizon beneath the stars of the constellation Pisces shortly before midnight for viewers in the U.S. on July 15, with the waning gibbous moon shining roughly three degrees to its upper right. For context, the width of your little finger held at arms length against the night sky accounts for roughly 1 degree.

The planet Neptune can also be found lurking approximately 1 degree to the upper left of Saturn around this time, though its dim brightness, or magnitude of +7.8, will make it impossible to see with the naked eye. Remember: magnitude is the scale used by astronomers to measure the apparent brightness of night sky objects. The lower the number, the brighter a planet or star will appear in the night sky. The human eye is capable of picking out objects with a brightness of +6.5 or greater from a dark sky location.

All three celestial targets will fit nicely within the field of view of a pair of 10x50 binoculars, though Neptune will appear as nothing more than a dim point of blueish light —if it’s visible at all against the glare of the waning moon — so don't expect much too much from the ice giant.

Gazing through a telescope with a 6-inch aperture will help reveal the rings around Saturn, while an 8-inch scope may allow you to spot variations in color on the gas giant's cloud surface. A range of exciting observing targets will also be visible on the 75%-lit moon on July 15, including the long, thin form of Mare Frigolis — a vast basalt plain visible as a dark scar running across the northern extreme of the lunar surface.

The celestial trio will remain close to each other throughout the night, with Saturn and Neptune eventually fading from sight in the southern sky when the sun rises on July 16.

Stargazers looking to get a closer look at the myriad worlds of our solar system should check out our guides to the best telescopes and binoculars for exploring the night sky. We also have a handy roundup of the best cameras and lenses for astrophotography for those looking to immortalize their skywatching sessions.

The half-lit lunar disk will rise alongside the ringed giant Saturn and dimmer Neptune in the early morning hours of June 19, putting on a spectacular show just six hours after the moon hits its third quarter phase.

Saturn, the moon and Neptune will be at their closest in Earth's sky at 9:11 p.m. EDT on June 18 (0111 GMT on June 19), at which time the trio will be separated by a mere 2.58 degrees while below the horizon for those in the U.S., according to stargazing website in-the-sky.org. Remember, it's possible to measure distances by holding your hand at arms length against the night sky. The width of the tip of your little finger accounts for 1 degree in the night sky, while the width of your clenched fist measures roughly 10 degrees.

The best time to spot the solar system alignment will come during the early morning hours on June 19, at around 1:30 am EDT for viewers in New York, when the giant planets rise alongside the moon on the eastern horizon. The exact time that the trio will become visible will vary depending on your location, so be sure to check a trusted source such as the Stellarium smartphone app to get precise timings for your locale.

The half-lit form of the third quarter moon will be the first to rise, with Saturn following shortly after, visible as a bright morning star a little under 4 degrees to the lower right of the lunar disk. The ice giant Neptune - too dim to spot with the naked eye - will be positioned roughly 1 degree to the upper left of Saturn and can be observed using a telescope with an aperture of 8-inches (200 mm) or greater, according to telescope-maker Celestron.

In the following days, Earth's natural satellite will leave the giant planets behind as it tracks a path towards Venus, with its disk growing ever thinner as it approaches its new moon phase on June 25. Saturn and Neptune meanwhile will remain close to each other in Earth's sky over the coming months.

Stargazers looking to explore the planets of our solar system for themselves should check out our guides to the best binoculars and telescope deals available in 2025. Photographers hoping to upgrade their gear ahead of the next celestial alignment should also read up on our roundups of the best cameras and lenses for astrophotography.

Editor's Note: If you capture an image of the moon with Neptune and Saturn and want to share it with Space.com's readers, then please send your photo(s), name, shooting location and comments to spacephotos@space.com.

The moon will rise with Venus and the ice giant Neptune in the pre-dawn sky on Thursday, May 22.

Stargazers in the U.S. will see the celestial trio rise around 3:30 a.m. EDT (0715 GMT), with the waning crescent moon holding the high ground over magnitude 1.14 Saturn, which will be visible around four degrees to its lower left in the eastern sky. Neptune — invisible to the naked eye at magnitude 7.92 — can be found lurking roughly two degrees (or two finger widths) to the left of Saturn. (On the magnitude scale used by astronomers, lower numbers signify brighter objects). For example, at its brightest, the planet Venus shines with a magnitude of about -4.6.)

Neptune may be visible under dark skies with the help of powerful 25x100 binoculars as a star-like point of light, but a small, 4-inch telescope capable of around 150x magnification will be needed to resolve its pale blue disk, according to telescope manufacturer Celestron. Saturn, meanwhile, will shine brightly through binoculars, with the planet's iconic ring system appearing as small bumps, or 'ears' either side of the planet's disk, according to NASA.

However, the Saturnian system truly comes alive when viewed through a telescope, which will reveal details in the gas giant's rings, along with a diverse collection of gravitationally bound moons. Larger backyard telescopes with a roughly 8-inch aperture may even be able to resolve the Cassini Division — a gap between Saturn's outer A ring and B ring that comes close to spanning the width of the planet Mercury, under good conditions.

The crescent moon also makes for a fascinating viewing target. The northwestern region is home to the smooth, dark plains of the lunar maria (Latin for "seas"), while the brighter southern highlands are covered in craters left by ancient asteroid impacts. The moon's crescent will slim over the coming days as it approaches the new moon phase on May 27, when it will vanish into the glare of the sun.

The following morning, on May 23, the moon will rise to the left of Saturn and Neptune, closing in on a striking close encounter with Venus, a brilliant "morning star" hovering close to the eastern horizon. Venus —often dubbed Earth's twin is climbing higher each morning as it heads towards greatest western elongation on May 31 — the point in its orbit when it appears farthest from the sun in the morning sky, according to in-the-sky.org.

Stargazers interested in exploring the wonders of the solar system planets and Earth's moon for themselves should check out our guides to the best binoculars deals and the best telescope deals in 2025.

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.

Venus will partner up with the giant planets Saturn and Neptune to form a line up in the pre-dawn sky on May 8, with fleet-footed Mercury remaining nearby close to With Mercury sticking low to the horizon in the hour preceding

To find the planetary line-up, stargazers should look to the eastern sky below the head of the western great fish represented in the constellation Pisces a few hours before sunrise on May 8, which will occur for viewers in New York at 5:46 a.m. (0946 GMT). All three of the tightly packed worlds will have risen above the horizon by 4:15 a.m., with Venus (magnitude -4.38) on the left, and Saturn (magnitude 1.18) on the right.

Neptune will make for a trickier viewing target, given that it is the only major planet in our solar system that is not visible to the naked eye. The ice giant's relative dimness comes as a result of its far flung orbit, which takes it over 30 times further from our sun than the average distance between our star and Earth, according to NASA.

In order to spot Neptune, stargazers will need to get their hands on a good pair of binoculars or a telescope, which will reveal the reclusive world as a blueish point of light. On the morning of May 8, Neptune will be particularly easy to find sitting around half way between Venus and Saturn. The pre-dawn hour will see the planetary trio crammed into a 10 degree patch of sky (about as wide as your fist at arm's length), making them a tempting target for the astrophotography community.

Planet Mercury will also peek its head above the horizon shortly before the sun rises. As always astronomy enthusiasts must always take care to never point binoculars or any telescopic equipment towards the rising sun, and to avoid staring in its direction with the naked eye, as doing so can lead to permanent loss of vision.

This configuration of planets will hold relatively stable from the perspective of Earth for the following two nights. However, by May 11 it will become apparent that Neptune and Saturn are growing ever more distant from brighter Venus. As the month wears on, Venus will remain relatively close to the eastern horizon, while its two planetary siblings drift maintain a close formation as they drift to a more south easterly position, and rise ever higher in the morning sky.

Interested in seeing the planets of the solar system for yourself? Then be sure to check out our guides for the best binoculars deals and the best telescope deals available in 2025. Those looking to create a permanent record of their stargazing sessions should also read our guides on the best cameras for astrophotography, and best lenses for astrophotography can lenses to help you focus in on your next celestial target.

In a distant corner of our solar system called the Kuiper Belt, icy bodies lurk in the darkness, orbiting our sun at vast distances.

These ancient minor planets are called trans-Neptunian objects (TNOs), and they date back to the formation of the solar system.

Researchers participating in the Discovering the Surface Compositions of Trans-Neptunian Objects program, led by the University of Central Florida (UCF), recently studied these dim objects using NASA's James Webb Space Telescope. Their work has revealed new information about surface ice methanol — a key building block for organic compounds necessary for life, including sugars — on TNOs.

"Methanol, a simple alcohol, has been found on comets and distant TNOs, hinting that it may be a primitive ingredient inherited from the early days of our solar system — or even from interstellar space," former UCF professor Noemí Pinilla-Alonso, who now works at Spain's University of Oviedo, said in a statement.

“But methanol is more than just a leftover from the past," Pinilla-Alonso added. "When exposed to radiation, it transforms into new compounds, acting as a chemical time capsule that reveals how these icy worlds have evolved over billions of years."

The Webb observations identified two groups of TNOs: one with depleted surface ice methanol and one with subsurface methanol reservoirs.

"What excited me the most was realizing that these differences were linked to the behavior of methanol — a key ingredient that had long been elusive on TNOs from Earth-based observations," said Pinilla-Alonso. "Our findings suggest that methanol is being destroyed on the surface of TNOs by irradiation, but remains more abundant in the subsurface, protected from this exposure."

While this discovery might not provide all answers about the origins and development of TNOs, it certainly furthers our understanding of these distant icy bodies — and inspires more research.

The findings were published in March in The Astrophysical Journal Letters.

Friday, May 2, presents a perfect opportunity to catch the mighty ice giant Neptune close to the planets Saturn and Venus in the pre-dawn sky, before they break their close-knit formation later in the month.

To find the planetary trio, find a stargazing spot with a clear horizon and head out a little over an hour before sunrise, which will occur at 5:53 a.m. EDT (0953 GMT) for night sky enthusiasts based in New York. The three distant worlds will have risen just above the horizon by 4:40 a.m. EDT (0830 GMT) for stargazers in this locale, and will climb visibly higher until the sun bleaches the sky with its light.

Venus (magnitude -4.41) will appear as the brightest world by far in the planetary formation, and will hold the highest position over the horizon with Saturn (magnitude +1.19) located to its lower right just a few degrees — or finger widths — away. Dimmer Neptune can be found down and slightly to the right of Venus with a separation of roughly two finger widths, or half the distance between Venus and Saturn.

Remember, the lower a celestial body's magnitude is, the brighter that night sky object will appear against the inky blackness of space. Neptune will shine at a magnitude of +7.94, which is fainter than the human eye can detect (typically around +6.5 under dark sky conditions). This means you'll need a pair of high-powered binoculars under dark skies — or better yet, a quality telescope — to resolve the distant world as a tiny blue orb.

All three planets will fit nicely in the field of view of a pair of standard binoculars. However, if you do go planet hunting, viewers must remember to never look directly at the rising sun, which appears in the east shortly after Neptune. Doing so can cause serious and permanent eye damage.

During early May, the triangular formation of the planets will gradually shift in the morning sky. For instance, on the morning of May 9, Neptune, Venus and Saturn will align in a nearly perfect line across the eastern horizon. By the end of the month, Saturn and Neptune will appear to have slipped Venus' grasp, rising ever higher in the pre-dawn sky while Venus lingers near the horizon.

If you're looking for a telescope or binoculars to observe the planets of our solar system? Well our guides for the best binoculars deals and the best telescope deals can help. Our guides on the best cameras for astrophotography and best lenses for astrophotography can also help you prepare to capture the next skywatching sight, whether it be stunning aurora, a planetary conjunction, or simply a calm, star-filled night.

Editor's note: If you want to share your night sky pictures with the readers of Space.com, please email them to spacephotos@space.com.

The predawn hours of April 28 will see a planetary triangle form in the night sky, as Venus makes a close approach to Saturn following a conjunction, while Neptune, invisible to the naked eye, will sit just a few degrees away towards the horizon.

Saturn and Venus will be below the horizon for viewers in the U.S. when they reach the point of conjunction in the hours before their appearance on the morning of the 28th. A planetary conjunction occurs when two worlds share the same right ascension  —  a value similar to longitude that is used by astronomers to chart the locations of objects in the night sky  —  when viewed from the night sky from Earth.

At this point the planetary duo will be separated by a little under 3.5 degrees in the sky, according to stargazing website in-the-sky.org (the width of your first at arm's length equals about 10 degrees).

To catch Saturn, Venus and Neptune at play, stargazers need only find a clear, unobstructed view of the horizon, and look eastward in the hour preceding sunrise on April 28.

Venus will be visible as a bright magnitude -4.42 morning star near the horizon, while Saturn will appear just a few degrees away to the bottom left, significantly dimmer than its planetary neighbor.

Neptune will be altogether invisible to the naked eye, but can be picked out with a decent pair of binoculars, or a telescope, appearing as a small blueish green point of light below and slightly to the left of Venus. However, as always the utmost care must be taken to never point a pair of binoculars or telescope at the sun, or to look directly at the stellar body with the naked eye.

Mercury will also be present close to the eastern horizon in the hour before dawn, but will be quickly hidden by light from our rising sun.

Looking to explore the solar system for yourself? well our guides for the best binoculars deals and the best telescope deals now can help. Our guides on the best cameras for astrophotography and best lenses for astrophotography can also help you prepare to capture the next skywatching sight.

Editor's note: If you want to share your planetary photographs with our readers at Space.com, please email them to spacephotos@space.com.

For the first time, the James Webb Space Telescope (JSWT) has revealed bright auroral activity on the planet Neptune.

Capturing the auroral activity on the ice giant has been long in coming, even though similar areas of trapped solar energetic particles have been successfully imaged in the atmospheres of Jupiter, Saturn and Uranus.

Why is this amazing?

Previously, the existence of auroral activity on Neptune was only hinted at, as instruments on NASA’s Voyager 2 probe, which flew by the planet in 1989, and the Hubble Space Telescope were unable to capture the glow.

“Turns out, actually imaging the auroral activity on Neptune was only possible with Webb’s near-infrared sensitivity,” said Henrik Melin of Northumbria University, whose research while at the University of Leicester has now been published in the journal Nature. “It was so stunning to not just see the auroras, but the detail and clarity of the signature really shocked me.”

In Webb's images of Neptune, the aurora appears as lighter blue or cyan areas set against the blue planet.

Is this the same as the northern or southern lights on Earth?

The auroral glow occurs because of the same basic interaction of solar particles interacting with the planet's atmosphere, but instead of being confined to the north and south poles, Neptune’s auroras are located at the planet’s mid-latitudes — roughly where South America is located on Earth.

The location of Neptune's auroral glow is the result the planet's magnetic field, which is tilted by 47 degrees from the planet’s rotation axis. Auroral activity occurs where a planet's magnetic fields converge into its atmosphere, so Neptune’s auroras are found far from its rotational poles.

What can we learn from Neptune's auroras?

The detection of Neptune's auroras will help astronomers better understand how particles from the sun interact with its atmosphere, providing a new area of study about ice giant planets.

The data from the Webb Space Telescope also enabled measurements of the temperature at the top of Neptune's atmosphere for the first time since Voyager 2's flyby. Those results may point to why Neptune’s auroras have gone unseen until now.

"I was astonished — Neptune's upper atmosphere has cooled by several hundreds of degrees,” Melin said in a Space Telescope Science Institute release. "In fact, the temperature in 2023 was just over half of that in 1989."

Where can I learn more?

You can read more about Neptune and aurora on Earth. You can also read what it would be like to see aurora on other planets and how infrared aurora was first detected on Uranus in 2023.

For the first time, astronomers have captured direct images of Neptune's elusive auroras.

Scientists have long suspected that the distant ice giant hosts shimmering light displays, based on fleeting hints from the Voyager 2 probe's flyby and observations of similar activity on Jupiter, Saturn and Uranus. Capturing images of Neptune's auroras had remained out of reach until the James Webb Space Telescope (JWST or Webb) turned its powerful eye towards the icy planet.

"Turns out, actually imaging the auroral activity on Neptune was only possible with Webb's near-infrared sensitivity," said Henrik Melin of Northumbria University, who conducted the research while at the University of Leicester, in a statement accompanying the photos. "It was so stunning to not just see the auroras, but the detail and clarity of the signature really shocked me."

Even more significant is the unique nature of Neptune's aurora, which scientists say differs from those seen on Earth, Jupiter, and Saturn, where auroras are typically confined to the poles. This is because their magnetic fields are relatively well aligned with their rotation axes, guiding charged particles from the solar wind toward the polar regions.

Neptune, on the other hand, has a highly tilted and offset magnetic field, which means its auroras appear at unexpected locations, such as the planet's mid latitudes.

These observations were made possible by the James Webb Space Telescope's Near-Infrared Spectrograph (NIRSpec), an instrument that analyzes the light absorbed or emitted by celestial objects. By breaking down the different wavelenghts of this light, scientists can determine key physical properties, such as temperature, mass and chemical composition.

In this case, NIRSpec captured detailed images of Neptune's ionosphere — the electrically charged layer of its upper atmosphere, similar to Earth's ionosphere, where auroras form. Excitingly, Webb's data revealed emissions of trihydrogen cation (H₃⁺), one of the most abundant ions in the universe. This discovery is significant because H₃⁺ plays a crucial role in planetary auroras, glowing in response to interactions between planets' atmospheres and charged particles from the solar wind.

"H3+ has a been a clear signifier on all the gas giants — Jupiter, Saturn, and Uranus — of auroral activity, and we expected to see the same on Neptune as we investigated the planet over the years with the best ground-based facilities available," explained JWST scientist Heidi Hammel. "Only with a machine-like Webb have we finally gotten that confirmation."

The team was also able to take a temperature reading of Neptune, something that hasn't been done since Voyager 2's flyby in August, 1989. "I was astonished [by the results]," Melin said. "Neptune's upper atmosphere has cooled by several hundreds of degrees [in that time]. In fact, the temperature in 2023 was just over half of that in 1989."

The dip in planetary temperature may help explain why the aurora have been so difficult to view. This is because auroras occur when charged particles excite atmospheric gases, causing them to emit light. Higher temperatures generally mean more energetic particles and a higher rate of collisions, leading to brighter auroras. A substantially colder temperature would reduce the density of energetic ions, leading to weaker emissions that are harder to detect.

Astronomers will continue to study Neptune using the JWST, hoping to gain a deeper understanding of our solar system's strangest planet.

"As we look ahead and dream of future missions to Uranus and Neptune, we now know how important it will be to have instruments tuned to the wavelengths of infrared light to continue to study the auroras," added Leigh Fletcher of Leicester University, co-author on the paper. "This observatory has finally opened the window onto this last, previously hidden ionosphere of the giant planets."

The James Webb Space Telescope has discovered that the centaur called 2060 Chiron is an oddball. The object, which is a minor body that orbits the sun in the expanse between Jupiter and Neptune, has a mixture of ices and gases that make it stand out from other objects in the distant outer solar system.

Around a thousand centaurs are currently known, but the 135-mile-wide (218-km-wide) Chiron was the first to be discovered in 1977. Centaurs are thought to have originated out in the frozen realm beyond Neptune, but later moved in-system after their orbits were perturbed by gravitational resonances with the ice giant. Because they move closer to the sun, solar heating can cause certain ices to sublimate, forming a gaseous halo or coma around the centaur, a bit like a comet.

Charles Schambeau of the University of Central Florida describes Chiron as an oddball among all the other centaurs, and even among trans-Neptunian objects (TNOs), which have intriguing stories of their own. "It has periods where it behaves like a comet, it has rings of material around it, and potentially a debris field of small dust or rocky material orbiting around it," he said in a statement.

New James Webb Space Telescope (JWST) observations of Chiron, led by Schambeau and Noemí Pinilla-Alonso of the University of Oviedo in Spain, have found that the composition of Chiron's surface ices are quite unlike any other centaur observed thus far. While none of the ices on their own are particularly unusual, the combination of them on Chiron is a surprise.

The JWST found carbon monoxide and carbon dioxide ice on the surface, and carbon dioxide and methane gas in Chiron's thin coma. The presence and abundance of methane is consistent with the substance sublimating from ice on an area of the surface that has been exposed to the greatest amount of solar heating. While its temperature from the sun never climbs above -220 degrees Fahrenheit (-140 degrees Celsius), this is still warm enough to cause these ices to sublimate.

Furthermore, the action of the sun's radiation on these ices spurs chemical reactions that produce organic byproducts such as acetylene, ethane, propane, as well as various carbon oxides, all of which were found as ices on Chiron's surface by the JWST.

"Discovering which gases are part of the coma and their different relationships with the ices on the surface help us learn the physical and chemical properties, such as the thickness and the porosity of the ice layer, its composition and how irradiation is affecting it," said Pinilla-Alonso.

Centaurs, and trans-Neptunian objects in general, are believed to be pristine; they've remained untouched since they formed 4.5 billion years ago at the dawn of the solar system. As such, they're like time machines that give us a glimpse into how and what the solar system was made from, where certain objects formed in the protoplanetary disk around the young sun, and whether those objects have migrated from that location since.

Active centaurs such as Chiron are especially precious because they reveal much more than inert bodies.

"They are undergoing transformation driven by solar heating and they provide a unique opportunity to learn about the surface and subsurface layers," said Pinilla-Alonso. "What is unique about Chiron is that we can observe both the surface, where most of the ices can be found, and the coma, where we see the gases that are originating from the surface or just below it."

Chiron's 50-year elliptical orbit around the sun saw it pass through aphelion — its greatest distance from the sun at 18.87 astronomical units (2.8 billion kilometers, or 1.75 billion miles) in 2021. It next reaches perihelion in 2047, when it will get within 8.5 astronomical units (1.27 billion kilometers, or 790 million miles) of the sun, which is just inside the orbit of Saturn. As it moves closer to the sun over the next 20 years or so, Chiron will grow brighter and more active, allowing more accurate observations of the abundance and nature of its ices, its organic chemistry and how solar irradiation and sunlight can affect its freezing surface. And there is much still to learn.

"Based on our new JWST data, I'm not sure we have a standard centaur," said Pinilla-Alonso. "Every active centaur that we are observing with JWST shows some peculiarity. There must be something that explains why they appear to behave differently or something that is common between them all that we cannot yet see."

Alas, Chiron and all its fellow centaurs are in a transitory phase, and over the next million years its ultimate fate will be decided. Either Jupiter's family will scatter it in-system again, where it will become a Jupiter-family comet with an orbital period of less than 20 years, or it will be thrown back into the Kuiper Belt, rejected from the inner solar system by the gatekeeper, Jupiter itself. It's impossible to say which fate will befall it, but as is fitting for an object named after a figure from Greek mythology, its destiny will be in the lap of the gods.

The new JWST findings were published in December in the journal Astronomy & Astrophysics.

The Hubble Space Telescope has spent more than thirty years providing some of the most incredible images of the known universe, but it's only for the last ten that scientists have pointed its gaze at our solar system's outer planets to observe them like never before.

For the past decade, NASA's Outer Planet Atmospheres Legacy program (OPAL) has been obtaining detailed views of the long-term changes in the skies of the four closest giants to Earth: Jupiter, Saturn, Uranus and Neptune, each home to a unique set of atmospheric variables. OPAL data has allowed astronomers to observe weather patterns and seasons of these outer planets to better understand their dynamics and changes over time.

Hubble is capable of viewing wavelengths from ultraviolet to near-infrared light, and routinely provides high-resolution images of the gas giants once a year, as each of their orbit's brings them closest to Earth. Now, with ten years of operation behind them, Hubble's OPAL team at NASA will present a decadal overview of the program's findings at the December meeting of the American Geophysical Union in Washington, D.C.

"Because OPAL now spans 10 years and counting, our database of planetary observations is ever growing. That longevity allows for serendipitous discoveries, but also for tracking long-term atmospheric changes as the planets orbit the sun. The scientific value of these data is underscored by the more than 60 publications to date that include OPAL data," said Amy Simon of NASA's Goddard Space Flight Center in a statement.

Jupiter

Jupiter is the solar system's largest planet. The gases of the planet's atmosphere churn all the way down to its core, tens of thousands of miles beneath the cloud tops. Besides its enormity, Jupiter is also known for its Great Red Spot. The unmistakable swirling red vortex on the gas giant's face is the largest storm in the solar system; a raging typhoon nearly three times the size of Earth.

Jupiter's orbit around the sun takes 12 years, allowing OPAL to have observed nearly a full Jovian year's worth of seasons. Over that time, notable changes were observed in size and shape of the Great Red Spot, as well as other atmospheric phenomena in the bands wrapping the gas giant. Seasonal changes on Jupiter are minimal, because its axial tilt of only three degrees results in only about a five percent atmospheric variability through the course of its orbit, according to NASA. (Earth, on the other hand, has an axial tilt of around 23.5 degrees, which creates the different seasons our planet experiences.)

Saturn

Saturn takes more than twice as long to circle the sun, with an orbital period lasting 29 years. The ringed giant is tilted at a much steeper 26.7 degrees, leading to much higher seasonal shifts, compared to Jupiter. Over its ten-year observation, OPAL has tracked color variation and cloud depth of Saturn's atmosphere as it cycles through the planet's changing seasons.

Hubble has also been able to observe Saturn's elusive dark ring spokes. First discovered by NASA's Voyager mission in the 1980s, these dark rings only last for two or three rotations around Saturn. Thanks to Hubble, astronomers now know the rings to be a seasonally-driven phenomenon.

Uranus

Uranus is tilted almost completely on its side, placing its rotation on nearly the same plane as the planet's orbit around the sun, which lasts a staggering 84 years.

Over the last ten years, OPAL has observed Uranus' northern hemisphere, which has faced the inner solar system for the entirety of Hubble's time in space, as it slowly tips toward the sun. Throughout its slow orbit around the sun, Uranus' north polar cap has increased in brightness as the hemisphere nears a summer solstice in 2028.

Neptune

A storm like a giant dark splotch the size of Earth's Atlantic Ocean was spotted in the atmosphere of Neptune in 2018, which Hubble followed until the storm's demise toward the planet's equator.

Another, in 2021, was observed through its formation and similar equatorial dissipation. Using OPAL data from Hubble, scientists were able to determine that the behavior of Neptune's clouds is somehow linked to the 11-year solar cycle, responsible for recent occurrences of lower-latitude northern lights on Earth.

A Neptune-sized planet closely orbiting its host star has just been discovered, making it only the fourth object of its kind ever identified.

Scientists detected the planet, designated TOI-3261 b, using NASA’s Transiting Exoplanet Survey Satellite (TESS). This Earth-orbiting spacecraft, which launched in 2018 and is still going strong, was specifically designed to search for exoplanets around the brightest dwarf stars with its wide-field cameras.

To confirm the discovery, the international research team conducted follow-up observations using ground-based telescopes in Australia, Chile, and South Africa.

The newly discovered planet belongs to a rare category known as the "hot Neptune desert," so named because so few such planets exist that the term "evokes a deserted landscape," NASA officials wrote in a statement. The first hot Neptune, LTT-9779 b, was discovered in 2020, followed by TOI-849 b and TOI-332 b.

Related: Why are there so few 'hot Neptune' exoplanets?

As the name suggests, these planets are roughly the size of Neptune but differ significantly in that they orbit extremely close to their host stars. For instance, TOI-3261 b completes its orbit in just 21 hours, making a year on the planet shorter than a single day on Earth.

Scientists have proposed numerous hypotheses to explain the scarcity of hot Neptunes. While our Milky Way galaxy is abundant with super-Earths and hot Jupiters, the question remains: Why are Neptunes so rare in such close orbits?

The scientists of the current study propose that part of the reason these types of exoplanets are so rare is because, at such close proximity to a star, it is more likely than not that a planet’s atmosphere would be stripped away by powerful gravitational forces and high-energy radiation.

In fact, the team calculated that TOI-3261 b is about twice as dense as Neptune, which suggests that the lighter parts of its atmosphere have already been stripped away.

The formation process of hot Neptunes remains unclear, but the team put computer models to the test, finding two possible scenarios. One posits that these planets may have initially been Jupiter-sized, gradually losing mass over time. Alternatively, they might have formed farther from their host star, where conditions allowed them to retain their atmospheres before migrating to their current close orbits.

More information will be gleaned through future observations. The team notes that both LTT-9779 b and TOI-849 b are scheduled for infrared studies with the James Webb Space Telescope, which will deepen our understanding of these planets’ atmospheres and may offer new insights into their formation, providing a glimpse into the mysteries of these mysterious, scorching-hot worlds.

For sure, it was a far-reaching recommendation: The planet Uranus and its moons should be NASA's highest-priority new flagship mission for startup in the decade 2023-2032.

The proposed mission, known as Uranus Orbiter and Probe (UOP), would conduct a multiyear orbital tour to yield knowledge of ice giants in general and the Uranus system in particular, doing so through flybys and the delivery of an atmospheric probe. The payoff: "transformative, breakthrough science across a broad range of topics."

UOP was advocated within the pages of "Origins, Worlds, and Life — A Decadal Strategy for Planetary Science and Astrobiology 2023-2032." Released in 2022, that heady document came from the prestigious U.S. National Academies of Sciences, Engineering, and Medicine and was sponsored by NASA and the National Science Foundation.

Improving our knowledge

Underscoring the importance of Uranus, the Keck Institute for Space Studies (KISS) at the California Institute of Technology in Pasadena held a workshop late last year to look into how best to improve our knowledge of Uranus' internal structure in the context of a future mission that includes an orbiter and a probe.

Related: Uranus up close: What proposed NASA 'ice giant' mission could teach us

Spearheading that KISS workshop was Mark Hofstadter, a planetary scientist working at NASA's Jet Propulsion Laboratory (JPL) in Southern California. He's not solar system shy and admits Uranus is his favorite planet.

Space.com caught up with Hofstadter to discuss what exploration of Uranus — that far-flung, ice giant of a world with a mass roughly 14.5 times that of Earth — can offer. The planet has been visited only once, by NASA's Voyager 2 spacecraft during a brief flyby back in 1986.

Within the planetary community, many people are very much focused on a Uranus mission, Hofstadter said. As for the KISS study, it was focused on one aspect of the Uranus system, he said: Understanding the current structure and composition of the planet's interior, in order to learn about its formation and evolution.

"I personally believe learning about the interior is the most important reason to go to Uranus," Hofstadter said. But he also stressed that Uranus is a complex system, consisting of the planet's interior, its atmosphere, its rings and small moons, larger satellites, its magnetosphere and its interactions with the solar wind.

Thus, studying Uranus has the potential to produce transformative, breakthrough science across a broad range of topics, as the Decadal Survey pointed out, said Hofstadter.

"You could even expand that idea of 'system' to include how Uranus, over its lifetime, gravitationally altered the paths of other objects in the solar system, potentially influencing the Earth," Hofstadter added. "Every component of that system has features that violate some of our ideas about how planets work."

Ice giant

That's why the UOP's plan to put an orbiter into the middle of that system — a spacecraft equipped with a wide range of instruments, as well as a probe to enter the atmosphere — is expected to dramatically increase our understanding of our entire solar system, as well as planets that orbit other stars, Hofstadter advised.

Why does he rate Uranus' interior as the most compelling investigation for a mission?

"Of the thousands of planets we have discovered in our galaxy, most are roughly the size of Uranus and Neptune. That makes Uranus an important type of planet, and we'll apply what we learn at Uranus to all those other faraway planets we cannot study in detail," responded the JPL planetary scientist.

Complex system

Hofstadter emphasized that there are many unknowns about the composition and structure of both Uranus and Neptune. For example, scientists aren't sure if Uranus has a deep, solid region.

"We call them 'ice giants' because we originally thought they formed primarily from water ice, but recently some have argued they should be mostly rock," Hofstadter said. "Learning basic things about the interior — something we can only learn by going there with a spacecraft — will help us understand how this type of planet forms and evolves."

Related: What is Uranus made of?

Naive Earth-centric view

There's also the question of Uranus' astrobiology potential. The history of reconnoitering the outer solar system — planets beyond Mars — has been one of surprises, Hofstadter said.

Indeed, our naive Earth-centric view originally indicated that sunlight is needed to provide the energy for life, and we thought places beyond Mars would be cold, inactive, dead worlds.

"We now know that there are other ways to heat up icy objects in the outer solar system and create liquid oceans," said Hofstadter. "And we still believe liquid water is critical for life, and that the chemistry of life elsewhere might work differently than that on the Earth."

Moons of Uranus

Given that, some of the moons of Jupiter and Saturn are now considered the most likely places in our solar system to find alien life.

"We don't know enough about the Uranian moons to say whether or not they also harbor liquid oceans, but theoretical studies have shown they might," said Hofstadter. "That, combined with Voyager's images showing that some of Uranus' moons have geologically young surfaces, makes it plausible that life could exist under the icy crust of one of Uranus' moons."

Putting on his more speculative hat, Hofstadter said that some have asked if life might exist within Jupiter, Saturn, Uranus or Neptune.

"Such life would probably have a very different genesis than that of the Earth, and I don't think anyone can say if it is plausible. Nor is it clear how one might detect such life," Hofstadter said.

Weird world

Meanwhile, Earth-based work is also critical for understanding Uranus. Laboratory and theoretical studies, the KISS study explains, as well as Earth-based and space-based observations of Uranus can enable researchers to properly interpret future on-the-spot spacecraft measurements and guide what measurements a visiting craft should make, as well as where they should be made.

Uranus is the seventh planet from the sun and the third-largest world in our solar system. It is definitely and defiantly a weird world, appearing to spin sideways, rotating at a nearly 90-degree angle from the plane of its orbit.

The surprises that the Uranus Orbiter and Probe mission, should it indeed fly, will reveal at that enigmatic world will likely put scientists in a sideways spin, too.

When NASA's Voyager 2 spacecraft made its way to outer regions of the solar system in the late 80's, it noticed something odd. Both of the ice giant planets, Uranus and Neptune, lacked what's known as a "dipole magnetic field." This was in stark contrast to our own rocky world, as well as the two gas giants Jupitar and Saturn.

As dense materials near a planet's surface cool, they tend to sink into the planet's interior. On the other hand, hotter materials near the planet's interior will rise. The combination of sinking and rising materials creates convection, leading to the movement and mixing of materials within a planet. And if the interior of a planet is electrically conducting (as in, made of liquid metal or water), the convecting material — often described as a dynamo — will generate a dipole magnetic field. Think of it like a magnet with north and south poles. It is this process which generates Earth's magnetic field — the protective barrier that shields us from charged particles.

This process, however, is absent from Uranus and Neptune. So, scientists wondered: Why would that be?

For the last two decades, researchers had speculated that this was because layers of material within these worlds were unable to mix, halting any convection movement which gives rise to dipole magnetic fields in planets like our own. But, while researchers eventually agreed the problem indeed came down to the separation of layers within these worlds, the jury was still out on the compositions of these layers. Now, Burkhard Militzer, a planetary scientist at the University of California, Berkeley, thinks he has an answer.

Related: Why is Neptune's magnetic field so weird? An exotic molecule may be the answer

"We now have, I would say, a good theory why Uranus and Neptune have really different fields, and it's very different from Earth, Jupiter and Saturn," Militzer said in a statement.

Knowing this, 10 years ago, Militzer tried to simulate with computers the interiors of these worlds by cramming roughly 100 atoms of carbon, oxygen, nitrogen and hydrogen (in proportions that mirrored their abundances at the early stages on the solar system) at pressure and temperatures that mirrored their interiors. Yet, they yielded no distinct layers.

Fast forward to last year, and with the help of machine learning, Militzer was able to simulate the behavior of 540 atoms with similar ratios, and he found that layers would naturally form as the atoms were heated and compressed. "One day," he said, "I looked at the model, and the water had separated from the carbon and nitrogen. What I couldn't do 10 years ago was now happening."

"I thought, 'Wow! Now I know why the layers form: One is water-rich and the other is carbon-rich, and in Uranus and Neptune, it's the carbon-rich system that is below. The heavy part stays in the bottom, and the lighter part stays on top and it cannot do any convecting," he said.

Militzer's model predicts that underneath the 3,000-mile-thick (just over 4,800 kilometers) Uranian atmosphere sits a vast water-rich layer 5,000 miles deep (just over 8,000 kilometers). Below that, a 5,000 mile thick hydrocarbon-rich layer also exists, with a rocky core about the size of Mercury at its center.

Despite being more massive than Uranus, Neptune has a smaller total diameter and thinner atmosphere compared to its icy compatriot. However, it is likely to share similar differentiated water-rich and hydrocarbon-rich layers, with a Mars-size rocky core (providing the extra mass).

"If you ask my colleagues, 'What do you think explains the fields of Uranus and Neptune?' they may say, ‘Well, maybe it's this diamond rain, but maybe it's this water property which we call superionic,'" Militzer said. "From my perspective, this is not plausible. But if we have this separation into two separate layers, that should explain it."

Militzer hopes he might one day be able to test his hypothesis with laboratory experiments that mirror the interior conditions of these worlds. A mission to Uranus could also provide answers, Militzer says.

The paper was published on Nov. 25 in the Proceedings of the National Academy of Sciences.

Using the James Webb Space Telescope (JWST), scientists have witnessed jets of primordial gas from the birth of the solar system spewing from a distant, comet-like object called a centaur.

The observations provide clues as to how this centaur and others formed, what they are made of, and how they eventually transition into full-fledged comets, the research team said in a study published in the journal Nature.

Centaurs once resided in the frozen Kuiper Belt beyond the orbit of Neptune. However, the gravitational interplay with Neptune, or even occasionally with a close encounter with a star, acts to nudge some of them farther inward, where they orbit the sun between Jupiter and Neptune. There, the centaurs come under the influence of Jupiter's orbit, which can drag some of them even closer to the sun, turning them into short-period comets that orbit our star in less than 200 years. 

Over 500 centaurs have been discovered, but astronomers estimate that there could be as many as 10 million out there.

"Centaurs can be considered as some of the leftovers of our planetary system's formation," Sara Faggi, a postdoctoral researcher at NASA's Goddard Space Flight Center who led the research, said in a statement. "Because they are stored at very cold temperatures, they preserve information about volatiles [gases with low boiling points, such as water] in the very early stages of the solar system."

Related: What cosmic object 'Arrokoth' can tell us about our solar system's formation

One of the most prominent centaurs is 29P/Schwassmann-Wachmann 1, which undergoes outbursts every six to eight weeks. Previous radio wavelength observations had shown a jet of carbon monoxide gas pointed roughly at the sun, but JWST's Near-Infrared Spectrograph (NIRSpec) showed much, much more.

NIRSpec revealed a second carbon monoxide (CO) jet emanating from 29P and pointing northward (with respect to the plane of the solar system). It also discovered two never-before-seen jets of carbon dioxide (CO2), pointing north and south.

What is prompting the outgassing is uncertain. On regular comets, gaseous jets form when water ice warms in the sun's heat, vaporizing and bursting through the surface to form the comet's tail and carrying these gases with it. Yet JWST found no evidence for water vapor in the jets. This was unsurprising to the researchers, because 29P is too far from the sun for water ice to sublimate. Instead, it remains frozen. So what's causing the outgassing?

Faggi's team cannot answer that yet, but the details of the jets hint at the remarkable conclusion that 29P is not one object but rather several objects that have become stuck together. Such objects are called "contact binaries," and astronomers are finding more and more of them. For example, Comet 67P/Churyumov-Gerasimenko, which was visited by the European Space Agency's Rosetta mission, was a contact binary, as was Arrokoth, the distant Kuiper Belt object encountered by the New Horizons spacecraft on New Year's Day 2019.

Centaur 29P is too distant for even JWST to resolve its nucleus. But 3D computer modeling of the points of origin of the outgassing jets suggests they are in different locations and that different parts of 29P are made from different materials.

"The fact that centaur 29P has such dramatic differences in the abundance of CO and CO2 across its surface suggests that 29P may be made of several pieces," Geronimo Villanueva, associate director of the Solar System Exploration Division at NASA's Goddard Space Flight Center and a member of the research team, said in the statement. "Maybe two pieces coalesced together and made this centaur, which is a mixture between very different bodies that underwent separate formation pathways. It challenges our ideas about how primordial objects are created and stored in the Kuiper Belt."

Asteroids, comets, Kuiper Belt objects and centaurs are all relics of the formation of the solar system, and most of them have gone untouched for 4.5 billion years. Therefore, any materials we see outgassing from them are from the era of our solar system's birth and could contribute to our understanding of how the solar system formed.

The next step is to look back at 29P with JWST for longer, to watch if the jets change direction — perhaps if 29P rotates, the jets switch off or new jets switch on. 

Researchers may have discovered the secret ingredient of planet growth, which causes some worlds to grow rapidly in disks of gas and dust around infant stars. The model could be of specific value in understanding the growth of the solar system's giant planets.

Scientists have a fairly good understanding of how the rocky inner planets of the solar system, Mercury, Venus, Earth and Mars, formed and evolved. But the current model of collisions and gathering of asteroid-like bodies called "planetesimals" and the accretion of gas over millions of years leaves a lot to be explained when it comes to the formation of the gas giants Jupiter and Saturn and the ice giants Neptune and Uranus. 

All these giants seem to have formed too far out from the sun to grow so massive, with the growth of the outer ice giants being particularly puzzling. Jupiter is 15 times further away from the sun than our planet, and Neptune is 30 times farther away from our star than Earth. 

To help solve this planetary puzzle, a team of scientists from the ORIGINS Excellence Cluster, the Max Planck Institute for Solar System Research (MPS), and the Ludwig Maximilian University of Munich (LMU) have developed a new model of planet evolution that could account for these apparent discrepancies.

The scientists say their model is the first to incorporate all the physical processes needed for planet formation. 

"This is the first time a simulation has traced the process whereby fine dust grows into giant planets," team member Tommy Chi Ho Lau, an LMU doctoral candidate, said in a statement.

The simulation performed by the researchers suggests that disturbances in the disk of gas and dust around infant stars, called "protoplanetary disks," can trigger the rapid formation of multiple gas giants.

Their results seem to line up well with recent observations of young extrasolar planets or "exoplanets" and may reveal that giant planets can form much faster and much more efficiently than currently thought.

Related: Evidence of water found in atmosphere of mysterious 'metal god of war' exoplanet

Even giant planets start out small

Young stars are born when overdense patches form in vast clouds of interstellar gas and dust. As this gas clump accumulates material, it eventually collapses and gives birth to a "protostar."

This progenitor stellar body continues to gather material until its mass is sufficient enough to generate the pressure and temperatures at its core to trigger the nuclear fusion of hydrogen to helium, the process that defines a star's "main sequence" lifetime.

Material that remains in this newborn star's prenatal cocoon flattens out as it swirls around the star, creating a protoplanetary disk. As the name suggests, it is from this disk of gas and dust that the planets emerge.

The team's model suggests that millimeter-sized dust particles accumulate aerodynamically in the turbulent protoplanetary disk. This perturbation traps dust and prevents it from heading toward the central infant star. This spurs an accumulation of planetary "building blocks" in a relatively small region of the protoplanetary disk. These are just the conditions needed for a planet to form.

"When a planet gets large enough to influence the gas disk, this leads to renewed dust enrichment farther out in the disk," Til Birnstiel, Professor of Theoretical Astrophysics at LMU and member of the ORIGINS Cluster of Excellence said. "In the process, the planet drives the dust – like a sheepdog chasing its herd – into the area outside its own orbit."

This could lead to the formation of planets as far away from their star as 200 times the distance between Earth and the sun, more than enough to explain the formation of the solar system's giant planets around 4.5 billion years ago.

The team's model also implies that the solar system stopped birthing planets after Neptune simply because planetary building blocks had been exhausted.

The results generated by the team's simulations seem to match observations of young planetary systems made by the Atacama Large Millimeter/submillimeter Array (ALMA), a collection of 66 radio antennas located in northern Chile.

Not only could this research help us understand the birth and evolution of giants in our own planetary system, but it could also give astronomers hints as to the diversity of exoplanets in the wider Milky Way galaxy.

The team's research was published in the journal Astronomy & Astrophysics.

Some experts believe that we could be just a few years away from discovering the elusive "Planet Nine" — or ruling out the existence of the hypothetical world for good. 

But if we do find it, how long would it take for us to send a spacecraft to the far-flung world? And could humans ever make the trip?

Planet Nine is the name given to a proposed planet supposedly lurking near the edge of the solar system. If it exists, Planet Nine is likely a dark, gas or ice giant planet somewhere between five and 10 times the mass of Earth that circles the sun on a highly elliptical, or stretched, orbit — out of sync with the rest of the planets.

Researchers suspect Planet Nine is out there because around a dozen objects beyond the orbit of Neptune, move as if a large object is tugging on them. However, finding this missing world has proved to be extremely tricky.

But some astronomers believe Planet Nine could be discovered within the next few years once the state-of-the-art Vera C. Rubin Observatory starts to survey the night sky in late 2025. 

Related: The evidence for 'Planet Nine' in our solar system (gallery)

If Planet Nine is ever detected, space agencies like NASA will want to send a probe to visit the distant world. But first, they will have to plan and get approval for such a mission. 

"This will take at least a decade or more," Andreas Hein, a space systems engineer at the University of Luxembourg, told Live Science in an email. This is mostly because missions have to go through a lengthy and rigorous government selection process, he added.

But this process could be sped up depending on how odd the world appears in initial readings, Manasvi Lingam, a theoretical astrobiologist at the Florida Institute of Technology, told Live Science in an email. "If Planet 9 is anomalous in some respect, there could be more interest in expediting such a mission."

It is also possible that a private space exploration company, such as SpaceX, could launch missions sooner — potentially as soon as five years after discovery — because they are not hindered by as much bureaucracy, Hein said.

Reaching Planet Nine

Once a probe is sent to Planet Nine, the next question is how long will it take to arrive?

In 2022, Hein, Lingam and part-time astronomer Adam Hibberd attempted to answer this question in a theoretical paper that was posted to the pre-print database arXiv. In this paper, which has not been peer-reviewed, the researchers estimated that it would likely take between 45 and 75 years for a spacecraft akin to NASA's Voyager probes to reach Planet Nine.

These calculations were based on the assumption that Planet Nine is around 400 astronomical units from the sun on average, or 400 times farther away from the sun than Earth. That's also around 13 times further away from the sun than Neptune, the farthest known planet in the solar system. 

But subsequent studies suggest that Planet Nine's true average distance from the sun is actually closer to 500 astronomical units. And the most recent survey, which narrowed down the elusive world's potential hiding place, also hints that the planet could currently be more than 550 astronomical units away, near its farthest point from the sun.

However, these developments don't dramatically alter the timeline laid out in the 2022 paper, Lingam said. The team's estimates were "conservative," meaning that the upper end of their uncertainty range "still seems tenable," he added.

Pushing boundaries

Seventy-five years may seem like a long time for a one-way trip. But this is quite fast compared to the journeys of existing probes; for example, Voyager 1 — the most distant spacecraft from Earth — has been traveling through space for 46 years and is only around 163 astronomical units from Earth, according to NASA. As a result, a Planet Nine probe would have to travel around three times faster than Voyager 1 to reach Planet Nine in the researcher's timeframe. 

This may seem unlikely but it is possible, Lingam said. 

Probes traveling toward the outer solar system must be gravitationally slingshotted around the sun, planets and their moons to propel them across the vast distances involved. Voyager 1's trajectory was carefully planned to allow it to fly closely past Jupiter, Saturn, Uranus and Neptune, as well as some of their respective moons. To do so, Voyager 1 had to also be slingshotted around objects to slow it down and redirect it to where it needed to go. However, a Planet Nine probe could go as directly as possible straight to the mysterious planet, allowing it to pick up more speed and travel much further in the same amount of time.

Mike Brown, an astronomer at Caltech who co-proposed the Planet Nine hypothesis in 2016, originally estimated that a probe could potentially get to Planet Nine in as few as 20 years using a similar method. However, it is "difficult" to see how a probe could get to Planet Nine this fast using current technology, Lingam said. 

But it might be possible to reach Planet Nine quicker if we could crack more advanced propulsion technologies, such as light sails — giant sails that catch sunlight or lasers to accelerate spacecraft, Hein and Lingam said. 

In the 2022 study, the researchers suggested that a light sail could take as little as seven years to reach Planet Nine. However, it could take at least 20 years for light sails to become a reality, the team estimated. 

As a result, if we found Planet Nine tomorrow, it would be better to send a current probe than to wait for alternative technologies to become available, Lingam said. "Laser sails can be launched later, if and when they become practical and cost-effective."

As propulsion systems advance further, it may also be possible to send people to Planet Nine. But probably not anytime soon.

"I am confident that in the far future, humans will be able to visit Planet Nine," potentially even as they make their way to other stars, Hein said. 

A 'hot Neptune' exoplanet has been found to contain sulfur dioxide in its atmosphere — an atmosphere that's also gushing into space as the planet loops over its star's poles on a steeply inclined orbit every three-and-a-third days.

The existence of sulfur dioxide in the atmosphere of the exoplanet, dubbed GJ 3470b and located 96 light-years from Earth, came as a shock when it was spotted by the James Webb Space Telescope (JWST).

"We didn't think we'd see sulfur dioxide on planets this small, and it's exciting to see this new molecule in a place we didn't expect, since it gives us a new way to figure out how these planets formed," sThomas Beatty of the University of Wisconsin, Madison said in a statement. "And small planets are especially interesting, because their compositions are really dependent on how the planet-formation process happened." 

Everything about GJ 3470b tells us it has a fascinating and eventful history. 

Planets form in a disk of gas and dust that swirls around a plane aligned with a star's rotational axis. In our solar system, we can see evidence of this disk in that all the planets from Mercury to Neptune orbit in the ecliptic plane. GJ 3470b, on the other hand, follows a path inclined by 89 degrees to the rotational axis of its cool red dwarf star. In other words, it's on a steep orbit that loops over the star's poles. Planets don't typically form on such orbits.

Related: Why are there so few 'hot Neptune' exoplanets?

With a mass 13.9 times greater than Earth's mass, and a diameter about 40% that of Jupiter, GJ 3470b is a bloated gas bag. When such worlds are close to their star, astronomers call them 'hot Neptunes." GJ 3470b has an atmospheric temperature of 325 degrees Celsius (617 degrees Fahrenheit); the temperature of Neptune in our solar system is –200 degrees Celsius (–330 degrees Fahrenheit).

Present models of planet formation describe how gas giants typically form farther out from their star than rocky planets, in the cold depths where gas is more plentiful. Yet, GJ 3470b orbits at a distance of just 5.3 million kilometers (3.3 million miles) from its star. For comparison, Mercury, the closest planet to our sun, orbits at an average distance of 58 million kilometers (36 million miles) from our star, although red dwarf systems are usually scaled down compared to our solar system.

Ordinarily, we would expect GJ 3470b to have formed farther out and then migrated inward as a result of interactions with its star's planet-forming disk. Meanwhile, scientists would normally suspect the world would've been shoved out of the orbital plane via a gravitational interaction with another planet, or perhaps even upheaval caused by a close-passing star.

However, the planet's atmospheric mix suggests otherwise. 

Despite the JWST's detection of molecules within, such as sulfur dioxide, GJ 3470b's atmosphere remains overwhelmingly made from hydrogen and helium, even more so than the gas planets in our solar system — a fact discerned by the Hubble Space Telescope in 2019. So, the explanation put forward is that GJ 3470b actually formed close to its star as a rocky planet before accruing a thick atmosphere of almost pure hydrogen and helium — but, at the moment, this is just a hypothesis. That's why the JWST's detection of sulfur dioxide is so important, because its presence could help differentiate between different theories of how the planet formed.

The sulfur dioxide detection came to light thanks to the fact that GJ 3470b transits its star, which allows astronomers to conduct what's called "transmission spectroscopy." As light from its parent star shines through itsthe GJ 3470b's atmosphere, molecules in the world's atmosphere absorb some of the starlight, leaving dark absorption lines in the star's spectrum.

Teasing out these absorption lines is difficult, however, especially for a hot Neptune that is likely covered in featureless haze.

"The thing is, everybody looks at these planets and often everybody sees flat lines," said Beatty. "But when we looked at this planet, we really didn't get a flat line."

Instead, the JWST was able to confirm absorption lines from carbon dioxide, methane and water vapor, and indeed detect sulfur dioxide in the region for the first time. This actually makes GJ 3470b the lightest and coldest exoplanet yet known to have sulfur dioxide in its atmosphere. Previous detections have related to the atmospheres of hot Jupiters with temperatures above a thousand degrees Celsius (1,830 degrees Fahrenheit).

"Discovering sulfur dioxide in a planet as small as GJ 3470b gives us one more important item on the planet-formation ingredient list," said Beatty.

The sulfur probably began as a component in hydrogen sulphide, the team believes. However, because GJ 3470b orbits so closely to its star, ultraviolet light from the stellar body packs a powerful-enough punch to break atmospheric molecules apart with ease, leading to a kind of chemical churn formed from smashed molecular components recombining with other atoms and molecules. A sulfur atom combined with two oxygen atoms forms sulfur dioxide.

The planet's parent star doesn't just break up atmospheric molecules, however; hydrogen liberated from those molecules can be stripped them from the planet entirely. GJ 3470b is therefore literally evaporating before our very eyes, the stellar wind gradually blowing its atmosphere away into space, leaving a stream of hydrogen gas trailing behind. Already, the planet has lost an estimated 40% of its original mass.

The presence of sulfur dioxide in its atmosphere, the inclined orbit that remains unexplained and the mass loss that is dramatically changing GJ 3470b forever are significant clues as to the origin of this weird and wonderful planet, according to Beatty.

"Those are important steps in the recipe that created this particular planet and can help us understand how planets like it are made," he said.

Beatty presented the results at the 244th meeting of the American Astronomical Society on June 10, and they have been accepted for publication in Astrophysical Journal Letters.

Humanity has lost an interstellar pioneer.

Ed Stone, who served as the project scientist for NASA's groundbreaking Voyager mission from 1972 to 2022, died on Sunday (June 9) at the age of 88.

"Ed Stone was a trailblazer who dared mighty things in space. He was a dear friend to all who knew him, and a cherished mentor to me personally," Nicola Fox, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington, said in NASA's obituary for Stone, which the agency posted on Tuesday (June 11). 

"Ed took humanity on a planetary tour of our solar system and beyond, sending NASA where no spacecraft had gone before," Fox added. "His legacy has left a tremendous and profound impact on NASA, the scientific community, and the world. My condolences to his family and everyone who loved him. Thank you, Ed, for everything."

Related: Going interstellar: Q&A with Voyager project scientist Ed Stone

Voyager launched twin probes on a "grand tour" of the solar system's giant planets in 1977. The two spacecraft made many discoveries in our cosmic backyard — finding intense volcanism on the Jupiter moon Io and 10 new moons of Uranus, for example — and then kept on flying, into exciting and unexplored realms.

In 2012, Voyager 1 popped free of the heliosphere, the huge bubble of charged particles and magnetic fields that the sun blows around itself, becoming the first human-made object ever to reach interstellar space. Voyager 2, which took a different path and is moving slightly more slowly than its partner, followed suit in late 2018.

Both Voyagers remain operational today, studying the exotic environment between our star and the next. Voyager 1 is currently more than 15 billion miles (24 billion kilometers) from home, and its twin is about 13 billion miles (21 billion km) into the void. That's about 162 and 136 Earth-sun distances (or astronomical units), respectively.

"It has been an honor and a joy to serve as the Voyager project scientist for 50 years," Stone said in a NASA statement in October 2022, when he announced his retirement from the role.

"The spacecraft have succeeded beyond expectation, and I have cherished the opportunity to work with so many talented and dedicated people on this mission," he added. "It has been a remarkable journey, and I'm thankful to everyone around the world who has followed Voyager and joined us on this adventure."

Related: Voyager: 15 incredible images of our solar system (gallery)

Stone was born on Jan. 23, 1936, in Knoxville, Iowa, according to NASA's obituary. His father was a construction superintendent who loved showing his son how to take things apart and put them back together — and young Ed was an eager student.

"I was always interested in learning about why something is this way and not that way," Stone said in an interview in 2018, according to NASA's obituary. "I wanted to understand and measure and observe."

He studied physics in junior college, then went to the University of Chicago for graduate school, where he helped build science instruments for spacecraft — still a very young field at this stage.

"The first he designed rode aboard Discoverer 36, a since-declassified spy satellite that launched in 1961 and took photographs of Earth from space as part of the Corona program," NASA wrote in the obituary. "Stone's instrument, which measured the sun's energetic particles, helped scientists figure out why solar radiation was fogging the film and ultimately improved their understanding of the Van Allen belts, energetic particles trapped in Earth's magnetic field."

Stone became a post-doctoral fellow at the California Institute of Technology (Caltech) in 1964 and soon began working on NASA missions. Over the years, he served as the principal investigator or a science instrument lead on nine different agency missions and a co-investigator on five others, according to the agency. 

Stone also served as director of the Jet Propulsion Laboratory (JPL) in Southern California — the agency's lead center for robotic planetary exploration — from 1991 to 2001. That stretch saw some major milestones, including the landing of NASA's first-ever Mars rover, Sojourner, in 1996 with the Pathfinder mission and the launch of the Cassini-Huygens mission to Saturn (a joint effort with the European Space Agency) in 1997.

"Ed will be remembered as an energetic leader and scientist who expanded our knowledge about the universe — from the sun to the planets to distant stars — and sparked our collective imaginations about the mysteries and wonders of deep space," JPL Director Laurie Leshin, who's also the vice president of Caltech, said in NASA's obituary.

"Ed’s discoveries have fueled exploration of previously unseen corners of our solar system and will inspire future generations to reach new frontiers," Leshin added. "He will be greatly missed and always remembered by the NASA, JPL and Caltech communities and beyond."

Stone's colleagues have repeatedly noted his commitment to science education and communication, his genuine desire to help tell the world about scientific results in a manner both accurate and engaging.

I can attest to this commitment, for I witnessed it first-hand on multiple occasions. Despite being a very busy man, Stone was open and available to the media; he took our phone calls and stayed on after press conferences to answer more and more of our questions.

And he was unfailingly nice, polite and patient in all of these interactions. I didn't know Ed Stone well, but I could tell he was a good man. And I, like countless others, will miss him.

In the depths of our solar system — a realm where chemistry meets speculation — scientists have reported the possible existence of a molecule known as aquodiium, an elusive cousin of the ammonium ion. If true, that could explain oddities in Neptune and Uranus’ magnetic fields.

This is a big deal because stable aquodiium, which consists of four atoms of hydrogen and one atom of oxygen (H4O2+), has never been observed before due to the high energy barrier involved in adding a second proton to the molecule hydronium (H3O+), which is how aquodiium must be formed. Hydronium, however, is a bit easier to create. It forms through the fundamental process of adding a proton to water. The jump from hydronium to aquodiium is the hard part.

Related: 3 tiny new moons found around Uranus and Neptune — and one is exceptionally tiny

However, with the help of advanced computer models, researchers have pinpointed a potential habitat for aquodiium: the extreme pressures found in the cores of ice giants Uranus and Neptune. And, importantly, its presence in this intense, icy environment may help explain the planets' unusual magnetic fields — weirdly, they're both highly tilted relative to their axis of rotation and significantly offset from the planets' centers. 

Could aquodiium be to blame?

Peculiar chemistry for peculiar worlds

Due to having a similar size and mass, the cores of Neptune and Uranus are almost identical. Both have rocky cores like Jupiter and Saturn, but unlike their larger neighbors, their internal pressures are not sufficient to convert molecular hydrogen into an electrically conducting liquid metal. Instead, a large mantle of icy water and ammonia forms about 12,427 miles (20,000 kilometers) below these worlds' surfaces.

This is where things get interesting: the study's authors suggest the planets' unusual magnetic fields could be generated by ions acting as charge carriers. Ions are atoms or molecules with a net electrical charge resulting from the loss or gain of one or more electrons. These ions pertaining to Uranus and Neptune's magnetic fields don't have to exist solely as standalone protons but could also include hydronium, ammonium — and aquodiium.

In chemistry, a molecule typically exists in its lowest energy form, known as the ground state. This is because nature tends to follow the path of least resistance, and the ground state minimizes factors such as bond strain, meaning atoms within the molecule are connected at less-than-ideal angles, and electrostatic repulsion, where charged atoms or groups within the molecule repel one another. The challenge with forming aquodiium (H4O2+) lies in the increased electrostatic repulsion and strain that occur when adding a second proton to the hydronium ion — it's like trying to bring together two positively charged magnets. 

When a proton is added to water to form hydronium, those two factors are more easily overcome; the resulting molecule has a positive charge localized on only one of the oxygen atoms, with the hydrogen atoms arranged in a stable geometry around the oxygen atom in the center. To go from this situation to aquodiium, you'd need to adding a second proton to the structure — but that would increase the amount of positive charge in the molecule, leading to significant electrostatic repulsion between both the positively charged protons and disrupting the hydronium's existing molecular structure, creating strain.

Under normal conditions, these factors don't allow stable aquodiium to form. The only way it'd be possible would be if enough energy were present in the reaction to force the molecule to come together anyway, amid all the strain, repulsion, and other complications not even discussed. We don't have that kind of energy on Earth. However, under the extreme conditions in Uranus and Neptune, there may indeed be enough energy.

The scientists reported that aquodiium appeared as a plausible outcome in their simulations specifically because the very high pressures found in these worlds encourages the bonding of oxygen and hydrogen ions such that aquodiium can be stabilized. And if stable aquodiium lurks in these planets, well, we may finally be on the road to decoding where they get their odd magnetic fields.

The study was published in May in the journal Physical Review B.

I was once sitting with my father while Googling how far away various things in the solar system are from Earth. He was looking for exact numbers, and very obviously grew more invested with each new figure I shouted out. I was thrilled. The moon? On average, 238,855 miles (384,400 kilometers) away. The James Webb Space Telescope? Bump that up to about a million miles (1,609,344 km) away. The sun? 93 million miles (149,668,992 km) away. Neptune? 2.8 billion miles (4.5 billion km) away. "Well, wait until you hear about Voyager 1," I eventually said, assuming he was aware of what was coming. He was not.

"NASA's Voyager 1 interstellar spacecraft actually isn't even in the solar system anymore," I announced. "Nope, it's more than 15 billion miles (24 billion km) away from us — and it's getting even farther as we speak." I can't quite remember his response, but I do indeed recall an expression of sheer disbelief. There were immediate inquiries about how that's even physically possible. There were bewildered laughs, different ways of saying "wow," and mostly, there was a contagious sense of awe. And just like that, a new Voyager 1 fan was born.

It is easy to see why Voyager 1 is among the most beloved robotic space explorers we have — and it is thus easy to understand why so many people felt a pang to their hearts several months ago, when Voyager 1 stopped talking to us.

Related: NASA's Voyager 1 spacecraft finally phones home after 5 months of no contact

For reasons unknown at the time, this spacecraft began sending back gibberish in place of the neatly organized and data-rich 0's and 1's it had been providing since its launch in 1977. It was this classic computer language which allowed Voyager 1 to converse with its creators while earning the title of "farthest human made object." It's how the spacecraft relayed vital insight that led to the discovery of new Jovian moons and, thanks to this sort of binary podcast, scientists incredibly identified a new ring of Saturn and created the solar system's first and only "family portrait." This code, in essence, is crucial to Voyager 1's very being.

Plus, to make matters worse, the issue behind the glitch turned out to be associated with the craft's Flight Data System, which is literally the system that transmits information about Voyager 1's health so scientists can correct any issues that arise. Issues like this one. Furthermore, because of the spacecraft's immense distance from its operators on Earth, it takes about 22.5 hours for a transmission to reach the spacecraft, and then 22.5 hours to receive a transmission back. Alas, things weren't looking good for a while — for about five months, to be precise.

But then, on April 20, Voyager 1 finally phoned home with legible 0's and legible 1's.

"The team had gathered early on a weekend morning to see whether telemetry would return," Bob Rasmussen, a member of the Voyager flight team, told Space.com. "It was nice to have everyone assembled in one place like this to share in the moment of learning that our efforts had been successful. Our cheer was both for the intrepid spacecraft and for the comradery that enabled its recovery."

And then, on May 22, Voyager scientists released the welcome announcement that the spacecraft has successfully resumed returning science data from two of its four instruments, the plasma wave subsystem and magnetometer instrument. They're now working on getting the other two, the cosmic ray subsystem and low energy charged particle instrument, back online as well. Though there technically are six other instruments onboard Voyager, those had been out of commission for some time.

The comeback

Rasmussen was actually a member of the Voyager team in the 1970s, having worked on the project as a computer engineer before leaving for other missions including Cassini, which launched the spacecraft that taught us almost everything we currently know about Saturn. In 2022, however, he returned to Voyager because of a separate dilemma with the mission — and has remained on the team ever since.

"There are many of the original people who were there when Voyager launched, or even before, who were part of both the flight team and the science team," Linda Spilker, a planetary scientist at NASA's Jet Propulsion Laboratory, who also worked on the Voyager mission, told Space.com in the This Week from Space podcast on the TWiT network. "It's a real tribute to Voyager — the longevity not only of the spacecraft, but of the people on the team."

To get Voyager 1 back online, in rather cinematic fashion, the team devised a complex workaround that prompted the FDS to send a copy of its memory back to Earth. Within that memory readout, operators managed to discover the crux of the problem — a corrupted code spanning a single chip — which was then remedied through another (honestly, super interesting) process to modify the code. On the day Voyager 1 finally spoke again, "you could have heard a pin drop in the room," Spilker said. "It was very silent. Everybody's looking at the screen, waiting and watching." 

Of course, Spilker also brought in some peanuts for the team to munch on — but not just any peanuts. Lucky peanuts. 

It's a longstanding tradition at JPL to have a peanut feast before major mission events like launches, milestones and, well, the possible resurrection of Voyager 1. It began in the 1960s, when the agency was trying to launch the Ranger 7 mission that was meant to take pictures of and collect data about the moon's surface. Rangers 1 through 6 had all failed, so Ranger 7 was a big deal. As such, the mission's trajectory engineer, Dick Wallace, brought lots of peanuts for the team to nibble on and relax. Sure enough, Ranger 7 was a success and, as Wallace once said, "the rest is history." 

Voyager 1 needed some of those positive snacky vibes. 

"It'd been five months since we'd had any information," Spilker explained. So, in this room of silence besides peanut-eating-noises, Voyager 1 operators sat at their respective system screens, waiting. 

"All of a sudden it started to populate — the data," Spilker said. That's when the programmers who had been staring at those screens in anticipation leapt out of their seats and began to cheer: "They were the happiest people in the room, I think, and there was just a sense of joy that we had Voyager 1 back."

Eventually, Rasmussen says the team was able to conclude that the failure probably occurred due to a combination of aging and radiation damage by which energetic particles in space bombarded the craft. This is also why he believes it wouldn't be terribly surprising to see a similar failure occur in the future, seeing as Voyager 1 is still roaming beyond the distant boundaries of our stellar neighborhood just like its spacecraft twin, Voyager 2.

To be sure, the spacecraft isn't fully fixed yet — but it's lovely to know things are finally looking up, especially with the recent news that some of its science instruments are back on track. And, at the very least, Rasmussen assures that nothing the team has learned so far has been alarming. "We're confident that we understand the problem well," he said, "and we remain optimistic about getting everything back to normal — but we also expect this won't be the last."

In fact, as Rasmussen explains, Voyager 1 operators first became optimistic about the situation just after the root cause of the glitch had been determined with certainty. He also emphasizes that the team's spirits were never down. "We knew from indirect evidence that we had a spacecraft that was mostly healthy," he said. "Saying goodbye was not on our minds."

"Rather," he continued, "we wanted to push toward a solution as quickly as possible so other matters on board that had been neglected for months could be addressed. We're now calmly moving toward that goal."

The future of Voyager's voyage

It can't be ignored that, over the last few months, there has been an air of anxiety and fear across the public sphere that Voyager 1 was slowly moving toward sending us its final 0 and final 1. Headlines all over the internet, one written by myself included, have carried clear, negative weight. I think it's because even if Voyager 2 could technically carry the interstellar torch post-Voyager 1, the prospect of losing Voyager 1 felt like the prospect of losing a piece of history. 

"We've crossed this boundary called the heliopause," Spilker explained of the Voyagers. "Voyager 1 crossed this boundary in 2012; Voyager 2 crossed it in 2018 — and, since that time, were the first spacecraft ever to make direct measurements of the interstellar medium." That medium basically refers to material that fills the space between stars. In this case, that's the space between other stars and our sun, which, though we don't always think of it as one, is simply another star in the universe. A drop in the cosmic ocean.

"JPL started building the two Voyager spacecraft in 1972," Spilker explained. "For context, that was only three years after we had the first human walk on the moon — and the reason we started that early is that we had this rare alignment of the planets that happens once every 176 years." It was this alignment that could promise the spacecraft checkpoints across the solar system, including at Jupiter, Saturn, Uranus and Neptune. Those checkpoints were important for the Voyagers in particular. Alongside planetary visits come gravity assists, and gravity assists can help fling stuff within the solar system — and, now we know, beyond.

As the first humanmade object to leave the solar system, as a relic of America's early space program, and as a testament to how robust even decades-old technology can be, Voyager 1 has carved out the kind of legacy usually reserved for remarkable things lost to time.

"Our scientists are eager to see what they’ve been missing," Rasmussen remarked. "Everyone on the team is self-motivated by their commitment to this unique and important project. That's where the real pressure comes from." 

Still, in terms of energy, the team's approach has been clinical and determined. 

"No one was ever especially excited or depressed," he said. "We're confident that we can get back to business as usual soon, but we also know that we're dealing with an aging spacecraft that is bound to have trouble again in the future. That's just a fact of life on this mission, so not worth getting worked up about."

Nonetheless, I imagine it's always a delight for Voyager 1's engineers to remember this robotic explorer occupies curious minds around the globe. (Including my dad's mind now, thanks to me and Google.)

As Rasmussen puts it: "It's wonderful to know how much the world appreciates this mission."

More evidence for a hypothetical extra planet lurking in the most distant reaches of our solar system has come to light — and the clues are associated with icy bodies that cross the orbit of Neptune while traversing  long, looping paths around the sun.

Planet Nine, as the predicted planet is referred to, was first postulated in 2016 by Caltech's Konstantin Batygin and Michael Brown, the latter having also discovered the dwarf planet Eris in 2005. Their original evidence predominantly focused on the clustering of trans-Neptunian objects (TNOs), which are objects that spend the majority of their orbits farther from the sun than Neptune is. That's quite far. More specifically, the duo had zoomed in on TNOs with high inclinations, meaning the objects orbited the sun at steep angles to the ecliptic plane. 

Because the solar system's contents formed from a disk around the sun, we would expect the orbits of everything orbiting the sun to keep relatively close to the plane of that disk. However, some don’t — and the team infers this as evidence that Planet Nine's gravity could be pulling the objects out of the ecliptic and bunching them together in highly inclined orbits that share similar "apsides" (closest and most distant points in their orbits around the sun) and which are orientated with a similar tilt away from the ecliptic.

Related: Evidence for 'Planet 9' may actually show our theory of gravity is incomplete

However, some astronomers remained skeptical, arguing that what Batygin and Brown saw as clustering is just an illusion caused by observational bias. The Caltech duo dispute this, and have actually now published a paper that focuses particularly on observations of low-inclination TNOs that don't cluster, but which still have peculiarities.

These icy TNOs are strange because they spend most of their life hundreds of times farther from the sun than Earth is, but their orbits are so elongated that they swoop in and spend a short while closer to the sun than Neptune, which is just 30 times farther from the sun than Earth. "With this work, we looked at objects with long-period orbits but which also strongly interact with Neptune, specifically those that cross Neptune'’s orbit," Batygin told Space.com.

This doesn't include every object that crosses Neptune's orbit, to be clear. Pluto is a good counterexample. Like Pluto, the majority of TNOs don't have orbits that are as elongated as the ones included in the team's new research. Rather, most TNOs have trajectories that keep them relatively close enough to Neptune for extended periods of time such that they can be controlled by the ice giant's gravity. 

The team, however, concerned itself only with those TNOs that get hundreds of astronomical units away from Neptune's gravitational tides, where Planet Nine can exert influence over them — if it so exists, of course. Because these studied objects come from all directions close to the ecliptic plane, without exhibiting any clustering behavior, the same claim of bias leveled at previous evidence regarding high-inclination, clustering TNOs does not hold.

The studied TNOs, and any on similar paths, don't spend too much time in their orbits; over the course of millions of years the gravity of the azure blue ice giant Neptune inevitably bats them away, scattering them far and wide and sometimes even out of the solar system entirely. This means that whatever is sending TNOs onto Neptune-crossing orbits is doing so continuously. There must be an ongoing process in place to keep the TNO supply replenished. This means that the culprit can't be something that happened in the distant past, like a star passing particularly close by. It has to be something that still exists.

There are two scenarios that could regularly place TNOs on long, looping orbits that cross Neptune's path. One scenario is that of the galactic tide, which is the gravitational tidal force of the Milky Way galaxy all around us acting on objects within the Oort Cloud, which lies far away beyond Neptune. These objects only loosely feel the sun's gravity due to their distance from our host star, but the galactic tide can usher them closer towards Neptune.

The other scenario — perhaps the more interesting one — is that the gravity of Planet Nine is perturbing these Oort Cloud objects enough that they tread closer to Neptune over time.

Batygin and his team — Michael Brown, Alessandro Morbidelli of the Observatoire de la Côte d’Azur in Nice, France, and David Nesvorny of the South-west Research Institute in Boulder, Colorado — performed two sets of simulations using observational data of real, low-inclination, Neptune-crossing TNOs to learn which scenario is more accurate. 

One simulation involved a planet with a mass five times that of Earth influencing the TNOs (the simulated properties they used for Planet Nine are derived from the characteristics that best explained previous evidence such as the clustering of the high-inclination TNOs), while the other simulation had no Planet Nine at all and modeled just the galactic tide. Which would be most adept at getting TNOs to pass by Neptune?

The simulations showed that low-inclination TNOs can only regularly penetrate Neptune's orbit if Planet Nine is indeed there to slingshot them. On their own, the eddies of the galactic tides were calculated as too weak to get TNOs past Neptune. Hence, in the galactic tides simulation, the TNOs get to within a certain distance of the sun and no closer —  but in the Planet Nine scenario, the TNOs are spread across a range of Neptune-crossing orbits, which matches what we see in reality.

"We show that you can reject the scenario where this is all happening because of the galactic tides with an astonishing degree of statistical significance," said Batygin. "Conversely, the Planet Nine scenario is perfectly compatible with the data."

Batygin likens it to a football (soccer, for you Americans reading) match, where Neptune is the goalkeeper. The galactic tides can shoot the TNOs towards the goal, but not with enough oomph to get them past the goalkeeper. Planet Nine, on the other hand, is like a planetary Harry Kane, regularly shooting the TNOs past Neptune with finesse.

"What we see in the data are a bunch of footballs inside the goal," said Batygin.

Still, the hunt for the football striker continues.

Later this decade, the Vera Rubin Observatory in Chile will open and begin conducting a nightly, all-sky survey with its 8.4-meter telescope mirror. It will be able to test the evidence for Planet Nine available so far — the clustering of the orbits, the alignment of their orbital planes, their steep orbital inclinations, and the prevalence of retrograde (backwards orbiting) Centaurs. Those refer to icy bodies that have come in from the Oort Cloud and which currently orbit among the solar system's outer planets. If any of these are illusions caused by observational biases, then the Vera Rubin observations will reveal them to be. Though conversely, it could strengthen the evidence, and find many more TNOs that exhibit the same potential influences of Planet Nine. 

"It will test all of these gravitational lines of evidence with an independent new survey that is not subject to the same biases as the previous ones," said Batygin. 

It is even possible that the Vera Rubin Observatory will go all the way and actually find the big tamale. 

"By virtue of its efficiency, maybe — just maybe — it will find Planet Nine," said Batygin. "That would be pretty cool."

The new results have been accepted for publication in The Astrophysical Journal Letters, and are presently available as a pre-print.

Astronomers have long believed that the ice giants Uranus and Neptune are rich in frozen water. However, a new study suggests they may also have tons of methane ice.

The findings could help solve a puzzle about how these icy worlds formed.

Much about Uranus and Neptune remains unknown. These ice giant worlds have had just a single spacecraft visitor, Voyager 2, which flew past them in the 1980s. As a result, scientists have only a hazy idea of the ice giants' compositions — for example, that they contain significant amounts of oxygen, carbon and hydrogen.

Related:The rings of Uranus are being held back by its pesky moons

To learn more about what Uranus and Neptune are made of, astronomers have devised models that match the physical properties that Voyager 2 and Earth-based telescopes have measured. Many models assume the planets have a thin hydrogen and helium envelope; an underlying layer of compressed, superionic water and ammonia; and a central rocky core. (The water is what gives them their "ice giant" tag.) Some estimates suggest Uranus and Neptune may each have 50,000 times the quantity of water in Earth's oceans.

But the authors of the new study say these models ignore the way the ice giants formed. As Uranus and Neptune coalesced from the dust cloud surrounding the young sun, they gobbled up, or accreted, objects called planetesimals. The team says these planetesimals resemble present-day comets such as 67P/Churyumov-Gerasimenko, which originate in the Kuiper Belt, the doughnut-shaped region of icy bodies beyond the orbit of Neptune.

Unlike the supposedly water-rich ice giants, though, a large fraction of these planetesimal-like objects are rich in carbon. So "how is it possible to form an icy giant from ice-poor building blocks?" said Uri Malamud, the study's lead author and a planetary scientist at Technion – Israel Institute of Technology.

To resolve this apparent paradox, Malamud and his co-authors built hundreds of thousands of models of Uranus' and Neptune's interiors. The algorithm they used "starts matching a suitable composition for the surface of the planet, and it gradually works its way deeper into the central point of the planet." They considered several chemicals, including iron, water and methane, the main component of natural gas. Then, they tried to determine which model most resembled the actual ice giants in traits such as radius and mass.

Of the various models they built, the astronomers found that those with methane fit their criteria, with the methane — either in solid chunks or, given the pressure, in a mushy state — forming a thick layer between the hydrogen-helium envelope and the water layer. In some models, methane accounted for 10% of the planet's mass.

The team published their results, which have not yet been peer-reviewed, to the preprint server arXiv in March.

This methane holds the key to resolving the ice paradox. The ice could have formed when hydrogen in the growing planets chemically reacted with the carbon in the planetesimals the planets accreted, the researchers said. Such reactions happen under high temperatures and superhigh pressures — millions of times the air pressure we experience on Earth. These are the exact conditions scientists think existed in the developing planets.

The findings could provide greater insight into these little-understood planets, although verifying if they are actually rich in methane would be challenging, Malamud said. That would be a goal for one of several proposed missions from NASA and other space agencies that aim to explore Uranus.

In examining a pair of icy asteroids at the edge of the solar system, the James Webb Space Telescope is helping scientists understand the evolution of an ice giant: Neptune. These findings could also help reveal how ancient Earth grew saturated with water, the ingredient that ultimately led to the emergence of life. 

The binary asteroid system Mors-Somnus was recently discovered to have originated within an icy band of objects that make up what's known as the "the Kuiper Belt." This region exists beyond the orbit of Neptune, the eighth and furthest planet from the sun. Mors-Somnus can therefore be used as a proxy to study the dynamic history of Neptune as well as other icy bodies in the Kuiper Belt, also known as trans-Neptunian objects (TNOs). 

Some larger TNOs have been investigated in detail before, but this research, conducted by the James Webb Space Telescope's Surface Compositions of Trans-Neptunian Objects  (Disco-TNOs) program, represents the first time the surface composition of two parts of a small, binary pair of TNOs has been investigated. It's also the first time, therefore, that their chemical compositions have been revealed.

Related: 3 tiny new moons found around Uranus and Neptune — and one is exceptionally tiny

"We are studying how the actual chemistry and physics of the TNOs reflect the distribution of molecules based on carbon, oxygen, nitrogen and hydrogen in the cloud that gave birth to the planets, their moons, and the small bodies," Ana Carolina de Souza Feliciano, research leader and Disco-TNOs program scientist at the Florida Space Institute, said in a statement. "These molecules were also the origin of life and water on Earth."

Binaries like Mors-Somnus are rare finds outside the Kuiper Belt. This is because the gravitational bond between such distantly separated binaries is disturbed when they are not protected by other icy bodies and fragments within the belt. This indicates to the team that the process by which Mors-Somnus was transported to its current position outside the Kuiper Belt must have been relatively slow.

De Souza Feliciano and colleagues used the JWST to compare the surface of Mors-Somnus to the surfaces of six other undisturbed TNOs, or "cold classical" ones, to determine they have many commonalities. This revealed that these cold, classical bodies as well as the asteroids Mors and Somnus all formed around 2.7 billion miles away in the same Kuiper Belt region. In this region, other TNOs are thought to have formed, too. 

Furthermore, the fact that these bodies appear perturbed from their original positions in the Kuiper Belt means that scientists can compare them to undisturbed cold classical TNOs and perhaps track down how Neptune has migrated to reach its current orbit.

These are exactly the kind of results researchers were hoping to find once Disco-TNOs data of nearly 60 TNOs started getting delivered from the JWST in late 2022.

"As we started to analyze the Mors and Somnus spectra, more data were arriving, and the connection between the dynamic groups and compositional behavior was natural," de Souza Feliciano said.

Research co-leader and Florida Space Institute researcher Noemí Pinilla-Alonso conceived the Disco-TNOs program. Thanks to its unprecedented spectral observation capabilities, she believes the JWST will deliver even more information about objects in the Kuiper Belt and even beyond Neptune someday.

"For the first time, we can not only resolve images of systems with multiple components, but we can also study their composition with a level of detail that only the JWST can provide," Pinilla-Alonso said. "We can now investigate the formation process of these binaries like never before."

Though the JWST was designed to view objects like galaxies and quasars in the early universe, and thus billions of light-years away from Earth, de Souza Feliciano believes this research emphasizes how the JWST is a true trailblazer.

"Before JWST, there was no instrument able to obtain information from these objects in that wavelength range," she said. "I feel happy to be able to participate in the era inaugurated by the JWST."

The team's research was published on Jan. 9 in the journal Astronomy & Astrophysics.

Astronomers have discovered two tiny moons orbiting Neptune and one circling Uranus, bringing the number of their known moons to 16 and 28 respectively.

Uranus' new moon, the first detected around the ice giant in over two decades and possibly the smallest of its ilk, is just 5 miles (8 kilometers) wide; it takes 680 days to complete one orbit around Uranus. In comparison, one Mars' moons named Deimos, considered to be among the tiniest known moons in our solar system, is 8 miles (13 km) wide. 

The new moon of the blue-green planet is currently referred to as "S/2023 U1" while it awaits being named for a Shakespearean character, according to a statement by Carnegie Institution for Science (or Carnegie Science). 

The brighter of Neptune's two new moons is provisionally named "S/2002 N5." At 14 miles (23 km) wide, this newly discovered satellite seems to be in a 9-year orbit around Neptune. The fainter moon, currently assigned the name "S/2021 N1," is 8.6 miles wide (14 km) and circles Neptune once every 27 years. Both Neptunian moons will be assigned permanent names based on sea gods and nymphs in Greek mythology.

Related: Uranus and Neptune are actually similar blues, 'true' color images reveal

The three new moons were announced Friday (Feb. 23) by the International Astronomical Union's Minor Planet Center, a Massachusetts-based scientific body responsible for designating planets, comets and moons in our solar system. 

The discovery was made using observatories in Hawaii and Chile by Scott Sheppard, a staff scientist at Carnegie Science, in collaboration with Marina Brozovic and Bob Jacobson of NASA's Jet Propulsion Laboratory (JPL), David Tholen of the University of Hawaii, Chad Trujillo of Northern Arizona University and Patryk Sofia Lykawa of Kindai University.

The new moons are "the faintest ever found around these two ice giant planets using ground-based telescopes," Sheppard said in Friday's statement. "It took special image processing to reveal such faint objects."

He first detected the new Uranian moon in November of last year while using Chile's Magellan telescopes. A month later, follow up observations combined with JPL scientists' predictions of a possible orbit for the new moon confirmed the find.

The two new residents in Neptune's moon system were first seen in September 2021. After the orbit of the brighter of the two natural satellites, S/2002 N5, was confirmed, "it was traced back to an object that was spotted near Neptune in 2003 but lost before it could be confirmed as orbiting the planet," said Sheppard.

Determining the orbit of the fainter Neptunian moon "required special observing time under ultra-pristine conditions" with Europe's Very Large Telescope in Chile and Gemini Observatory in Hawaii, according to the statement.

Using these telescopes, Sheppard and colleagues clicked a series of five-minute exposures over three-to four-hour periods. These short-burst images were later “layered” such that the three newfound moons came into clearer view.

All three moons have egg-shaped orbits highly inclined to the plane of their respective ice giants. This implies they did not birth around their host planet but were instead gravitationally seized later on.

The world of astronomy has already offered a pretty fascinating start to 2024. In just the first five days of the year, we've seen incredible discoveries like the true colors of Neptune and Uranus as well as a massive cyclone raging on a distant exoplanet thanks to the trusty Hubble Space Telescope. But things are only going to ramp up over the next week. By a lot. 

From Jan. 7 to Jan. 11, the 243rd meeting of the American Astronomical Society will convene in the vibrant city of New Orleans, Louisiana. 

Thousands of scientists specializing in an absolutely incredible array of subjects ranging from dark matter mysteries to star explosions and the search for habitable exoplanets to the technology required to propel spacecraft across the solar system will gather in one area. They'll get ready to announce some of the best and brightest studies they've been working on; meanwhile, they'll be figuring out how to get even bigger and brighter with their next by listening to wild ideas, strange contradictions and telescopic achievements their colleagues will lay out. Some have even called this event the "Super Bowl of Astronomy." 

Related: The Magellanic Clouds must be renamed, astronomers say

NASA will be there too, to offer updates on major missions like the trailblazing, $10 billion James Webb Space Telescope and the upcoming, highly anticipated, Habitable Worlds Observatory. According to a statement released on Jan. 5, NASA will also be discussing the 2024 total solar eclipse, which will take place on April 8, the Transiting Exoplanet Survey Satellite (TESS), the Nancy Grace Roman Telescope currently under construction and even its scientific balloon program.

"Experts will discuss new research from NASA missions at the 243rd meeting of the American Astronomical Society (AAS) on topics ranging from planets outside our solar system to fleeting, high-energy explosions in the universe," the agency said in the statement.

All NASA press conferences will be streamed for the public to view on AAS's Press Office YouTube channel; other conferences during the meeting will be found there as well. After the meeting concludes, the streams will be available to view on an online archive provided by the organization. You'll notice that this archive includes a wealth of presentations from previous years as well.

Beyond NASA, teams from other iconic space facilities, current and upcoming, are scheduled to speak, too. Members of the Rubin Observatory, for instance, are expected to let everyone know how things are going with their efforts to discover tens of billions of galaxies once its construction is complete in Chile. But, as we'd mentioned, perhaps the most interesting and hopefully mind-blowing presentations will be coming from researchers speaking during the event. 

Though we don't have a ton of information yet on each of those talks, we're able to see some of the study headlines. And they look quite intriguing. For instance, Jan. 8 is poised to bring us an update on a "dark galaxy," the origins of "odd radio circles," and a "famous exploded star in its best light." Jan. 9 appears to have information concerning an exoplanet's tail-like escaping atmosphere and a highly distant fast radio burst seen by the Hubble Space Telescope. Jan. 10 has something about a "supernova imposter" on its schedule and Jan. 11 beholds an entire category of presentation dubbed "Oddities in the Sky." This honestly barely scratches the surface. You can have a look at the full list of presentations here.

Briefings are scheduled to begin between (and including) Jan. 8 to Jan. 11 at 10:15 a.m. CST (11:15 a.m. EST) and then again at 2:15 p.m. CST (3:15 p.m. EST). During the week, you can follow along with Space.com as we bring you some of the AAS's 243rd meeting highlights.

In the summer of 1989, from a remote expanse of our solar system where sunlight is merely a tepid glow, NASA's Voyager 2 spacecraft radioed to Earth humankind's very first images of Neptune. The pictures revealed the sun's outermost planet was a stunning, deep blue orb. In contrast, Uranus, Neptune's planetary neighbor and the first to be discovered with a telescope, appeared noticeably paler.

Both seemingly twin worlds have a lot in common. They're roughly the same size, almost equally massive and are both enveloped with deep atmospheres made of similar materials. So why were the two orbs different shades of blue? This is a question that has puzzled scientists for decades. 

Now, however, a fresh analysis of Voyager 2's images show both ice giants are in fact a similar shade of greenish blue, which is the "most accurate representation yet" of the planets' colors, the new study finds.

Related: The rings of Uranus look positively festive in epic James Webb Space Telescope holiday photo

How could we miss this?

Back in the late 1900s, the images Voyager 2 recorded of Uranus and Neptune were in single colors combined to create composite images that showed the planets to be cyan and azure, respectively. While Uranus' published pictures were processed close to its true color, early Neptune images had been "stretched and enhanced" to display its clouds, bands and winds, "and therefore made artificially too blue," study lead author Patrick Irwin, a planetary physicist at the Oxford University in the U.K., said in a statement.

"Even though the artificially-saturated color was known at the time amongst planetary scientists — and the images were released with captions explaining it — that distinction had become lost over time."

To resolve the misconception, Irwin and colleagues used new images from NASA's Hubble Space Telescope and European Space Agency's Very Large Telescope, whose instruments capture a rich spectrum of colors in each pixel, so processing them determined the "true apparent colors" of Uranus and Neptune. 

Then, the team revisited Voyager 2's images and rebalanced them in line with the new data, showing both planets are actually similar shades of blue. The color comes from a layer of methane in the planets' atmospheres, which absorbs red color from the sun's light.

Uranus is slightly whiter, the new study finds, possibly because its somewhat "stagnant, sluggish" atmosphere permits the methane haze to accumulate, which reflects red portions of sunlight to a greater extent than Neptune does.

The presence of amassed methane ice particles may also explain why Uranus changes its color slightly during its 84-year orbit around the sun. Images recorded between 1950 and 2016 by the Lowell Observatory in Arizona show the planet appears greener during its solstices — when one of its poles points toward the sun — and bluer during equinoxes, when the sun shines directly above its equator.

By comparing brightness of Uranus' poles to its equatorial regions in these images, Irwin and his team concluded methane is likely half as abundant near poles than at the equator, which accounts for the changing colors.

"The misperception of Neptune's color, as well as the unusual color changes of Uranus, have bedeviled us for decades," said Heidi Hammel of the Association of Universities for Research in Astronomy, who is not affiliated with the new study. "This comprehensive study should finally put both issues to rest."

This research is described in a paper published Thursday (Jan. 4) in the journal Monthly Notices of the Royal Astronomical Society.

When will we be able to see the planets at their best during this upcoming year of 2024?  Well, this guide will tell you. It will also provide information as to when a particular planet might be passing near to another planet, or a bright star for that matter, as well as the constellation that each will occupy during the course of the year. Read on to learn more about various circumstances like conjunctions, oppositions and elongations that are on this upcoming year's skywatching schedule. 

1. Mercury

As an evening star, Mercury appears in the western sky and sets about an hour after the sun does. As a morning star, it appears in the eastern sky, rising about an hour before the sun. There must be a clear, unobstructed horizon on these occasions. Mercury usually appears as a bright "star" with a yellowish or ochre hue. You can catch sight of the planet in the mornings of Jan. 5 to Jan. 26, May 2 to May 23, Aug. 30 to Sept. 19 and Dec. 18 to Dec. 31.  You can also catch some Mercury action in the evenings of March 10 to March 31, July 8 to July 29 and Nov. 2 to Nov. 23. 

Mercury will be brightest and easiest to spot in the evening sky between March 10 to March 31, and brightest and easiest to spot in the morning sky between Jan. 5 to Jan. 26 and again between Dec. 18 to Dec. 31.  

2. Venus

Always brilliant, and shining with a steady, silvery light, you can catch Venus during mornings in the eastern sky at dawn from Jan. 1 to April 8; evenings in the western sky at dusk from July 30 to Dec. 31.

The est time to view Venus in the morning sky in 2024 will come from Jan. 1 to Feb. 11. The best time to view Venus in the evening sky in 2024 will come from Oct. 5 through Dec. 31. On Feb. 22, Venus will be very close to Mars (passing 0.6-degree north of the Red Planet). Venus and Saturn will appear dramatically close to each other (Venus just 0.2-degree N) on the morning of March 21.

On April 3, Venus will slide just 0.3 degrees S of Neptune. On Aug. 5, Venus will pass 1.1-degree N of a bluish Regulus, the brightest star in the constellation of Leo, the Lion. On Nov. 22, Venus passes 1.1-degree N of Nunki, a second-magnitude star in the constellation Sagittarius.

3. Mars

This will be another "off" year for Mars, as for much of 2024 it will appear relatively dim while dawdling in the morning sky. Mars will actually be invisible for the first 10 days of the new year, too deeply immersed in the bright dawn twilight to be seen. On New Year's Day it will reside in the constellation of Sagittarius at a distance of 225.2 million miles (362.4 million kilometers) from the Earth. By April Fool's Day, it will be in the constellation of Aquarius and become visible low in the southeast for a few hours before sunrise, shining at magnitude +1.2. On July 1, it will be visible after midnight in the eastern sky, having brightened slightly to magnitude +1.0.

On Halloween, during late night hours, Mars will be readily seen in the northeast sky, with the "Twin Stars" of Gemini, Castor and Pollux, pointing directly at this yellow-orange planet, now shining at magnitude +0.1. 

From then on, through the balance of the year, Mars will rapidly ramp-up in brightness as it approaches the Earth. It will become stationary against the starry background of space on Dec. 6, performing a retrograde loop as a prelude to its first opposition since 2022 on Jan. 16, 2025. On New Year’s Eve, now in the constellation of Cancer, Mars will be 61.3 million miles (98.6 million km) from Earth and shine at magnitude -1.2, which is just a bit dimmer than Sirius, the brightest star in the night sky; this will be its brightest in 2024. 

Mars will pass 2.7 degrees north of the second magnitude star Nunki in the constellation Sagittarius on Jan. 21 and will get very close to Venus (passing 0.6 degrees south of that dazzling world) on February 22. Mars will make even closer approaches to Saturn (0.4-degree N) on April 10 and to Neptune (0.1-degree S) on April 29. The Red Planet will pass 4.9 degrees north of the similarly bright and orange tinted star Aldebaran on Aug. 4 and slide 0.3-degrees north of Jupiter on Aug. 14. 

Finally, early on the morning of Dec. 18, a waning gibbous moon will slide just above Mars. Across northern sections of North America, the moon will actually occult, or eclipse, the planet.      

4. Jupiter

Jupiter will be quite brilliant with a silver-white luster in 2024. It starts the year in the constellation Aries the Ram, then crosses over into Taurus the Bull on April 28 where it will remain for the balance of the year. 

During evenings from Jan. 1 to April 26, it'll shine brightly, as well as during mornings from June 8 to Dec. 6. Evening viewing will be optimal again from Decc. 7 to December 31.  

It's brightest in 2024 will fall between Nov. 14 to Dec. 28. Jupiter will be  in opposition to the sun on Dec. 7. It will pass 4.8-degrees north of the first magnitude star Aldebaran on July 9 and will be only 0.3-degrees south of a much-dimmer Mars on Aug. 14.

5. Saturn

Saturn shines like a yellowish-white "star" of moderate brightness. The famous rings, however, are only visible in a telescope. 

The rings were at their maximum tilt toward Earth in Oct. 2017, but are now rapidly closing to our line of sight. They will turn edge-on to the Earth during the spring of 2025. The process will begin in 2024 within the boundaries of the constellation Aquarius, the Water Carrier, and the planet will remain there for the rest of the year. 

You can catch Saturn during evenings from Jan. 1 to Feb. 11, mornings from March 17 to Sept. 7, then evenings again from Sept. 8 to Dec. 31. Saturn's brightest in 2024 will fall between Aug. 25 to Oct. 1. Saturn will be in opposition to the sun on Sept. 8. Saturn and Venus will appear dramatically close to each other (with Saturn just 0.2-degree S) on the morning of March 21 and will be 0.4-degree S of Mars on April 10.  

6. Uranus

Uranus can be glimpsed as a naked-eye object by people who are blessed with good eyesight and a clear, dark sky, as well as a forehand knowledge of exactly where to look for it. 

At its brightest, this planet shines at magnitude +5.6 and can be readily identified with good binoculars. A small telescope may reveal its tiny, greenish disk. Uranus spends all of 2024 in the constellation of Aries the Ram. You can catch sight of it during evenings from Jan. 1 to April 27, mornings from May 31 to Nov. 16, then evenings again from Nov. 17 to Dec. 31. It's brightest in 2024 will happen from Oct. 15 to Dec. 21. Uranus will arrive at opposition to the sun on Nov. 16.  

7. Neptune

Last but not least, Neptune will spends all of 2024 in the constellation of Pisces, the Fishes.  At a peak magnitude of +7.8, this bluish-hued world is only visible with good binoculars or a telescope. It'll be in the sky for optimal viewing during evenings from Jan. 1 through March 1, mornings from April 3 through Sept. 19, then evenings again from Sept. 20 to Dec. 31. 

It's brightest in 2024 will happen from July 23 to Nov. 19. Opposition is on Sept. 20. Two excellent opportunities to identify Neptune will come first on April 3, when Venus slips 0.3-degree S of Neptune, and again on April 29, when Mars passes a mere 0.1-degree S of Neptune. Keep in mind that, compared to Neptune, Mars will appear over 500 times brighter and Venus some 58,000 times more dazzling. 

When you're standing on Earth's surface, it's easy to forget that our planet is hurtling around the sun at more than 67,000 mph (107,800 km/h). And it's even easier to forget that there are seven other planets also making their way around our home star at similar breakneck speeds, or that all eight have been ceaselessly circling the solar system for billions of years. 

But what might really blow your mind is finding out how many trips around the sun each planet has under its belt. This may seem like a tricky thing to calculate, but because the planets' orbits have remained largely unaltered for most of their existence, all it takes is a bit of basic math.

Related: What's the maximum number of planets that could orbit the sun?

The solar system was born around 4.6 billion years ago, when the sun began to form from a cloud of dust left behind by prior stellar explosions. Around 4.59 billion years ago, the giant planets — Jupiter, Saturn, Uranus and Neptune — were born. And around 4.5 billion years ago, the smaller, rocky planets — Mercury, Venus, Earth and Mars — took shape, according to The Planetary Society.

But when the planets were born, their orbits around the sun were not the same as they are today (especially those of the giant planets). For around 100 million years after the first planets formed, there was a "dynamical instability" among them, which resulted in a gravitational tug-of-war between these large bodies and caused the rest of the outer solar system's planetary material, and even some emerging protoplanets, to be catapulted out of the solar system, Sean Raymond, an astronomer at the Bordeaux Astrophysics Laboratory in France and an expert on planetary systems, told Live Science in an email. 

However, once all of the planets had emerged and finished jostling with one another for their positions, they settled into consistent, stable orbits that haven't changed much since.

"For 98% to 99% of the solar system's lifetime, the planets' orbits have been nice and stable," Raymond said. As a result, you can use the planets' current orbital dynamics to make a pretty accurate guess at how many trips they have made around the sun, he added.

Take Earth, for example. Our planet takes a year to orbit the sun and has existed for 4.5 billion years, so it has taken roughly 4.5 billion trips around the solar system. 

However, the number of total orbits varies greatly among the other planets because their years are either shorter or longer than Earth's.

Mercury, the closest planet to the sun, takes only 88 days (or roughly 0.24 years, based on a year with 365.25 days) to travel around the sun once. So, over the past 4.5 billion years, it has completed around 18.7 billion solar orbits. But Neptune, the farthest planet from the sun, takes around 60,190 days (or 164.7 years) to complete an orbit, which means it has managed only about 27.9 million trips around the sun during its 4.59 billion years of existence. That means Mercury has orbited the sun around 18.7 billion times more than Neptune has.

Here is the full list of the planets, their year length and their total number of trips around the sun:

These sound like impressive numbers (and they are) but most of the planets could potentially double their number of orbits in their remaining lifetimes. 

In around 4.5 billion years, the sun will have swollen outward to reach Earth's orbit and transition into a red dwarf star, which will destroy Mercury, Venus and Earth. The other planets may live on for a time if they are not burned up but their orbits will likely be majorly altered.

What would it be like to fall through the clouds of our solar system's ice giants, Uranus or Neptune? Well, no one truly knows — but we might be close to finding out.

We have landed on, crashed into, or descended into the clouds of all of the planets in the solar system except for two: Uranus and Neptune. The farthest planets from the sun, these worlds are still shrouded in a certain degree of mystery. This may soon change, however. That's because both NASA, in the 2023-2032 Planetary Sciences Decadal Survey, and the ESA, in the Voyage 2050 programme, have stated that a visit to these outer planets is a high priority. 

To that end, simulated probes can help us understand what descending into the clouds of these planets might entail.

As such, scientists recently simulated a probe descending into the atmosphere of the two planets. The tests took place at the hypersonic plasma T6 Stalker Tunnel at Oxford University and the University of Stuttgart’s High Enthalpy Flow Diagnostics Group’s plasma wind tunnels. 

Related: Uranus up close: What proposed NASA 'ice giant' mission could teach us

The T6 Stalker Tunnel is the fastest wind tunnel in Europe, reaching test speeds of 20 kilometers per second (12.4 miles per second.) These tests simulated what a probe descending into the atmosphere of Uranus or Neptune would need to contend with, including heat fluxes and convective heating. Even though the atmospheres of these icy giants are very cold, a probe would heat up significantly from entry into the atmosphere. And the rate of such heating is orders of magnitude higher than anything ESA, for instance, has had to deal with so far.

The tests have already managed to simulate speeds of 19 km per second (11.8 miles per second), but further tests will simulate actual entry rates of 24 km per second (14.9 miles per second.) This speed is equivalent to the speed required for a probe to orbit the ice giants. 

"To begin designing such a system we need first to adapt current European testing facilities in order to reproduce the atmospheric compositions and velocities involved," Louis Walpot, an aerothermodynamics engineer at ESA, said in a statement. 

Unlike their larger siblings Jupiter and Saturn, Uranus and Neptune contain a notable amount of heavier elements, along with significant levels of methane, the latter of which turn their clouds blue. These planets may also harbor oceans of liquid within their atmospheres and experience diamond rain. 

Nonetheless, Uranus and Neptune are the least understood planets in our solar system, so any probe sent over there would give us enormous information about the worlds' natures. Plus, learning about these ice giants may also help us better understand planetary system formation. 

Almost everyday, the number of confirmed exoplanet discoveries grows. 

The majority of those planets, which sit just above 5,500 in total, have been identified by the Kepler space telescope. But for the last few years, NASA's Transiting Exoplanet Survey Satellite (TESS) has been steadily adding new alien worlds to our growing planetary catalog of the cosmos. 

Using a statistical method to comb through TESS's large quantities of data on the night sky, a group of scientists led by Priyashkumar Mistry, a Ph.D. student at the University of New South Wales, have reported on the potential discovery of eight new exoplanets. What's more, each one of these planets is considered to be a "super-Earth," a class of exoplanet that is larger than Earth but smaller than Neptune, according to NASA. 

Related: Super-Earths are more common and more habitable than Earth. Astronomers are finding more of the billions out there.

To date, TESS has confirmed almost 400 exoplanets, and yet another 6,977 await confirmation. The satellite observes nearby stars, waiting for dips, or fluctuations in the brightness of the stars. Such dips indicate to astronomers that something likely passed in between us and the star — and that something could be a new exoplanet. 

"If this orbital motion ever comes between us and the star we will observe a dip in the brightness of that observed star. This is what we call a transit," Mistry told Space.com. 

Mistry and his team used the Validation of Transiting Exoplanets using Statistical Tools (VaTEST) project to identify anomalies, which could indicate the presence of exoplanets, in TESS's data. 

Why do we need statistical tools?  

It's not only the case that these dips are caused by transiting exoplanets. Such false positives, which could include a star orbiting another star (binary system), or a background source, could generate a transit-like signal. 

Mistry explains that the transit method can only provide the radius of an orbiting body. What if a planet sized star, such as a brown or red dwarf is in orbit? Astronomers would usually work out the mass of a transiting object using a method called radial velocity (RV), which is where an orbiting body exerts a gravitational pull on its home star. This results in the star doing a little dance, or 'wobble'. 

To detect the RV signal, though, it can take a lot of time observing just one star, especially if the exoplanet has a long orbital period — time and resources that the researchers didn't have. 

However, the VaTEST provided Mistry and his team with another means of confirming whether these transiting events were actually the result of orbiting exoplanets. 

"The tool takes in the transit data and some inputs such as transit depth, period, TESS identifier, etc. Then based on that it starts fitting different models on the data and performs some probability calculations. And then finally it calculates False Positive Probability (FPP), if it turns out to be < 1% then we can validate that transit signal as a planetary transit," Mistry says. 

The statistical tool calculated that eight such transiting events were likely caused by a class of  exoplanet that astronomers call 'super-Earths' — and that six of them fall into the region known as 'keystone planets,' which have characteristics that help astronomers better understand the overall exoplanet population. This makes them highly attractive for further study.

What is a keystone planet?  

To understand what astronomers mean by 'keystone planet', we first have to understand the radius valley concept. The radius valley reveals a scarcity of planets between 1.5 and 2 Earth radii, with orbital periods less than 100 days in the known population of exoplanets that orbit low-mass and sun-like stars. This radius range covers super-Earths, and another class of planet — sub-Neptunes, which are exoplanets with a smaller radius than Neptune. 

Why does this scarcity exist? Some theories suggest this may be due to photoevaporation mass loss, where intense radiation from a home star could gradually strip away a planet's atmosphere over time. This suggests that planets within this keystone region should be predominantly rocky, but observations are yet to confirm whether this is in fact the case. 

"To understand this contradiction we need more and more keystone region planets. And that's the reason why our validated exoplanets are interesting to study," explains Mistry. Adding more keystone planets to our exoplanet catalog, with the potential to do follow up observations with the James Webb Space Telescope (JWST), should help astronomers resolve what explanation best fits this mystery in the exoplanet data.  

Could one of these super-Earth's be a home to life?  

While super-Earth's do have the name 'Earth' in their title, this doesn't necessarily refer to their life-giving potential. Rather, life would likely find it hard to establish itself on any of the super-Earths discovered by Mistry and his team. The reason being the close proximity these planets have to their home stars. 

"They are closer to their host star than Mercury is from the sun," says Mistry. This usually means they are tidally locked, where one side of the planet is forever facing the star, with the other side cloaked in eternal darkness. In this sense, it's either scorching or freezing temperatures, neither of which are particularly life-friendly. 

"But who knows. The cosmos is filled with so many surprises," Mistry quips. 

A study of the eight super-Earths can be found on the preprint server arXiv, with the paper currently under review at the Publications of the Astronomical Society of Australia. 

The only spacecraft to visit Neptune was the Voyager 2 probe, which spent just a few precious minutes in the vicinity of this mysterious world during its historic flyby tour of the outer solar system in the 1980s. It's been over 40 years since that mission launched. And while space agencies around the world have developed dozens of probes, landers and rovers in the decades since, none have visited the solar system's outermost planet, let alone orbit it.

Planetary scientists have long been interested in a return visit to Neptune, but the planet is so distant that an orbiter or lander mission is next to impossible. While the New Horizons spacecraft has visited the dwarf planet Pluto, that was a brief fly-by mission. So far, the most distant orbiter that we've sent has been to Saturn.

Neptune is so far away that it's difficult to fathom: It sits roughly 30 times farther from the sun than Earth does. To put that into context, Jupiter is only five times farther from the sun than Earth is. It takes years for an orbiter to reach Jupiter, and Neptune is five times farther away. While Voyager 2 took 12 years to fly past Neptune, it zoomed by without stopping, quite a very different mission profile. New Horizons flew past Neptune and its moon Triton in 2014 from a distance of about 2.45 billion miles (3.96 billion kilometers), but also just zoomed past the planet. Placing a spacecraft in orbit around the planet is quite a different matter, and remains infeasible with current technologies.

Related: Neptune is cooling down, and scientists don't know why 

One problem with a return mission to Neptune is that a flyby focused solely on that world does not provide significant bang for the buck. Without the lucky alignment available to missions in the 1970s and '80s, we'd have to spend even more fuel to send a probe in that direction, and we wouldn't get that much more science than we did decades ago. 

The next logical step after a successful flyby mission is an orbiter, but the extreme distance to Neptune poses significant challenges. We have no clear way to haul a large enough orbiter to the Neptune system, pack enough fuel to allow it to slow down and do it all in a reasonably short amount of time.

However, researchers have shared a radical new idea for how to overcome these challenges: Use the thin atmosphere of Triton, Neptune's largest moon, to capture a spacecraft. 

In a paper appearing in the preprint database arXiv, the researchers pointed out that in 2022, NASA successfully completed the Low-Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID). The goal of that program was to develop an inflatable shield to protect a spacecraft as it descended through Earth's atmosphere and slow the craft so it didn't crash upon landing.

The researchers proposed to aim a future Neptune orbiter at Triton and use a LOFTID-like apparatus, known as an aeroshell, to slow the spacecraft. They found that the atmosphere of Triton, despite having less than 1/70,000 the air pressure of Earth's atmosphere, could sufficiently slow a spacecraft and allow it to enter into a captured orbit around Neptune. Additionally, they could change the angle of the aeroshell to tweak the orbiter's alignment and fine-tune the course to get it into the perfect orbit.

To get it right, the orbiter would have to get as low as 6 miles (10 kilometers) above the surface of Triton. That's not much higher than a typical intercontinental flight, but because Triton doesn't have any seriously large mountain ranges (the tallest known peaks are barely a kilometer tall), there's very little risk of a catastrophic collision with the surface.

Similar ideas have been proposed for using an aeroshell to insert an orbiter around Saturn using its moon Titan, but Titan has a much thicker atmosphere, making the job a lot easier. Although Triton's atmosphere is incredibly thin, the moon sits relatively far away from Neptune, meaning the spacecraft would not be traveling as quickly, and would not have to reduce its speed as much, to be captured.

The researchers estimate that, using this aeroshell technique, a mission to Neptune could take as little as 15 years, which is far shorter than any other current mission ideas would allow. With current approaches, an orbiter would need to pack so much fuel for use in slowing itself down at Neptune that it would never be able to reach a high velocity, making the trip extremely long.

And there's a bonus to the plan: It would give us an up-close view of Triton, which is one of the strangest objects in the solar system and likely a captured Kuiper Belt object. We'd get to see this odd world from a vantage point of only a few kilometers above the ground, thus delivering some great extra science.

The ice giant Neptune will be at opposition on Tuesday (Sept. 19), meaning it will be in a straight line with our planet and the sun, with Earth in in the center. 

The eighth and most distant planet from the sun, Neptune, will also make its closest approach to Earth, known as perigee, at around the same time. This means the distant planet will be at its largest and brightest in the sky tonight, making it an excellent time to locate and observe Neptune.

From New York City, Neptune will rise in the east at around 6:58 p.m. EDT (2258 GMT) and will become visible a few hours later, according to In the Sky. The ice giant will be at its highest point in the sky, 46 degrees above the horizon (nearly five widths of your fist at arm's length), at 12:51 a.m. EDT (0451 GMT) on Wednesday, Sept. 20. Neptune will be in the Pisces constellation.

Neptune will then disappear at around 4:41 a.m. EDT (0841 GMT) when it drops below 21 degrees over the horizon to the southwest. The planet will set at around 6:41 a.m. EDT (1041 GMT). 

Related: Night sky, September 2023: What you can see tonight [maps]

Even though the distant ice giant is at perigee, its closest point to Earth, Earth and Neptune will still be anything but close in real terms. During this closest approach on Tuesday, Neptune will still be around 2.7 billion miles (4.3 billion kilometers) from our planet. 

For comparison, Earth and Mars are separated by an average of 140 million miles (225 million kilometers). This means that the average distance between Mars and Earth would fit between Earth and Neptune almost 20 times over. 

And while the Earth is around 93 million miles (150 million kilometers) from the sun, Neptune is around 30 times further away at around 2.8 billion miles (4.5 billion kilometers) from our solar system's star. The distance between Neptune and the sun means that the ice giant takes 165 Earth years to orbit the sun.

The distance between Earth and Neptune means that the blue marble-like world isn't visible in the sky over Earth with the naked eye. This is despite the fact that the planet has a width of around 31,000 miles (50,000 kilometers), around 4 times the size of Earth, and is the fourth largest planet in the solar system. 

The ice giant at the outskirts of the solar system is visible with the aid of a telescope or good binoculars in dark skies and in favorable weather conditions. Want to check out Neptune in the night sky? See our guides on the best telescopes, the best binoculars, and the best telescopes for seeing planets.

And if you're looking to snap photos of Neptune or the night sky in general, check out our guide on how to photograph the planets, as well as our best cameras for astrophotography and best lenses for astrophotography.

Editor's Note: If you snap an image of Neptune at opposition and would like to share it with Space.com’s readers, send your photo(s), comments, and your name and location to spacephotos@space.com.

Most people have seen the five brightest naked-eye planets, and yet there is a sixth planet that can be spied without optical aid — the planet Uranus.  Of course, you'll have to know exactly where to look for it. 

Fortunately, it is currently well placed for viewing in our sky and with the bright moon now out of the way this week; it will be a good time to look for it.

Barely visible to the unaided eye on very dark, clear nights, Uranus is currently shining at magnitude +5.7 (On this scale, larger numbers represent dimmer objects.).

So, Uranus verges near the limit of what's visible with the naked eye under dark skies. It's now visible during the late-evening hours in the constellation of Aries, the Ram. By around midnight, it will be situated about one-third of the way up from the eastern horizon to the point directly overhead, and is positioned roughly midway between two prominent sky landmarks. To its west or right is the brilliant planet Jupiter, while to the east or left is the Pleiades star cluster. 

Related: Night sky, September 2023: What you can see tonight [maps]

It is best to study the accompanying map first, then scan that region with binoculars; you'll be looking for a small starlike object shining with a pale-greenish tinge.

Using a magnification of 150-power with a telescope of at least three-inch aperture, you should be able to resolve it into a tiny, featureless disk. Uranus, which lies nearly 2 billion miles (3.2 billion km) from the sun, has a diameter of 31,800 miles (51,200 km) and according to flyby magnetic data from NASA's Voyager 2 probe in 1986, has a rotation period of 17.4 hours. 

At last count, Uranus has 27 moons, all in orbits lying in the planet's equator in which there is also a complex of eleven narrow, nearly opaque rings, which were discovered in 1978. 

Uranus likely has a rocky core, surrounded by a liquid mantle of water, methane, and ammonia, encased in an atmosphere of hydrogen, helium, methane and small amounts of acetylene and hydrocarbons. A bizarre feature is how far over Uranus is tipped. Its north pole lies 98 degrees from being directly up and down to its orbit plane. Thus, its seasons are extreme: when the sun rises at its north pole, it stays up for 42 Earth years; then it sets and subsequently, the north pole is in darkness for 42 Earth years.

First thought to be a comet

The man who discovered Uranus was William Herschel, an English organist who was also an amateur astronomer.

In late winter of 1781, Herschel finished building a new seven-inch reflecting telescope and began to explore the sky with it. On the night of March 13, he had his telescope trained on the constellation of Gemini, the Twins. There to his great surprise he noticed a star with a greenish hue that was not charted on any of his sky maps. 

An assiduous amateur observer, Herschel was quick to realize that what he found could not be a star, for it appeared in his telescope as a glowing disk as opposed to a twinkling point of light. Continuing to observe his find night after night, Herschel discovered that it was moving among the stars of Gemini. Finally, he decided that he had discovered a new comet and wrote up a detailed report of his observations. 

The report of a new comet excited astronomers all over Europe, and they eagerly trained their telescopes on Herschel's discovery. But the more they studied it, the more they began to wonder if it really was a comet. For one thing, it seemed to be following a nearly circular orbit out beyond Saturn. Finally, it became clear that Herschel had not discovered a comet but a new planet. 

For a while, it actually bore Herschel's name.  Herschel himself proposed the name Georgium Sidus — "The Star of George" — after his benefactor, the King of England.  However, the custom for a mythological name ultimately prevailed and the new planet was finally christened Uranus after the Greek god of the sky. 

Prior to Uranus' discovery, the outermost planet was considered to be Saturn, named for the ancient god of time and destiny, but Uranus was the father of Saturn and considered the most ancient deity of all. It takes 84 years to make one circuit around the sun.

Uranus led to Neptune

Interestingly, the discovery of Uranus in 1781 eventually led to the discovery of yet another new world, some 65 years later. Since it appeared bluish in color, the new planet was named Neptune after the god of the sea. More on this in a moment. 

But in contrast to Uranus, which is right on the threshold of naked-eye visibility, Neptune is much too faint to be perceived without any optical aid. 

At magnitude +7.8, Neptune is more than six times dimmer than Uranus. It is also slightly smaller than Uranus, with a diameter of 30,800 miles (49,600 km). With the demotion of Pluto to the category of a "dwarf" planet in 2006, Neptune acquired the title of the farthest of the "classical" planets from the sun; it currently lies at a distance of 2.74 billion miles (4.41 billion kilometers) from Earth. In the year 2011, Neptune completed one full trip around the sun since its 1846 discovery.

How to locate Neptune

Nonetheless, if you have access to a dark, clear sky and carefully examine our map, you should have no trouble in finding it with a good pair of binoculars. 

Once again, study the accompanying map.

Neptune is now among the faint stars of Pisces the Fishes. In Pisces, there is a dim, albeit popular asterism known at the Circlet whose ring-like shape is easily recognized south of the southern side of the Great Square. Your clenched fist held at arm's length is equal to about 10 degrees in width. About 5 degrees (or a "half fist") below the Circlet is a +5.5 magnitude star 20 Piscium. Now center binoculars or a low-power telescope on this star and Neptune will be less than a half-degree away. It will appear as a tiny, bluish star. 

But trying to resolve Neptune into a disk will be more difficult than it is with Uranus. You're going to need at least a four-inch telescope with a magnification of no less than 200 power just to turn Neptune into a tiny dot of light.

Gas world

Voyager 2 passed Neptune in 1989 and showed it to possess a deep blue atmosphere, with rapidly moving wisps of white clouds. Also evident was a Great Dark Spot, rather similar in nature to Jupiter's famous Great Red Spot. That storm has since disappeared, but new ones have appeared on different parts of the planet. Voyager 2 also revealed the existence of at least five rings and four ring arcs around Neptune, mostly composed of very fine particles. 

The atmosphere of Neptune is apparently composed chiefly of hydrocarbon compounds. Based on the rotation rate of its magnetic field, a rotation rate of 16.1 hours has been assigned to Neptune. Neptune is also our solar system's windiest planet with winds whipping clouds of frozen methane across the planet at speeds of more than 1,200 miles (2,000 km) per hour. 

Neptune has 14 moons, one of which, Triton, was discovered just 17 days after Neptune itself was discovered. Triton has a tenuous atmosphere of nitrogen and at nearly 1,700 miles (2,700 km) in diameter, it is even larger than Pluto. Because Triton is moving in a retrograde (backward) orbit around Neptune, there has been some suggestion that it was originally a Kuiper Belt asteroid that Neptune may actually captured in the distant past.

Perturbing Uranus

As was alluded to earlier, Neptune's discovery came about from long-term observations of Uranus. By plotting the path of a planet, astronomers can draw up tables that show them exactly where the planet will be at any given time. So, after the discovery of Uranus, they set about plotting is orbit. But this methodology didn't seem to work. Sometimes Uranus turned up ahead of its predicted position; sometimes it lagged behind. So, astronomers began to think that an unseen body lay beyond Uranus. Perhaps its gravitational field was perturbing its motion and that was the explanation of Uranus' odd behavior. 

Not until the 1840's did anyone attempt to put that idea to the test. Then, as so often happens in science, two men attacked the problem at the same time without knowing of each other's work. In England, young John Couch Adams (1819-1892), a student at Cambridge University, proved by mathematics that there must be an unknown object beyond Uranus and indicated where it might be found. Meanwhile in France, the astronomer Urbain J.J. Leverrier (1811-1877) also solved the problem. 

Neither knew what the other was doing, but ultimately, both men had figured out the probable path of the supposed object that was disturbing the orbit of Uranus. Both believed that the unseen body was then in the constellation of Aquarius the Water Carrier. 

So, both Adams and Leverrier appealed to their fellow astronomers for help in locating the planet. 

Adams forwarded his results to Sir George Airy (1801-1892), the Astronomer Royal, with specific instructions on where to look for it. For some unknown reason, however, Airy delayed a year before starting the search. Was it because of his lofty position as Astronomer Royal that he was reticent on following instructions from a mere student?

In contrast, Leverrier wrote to the Berlin Observatory requesting that they search in the place his directed. Upon receiving Leverrier's letter, Johann Gottfried Galle (1812-1910) and Heinrich d'Arrest (1822-1875) at Berlin did exactly as they were instructed and found the new planet in less than an hour! 

"Almost" discoveries

A strange fact about Neptune is that it was very nearly discovered by none other than Galileo with his crude telescope, more than two-and-a-half centuries earlier.

It was while observing Jupiter and its system of four large satellites on Dec. 28th, 1612 that, in the same field of view, Galileo unknowingly recorded Neptune as an eighth magnitude star. Just over one month later on Jan. 27, 1613, Galileo recorded two stars in his telescope field, one of which was Neptune. The next night when he looked again, he noted that the two stars seemed further apart. If he had only continued to keep watch in the following nights, he would have almost certainly would have realized that one of the "stars" was indeed moving.

But Galileo should not be faulted for not recognizing Neptune, for later observers too, stumbled across it without realizing what it really was. Among them was the skilled French astronomer, Lalande (1795); the English astronomer, John Herschel (1830); and the Scottish astronomer, Von Lamont, just days before Neptune was actually discovered by Galle and d'Arrest in 1846. All thought it was nothing more than an ordinary star.

And yet, if only Galileo had followed through with his observations, the eighth planet would have been discovered before the seventh!

Want to check out Uranus and Neptune? See our guides on the best telescopes, the best binoculars, and the best telescopes for seeing planets.

And if you're looking to snap photos of Uranus, Neptune or the night sky in general, check out our guide on how to photograph the planets, as well as our best cameras for astrophotography and best lenses for astrophotography.

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

Sometimes, astronomy is like a forensic investigation: We can't just rerun the past, so we have to study clues to figure out what happened. And the outer solar system contains one striking crime scene holding a big mystery: How the environment around Neptune got a moon like Triton.

Neptune has 14 known moons. With the exception of Triton, all of Neptune's moons are very small, and they come in two general flavors: regular and irregular. The regular ones orbit close to the planet, and the irregular ones are generally farther from Neptune, with all sorts of crazy orbits. 

And then there's Triton. It was discovered by English merchant and amateur astronomer William Lassell, who, in 1846, spotted the moon a mere 17 days after the discovery of Neptune itself. But it wasn't until Aug. 25, 1989, that we got our first close-up look at Triton when the Voyager 2 probe flew by on the last leg of its historic "grand tour" of the outer solar system. Although Voyager 2 mapped only 40% of Triton's surface, the mission revealed just how strange the Neptunian moon is.

Related: James Webb Space Telescope captures stunning image of Neptune's rings and moons

For one, Triton is big. It's the seventh-largest moon in the solar system, and it's over 200 times bigger than all of the other moons of Neptune combined, which makes it really stick out.

Second, Triton is one of the irregular moons. It orbits backward relative to Neptune's spin, and its orbit is inclined at a stunning 67 degrees — almost perpendicular to its parent planet. Despite its irregularity, Triton's orbit is surprisingly circular — in fact, one of the most perfectly circular orbits out of all the objects in the solar system.

As for the surface, it looks like a cantaloupe. A large chunk of Triton's midlatitudes is covered in bumpy, wrinkly features nicknamed, appropriately enough, cantaloupe terrain. Another large section features broad, featureless plains dotted with massive calderas, while the southern portion is dominated by a vast nitrogen ice cap, dotted with dozens of cryovolcanoes — volcanoes that spew jets of water.

What the surface of Triton doesn't have is a lot of craters, signifying that it's capable of resurfacing itself and erasing them. That ability to resurface is uncommon in the solar system, and it's a sign that the moon is still partially warm.

The leading suspects

So we've gathered the facts of the crime scene investigation: This moon of Neptune is way bigger than it should be, has a completely wonky orbit, formed in a nontraditional way, and has a young, dynamic and active surface.

What's the story behind these oddities? The best answer is that Triton is no mere moon but instead a victim of an interplanetary kidnapping. Perhaps it is really a Kuiper Belt object more akin to Pluto or Eris than to the other moons of the solar system. Perhaps long ago, Triton fell into the vicinity of Neptune, got captured by the planet's gravity and was forced to spend the remaining billions of years in orbit in its unwelcome home. 

Either Triton just got unlucky and had the exact wrong orbit to land itself near Neptune, or it suffered some fateful collision with one of Neptune's original moons and, in the process, lost enough energy to remain in orbit. Another possibility is that Triton originally formed as a small binary system, much like many other Kuiper Belt objects, and a close encounter with Neptune sent Triton's twin flying away and left Triton itself trapped.

The capturing of Triton explains its strange orbit. If it didn't form organically in the Neptunian system, it would have no reason to share the orbital plane with the regular moons. And if it was captured early enough, it would have had to swim through the debris surrounding the still-forming Neptune, which would be enough to shape its orbit into a nearly perfect circle.

Triton remains warm because, like other Kuiper Belt objects, it has enough radioactive elements to release heat. That heat turns water, carbon dioxide and nitrogen ices into slush, keeping the surface young and active (much like Pluto has a giant, slushy, nitrogen-ice glacier field). Indeed, Triton may be so warm that it sports a liquid water ocean underneath its crust.

It's been over a generation since our last, brief encounter with Triton. Those images captured by Voyager 2 are the only ones we have. Unfortunately, no mission concepts to return to the Neptunian system have advanced past the proposal stage within NASA's funding structure. Given the agency's interest in the moons of Jupiter and Saturn (which, to be fair, also are homes to vast oceans of liquid water and are far, far closer than Neptune), there will likely be no follow-up mission in our lifetimes.

And so this crime scene will have to wait until the next generation of explorers to be fully investigated.

Astronomers have unexpectedly discovered the heaviest Neptune-like planet yet — one more than four times the mass of our solar system's Neptune — yet it remains a mystery how the world might have formed.

Between rocky planets about the mass of Earth and gas giants the mass of Jupiter, which holds more than 300 times our planet's mass, there are worlds the size of Neptune, which holds just about 17 times Earth's mass. Previous research has found that Neptune-size planets display a great deal of variety, ranging from icy worlds clad in thick atmospheres of hydrogen and helium, such as the Neptune we know and love, to very dense planets made of either substantial amounts of water or bundles of rock wrapped in thinner atmospheres, such as the exoplanets HD 95338 b, TOI-849 b and TOI-2196 b.

In the new study, astronomers investigated TOI-1853, an orange dwarf star about 80 percent of the sun's mass and diameter. TOI-1853 is located about 544 light-years from Earth in the Boötes constellation. Using NASA's Transiting Exoplanet Survey Satellite (TESS), they discovered an exoplanet around a star they dubbed TOI-1853 b. 

The newfound planet sits about 50 times closer to its star than Earth is to the sun, completing one orbit in just 30 hours instead of the 365 days it takes Earth. The planet's extreme proximity to its host star also makes it searing hot at about 2,200 degrees Fahrenheit (1,200 degrees Celsius).

Related: Why are there so few 'hot Neptune' exoplanets?

The newfound planet's diameter is about 3.46 times larger than Earth's, making it a bit smaller than Neptune, which is about 3.8 times wider than Earth. However, upon using Italy's Galileo National Telescope on the island of La Palma to measure the strength of TOI-1853 b's gravitational tug on its star, the scientists estimated this exoplanet's mass is about 73 times greater than Earth's. This means its mass is nearly equal to the mass of Saturn, which is about 95 times more massive than Earth.

All in all, TOI-1853 b is about six times denser than Neptune and nearly twice as dense as Earth. This makes it the densest Neptune-size planet known to date. 

"Our result is yet another proof that exoplanet research is constantly holding surprises," study lead author Luca Naponiello, an astrophysicist at the University of Rome, told Space.com. "We are still finding truly unique worlds decades after the first discovery. It's exciting to be part of this journey."

"The discovery of TOI-1853 b implies that large planets can have surprising amounts of heavy elements, much more than previously thought," Naponiello added. "Neptunian planets show an astonishing variety of density and compositions, but we didn't believe they could be so compact."

For the most part, exoplanets that orbit their stars as closely as TOI-1853 b does are either rocky planets with diameters less than twice Earth's or so-called hot Jupiters, gas giants sizing in at more than 10 times Earth's diameter. Mysteriously, scientists have only found a few hot Neptunes such as TOI-1853 b, a phenomenon dubbed the "hot Neptune desert." 

Conventional theories of planetary formation would suggest that TOI-1853 b should not exist, Naponiello said. But seeing as it clearly does, one possibility for the planet's formation is that it was born catastrophically from collisions "between large proto-planets such as super-Earths," he explained. "These huge impacts would have removed part of the original atmosphere and water, leaving mostly rock behind. If this is the case, TOI-1853b is likely to have a brother not too far away."

If astronomers do not end up finding a sibling of TOI-1853 b nearby, another possible explanation for the planet's origin is that it was a giant planet in a highly "eccentric" or oval-shaped orbit. This would have led to regular close encounters with its star, causing the world to lose much of its atmosphere and leaving behind a dense core. These stellar flybys could also have eventually made the planet's orbit less eccentric over time, explaining the trajectory's currently circular shape.

The researchers suggested TOI-1853 b may be mostly rocky and surrounded by a small envelope of hydrogen and helium that makes up 1 percent of the planet's mass – at most. Another possibility is that TOI-1853 b may be composed of about 50 percent rock and 50 percent water. If true, it would mean  its atmosphere may be rich in water vapor, Naponiello said, due to the planet's extreme heat

To really figure out TOI-1853 b's composition, scientists would have to analyze its atmosphere, Naponiello said. However, this will likely prove difficult even with NASA's extraordinarily powerful James Webb Space Telescope, since "we expect its atmosphere to be very thin, if existent at all," he said. 

"Understanding the nature of this planet will definitely be challenging."

The scientists detailed their findings online Aug. 30 in the journal Nature. 

In 2018, a dark spot appeared in Neptune’s atmosphere, giving astronomers a terrific opportunity to finally figure out what these sorts of shadowy apparitions are.

When Voyager 2 encountered Neptune in 1989, it saw that the blue ice giant’s northern hemisphere was adorned with a huge, dark anticyclonic vortex that was thousands of miles in diameter. Then, the blemish went away. 

Over the years since that Voyager 2 fly-by, the Hubble Space Telescope has observed similar dark spots come and go in both of Neptune’s hemispheres. At first glance, the blobs appear similar to Jupiter’s famous Great Red Spot (GRS), but the GRS has been steadily swirling for at least 350 years and is found high up in Jupiter’s atmosphere. By contrast, Neptune’s dark spots seem to only last for a few years and reside deeper into the ice giant’s atmosphere. 

So when Hubble observed another dark spot on Neptune in 2018, a team of astronomers, led by Patrick Irwin of the University of Oxford, sprang into action. 

Related: Neptune's clouds have vanished, and the sun may be to blame (video)

Neptune’s dark spots had never been observed by a ground-based telescope before, but with the European Southern Observatory’s Very Large Telescope (VLT) in Chile and its MUSE (Multi Unit Spectroscopic Explorer) instrument, Irwin’s team was able to detect the dark spot and spectroscopically measure it in 3D, revealing what was going on with this entity at different atmospheric depths. 

In doing so, they discovered some possible answers as to the dark spot’s mysterious origin. They published a paper on their findings on Thursday (Aug. 24) in the journal Nature Astronomy.

"Since the first discovery of a dark spot, I’ve always wondered what these short-lived and elusive dark features are," Irwin said in the statement.

Different wavelengths of light are able to probe different depths of Neptune’s atmosphere, dictated by things like atmospheric composition and how that composition reflects light. 

Using MUSE, Irwin’s team created a three-dimensional reflection spectrum, which showed how the planet's atmosphere at varying depths reflects sunlight. The dark spot, designated NDS-2018, appeared to fall within a region of the atmosphere that doesn’t reflect much of that light. These observations, made in 2019, thus rule out the possibility that the dark spot is simply a clearing in Neptune’s clouds providing a view of darker layers situated below. 

Instead, the team reasoned, something in the atmosphere's aerosol haze must be making this spot dark. MUSE’s observations showed the dark spot likely lies at a depth where the pressure is about 5 bar, which is the pressure layer where hydrogen sulfide is able to condense out into ice crystals. 

Irwin’s team has identified two explanations for why this is the case. 

Since hydrogen sulfide is a light-sensitive gas, one possibility is the dark spot is caused by an upwelling at the center of the vortex that is bringing up hydrogen sulfide from deeper inside the planet. When the hydrogen sulfide reaches an altitude where it can react with solar ultraviolet light, the reaction perhaps causes the atmosphere to darken. The other possibility is the hydrogen sulfide has condensed around darker particles, and local heating caused by anticyclonic conditions causes the hydrogen sulfide to sublimate, revealing those darker particles beneath.

The VLT’s observations also offered up an additional surprise: a small bright spot, designated DBS-2019, on the south-west edge of the dark spot.

"In the process [of observing the dark spot] we discovered a rare, deep, bright cloud type that had never been identified before, even from space," Michael Wong, a planetary scientist from the University of California, Berkeley, and a member of Irwin’s team, said in the statement.

Bright spots of one kind or another have been seen regularly, even from Earth, in the atmosphere of Neptune. Voyager 2, for instance, discovered bright clouds of methane that were nicknamed "scooters" because of how they moved around the planet so quickly. However, DBS-2019 seems to be at a much lower depth than the scooters, sharing an altitude with the dark spot itself. It may actually be that the bright spot is the result of convection at the edge of the dark spot’s vortex, perhaps pumping brighter material up from the murky, frozen depths below.

Alas, the observations of both the dark and bright spots were fleeting; they disappeared in 2022. 

Currently, Neptune’s atmosphere appears spotless, its cloud coverage having vanished. The disappearance of the clouds may be related to the sun’s solar cycle of activity and a drop in photoionizing ultraviolet light during solar minimum in 2019. This process may have a role to play in the formation of Neptune’s clouds; take it away and the clouds begin to disappear. If this hypothesis is correct, we should expect to see a more active Neptunian atmosphere after solar maximum in 2024-2025.

Now astronomers must wait for a new dark spot to arise to continue their studies from Earth, at least until a space mission sets sail once again to follow in Voyager 2’s footsteps and visit the last planet of the solar system.

A paper on the research was published on Aug. 24 in the journal Nature Astronomy.