Scientists argue that limiting the search for life strictly to a star’s traditional habitable zone is too restrictive. That is in light of new climate models, and observations that suggest that liquid water—and therefore potentially life-supporting conditions—can exist well beyond these classical boundaries.

The habitable zone is defined as the region around a star where a planet could maintain liquid water on its surface without turning to ice or gas.

The fact that this water is neither too hot nor too cool has also led to the habitable zone being nicknamed the Goldilocks zone. In our solar system, this zone begins at around the orbit of Venus, the second planet from the sun, past the orbit of Earth, and out to roughly the orbit of Mars.

“[However,] this concept is rooted in the principle that liquid water is necessary for biochemical processes essential to life,” writes a team of researchers in a paper published on Jan. 12 in the Astrophysical Journal. “Although other factors, such as chemical energy sources, elemental diversity, and long-term environmental stability, are also important.”

Using an analytical climate model, the scientists have shown that tidally locked planets—which always show the same face to their star—can maintain liquid water on their permanent night side, even when orbiting much closer to their star than the traditional inner edge of the habitable zone.

“Initially, this configuration raised concerns about extreme temperature gradients and atmospheric collapse on the dark side,” the team writes. “However, 3D climate models have demonstrated that given a sufficient atmospheric pressure, or the presence of an ocean, efficient heat redistribution between the day and night sides can stabilize temperatures and maintain habitable conditions.”

This suggests that for tidally locked planets, common around small M-class and K-class stars, the inner edge of the habitable zone may actually lie closer to the star than in the case of rapidly rotating planets. This extended habitable zone could help explain recent observations made by the James Webb Space Telescope (JWST) of water vapor and other volatile gases in the atmospheres of warm super-Earths closely orbiting their M dwarf stars.

“Signs of water vapor and volatiles have been detected in JWST transmission spectra of small exoplanets,” they write. “Some of these exoplanets are closer to their M dwarf hosts than the inner [habitable zone] boundary […] Water detection on such planets is intriguing, since one would doubt the survival of atmosphere and water under such harsh conditions.”

These findings suggest that such planets can retain significant amounts of water despite lying outside the classical habitable zones—and this doesn’t apply to planets orbiting their stars too closely. The team argues that the habitable zone should be extended in both directions. Even on cold planets far from their stars, liquid water can exist beneath thick ice layers, as subglacial lakes or through internal heating. Similar environments on Earth, such as Antarctica’s subglacial lakes, support microbial life, demonstrating that surface liquid water is not the only possible habitat.

Through a reassessment of habitable zone models and boundary calculations, this study expands the range of worlds considered potentially habitable, revealing new targets in the search for life.

This article was originally published at The Conversation. The publication contributed the article to Space.com's Expert Voices: Op-Ed & Insights.

When astronomers search for planets that could host liquid water on their surface, they start by looking at a star's habitable zone. Water is a key ingredient for life, and on a planet too close to its star, water on its surface may "boil"; too far, and it could freeze. This zone marks the region in between.

But being in this sweet spot doesn't automatically mean a planet is hospitable to life. Other factors, like whether a planet is geologically active or has processes that regulate gases in its atmosphere, play a role.

The habitable zone provides a useful guide to search for signs of life on exoplanets – planets outside our solar system orbiting other stars. But what's in these planets' atmospheres holds the next clue about whether liquid water — and possibly life — exists beyond Earth.

On Earth, the greenhouse effect, caused by gases like carbon dioxide and water vapor, keeps the planet warm enough for liquid water and life as we know it. Without an atmosphere, Earth's surface temperature would average around zero degrees Fahrenheit (minus 18 degrees Celsius), far below the freezing point of water.

The boundaries of the habitable zone are defined by how much of a "greenhouse effect" is necessary to maintain the surface temperatures that allow for liquid water to persist. It's a balance between sunlight and atmospheric warming.

Many planetary scientists, including me, are seeking to understand if the processes responsible for regulating Earth's climate are operating on other habitable zone worlds. We use what we know about Earth’s geology and climate to predict how these processes might appear elsewhere, which is where my geoscience expertise comes in.

Why the habitable zone?

The habitable zone is a simple and powerful idea, and for good reason. It provides a starting point, directing astronomers to where they might expect to find planets with liquid water, without needing to know every detail about the planet's atmosphere or history.

Its definition is partially informed by what scientists know about Earth's rocky neighbors. Mars, which lies just outside the outer edge of the habitable zone, shows clear evidence of ancient rivers and lakes where liquid water once flowed.

Similarly, Venus is currently too close to the sun to be within the habitable zone. Yet, some geochemical evidence and modeling studies suggest Venus may have had water in its past, though how much and for how long remains uncertain.

These examples show that while the habitable zone is not a perfect predictor of habitability, it provides a useful starting point.

Planetary processes can inform habitability

What the habitable zone doesn't do is determine whether a planet can sustain habitable conditions over long periods of time. On Earth, a stable climate allowed life to emerge and persist. Liquid water could remain on the surface, giving slow chemical reactions enough time to build the molecules of life and let early ecosystems develop resilience to change, which reinforced habitability.

Life emerged on Earth, but continued to reshape the environments it evolved in, making them more conducive to life.

This stability likely unfolded over hundreds of millions of years, as the planets surface, oceans and atmosphere worked together as part of a slow but powerful system to regulate Earth’s temperature.

A key part of this system is how Earth recycles inorganic carbon between the atmosphere, surface and oceans over the course of millions of years. Inorganic carbon refers to carbon bound in atmospheric gases, dissolved in seawater or locked in minerals, rather than biological material. This part of the carbon cycle acts like a natural thermostat. When volcanoes release carbon dioxide into the atmosphere, the carbon dioxide molecules trap heat and warm the planet. As temperatures rise, rain and weathering draw carbon out of the air and store it in rocks and oceans.

If the planet cools, this process slows down, allowing carbon dioxide, a warming greenhouse gas, to build up in the atmosphere again. This part of the carbon cycle has helped Earth recover from past ice ages and avoid runaway warming.

Even as the sun has gradually brightened, this cycle has contributed to keeping temperatures on Earth within a range where liquid water and life can persist for long spans of time.

Now, scientists are asking whether similar geological processes might operate on other planets, and if so, how they might detect them. For example, if researchers could observe enough rocky planets in their stars' habitable zones, they could look for a pattern connecting the amount of sunlight a planet receives and how much carbon dioxide is in its atmosphere. Finding such a pattern may hint that the same kind of carbon-cycling process could be operating elsewhere.

The mix of gases in a planet's atmosphere is shaped by whats happening on or below its surface. One study shows that measuring atmospheric carbon dioxide in a number of rocky planets could reveal whether their surfaces are broken into a number of moving plates, like Earth's, or if their crusts are more rigid. On Earth, these shifting plates drive volcanism and rock weathering, which are key to carbon cycling.

Keeping an eye on distant atmospheres

The next step will be toward gaining a population-level perspective of planets in their stars' habitable zones. By analyzing atmospheric data from many rocky planets, researchers can look for trends that reveal the influence of underlying planetary processes, such as the carbon cycle.

Scientists could then compare these patterns with a planet's position in the habitable zone. Doing so would allow them to test whether the zone accurately predicts where habitable conditions are possible, or whether some planets maintain conditions suitable for liquid water beyond the zone’s edges.

This kind of approach is especially important given the diversity of exoplanets. Many exoplanets fall into categories that don't exist in our solar system — such as super Earths and mini Neptunes. Others orbit stars smaller and cooler than the sun.

The datasets needed to explore and understand this diversity are just on the horizon. NASA's upcoming Habitable Worlds Observatory will be the first space telescope designed specifically to search for signs of habitability and life on planets orbiting other stars. It will directly image Earth-sized planets around sun-like stars to study their atmospheres in detail.

Instruments on the observatory will analyze starlight passing through these atmospheres to detect gases like carbon dioxide, methane, water vapor and oxygen. As starlight filters through a planet's atmosphere, different molecules absorb specific wavelengths of light, leaving behind a chemical fingerprint that reveals which gases are present. These compounds offer insight into the processes shaping these worlds.

The Habitable Worlds Observatory is under active scientific and engineering development, with a potential launch targeted for the 2040s. Combined with today's telescopes, which are increasingly capable of observing atmospheres of Earth-sized worlds, scientists may soon be able to determine whether the same planetary processes that regulate Earth’s climate are common throughout the galaxy, or uniquely our own.

Small icy moons in the outer reaches of our solar system may hide boiling oceans underneath their surfaces, a new study finds.

Previous research found that some of the icy moons in the outer solar system, such as Saturn's moon Enceladus, are not frozen solid. Instead, they may host oceans between their ice shells and rocky cores. Because on Earth, there is virtually life wherever there is water, this has raised the hope that such hidden oceans may be the best sites in our solar system to look for extraterrestrial life.

To shed light on the buried oceans within these icy moons, geophysicist Maxwell Rudolph at the University of California, Davis, previously examined the forces that might result from changes in the thickness of the icy shells of these moons over the course of hundreds of millions of years.

"We were especially interested in whether the stresses could lead to the formation of cracks that connect the surface to the subsurface ocean, allowing the eruption of liquid water from a potentially habitable ocean to space," Rudolph told Space.com.

In prior work, Rudolph and his colleagues focused on what happens to these moons when their ice shells get thicker. As ice takes up a greater volume than a similar mass of liquid water, freezing places pressure on ice shells, generating features such as the "tiger stripes" seen on Enceladus.

In the new study, the researchers explored what happens when the icy shells of these moons become thinner due to melting from the bottom. For instance, previous research discovered a wobble in the orbit of Saturn's moon Mimas was potentially due to an ocean under its icy crust that likely arose in the past 10 million years, given how its surface still retains many ancient features, such as craters. This ocean likely resulted when Mimas's shell melted due to interactions with other Saturnian moons.

The scientists discovered that if these icy shells thin, the pressure they place on the oceans drops. On the smallest icy moons, such as Mimas and Enceladus or Uranus's Miranda, the pressure could lower enough to reach a so-called "triple point" — a specific combination of temperature and pressure in which ice, liquid water and water vapor can all co-exist. This can lead the layers of the oceans closest to their icy shells to boil after the icy shells thin by about three to nine miles (five to 15 kilometers).

"This is the kind of boiling that happens at low temperatures, not the kind of boiling that occurs in kitchens when you heat water up to past 100 degrees C [212 degrees F]," Rudolph said. "It's instead boiling very close to zero degrees C [32 degrees F]. So for any potential life forms below that boiling area, life could go on as usual."

In contrast, on larger ice moons more than 370 miles (600 km) wide, such as Uranus's Titania, the drop in pressure from melting ice would instead cause the ice shell to crack before the triple point for water is reached, the team calculated. The researchers suggest that features of Titania's geology, such as wrinkle ridges, might have resulted from a period of ice shell thinning followed by re-thickening.

The gases from boiling might have a number of effects, such as the formation of clathrates — complex icy structures that entrap gas molecules. "Future work will address these processes in detail to understand what happens to gas once it has been released from an ocean and what kinds of surface features we would expect to form in association with these processes," Rudolph said.

The scientists detailed their findings online Nov. 24 in the journal Nature Astronomy.

This article was originally published at The Conversation. The publication contributed the article to Space.com's Expert Voices: Op-Ed & Insights.

As humans began to explore outer space in the latter half of the 20th century, radio waves proved a powerful tool. Scientists could send out radio waves to communicate with satellites, rockets and other spacecraft, and use radio telescopes to take in radio waves emitted by objects throughout the universe.

However, sometimes radio telescopes would pick up the artificial radio signals from telecommunications. This interference threatened sensitive astronomy observations, causing inaccurate data and even damaging equipment. While this interference frustrated scientists, it also sparked an idea.

During the Cold War, a new field emerged at the intersection of radio astronomy and radio communications. It put forward the idea that astronomers could search for radio communications from possibly existing extraterrestrial civilizations. Astronomy usually dealt with observing the universe’s natural phenomena. But this new field made the detection of technologically, or artificially produced radio waves, the object of a natural science.

This field has continued today and is now called the search for extraterrestrial intelligence, or SETI. SETI encompasses all that scientists do to search for intelligent life beyond Earth. It includes one of the original uses of radio telescopes: to study signals from across the galaxy in hopes of detecting intelligent messages.

When the idea behind SETI was first proposed and pursued in the 1960s, only two countries, the U.S. and the USSR, had the technical capability for it. As the only space powers at the time, they were the key actors affected by radio frequency interference.

As a historian of science, I've worked to make sense of what happened throughout the history of Soviet SETI during the space race by analyzing a range of primary sources. SETI captured the scientific imagination of many prominent Soviet astronomers in the 1960s and early 1970s.

Astronomers have not yet confirmed any detection of radio signals – or any other kinds of signs – from extraterrestrial civilizations. But many scientists are still searching, even as their bold ideas run into obstacles. Some evidence suggests humans might be the only intelligent life in the universe.

Soviet SETI: The golden age of radio astronomy

SETI is intertwined with the profound changes brought by radio astronomy. Up until the second part of the 20th century, scientists could see astronomical objects and phenomena only in optical or visible light. Optical light is the same kind of light that the human eye is sensitive to.

After World War II, scientists figured out that they could peacefully use radar antennas, developed for use in that war, to detect radio signals coming from objects out in the universe. Deciphering these signals allowed researchers to study astronomical objects in the universe. They learned, for example, about the most abundant element: hydrogen.

In the former Soviet Union, the prominent radio astronomy pioneer Iosif Samuilovich Shklovsky played a key role in detecting radio signals from hydrogen.

Scientists knew that every chemical element would absorb certain wavelengths of light and reflect others, and the light signals that an object absorbed or reflected could tell astronomers what element it was. Most hydrogen could not be observed directly in optical light, so astronomers didn’t spot it out in space until they started looking beyond the visible light spectrum.

Shklovsky figured out how to detect hydrogen with radio waves, which helped astronomers map the distribution and motion of hydrogen gas in and between galaxies.

Historians generally consider the year 1960 the start of the golden age of radio astronomy. After the detection of hydrogen, astronomers discovered previously unknown types of stars, such as pulsars and quasars. These phenomena offered scientists new insights into the nature of astrophysical phenomena and fundamental physics.

Shklovsky later grew fascinated with the possibility of using radio waves to contact other intelligent beings in the universe. In 1960, he published an article on this topic in one of the country’s most prestigious scientific journals.

Shklovsky's article soon expanded into a widely popular book called "Universe, Life, Intelligence," published in 1962. That same year, the USSR's Academy of Sciences sent its first radio message in the direction of Venus from a radar in Crimea.

The experiment involved bouncing radio signals off the surface of Venus to transmit the following words using Morse code: Lenin, USSR and mir, which in Russian means both world and peace. Even though statistically increasing radio interference risk, this message was mainly symbolic. The Soviet Union wanted to depict its technological might and wasn't expecting to communicate with extraterrestrials. Soviet SETI was thus not yet a real pursuit.

Starting an organized search

Shklovsky and the majority of other radio astronomers pursuing the search for extraterrestrial intelligence were all located in central Russia at the time. The USSR Academy of Sciences was also located there. But this group needed more formal measures to move their search from a few initiatives into a coordinated effort.

Due to concerns over unwanted public attention, the scientists organized a conference far from Moscow, at the Byurakan Astrophysical Observatory in the Soviet Republic of Armenia, in 1964. At this conference, researchers formed a group specifically dedicated to studying artificial radio signals from space. With this group, SETI became a top-down, state-led activity.

With this validation, scientists could now theoretically look for artificial signals, potentially from an alien origin. However, any discussions about artificial radio signals were subject to strict government surveillance, given the fact that military satellites depended on them, too.

Soviet scientists faced several obstacles. For example, their own government's secrecy made coordination difficult. The Cold War also set limits on developing SETI internationally. However, they had a green light to search and study peculiar signals they suspected had artificial origin.

International collaboration

Efforts to collaborate internationally on artificial signals culminated in 1971 with a symposium, again at Byurakan. There, about 50 scientists – the majority from the U.S. and the USSR, but also some from Czechoslovakia, Hungary, the U.K. and Canada – agreed to disagree on how to best conduct SETI.

Some in attendance compared this gathering to Noah's Ark, because an almost equal number of prominent scientists from East and West of the Iron Curtain managed to meet that year. And the gathering took place in Armenia at the foot of Mount Ararat, located in neighboring Turkey. This mountain is where archaeologists believe Noah's Ark may have beached.

After almost a week of discussion at Byurakan, the two geopolitical blocks designated an official SETI group. That group still exists today, and it still connects researchers all around the world who conduct SETI research. Given the secrecy around radio signals in space, this international SETI group marked a momentous diplomatic achievement at the height of the Cold War.

SETI started in the Soviet Union with a few strong Moscow-based initiatives. It continued through group events in Armenia – from the first state-level Soviet conference to the international one.

SETI is the first and only domain of astronomy to study artificial radio signals themselves. It indirectly addressed radio frequency interference during a time when these frequencies were highly unregulated.

Stakeholder countries eventually addressed their radio frequency interference issues with international agreements on radio frequency usage and allocation. An international committee approved a feasible and comprehensive radio frequency allocation plan for the first time in the 1970s. This plan has been revised and renewed ever since. Today, space scientists and astronomers use an internationally agreed upon plan to minimize this interference.

Remarkably, SETI began even before this allocation plan. SETI continues its rich legacy today by continuing to search for signals – and along the way discovering new astrophysical objects and phenomena.

Read the original article here.

The search for life beyond Earth is one of the most profound quests in human history. It began not in laboratories, but in the minds of ancient stargazers who imagined other worlds teeming with beings like — or unlike — us.

Over centuries, this curiosity evolved into a scientific pursuit, blending astronomy, biology, chemistry, and philosophy into a single, thrilling endeavor: to find life elsewhere in the cosmos.

From Galileo's telescope to the James Webb Space Telescope, each technological leap has brought us closer to answering that age-old question. We've sent probes to Mars, listened for alien signals through SETI, and discovered thousands of exoplanets orbiting distant stars. Along the way, we've refined our understanding of what life is, how it might arise, and where it could thrive — even in the most extreme environments.

This quiz explores the milestones, theories, and missions that have defined the search for extraterrestrial life.

Whether you're a space science enthusiast or just curious about the universe's biggest mystery, this challenge will stretch your mind across time and space.

Try it out below and see how well you score!

A super-Earth exoplanet in the habitable zone of its star has been detected less than 20 light-years away, putting it near the top of the list for best places to look for life beyond our solar system.

The planet, known as GJ 251c, orbits a red dwarf star 18.2 light-years away in the constellation of Gemini, the Twins. The planet's mass is four times greater than that of Earth, making it a 'super-Earth' — a rocky planet larger and more massive than our own.

"While we can't yet confirm the presence of an atmosphere or life on GJ 251c, the planet represents a promising target for future exploration," said Suvrath Mahadevan, who is a professor of astronomy at Penn State University, said in a statement.

In the habitable zone, sometimes referred to as the Goldilocks zone, conditions are just right for liquid water to exist on the surface of a planet with an appropriate atmosphere.

GJ 251c was discovered thanks to observations spanning over 20 years, during which scientists looked for a slight wobble of the world's parent star incurred by the planet's gravity. As the star wobbles ever so slightly toward and away from us, we see a Doppler shift in its radial velocity that can be measured with a spectrograph.

One other planet is known to exist in the system, GJ 251b, which was discovered in 2020 and orbits its star every 14 days at a distance of 7.6 million miles (12.2 million kilometers). Using archive data from telescopes worldwide, a team of astronomers, including Mahadevan, was able to refine the accuracy of the radial velocity measurements for planet GJ 251b

The team then combined this refined data with brand new, high-precision observations from the Habitable-Zone Planet Finder (HPF), which is a near-infrared spectrograph on the Hobby-Eberly Telescope at McDonald Observatory in Texas. This revealed a second planetary signal belonging to a four-Earth-mass world orbiting the star every 54 days. That was then confirmed by measurements with the NEID spectrograph on the 3.5-meter WIYN telescope at Kitt Peak National Observatory in Arizona.

Though it may sound straightforward, in reality, the challenge of detecting the planet was formidable.

Stars are constantly roiling and churning as convective bubbles burst through to their visible surfaces and prominences splutter into space. This creates a noisy background of what's called asteroseismic activity that manifests as Doppler shifted lines in the star's spectrum. Picking out the Doppler shifted radial velocity signals from this noise is tricky, requiring a great deal of modeling what a planetary signal should look like.

"This is a hard game in terms of trying to beat down stellar activity as well as measuring its subtle signals, teasing out slight signals from what is essentially this frothing, magnetospheric cauldron of a star-surface," said Mahadevan.

Now that we know about the planet, astronomers can plan future observations.

GJ 251c is probably a little bit too far away from its star for the James Webb Space Telescope (JWST) to search for signs of an atmosphere around it. The next generation of 30-meter-class telescopes might be able to detect the planet's atmosphere via a method of searching for light reflected off its surface or atmosphere, but it will likely require the Habitable Worlds Observatory, which is a planned giant space telescope that is hoped to launch in the 2040s, to fully characterize GJ 251c.

"We are at the cutting edge of technology and analysis with this system," said Corey Beard of the University of California, Irvine, who participated in the research. "We need the next generation of telescopes to directly image this candidate."

Although GJ 251c is described by Mahadevan as being "one of the best candidates in the search for an atmospheric signature of life," referencing how we will search for biosignatures in the planet's atmosphere, there remains an elephant in the room: its star.

At 36% of the mass of our sun, the star GJ 251 is a red dwarf. Astronomers have now found numerous rocky planets in the habitable zone of red dwarfs, including Proxima Centauri b, TRAPPIST-1e and f, and Teegarden's Star b. However, red dwarfs are notorious for having violent tempers that bely their diminutive stature, releasing regular powerful flares that can over time strip a planet of its atmosphere. For example, the JWST's observations of the inner three planets of TRAPPIST-1 find no evidence for an atmosphere, while its observations of the fourth planet, e, are so far inconclusive. Some astronomers are now growing skeptical that Earth-like worlds can thrive around red dwarfs.

What GJ 251c has going for it is that it is slightly farther away from its star than habitable zone planets found around other red dwarfs are. This is thanks to its star being a little more massive than those other stars and therefore hotter, pushing the habitable zone farther out. It is possible that GJ 251c is far enough away from its star to have avoided the worst of its temper tantrums, and, if armed with a thick atmosphere and strong planetary magnetic field, it could have resisted the star's stellar wind from stripping its atmosphere away.

However, at present, this remains guesswork. "We made an exciting discovery," said Mahadevan, "But there’s still much more to learn about this planet."

The findings were reported on Oct. 23 in The Astronomical Journal.

Enceladus, one of Saturn's small icy moons, spans just 300 miles (500 kilometers) — yet despite its modest size, it has become a star in the search for life beyond Earth. From cracks near its south pole, the moon blasts towering geysers of water vapor, ice and organic molecules into space, which are tantalizing hints of a hidden ocean that could, in theory, be habitable.

But new research presented this week at a planetary science conference in Finland shows that many of the organic molecules detected in these plumes could also form right on the moon's surface, driven by relentless radiation from Saturn's magnetic field. The results cast doubt on whether the plumes truly carry whispers of alien life, or merely echoes of lifeless chemistry on the frozen shell.

"Although this doesn't rule out the possibility that Enceladus' ocean may be habitable, it does mean we need to be cautious in making that assumption just because of the composition of the plumes," study lead Grace Richards of Italy's National Institute for Astrophysics said in a statement.

For their experiment, Richards and her colleagues recreated conditions on Enceladus in miniature inside a specialized laboratory in Hungary. Using an ice chamber, the team froze mixtures of water, carbon dioxide, methane and ammonia to a bone-chilling –420 degrees Fahrenheit (-253 degrees Celsius), mimicking frigid conditions near the moon's surface. The ices were then bombarded with high-energy "water-group ions," the same charged particles trapped around Saturn that constantly irradiate Enceladus.

To monitor the chemical changes induced by radiation, the researchers used infrared spectroscopy to observe the molecular "fingerprints," or spectra, of the ices. As radiation interacted with the samples, the spectra shifted, signaling the formation of new molecules.

Each of the five experiments produced carbon monoxide, cyanate, and ammonium — compounds that were detected in Enceladus' plumes by NASA's Cassini spacecraft in 2005. When the samples were gently warmed, more complex organics appeared, including carbamic acid, ammonium carbamate and potential amino acid precursors including methanol and ethanol, as well as molecules like acetylene, acetaldehyde and formamide, which are building blocks that could contribute to the chemistry of life.

"Although many of these products have not previously been detected on Enceladus' surface, some have been detected in Enceladus' plumes," Richards and her colleagues wrote in the paper. This leads to "questions about whether plume material is formed within the radiation-rich space environment or whether it originates in the subsurface ocean."

Crucially, the timescales necessary for radiation to drive these chemical reactions are comparable to how long ice remains exposed on Enceladus' surface or in its plumes, so distinguishing ocean-sourced organics from surface-born ones may be difficult, the study notes.

"It is likely that the composition of the subsurface ocean may not be accurately reflected by the composition of the emergent plume, or by material deposited on the surface immediately adjacent to the plume," the paper reads.

For astrobiologists, the results are both sobering and exciting. On one hand, they complicate the story that organics in the plumes are definitive signs of a life-friendly ocean. On the other, they highlight that rich, potentially life-relevant chemistry can thrive even in extreme, radiation-battered environments, thereby expanding the ways scientists think about where prebiotic molecules might form and why Enceladus remains a prime target for exploration.

NASA's Cassini mission, which ended in 2017 with a dramatic plunge into Saturn's atmosphere, gave humanity its first and only direct "taste" of Enceladus' geysers. But instruments onboard the spacecraft weren't designed to distinguish between molecules forged in the moon's presumably deep ocean and those cooked up in the icy shell.

These answers could come in the coming decades with future missions. One concept under consideration as part of the European Space Agency's Voyage 2050 program envisions a dedicated probe that could land on the surface and collect material ejected from the moon's hidden ocean. NASA has also previously studied an "Orbilander" concept designed to sample Enceladus' plumes from orbit.

Meanwhile, China is exploring a multi-part mission architecture that would include an orbiter, a lander and a deep-drilling robot that would attempt to reach the subsurface ocean to search for potential biosignatures.

This research is described in a paper published in the October 15 edition of the journal Planetary & Space Science.

For researchers seeking answers to the question of whether we are alone in the universe, one event nearly half a century ago lingers even today — the so-called "Wow! Signal" detected back in 1977.

That strong, baffling radio episode was captured by Ohio State University's Search for Extraterrestrial Intelligence (SETI) project, also known as the "Big Ear." It has been viewed by some as one of the oddest radio transmissions from afar ever detected, also cited as compelling evidence for extraterrestrial intelligence.

The outburst was a strong narrowband radio signal received on Aug. 15, 1977 by Ohio State University's Big Ear radio telescope. Astronomer Jerry Ehman discovered the anomaly a few days later while reviewing the recorded data — writing on a computer printout "Wow!"

Unpublished observations, archival data

Jump ahead to today. Researchers from the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo are proposing a less extraterrestrial explanation. On-going assessments, led by Abel Méndez, are being pursued under the "Arecibo Wow!" Project, an initiative established to analyze unexplained radio signals from space in the search for extraterrestrial intelligence.

"We look at old archives with modern science methodologies. It's a bit like space archaeology," said Wow! Signal researcher Hector Socas Navarro, director of the European Solar Telescope Foundation and a staff scientist at the Instituto de Astrofísica de Canarias.

New clues

Researchers from that project have re-analyzed decades of previously unpublished observations and archival data from the Ohio State University SETI program. The result is the most precise characterization yet of the perplexing signal from afar and revealing new clues to its origin.

"Our newly derived properties may help finally pinpoint the source of the Wow! Signal," Méndez told Space.com. While the group's just-published paper focused on revising the known properties of the Wow! Signal, "we also discovered new properties that we look forward to sharing in an upcoming paper," he advised.

"We aim to archive and share all data from the Big Ear telescope by 2027, marking the 50th anniversary of the Wow! Signal," Méndez added.

Natural astrophysical origin?

In a recent posting on the Arecibo Wow! Project's website, Méndez underscored the team's output to date.

The research findings spotlight the prospect that the Wow! Signal was created by a natural astrophysical origin, Méndez and colleagues report. Also the work does make radio interference "an increasingly unlikely explanation," they add.

"This study doesn't close the case," Méndez points out. "It reopens it, but now with a much sharper map in hand."

Méndez and fellow researchers hypothesize that the Wow! Signal was caused by a sudden brightening of the hydrogen line in interstellar clouds, triggered by a powerful transient radiation source such as a magnetar flare or soft gamma repeater (SGR).

"Our results don't solve the mystery of the Wow! Signal," Méndez states. "But they give us the clearest picture yet of what it was and where it came from. This new precision allows us to target future observations more effectively than ever before."

Citizen science — join the search

The continuing research into the Wow! Signal has spurred the creation of the Wow@Home project. This initiative is a low-cost way that others can now actively search for similar signals and other rare cosmic events, including potential technosignatures of other star folk — in real time.

Wow@Home project officials found that the Wow! Signal was strong enough that even small telescopes could potentially detect similar signals.

Indeed, a network of small radio telescopes offers several distinct advantages compared to large professional observatories.

Low-cost systems can operate autonomously around the clock, "making them ideal for continuous monitoring of transient events or long-duration signals that professional telescopes cannot commit to observing full-time," Méndez and colleagues suggest.

Wow-like signal strength

Wow@Home is a cost-effective, engaging, and accessible, ideal for education, citizen science, and expanding participation in radio astronomy.

"A complete setup costs around $500, including a dedicated computer, but we are not selling these systems. Instead, we will provide recommendations for the necessary parts and offer free software to power the telescope and connect it to the Wow@Home network to search for transient events," a Wow@Home posting explains.

The software is built on analysis methods the project's developing to detect Wow-like signals in the archive data of professional observatories, as part of their Arecibo Wow! undertaking.

For more information on Wow@Home, visit the project's website. The group's recent research report is available on arXiv.org and will be submitted to the Astrophysical Journal.

One of the four nucleobases of RNA has been discovered in samples retrieved from the asteroid Ryugu, providing the strongest evidence yet that the organic building blocks for life on Earth came from space.

In December 2020, Hayabusa2, a mission of the Japan Aerospace Exploration Agency (JAXA), delivered by capsule and parachute 0.19 ounces (5.4 grams) of asteroid material from Ryugu to expectantly waiting scientists on Earth. 

Analysis of these samples have shown them to be the most primitive material ever studied in a laboratory, dating back to before the planets formed 4.5 billion years ago. The isotopic composition of gases contained in those materials revealed that Ryugu formed much farther out from the sun, close to the orbit of Neptune, compared to its present location near Earth.

Related: Facts about asteroid Ryugu, the twirling space rock visited by Hayabusa2

Now, new research has culminated in the discovery of concentrations of uracil in the samples. Uracil is a nucleobase, one of four (along with adenine, guanine and cytosine) that make up ribonucleic acid, or RNA, which is used by cells to communicate genetic information. The concentration of uracil was greater (32 parts per billion) in the sample taken from deep below Ryugu's surface than in the shallower sample (11 parts per billion), indicating that cosmic rays and ultraviolet light from the sun may have degraded the amount of uracil nearer the surface.

Ryugu's composition indicates that it belongs to the same family of asteroids as a type of carbon-rich meteorite known as CI chondrites, of which only five have been recovered on Earth so far. Previously, three nucleobases had been detected in the CI meteorites, while all five nucleobases (the four for RNA, plus thymine, which replaces uracil in DNA) have been found in a different type of meteorite, CM chondrites. 

However, the lead researcher of the new study, Yasuhiro Oba of Hokkaido University in Japan, told Space.com that "one could not completely exclude the possibility that they were terrestrial contaminants," referring to the meteorite nucleobases.

But the discovery of uracil in two samples from Ryugu confirms that nucleobases are indeed present in pristine asteroidal material dating back to the earliest days of the solar system.

"The discovery of biologically relevant molecules such as nucleobases in the most pristine extraterrestrial materials without any terrestrial contaminations guarantees that they are really present in extraterrestrial environments," said Oba.

The discovery is incredibly important for astrobiologists. It is a step along the road to understanding the origin of life, and whether the processes that led to the appearance of life on Earth can be repeated elsewhere in the universe.

When asked whether it means that the building blocks of RNA and DNA came to Earth from space, Oba said "Absolutely, yes — there is no doubt that extraterrestrial materials were falling to the early Earth."

Related: Asteroid Ryugu is rich in organic molecules that can be building blocks of life

So it seems that RNA and DNA initially formed on Earth from nucleobases brought here by asteroid impacts and meteorite falls long ago. However, there is another possibility, which is that RNA and DNA molecules may have formed in space themselves before being delivered to the young Earth. The question mark here is that biochemists currently do not fully understand what conditions are required for RNA and DNA to form on asteroids.

Another possibility is that uracil and other nucleobases may pre-date the formation of our solar system. They may have been formed in deep space via photochemical reactions — the action of ultraviolet light on organic molecules — on ices in interstellar clouds from which the solar system, and other planetary systems including their asteroids, formed. The basic stuff of life as we know it on Earth could potentially be spread across the galaxy. If nucleobases are common in the universe, then any hypothetical alien life may also possibly use RNA and DNA.

One clue could be in the additional discovery of two types of organic compound called an imidazole in the Ryugu samples. An imidazole is part of the molecular structure of uracil. One type of imidazole called 4-ICA was found with a similar concentration as the uracil in the samples, whereas 2-ICA had a lower concentration. The 4-ICA imidazole can form during chemical reactions involving poisonous hydrogen cyanide, which is a common icy ingredient in interstellar clouds. 

Oba said that the Ryugu samples have now been exhausted, and future searches for more nucleobases in asteroidal material will have to wait for NASA's OSIRIS-REx mission to bring at least 60 grams worth of samples from asteroid 101955 Bennu back to Earth in September 2023.

"Since we will have larger sample amounts than Ryugu, we expect to find [a] more diverse suite of nucleobases and other related molecules in the Bennu samples," said Oba.

The new study was published online Tuesday (March 21) in the journal Nature Communications.

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Scientists have long debated the possibility of that the microbial seeds of life did not originate on Earth, but were perhaps delivered here from an alien source, encased in comets or meteorites from Mars.

But to get here, simple life forms would have had to endure a litany of harsh cosmic conditions, including ejection into space, freezing temperatures, fiery re-entry and impact.

Now, a team of researchers found new evidence that a terrestrial algae just might be able to survive the physical strains of space travel, a discovery that may support the possibility that panspermia, the concept that microbial life is everywhere in the universe and can spread between planets, could potentially occur. [5 Bold Claims of Alien Life]

The scientists, who presented their findings at the European Planetary Science Congress in London on Sept. 12, focused on a type of single-celled ocean-dwelling algae called Nannochloropsis oculata.

Using a two-stage light gas gun, the researchers shot frozen pellets of the algae into water at extremely high speeds and then analyzed their sample to see if any of the organisms came out alive.

"As you might expect, increasing the speed of impact does increase the proportion of algae that die, but even at 6.93 kilometers per second (4.31 miles per second), a small proportion survived," study researcher Dina Pasini, of the University of Kent explained in a statement. "This sort of impact velocity would be what you would expect if a meteorite hit a planet similar to the Earth."

The researchers say their findings suggest that alien life and panspermia may not be impossible, though the theory still remains unproven. Pasini and colleagues noted that space travel might not be so bad for a tiny life-form. Enclosed in a natural spaceship of rock and ice, alien organisms might be protected from radiation and extreme heat.

"Our research raises several questions," Pasini said in the statement. "If we find life on another planet, will it be truly alien or will it be related to us? And if so, did it spawn us or did we spawn it? We cannot answer these questions just now, but the questions are not as farfetched as one might assume."

Pasini's research is not affiliated with another study announced Thursday (Sept. 19) that claims to have found evidence of alien life in Earth's upper atmosphere.

That separate study is based on findings by British scientists who deployed a research balloon over England. The balloon returned a sample containing the cell wall of a diatom, a type of microscopic algae.

The British researchers, led by astrobiology researcher Milton Wainwright, of the University of Sheffield in the United Kingdom, took the discovery as proof that life is continually arriving to Earth from space and perhaps didn't originate on our planet, but the claims have been met with wide skepticism.

Follow Megan Gannon on Twitter and Google+. Follow us @SPACEdotcom, Facebook or Google+. Originally published on SPACE.com.