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Detectate BIO-TRACCE sull'Esopianeta K2-18b (Nana rossa K2-18 a 124 AL dal Sole)

Nella costellazione del LEONE, la nana rossa K2-18 distante 124 AL dal Sole, ha un pianeta gigante 8.6 volte più denso della Terra e 2.6 volte più grande della Terra. Il pianeta K2-18b ha un periodo orbitale di 32.9gg sulla sua stella, il pianeta é nella zona abitabile, con acqua liquida, sono state detectate anche biotracce: metano, anidride carbonica ed il solfuro di dimetile (prodotto solitamente dal fitoplacton). Gli scienziati suppongono che il pianeta K2-18b sia una "Terra gigante" totalmente o prevalentemente coperta di Oceani!.

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17/4/2025 CNN: Scientists detect signature of life on a distant planet, study suggests

A team of astronomers have detected what they call the most promising signs to date of a possible biosignature, or signs of past or present life linked to biological activity, on an exoplanet named K2-18b. But the study authors, and other experts, remain cautious and have not declared a definitive discovery of life beyond our planet.

Using the James Webb Space Telescope, the team detected chemical fingerprints within the atmosphere of K2-18b that suggest the presence of dimethyl sulfide or DMS, and potentially dimethyl disulfide or DMDS. On Earth, both molecules are only produced by microbial life, typically marine phytoplankton.

A study detailing the findings was published Thursday in The Astrophysical Journal Letters.

K2-18b, located 124 light-years from Earth, could be a Hycean world: a potentially habitable planet entirely covered in liquid water with a hydrogen-rich atmosphere, said lead study author Nikku Madhusudhan, professor of astrophysics and exoplanetary science at the University of Cambridge’s Institute of Astronomy.

Madhusudhan and his colleagues first theorized the concept of Hycean worlds in 2021 after determining there may be liquid water oceans on K2-18b.

The planet is located within the habitable zone of its star, meaning that the world is at just the right temperature and distance from the star to host liquid water on its surface.

“Earlier theoretical work had predicted that high levels of sulfur-based gases like DMS and DMDS are possible on Hycean worlds,” Madhusudhan said in a statement. “And now we’ve observed it, in line with what was predicted. Given everything we know about this planet, a Hycean world with an ocean that is teeming with life is the scenario that best fits the data we have.”

It’s possible that the molecules were produced by another unknown chemical process on the planet which does not require life.

The latest findings build on previous research by the same group of astronomers, who also detected carbon dioxide and methane within the planet’s atmosphere using Webb’s Near-Infrared Imager and Slitless Spectrograph and Near-Infrared Spectrograph instruments. The team made the new detection using Webb’s Mid-Infrared Instrument.

“This is an independent line of evidence, using a different instrument than we did before and a different wavelength range of light, where there is no overlap with the previous observations,” Madhusudhan said. “The signal came through strong and clear.”

Previous data of K2-18b, obtained with Webb’s Near-Infrared Imager and Slitless Spectrograph and Near-Infrared Spectrograph, shows an abundance of methane and carbon dioxide in the exoplanet’s atmosphere, as well as a possible detection of a molecule called dimethyl sulfide. NASA, ESA, CSA, Ralf Crawford (STScI), Joseph Olmsted (STScI)

But Madhusudhan and his coauthors acknowledge that more data is needed before claiming direct evidence of life on another world. The team believes between 16 and 24 hours follow-up observations using Webb will make that possible.

“It’s important that we’re deeply (skeptical) of our own results, because it’s only by testing and testing again that we will be able to reach the point where we’re confident in them,” Madhusudhan said. “That’s how science has to work.”

However, other experts believe that while the results promise excitement, confirming the existence of life beyond Earth — and even deciding what type of exoplanet K2-18b is — will take much more time and data.

Astrophysicist Sara Seager, a professor of physics, planetary science, aeronautics and astronautics at the Massachusetts Institute of Technology, said independent teams have completely different interpretations of the planet itself. Seager was not involved in the new research.



Astronomers say they've found "the most promising signs yet" of chemicals on a planet beyond our Solar System that could indicate the presence of life on its surface.

Using the James Webb Space Telescope, the team found a possible 'biosignature' – the potential fingerprint of life – within its atmosphere, although they say they're remaining "cautious", and that this isn't a confirmed detection.

The chemicals detected are the same as those produced by marine-dwelling organisms on Earth.

The team, led by the University of Cambridge in the UK, detected signs of dimethyl sulfide and dimethyl disulfide in the atmosphere of exoplanet K2-18b.

This planet orbits its star in the habitable zone (sometimes called the Goldilocks Zone), which is the region around a star in which an orbiting planet might have conditions suitable for the emergence of life, such as the ability for liquid water to exist on its surface.

K2-18b is 8.6 times as massive and 2.6 times as large as Earth and lies 124 lightyears away from our planet.

This isn't the first study of exoplanet K2-18b.

A 2023 study of K2-18b by the same team identified methane and carbon dioxide in the planet's atmosphere.

This in itself was a huge discovery: the first time carbon-based molecules had been found in the atmosphere of an exoplanet – a planet beyond our Solar System – in the habitable zone.

Astronomers say the 2023 results showed K2-18b could be a ‘Hycean’ planet, meaning a habitable world with a liquid ocean and a hydrogen-rich atmosphere.

That earlier study found a tantalising hint of dimethyl sulfide and dimethyl disulfide, but this latest study has made a more promising detection.

"We didn’t know for sure whether the signal we saw last time was due to DMS, but just the hint of it was exciting enough for us to have another look with JWST using a different instrument," says Professor Nikku Madhusudhan from Cambridge’s Institute of Astronomy, who led the research.

The team say that on Earth, dimethyl sulfide and dimethyl disulfide are only produced by life, mainly microbial life like phytoplankton we see in our oceans.

However, there could be another explanation for the detection of the chemical.

Another unknown chemical process could be the source of the molecules detected in K2-18b’s atmosphere.

Nevertheless, the team say "the results are the "strongest evidence yet" that life may exist on a planet outside our Solar System.

They say their observations have reached the ‘three-sigma’ level of statistical significance.

This means there's a 0.3% probability the detection occurred by chance.

And to reach the accepted level that would mean scientific discovery, observations would have to meet the five-sigma threshold.

In other words, there would need to be below a 0.00006% probability they occurred by chance.

How can scientists know what chemicals exist on a planet orbiting a star beyond our Solar System?

Key to analysing exoplanets' atmospheres is analysing the light from their host stars.

As a planet passes in front of its host star from our perspective on Earth – known as a transit – light from that star passes through the planet's atmosphere.

That starlight picks up chemical fingerprints as it passes through the atmosphere, so astronomers can analyse the light to learn more about the atmosphere.

The tentative detection of dimethyl sulfide in 2023 was made using the James Webb Space Telescope's NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph) instruments.

This 2025 study used the Webb Telescope's MIRI (Mid-Infrared Instrument), which observes in a different wavelength of light, offering the team a new look at this intriguing world.

"This is an independent line of evidence, using a different instrument than we did before and a different wavelength range of light, where there is no overlap with the previous observations," says Madhusudhan.

"The signal came through strong and clear."

"It was an incredible realisation seeing the results emerge and remain consistent throughout the extensive independent analyses and robustness tests," says co-author Måns Holmberg, a researcher at the Space Telescope Science Institute in Baltimore, USA.

Does K2-18b have life?
The team say dimethyl sulfide and dimethyl disulfide are molecules from the same chemical family, and could be 'biosignatures'.

This is a term used to describe chemicals that, when detected around a distant planet, could indicate the presence of biological processes, i.e. life.

Yet the concentrations of dimethyl sulfide and dimethyl disulfide in K2-18b's atmosphere are different from those on Earth.

On Earth, dimethyl sulfide and dimethyl disulfide are below one part per billion by volume. On K2-18b, they're thought to be thousands of times stronger, over ten parts per million.

"Earlier theoretical work had predicted that high levels of sulfur-based gases like dimethyl sulfide and dimethyl disulfide are possible on Hycean worlds," says Madhusudhan.

"And now we’ve observed it, in line with what was predicted. Given everything we know about this planet, a Hycean world with an ocean that is teeming with life is the scenario that best fits the data we have."

The team now hope to carry out more research into whether dimethyl sulfide and dimethyl disulfide can be produced non-biologically at the level they're currently seeing.

"The inference of these biosignature molecules poses profound questions concerning the processes that might be producing them" says study co-author Subhajit Sarkar of Cardiff University.

"Our work is the starting point for all the investigations that are now needed to confirm and understand the implications of these exciting findings," says co-author Savvas Constantinou, also from Cambridge’s Institute of Astronomy.

"It’s important that we’re deeply sceptical of our own results, because it’s only by testing and testing again that we will be able to reach the point where we’re confident in them," says Madhusudhan. "That’s how science has to work.

"Decades from now, we may look back at this point in time and recognise it was when the living universe came within reach.

"This could be the tipping point, where suddenly the fundamental question of whether we’re alone in the universe is one we’re capable of answering."



Astronomers have detected the most promising signs yet of a possible biosignature outside the solar system, although they remain cautious.

Using data from the James Webb Space Telescope (JWST), the astronomers, led by the University of Cambridge, have detected the chemical fingerprints of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS), in the atmosphere of the exoplanet K2-18b, which orbits its star in the habitable zone.

On Earth, DMS and DMDS are only produced by life, primarily microbial life such as marine phytoplankton. While an unknown chemical process may be the source of these molecules in K2-18b's atmosphere, the results are the strongest evidence yet that life may exist on a planet outside our solar system.

The observations have reached the 'three-sigma' level of statistical significance—meaning there is a 0.3% probability that they occurred by chance. To reach the accepted classification for scientific discovery, the observations would have to cross the five-sigma threshold, meaning there would be below a 0.00006% probability they occurred by chance.

The researchers say between 16 and 24 hours of follow-up observation time with JWST may help them reach the all-important five-sigma significance. Their results are reported in The Astrophysical Journal Letters.

Earlier observations of K2-18b—which is 8.6 times as massive and 2.6 times as large as Earth, and lies 124 light years away in the constellation of Leo—identified methane and carbon dioxide in its atmosphere. This was the first time that carbon-based molecules were discovered in the atmosphere of an exoplanet in the habitable zone.

Those results were consistent with predictions for a 'Hycean' planet: a habitable ocean-covered world underneath a hydrogen-rich atmosphere.

However, another, weaker signal hinted at the possibility of something else happening on K2-18b. "We didn't know for sure whether the signal we saw last time was due to DMS, but just the hint of it was exciting enough for us to have another look with JWST using a different instrument," said Professor Nikku Madhusudhan from Cambridge's Institute of Astronomy, who led the research.

To determine the chemical composition of the atmospheres of faraway planets, astronomers analyze the light from its parent star as the planet transits, or passes in front of the star as seen from Earth. As K2-18b transits, JWST can detect a drop in stellar brightness, and a tiny fraction of starlight passes through the planet's atmosphere before reaching Earth.

The absorption of some of the starlight in the planet's atmosphere leaves imprints in the stellar spectrum that astronomers can piece together to determine the constituent gases of the exoplanet's atmosphere.

The earlier, tentative, inference of DMS was made using JWST's NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph) instruments, which together cover the near-infrared (0.8-5 micron) range of wavelengths. The new, independent observation used JWST's MIRI (Mid-Infrared Instrument) in the mid-infrared (6-12 micron) range.

"This is an independent line of evidence, using a different instrument than we did before and a different wavelength range of light, where there is no overlap with the previous observations," said Madhusudhan. "The signal came through strong and clear."

"It was an incredible realization seeing the results emerge and remain consistent throughout the extensive independent analyses and robustness tests," said co-author Måns Holmberg, a researcher at the Space Telescope Science Institute in Baltimore, U.S.

DMS and DMDS are molecules from the same chemical family, and both are predicted to be biosignatures. Both molecules have overlapping spectral features in the observed wavelength range, although further observations will help differentiate between the two molecules.

However, the concentrations of DMS and DMDS in K2-18b's atmosphere are very different than on Earth, where they are generally below one part per billion by volume. On K2-18b, they are estimated to be thousands of times stronger—over ten parts per million.

"Earlier theoretical work had predicted that high levels of sulfur-based gases like DMS and DMDS are possible on Hycean worlds," said Madhusudhan. "And now we've observed it, in line with what was predicted. Given everything we know about this planet, a Hycean world with an ocean that is teeming with life is the scenario that best fits the data we have."

Madhusudhan says that while the results are exciting, it's vital to obtain more data before claiming that life has been found on another world. He says that while he is cautiously optimistic, there could be previously unknown chemical processes at work on K2-18b that may account for the observations.

Working with colleagues, he is hoping to conduct further theoretical and experimental work to determine whether DMS and DMDS can be produced non-biologically at the level currently inferred.

"The inference of these biosignature molecules poses profound questions concerning the processes that might be producing them" said co-author Subhajit Sarkar of Cardiff University.

"Our work is the starting point for all the investigations that are now needed to confirm and understand the implications of these exciting findings," said co-author Savvas Constantinou, also from Cambridge's Institute of Astronomy.

"It's important that we're deeply skeptical of our own results, because it's only by testing and testing again that we will be able to reach the point where we're confident in them," Madhusudhan said. "That's how science has to work."

While he is not yet claiming a definitive discovery, Madhusudhan says that with powerful tools like JWST and future planned telescopes, humanity is taking new steps toward answering that most essential of questions: are we alone?

"Decades from now, we may look back at this point in time and recognize it was when the living universe came within reach," said Madhusudhan. "This could be the tipping point, where suddenly the fundamental question of whether we're alone in the universe is one we're capable of answering."



Astronomers announced Thursday that they had detected the most promising "hints" of potential life on a planet beyond our Solar System, though other scientists expressed scepticism.

There has been vigorous debate in scientific circles about whether the planet K2-18b, which is 124 light years away in the Leo constellation, could be an ocean world capable of hosting microbial life.

Using the James Webb Space Telescope, a British-US team of researchers detected signs of two chemicals in the planet's atmosphere long considered to be "biosignatures" indicating extraterrestrial life.

On Earth, the chemicals dimethyl sulfide (DMS) and dimethyl disulfide are produced only by life, mostly microscopic marine algae called phytoplankton.

The researchers emphasised caution, saying that more observations were needed to confirm these findings, and that they were not announcing a definitive discovery.

But the implications could be huge, according to Nikku Madhusudhan, a Cambridge University astrophysicist and lead author of the study, published in The Astrophysical Journal Letters.

"What we are finding at this point are hints of possible biological activity outside the solar system," he told a press conference.

"Frankly, I think this is the closest we have come to seeing a feature that we can attribute to life."

But outside experts pointed to disputes over previous discoveries about the exoplanet, adding that these chemicals could have been created by unknown means having nothing to do with life.

Chemical clues
More than eight times the mass of Earth and 2.5 times as big, K2-18b is a rare exoplanet that orbits its star in a habitable or "goldilocks" zone.

This means it is neither too hot nor too cold to have liquid water, considered the most important ingredient for life.

Telescopes observe such far-off exoplanets when they cross in front of their star, allowing astronomers to analyse how molecules block the light streaming through their atmosphere.

In 2023, the Webb telescope detected methane and carbon dioxide in K2-18b's atmosphere, the first time such carbon-based molecules were detected on an exoplanet in a habitable zone.

It also detected weak signals of the chemical DMS, leading astronomers to turn Webb towards the planet again a year ago, this time using its mid-infrared instrument to detect different wavelengths of light.

They found much stronger signs of the chemicals, though still well below the "five sigma" threshold of statistical significance scientists seek for such discoveries.

Even if the results are confirmed, it would not necessarily mean that the planet is home to life.

Last year, scientists found traces of DMS on a comet, which suggested it can be produced in non-organic ways.

However the concentration of the chemical observed on K2-18b appears to be thousands of times stronger than levels on Earth, strongly suggesting a biological origin, Madhusudhan said.

Are we alone in the universe?
K2-18b has long been considered the premier candidate for a "hycean planet" – an ocean world bigger than Earth with a hydrogen-rich atmosphere.

These planets would not be expected to be home to intelligent alien life, but rather tiny microbes similar to those in Earth's oceans billions of years ago.

Some research has questioned whether the currently proposed hycean planets are too close to their stars to support liquid water, including K2-18b, which orbits its star every 33 days.

Raymond Pierrehumbert, a planetary physics professor at Oxford University, has conducted separate research indicating K2-18b is too hot for life.

If the planet did have water, it would be "hellishly hot" and uninhabitable, he told AFP, adding that oceans of lava were more plausible.

Sara Seager, a professor of planetary science at MIT, called for patience, pointing to previous claims of water vapour in K2-18b's atmosphere that turned out to be a different gas.

And within our solar system, Mars, Venus and moons such as Saturn's Enceladus all have "more chance to be realised as life-hosting," she told AFP.

Madhusudhan estimated that it would take just 16 to 24 more hours of Webb's time to confirm their findings, which could happen in the next few years.

Even beyond K2-18b, Madhusudhan said Webb and future telescopes could allow humanity to discover life outside our home planet sooner than one might think.

"This could be the tipping point, where suddenly the fundamental question of whether we're alone in the universe is one we're capable of answering," he said.



A study suggesting the exoplanet K2-18b shows potential signs of alien life has been met with skepticism from the scientific community. Here’s the truth about what the James Webb Space Telescope saw.

The trendiest planet in the universe right now is K2-18b, a potentially habitable world swirling around a small, red star in the constellation Leo. Located 124 light-years from Earth, the mysterious planet will never host human visitors — but a recent glimpse with the James Webb Space Telescope (JWST) hints that alien life may already thrive there in a vast, warm ocean.

In a University of Cambridge-led study published April 17, scientists using JWST reported the detection of possible signs of life in the alien planet's atmosphere, offering what a Cambridge statement called the "most promising" evidence yet of life beyond Earth. However, in the week since the study's publication, a growing number of scientists are already pushing back on this big claim.

"The statistical significance of the detection is marginal," Eddie Schwieterman, an assistant professor of astrobiology at the University of California, Riverside who was not involved in the research, told Live Science in an email. "There are some reasons to be skeptical."

"It's almost certainly not life," Tessa Fisher, an astrobiologist at the University of Arizona who was not involved in the research, told Nature.com.

So what did JWST actually find on K2-18b, and how close are we to solving the ultimate mystery of space? Here's everything you need to know.

Unlike optical telescopes such as Hubble, JWST cannot image the surfaces of distant planets directly; instead, its infrared instruments hunt for chemical signs of life — or biosignatures — in planetary atmospheres by mapping how starlight is absorbed or reemitted by molecules in those atmospheres. The resulting graphs of light, called spectra, can reveal the composition of that planet's atmosphere, providing clues about its surface conditions.

Related: 32 alien planets that really exist

In the new Cambridge-led study, scientists using JWST's Mid-Infrared Instrument (MIRI) peered into K2-18b's atmosphere to detect traces of two sulfur-based molecules called dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) — compounds that are known to be produced only by microscopic life-forms like phytoplankton on Earth. If DMS can be produced by some natural mechanism, scientists currently don't know about it, and will have to run extensive tests to uncover it.

The findings add to earlier observations made by the same team using two different JWST instruments in 2023, which also reported possible traces of DMS in the planet's atmosphere.

While the Cambridge team admitted in the statement that they are "deeply sceptical" of their own results, the same release also trumpeted these detections as the "most promising" evidence yet of life beyond Earth, painting a picture of an oceanic planet that could be "teeming with life." (Other studies have argued that K2-18b's ocean may, in fact, be made of magma.)

Nikku Madhusudhan, lead author of both Cambridge studies, stressed that no actual life has been detected on K2-18b yet.

"That's not what we're claiming," Madhusudhan, a professor of astrophysics at Cambridge, told Live Science. "But in the best-case scenario, it's the potential for life."

The team's DMS detection reached the three-sigma level of statistical significance, meaning there is a 0.3% probability that the signals occurred by chance. However, this still falls far short of the required five-sigma level that denotes a statistically significant scientific discovery.

Responding to criticism that the team may have overstated their study's significance, Madhusudhan said it's in the public interest to know how this research is progressing.

"This is the taxpayer paying us, and they have a right to enjoy the process," Madhusudhan added. "If we're sending a robot to Mars, we're not waiting until it goes and finds life to celebrate the act of sending it. We announced that we are sending robots to Mars, and we're excited about the possibility. This is the equivalent of that."

"No strong evidence"
For now, the public has little more than the Cambridge team's study to go on. The complete set of MIRI data on which the team based their discovery will become publicly available April 27, according to NPR, at which point outside researchers can begin to comb through it and formulate peer-reviewed responses.

In the meantime, various researchers have already attempted to re-create the findings using their own data models and have come up short.

In January, a team of scientists independently analyzed K2-18b's atmosphere using the same JWST instruments used in the 2023 study. The team found "no statistically significant or reliable evidence" of DMS on K2-18b, the researchers wrote in a paper published to the preprint server arXiv.

More recently, on April 22, University of Oxford astrophysicist Jake Taylor reanalyzed the JWST spectra shared in the new Cambridge study, using a simple data model that's routinely utilized in exoplanet studies. Taylor's analysis, also published to arXiv, found no traces of DMS, either.

"There is no strong evidence for detected spectral features in K2-18b's MIRI transmission spectrum," Taylor wrote.

Looking only at the Cambridge team's study, Schwieterman also saw cause for hesitation in proclaiming that biosignatures exist on K2-18b.

"When DMS interacts with ultraviolet light from the star, it splits apart into components that reform into other molecules like ethane (C2H6) and ethylene (C2H4)," Schwieterman said. "The paper does not report the detection of these molecules, which is puzzling because you'd expect these gases to appear together."

What comes next?
Everyone, including the Cambridge team, agrees that more observations of K2-18b are necessary to bring clarity to this puzzle. This means researchers will have to request more time with JWST to observe the alien planet as it swoops in front of its star.

Luckily, this is a near-monthly occurrence, with K2-18b completing a transit of its star every 33 days. Budgeting more time to watch these transits should be "trivial" for the telescope, Madhusudhan said.

"One transit is eight hours, roughly," Madhusudhan added. "You only need about 16 to 24 hours of JWST time. To give you a sense of scale, JWST observes thousands of hours every year."

If additional observations can increase the statistical significance of the team's DMS detection, the next step will be to prove that some unknown natural process isn't producing the molecule instead, Schwieterman said. This will take rigorous experimentation and some creative thinking here on Earth. Finally, scientists will need to look at planets that are similar to K2-18b to see if DMS is a common signature around the cosmos.



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