Apr 17, 2025 03:38 AM
https://www.newscientist.com/article/247...-life-yet/
Astronomers first discovered the exoplanet K2-18b in 2015, and soon established that it was a promising place to look for life. About eight times as massive as Earth and orbiting a star 124 light years away from us, the planet sits in the habitable zone of its star, where liquid water can exist. Further observations, in 2019, found evidence of water vapour, which led to suggestions that the planet may be covered in oceans sitting under a hydrogen-rich atmosphere, though not all astronomers agreed.
In 2023, Madhusudhan and his colleagues used the instruments on the James Webb Space Telescope (JWST) to look at K2-18b’s atmosphere in near-infrared light, and again found evidence of water vapour, as well as carbon dioxide and methane. But they also found a tantalising hint of dimethyl sulphide (DMS), a molecule that, on Earth, is produced only by living organisms, mainly marine phytoplankton. The signs for DMS were extremely weak, however, and many astronomers argued that we would need much stronger evidence to be certain about the molecule’s presence.
Now, Madhusudhan and his colleagues have used a different instrument from JWST, the mid-infrared camera, to observe K2-18b. They found a much stronger signal for DMS, as well as a possible related molecule called dimethyl disulphide (DMDS), which is also produced on Earth only by life. ...
... Nicholas Wogan at the NASA Ames Research Center in California says the evidence is more convincing than the 2023 results, but it still needs to be verified by other groups...
...Madhusudhan and his colleagues calculate that the possible concentrations of DMS and DMDS on K2-18b appear to be over 10 parts per million, thousands of times greater than the concentrations in Earth’s atmosphere. This could indicate a far greater amount of biological activity than on Earth, if the signal proves to be correct, but establishing that the chemicals have a biological origin will take more work, he says.
“We have to be extremely careful,” said Madhusudhan. “We cannot, at this stage, make the claim that, even if we detect DMS and DMDS, that it is due to life. Let me be very clear about that. But if you take published studies so far, then there is no mechanism that can explain what we are seeing without life.”
Ruling out alternative mechanisms could take some time, says Wogan. “Something like this hasn’t really been studied. DMS in a hydrogen-rich atmosphere, we don’t know a tonne about it. There would have to be a lot of work.”
The difficulty in proving that it couldn’t have a non-biological explanation could put K2-18b in the category of a viable biosignature candidate for a long time, says Sara Seager at the Massachusetts Institute of Technology. “It may remain in that category for decades, since the question may never be fully resolved with the limited data exoplanets offer,” she says...
Astronomers first discovered the exoplanet K2-18b in 2015, and soon established that it was a promising place to look for life. About eight times as massive as Earth and orbiting a star 124 light years away from us, the planet sits in the habitable zone of its star, where liquid water can exist. Further observations, in 2019, found evidence of water vapour, which led to suggestions that the planet may be covered in oceans sitting under a hydrogen-rich atmosphere, though not all astronomers agreed.
In 2023, Madhusudhan and his colleagues used the instruments on the James Webb Space Telescope (JWST) to look at K2-18b’s atmosphere in near-infrared light, and again found evidence of water vapour, as well as carbon dioxide and methane. But they also found a tantalising hint of dimethyl sulphide (DMS), a molecule that, on Earth, is produced only by living organisms, mainly marine phytoplankton. The signs for DMS were extremely weak, however, and many astronomers argued that we would need much stronger evidence to be certain about the molecule’s presence.
Now, Madhusudhan and his colleagues have used a different instrument from JWST, the mid-infrared camera, to observe K2-18b. They found a much stronger signal for DMS, as well as a possible related molecule called dimethyl disulphide (DMDS), which is also produced on Earth only by life. ...
... Nicholas Wogan at the NASA Ames Research Center in California says the evidence is more convincing than the 2023 results, but it still needs to be verified by other groups...
...Madhusudhan and his colleagues calculate that the possible concentrations of DMS and DMDS on K2-18b appear to be over 10 parts per million, thousands of times greater than the concentrations in Earth’s atmosphere. This could indicate a far greater amount of biological activity than on Earth, if the signal proves to be correct, but establishing that the chemicals have a biological origin will take more work, he says.
“We have to be extremely careful,” said Madhusudhan. “We cannot, at this stage, make the claim that, even if we detect DMS and DMDS, that it is due to life. Let me be very clear about that. But if you take published studies so far, then there is no mechanism that can explain what we are seeing without life.”
Ruling out alternative mechanisms could take some time, says Wogan. “Something like this hasn’t really been studied. DMS in a hydrogen-rich atmosphere, we don’t know a tonne about it. There would have to be a lot of work.”
The difficulty in proving that it couldn’t have a non-biological explanation could put K2-18b in the category of a viable biosignature candidate for a long time, says Sara Seager at the Massachusetts Institute of Technology. “It may remain in that category for decades, since the question may never be fully resolved with the limited data exoplanets offer,” she says...
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