Astronomers claim strongest evidence of alien life yet

Summary

Artist’s impression of the planet K2-18b and its host starESA/Hubble, M. Kornmesser Astronomers claim to have seen the strongest evidence so far for life on another planet. But other astronomers have urged caution until the findings can be verified by other groups and alternative, non-biological explanations can be ruled out. “These are the first hints we are seeing of an alien world that is possibly inhabited,” Nikku Madhusudhan at the University of Cambridge told a press conference on 15 March. 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. “What we are finding is an independent line of evidence in a different wavelength range with a different instrument of possible biological activit...