Researchers using the James Webb Space Telescope reported tentative evidence of at least one chemical associated with life in the atmosphere of K2-18b, an exoplanet 124 light-years from Earth. The team detected a signal consistent with dimethyl sulphide, or DMS, and dimethyl disulphide, known as DMDS.
On Earth, marine phytoplankton and bacteria produce those gases. Lead researcher Nikku Madhusudhan of the University of Cambridge said the estimated atmospheric amount was thousands of times greater than Earth's and described the result as the strongest evidence yet for possible life elsewhere. However, he and other scientists stressed that the data neither confirms the molecules nor establishes a biological origin.
K2-18b is about two and a half times Earth's size and orbits a small red star. Webb studies its atmosphere by analysing starlight that filters through it, looking for patterns associated with particular chemicals. Because the measurement depends on very small changes in distant light, both statistical uncertainty and models of the planet can affect the interpretation.
The new result reached three sigma, corresponding to 99.7% statistical confidence under the team's analysis. That was stronger than an earlier one-sigma signal but still below the five-sigma threshold—about 99.99999%—normally expected for a discovery. Madhusudhan said further observations might reduce the chance of a statistical fluctuation to less than one in a million within one or two years.
Even a five-sigma detection would not prove biology. Catherine Heymans, Scotland's Astronomer Royal and an independent scientist, said unknown geological or chemical processes on an alien world might produce the gases. The Cambridge group agreed and was working with other teams to test non-biological production routes in laboratories.
Researchers also dispute the nature of K2-18b itself. One interpretation proposes a planet with a large ocean, partly because ammonia appears absent from its atmosphere. Cambridge scientist Oliver Shorttle noted that an ocean of molten rock could also explain the data and would rule out life as imagined in the ocean scenario. NASA Ames researcher Nicolas Wogan has proposed that the planet is a small gas giant with no solid surface. Other groups challenge both alternatives.
The observation is therefore a promising target for repeat study, not a detection of organisms. It raises two separate questions: whether DMS or DMDS is actually present, and, if so, what produced it. Webb data can refine the first through additional measurements. Answering the second requires ruling out plausible non-living chemistry and understanding the planet's structure—tasks that remain unresolved in the evidence reported. The findings were published as a step in that investigation, not as an announcement that life had been found.
