Signs of alien life on exoplanet K2-18b have all but vanished
Earlier this year, astronomers reported possible evidence of life on another planet – but new observations from JWST suggest the apparent biosignature isn’t there after all
By Alex Wilkins
28 July 2025
An artist’s impression of the exoplanet K2-18b
A. Smith/N. Mandhusudhan
Hopes of finding alien life on planet K2-18b are rapidly fading, as new observations appear to show no detectable evidence of the biomolecule previous studies had seen hints of. Most scientists agree this shows earlier claims were premature, but one of the researchers behind the previous finding argues that the new data in fact shows stronger evidence than prior observations.
In April, Nikku Madhusudhan at the University of Cambridge and his colleagues claimed that the planet K2-18b, a a rocky planet larger than Earth that is around 124 light years away, contained hints of the molecules dimethyl sulphide (DMS) and dimethyl disulphide (DMDS) in its atmosphere. On Earth, these molecules are produced only by life. At the time, Madhusudhan said these were the “first hints we are seeing of an alien world that is possibly inhabited”.
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However, when other researchers later analysed this same data from the James Webb Space Telescope (JWST) using different statistical models, they found no strong evidence for the presence of these molecules. But Madhusudhan and his colleagues also reanalysed their data more comprehensively, which he told New Scientist made him only “more confident” that DMS was the best explanation for the data. Without new observations of the planet, astronomers couldn’t agree on whether there was evidence for life on K2-18b.
Now, Renyu Hu at the California Institute of Technology and his colleagues have teamed up with Madhusudhan and his group to analyse new JWST observations of K2-18b. They found no statistical evidence of a detection. “The paper does not provide conclusive evidence for the existence of this molecule in the atmosphere,” says Hu.
Madhusadhan, Hu and their colleagues used JWST’s near-infrared camera to look at the light from K2-18b’s star, which, after passing through the planet’s atmosphere, can tell us about what molecules exist in the atmosphere. This camera looked at a different wavelength of light than the mid-infrared measurements that were used for the previous analysis in April. They then tried to explain the data using several different models of K2-18b’s atmosphere, each with different assumptions, such as ones that included different molecules or where K2-18b’s atmosphere was filled with water vapour.
