Exoplanet K2-18 b: No trace of extraterrestrial life on a water world after all
The alleged detection of dimethyl disulphide on an exoplanet caused a stir in April. A research team now rejects this twice over.
Artistic representation of the water world K2-18 b
(Image: University of Cambridge)
There may be significantly less dimethyl sulphide (DMS) on the exoplanet K2-18 b than assumed, and the remaining amount may be produced without the involvement of living organisms. This is at least the result of an evaluation of several further investigations of the celestial body with the James Webb space telescope. The work of an international research group is now available online, but has not yet been independently verified. However, it deepens the doubts about the claim made in April that K2-18 b was the clearest indication of extraterrestrial life discovered to date. Since then, this conclusion of the original research work has been increasingly criticized.
More and more doubts
As the research team led by Renyu Hu from NASA's Jet Propulsion Laboratory now explains, the new measurements have confirmed that there is "clearly" a lot of water on K2-18 b. However, it is still unclear whether there is actually a large ocean under a thin atmosphere or a deep, water-rich shell. However, the traces of DMS are at most marginal and well below the threshold of 3 sigma that was mentioned in April. In addition, the researchers have created their own models that allow abiotic production of the substance. This would not be a biosignature at all, i.e. a substance that can be traced back to the existence of life.
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With the new analysis, the excitement surrounding K2-18 b is likely to subside further. It had become the focus of attention when it was announced in fall 2023 that a biosignature might have been found there using DMS. However, the signal presented at the time was rather weak and last spring another research team rejected this initial conclusion. In the spring, however, the original research team led by Nikku Madhusudhan from the University of Cambridge followed up and allegedly presented clearer evidence. However, this was also not a discovery, but merely clearer evidence.
Even before the current criticism, there were other studies that cast doubt on the findings from the spring. The title of a research paper submitted for review in May even stated that the traces of DMS in the data were "insufficient". However, this paper has not yet been independently reviewed either – in contrast to the one in which the discovery was announced. But even if DMS were found in K2-18 b in quantities that could not be explained by abiotic processes, this would not be proof of extraterrestrial life. Four years ago, NASA broke down what it would take for this to happen and the discovery of a biosignature would only be the first of seven steps on the way to the potentially historic discovery.
(mho)
