Last month, astronomers using the James Webb Space Telescope made headlines by announcing they had detected hints of the chemicals dimethyl sulphide (DMS) and dimethyl disulfide (DMDS) on the exoplanet K2-18b, located 124 light-years away from the Earth. These chemicals are only produced by life such as marine algae on Earth, meaning they are considered potential «biosignatures» indicating life. recent follow-up research questions the reliability of this finding. A new study led by researchers from the University of Chicago reanalysed the James Webb Space Telescope (JWST) data and found the evidence for DMS far less convincing than previously reported.
Weakening of signals
According to a recent arxiv preprint, yet to be peer-reviewed, Rafael Luque, Caroline Piaulet-Ghorayeb, and Michael Zhang, used a joint approach by combining all JWST observations across its key instruments (NIRISS, NIRSpec, and MIRI). They found that the supposed DMS signal becomes significantly weaker when all data are considered together. Differences in data processing and modelling between the original studies also cast doubt on the initial results.
According to the team, even when DMS-like signals appear, they are weak, inconsistent, and can often be explained by other, non-biological molecules like ethane. The researchers stressed the importance of consistent modelling to avoid contradictory interpretations of planetary atmospheres.
Spectral Complexity
Molecules in an exoplanet’s atmosphere are typically detected through spectral analysis, which identifies unique «chemical fingerprints» based on how the planet’s atmosphere absorbs specific wavelengths of starlight as it passes or transits in front of its host star.
The difference between DMS and ethane a common molecule in exoplanet atmospheres is just one sulfur atom, and current spectrometers, including those on the JWST, have impressive sensitivity, but still face limits. The distance to exoplanets, the faintness of signals, and the complexity of atmospheres mean distinguishing between molecules that differ by just one atom is extremely challenging. The recent claim of a “3-sigma” detection of DMS falls short of the scientific standard for confirmation. The team calls for more rigorous standards in both scientific publication and media reporting.
