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Astronomers using the James Webb Space Telescope made headlines last month when they announced that they had identified traces of the compounds dimethyl sulphide (DMS) and dimethyl disulfide (DMDS) on the exoplanet K2-18b, which is 124 light-years distant from Earth. These molecules are exclusively created by life on Earth, such as sea algae, and are thus regarded possible "biosignatures" of life. Recent follow-up study calls into doubt the dependability of this conclusion. A recent study headed by experts at the University of Chicago reanalyzed James Webb Space Telescope (JWST) data and discovered that the evidence for DMS is significantly less strong than previously claimed.
Weakness of signals
According to a new arxiv release that has yet to be peer-reviewed, Rafael Luque, Caroline Piaulet-Ghorayeb, and Michael Zhang took a collaborative approach, merging all JWST observations from its primary instruments (NIRISS, NIRSpec, and MIRI). They discovered that when all data is analyzed collectively, the purported DMS signal weakens dramatically. Differences in data processing and modelling between the original research put doubt on the initial findings.
Even when DMS-like signals exist, the team claims that they are faint, inconsistent, and may frequently be explained by non-biological chemicals such as ethane. The researchers emphasized the need of consistent modeling in avoiding inconsistent interpretations of planetary atmospheres.
Spectral Complexity
Molecules in an exoplanet's atmosphere are usually found via spectral analysis, which finds distinct "chemical fingerprints" based on how the planet's atmosphere absorbs certain wavelengths of sunlight when it passes or transits in front of its home star.
The difference between DMS and ethane, a common chemical in planetary atmospheres, is only one sulfur atom, and contemporary spectrometers, including those on the JWST, have outstanding sensitivity but are still limited. The distance to exoplanets, the faintness of signals, and the complexity of atmospheres make detecting molecules that vary by only one atom exceedingly difficult. The recent claim of a "3-sigma" detection of DMS does not meet the scientific criteria for confirmation. The team advocates for higher standards in scientific publication and media reporting.
