Is dimethylsulfide a good biomarker?

Sagan et al. (1993) proposed that so-called biomarkers, i.e., unique molecular indicators of life on Earth, could be used to search for extraterrestrial life. This is especially interesting for places that are not reachable for in situ studies and where potential life can only be detected with remote spectroscopical methods, for instance exoplanets. One of the most recent examples that obtained world-wide media coverage is the tentative detection of dimethylsulfide (DMS) in the atmosphere of exoplanet K2-18b with James Webb Space Telescope by Madhusudhan et al. (2023). DMS has been suggested as potential biomarker (Seager et al. 2016) since on Earth this chemical compound is produced by biological activity exclusively and discussed as indicator of life in exoplanetary atmospheres (Madhusudhan et al. 2021). But what if this biomarker is present in the completely abiotic cometary matter? Comets are known to be rich in organic matter that has been well-preserved since the earliest times of our Solar System (Hänni et al. 2022, Hänni et al. 2023), and hence, are a relevant point of reference when it comes to abiotic chemical complexity. We inspected data collected by the high-resolution mass spectrometer DFMS (Balsiger et al. 2007) onboard ESA’s Rosetta spacecraft, which was studying comet 67P/Churyumov-Gerasimenko (hereafter 67P) for two years from up close, for the signature of DMS. Our detailed analysis of the sulfur-bearing hydrocarbon signals detectable in 67P’s coma yields strong evidence for the presence of DMS and thus provides the basis to argue that this molecule might not be a robust indicator of extraterrestrial life.

 

 

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