On the abiotic origin of dimethyl sulfide: discovery of DMS in the Interstellar Medium

Abstract

Following the discovery of dimethyl sulfide (CH${}_3$SCH${}_3$, DMS) signatures in comet 67P/Churyumov-Gerasimenko, we report the first detection of this organosulfur species in the interstellar medium, during the exploration of an ultradeep molecular line survey performed toward the Galactic Center molecular cloud G+0.693-0.027 with the Yebes 40m and IRAM 30m telescopes. We derive a molecular column density of $N$ = (2.6 $\pm$ 0.3)$\times$10${}^{13}$ cm${}^{-2}$, yielding a fractional abundance relative to H${}_2$ of $\sim$1.9$\times$10${}^{-10}$. This implies that DMS is a factor of $\sim$1.6 times less abundant than its structural isomer CH${}_3$CH${}_2$SH and $\sim$30 times less abundant than its O-analogue dimethyl ether (CH${}_3$OCH${}_3$) toward this cloud, in excellent agreement with previous results on various O/S pairs. Furthermore, we find a remarkable resemblance between the relative abundance of DMS/CH${}_3$OH in G+0.693-0.027 ($\sim$1.7$\times$10${}^{-3}$) and in the comet ($\sim$1.3$\times$10${}^{-3}$). Although the chemistry of DMS beyond Earth is yet to be fully disclosed, this discovery provides conclusive observational evidence on its efficient abiotic production in the interstellar medium, casting doubts about using DMS as a reliable biomarker in exoplanet science.

Accepted in ApJL

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• A detection of sulfur-bearing cyclic hydrocarbons in space
• Expanding the C${}_3$H${}_6$O${}_2$ Isomeric Interstellar Inventory: Discovery of Lactaldehyde and Methoxyacetaldehyde in G+0.693-0.027
• Gas-phase formation routes of dimethyl sulfide in the interstellar medium