On the Abiotic Origin of Dimethyl Sulfide: Discovery of Dimethyl Sulfide in the Interstellar Medium

Abstract

Following the discovery of dimethyl sulfide (DMS; CH _3 SCH _3 ) 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 40 m and IRAM 30 m telescopes. We derive a molecular column density of N = (2.6 ± 0.3) × 10 ^13 cm ^−2 , yielding a fractional abundance relative to H _2 of ∼1.9 × 10 ^−10 . This implies that DMS is a factor of ∼1.6 times less abundant than its structural isomer CH _3 CH _2 SH and ∼30 times less abundant than its O-analog 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 (∼1.7 × 10 ^−3 ) and in the comet (∼1.3 × 10 ^−3 ). Although the chemistry of DMS beyond Earth has yet to be fully disclosed, this discovery provides conclusive observational evidence on its efficient abiotic production in the interstellar medium, casting doubt on using DMS as a reliable biomarker in exoplanet science.

Keywords

• Interstellar molecules
• Interstellar clouds
• Galactic center
• Spectral line identification
• Astrochemistry