Sulfur ion irradiation experiments simulating space weathering of Solar System body surfaces: Organosulfur compound formation

Context. Sulfur (S) is of prime interest in the context of (astro)chemical evolution and habitability. However, the origin of S-bearing organic compounds in the Solar System is still not well constrained. Aims. We carried out laboratory experiments to test whether complex organosulfur compounds can be formed when surfaces of icy Solar System bodies are subject to high-energy S ions. Methods. Non-S-bearing organic residues, formed during the processing of astrophysical H2O:CH3OH:NH3-bearing ice analogs, were irradiated with 105 keV-S7+ ions at 10 K and analyzed by high-resolving FT-ICR-MS. The resulting data were comprehensively analyzed, including network analysis tools. Results. Out of several thousands of detected compounds, 16% contain at least one sulfur atom (organosulfur (CHNOS) compounds), as verified via isotopic fine structures. These residue-related organosulfur compounds are different from those formed during the S ion irradiation of ices at 10 K. Furthermore, insoluble, apolar material was formed during the sulfur irradiation of residues. Potential organosulfur precursors (CHNO molecules) were identified by means of molecular networks. Conclusions. This evidence of organosulfur compounds formed by sulfur irradiation of organic residues sheds new light onto the rich and complex scope of pristine organosulfur chemistry in the Solar System, presented in the context of current and future space missions. These results indicate that the space weathering of Solar System bodies may lead to the formation of organosulfur compounds.