H2SO4 and Organosulfur Compounds in Laboratory Analogue Aerosols of Warm High-metallicity Exoplanet Atmospheres

Recent transit spectra suggest organic aerosol formation in the atmosphere of sub-Neptunes. Sulfur gases are expected to be present in warm exoplanet atmospheres with high metallicity. Many aspects of the sulfur fixation process by photochemistry in planetary atmospheres are not fully understood. In this work, tholins produced in a CO2-rich atmosphere simulation experiment with H2S were analyzed with very high-resolution mass spectrometry (HRMS) that allows for searching specific molecules in addition to providing some insight on the mixture complexity. To our knowledge, this is the first experimental investigation of sulfur-bearing organic aerosol formation from irradiation of H2S at temperatures relevant to warm exoplanets. The analysis of the mass spectra shows that the soluble organic fraction of the solid particles contains over 2500 organosulfur (CHS/CHOS/CHNS/CHNOS) molecular formulas (73% of all assigned signals) within a broad mass range (from 50 to 400 u, atomic mass unit). In particular, 14 sulfuric acid derivatives were detected and 13 unique molecular formulae that could correspond to amino acid derivatives were identified. This high molecular diversity indicates a rich and active sulfur chemistry triggered by irradiation of H2S. The average elemental composition (wt%) of the soluble fraction of the particles is 40%C, 30%O, 21%S, 6%H, and 3%N, making the sulfur abundance a factor of ∼14 larger than in the initial gas composition. Our analysis of experimental simulations shows that organosulfur species are likely an important component of the haze in exoplanet atmospheres.