Abstract
Abstract 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.
Highlights
Transit spectra have suggested that condensate clouds and/ or photochemical haze are present in the atmospheres of several super-Earths and mini-Neptunes (GJ3470b, GJ1214b, Kepler 51b, and GJ436b) (Benneke et al 2019; Kreidberg et al 2014; Libby-Roberts et al 2020; Lothringer et al 2018)
We investigated the impact of H2S in high metallicity (10,000x solar) exoplanet atmospheres by studying the gasphase composition and the particle production rate and size (He et al 2020a)
The mass spectra of tholins produced from the gas mixture containing H2S show similar features as the mass spectra of tholins produced from other CO2-rich gas mixtures, but without H2S
Summary
Transit spectra have suggested that condensate clouds and/ or photochemical haze are present in the atmospheres of several super-Earths and mini-Neptunes (GJ3470b, GJ1214b, Kepler 51b, and GJ436b) (Benneke et al 2019; Kreidberg et al 2014; Libby-Roberts et al 2020; Lothringer et al 2018). Little is known about the composition and optical properties of these particles. It is extremely challenging to theoretically simulate the complex chemical processes for haze formation in planetary atmospheres due to a lack of chemical kinetics information under relevant conditions. Another way to study hazes is to synthesize analogues in the laboratory, called tholins, and to analyze them with state-of-the-art analytical instruments.
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