Organosulfur Chemistry On sub-Neptunes: Implications For Hazes And Biosignatures
The organosulfur biosignature gases dimethylsulfide (DMS) and dimethlydisulfide (DMDS) have recently been claimed to be present in the atmosphere of sub-Neptune exoplanet K2-18b, leading to the suggestion of possible extraterrestrial life.
Abiotic formation pathways for DMS and DMDS in reducing atmospheres have also been proposed, raising concern over the use of DMS and DMDS as biosignature gases more generally. In this paper we independently test and contrast the proposed abiotic formation pathways for DMS and DMDS using K2-18b as a case study, and explore the wider implications for the atmospheric carbon and sulfur chemistry of hydrogen-rich sub-Neptunes.
We demonstrate that one proposed formation pathway is capable of producing observable abundances of abiotic DMS and DMDS, however it depends sensitively on the energy barrier of the limiting step, which remains unmeasured experimentally. In contrast, hydrocarbons including C2H6 are formed abundantly in such atmospheres and offer a plausible alternative explanation to the reported suggestions of organosulfur compounds on K2-18b, having previously been shown to be degenerate observationally.
Finally, we demonstrate that sulfur hazes form via the photochemistry of H2S and condense in the atmosphere of K2-18b even at trace abundances. We propose that variation in atmospheric sulfur abundance can explain the diversity of haziness observed across the sub-Neptune population so far with JWST.
Sean Jordan, Shang-Min Tsai, Paul B. Rimmer, Oliver Shorttle
Comments: Submitted to The Astrophysical Journal Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2603.18923 [astro-ph.EP] (or arXiv:2603.18923v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2603.18923
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Submission history
From: Sean Jordan
[v1] Thu, 19 Mar 2026 14:00:44 UTC (463 KB)
https://arxiv.org/abs/2603.18923
Astrobiology,
