Evidence For Sulfur Chemistry In The Atmosphere Of The Warm Sub-Neptune TOI-270 d

Context: Recent JWST measurements allow access to the near-infrared spectrum of the sub-Neptune TOI-270 d, for which two different interpretations, a high-metallicity miscible envelope and a lower metallicity hycean world, are currently in conflict.

Aims: Here, we reanalyze the published data and reproduce previously retrieved molecular abundances based on an independent data reduction and a different retrieval framework. The aim of this study is to refine the understanding of TOI-270 d and highlight considerations for JWST data analysis. Additionally, we test the impact of data resolution on atmospheric retrieval calculations.

Methods: We reduce one JWST NIRSpec G395H and one NIRISS SOSS GR700XD transit dataset using the Eureka! pipeline and a custom MCMC-based light curve fitting algorithm at the instruments’ native resolutions. The atmospheric composition is estimated with the updated BeAR retrieval code across a grid of retrieval setups and spectral resolutions.

Results: Our transit spectrum is consistent with previous studies, except at the red end of the NIRISS data. Our retrievals support a higher mean molecular weight atmosphere for TOI-270 d. We provide refined abundance constraints and find statistically favored model extensions indicating either sulfur-rich chemistry with species such as CS₂, CS, and H2CS, or the possible presence of CH₃Cl or CH₃F. However, Bayesian inference cannot distinguish between these scenarios due to similar opacities below 4 microns.

Conclusions: Our analysis reinforces TOI-270 d as a highly interesting warm sub-Neptune for atmospheric studies, with a complex chemistry in a cloud-free upper atmosphere. However, its exact nature remains uncertain and warrants further detailed photochemical modeling and observations.

Lukas Felix, Daniel Kitzmann, Brice-Olivier Demory, Christoph Mordasini

Comments: Submitted to A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2504.13039 [astro-ph.EP] (or arXiv:2504.13039v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2504.13039
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Submission history
From: Daniel Kitzmann
[v1] Thu, 17 Apr 2025 15:52:23 UTC (34,096 KB)
https://arxiv.org/abs/2504.13039
Astrobiology, Astronomy, Astrochemistry, Biosignatures,