Photochemical Production of CS2 in Temperate-to-Warm Gas Giant Exoplanet Atmospheres
Abstract
Sulfur chemistry has emerged as an important probe of exoplanet atmospheres in the JWST era, although observational constraints have thus far been largely limited to SO2 and H2S in warm and hot exoplanets. Recent JWST observations have revealed CS2 in several cooler gas-giant exoplanets, yielding a new tracer of sulfur chemistry. However, the detailed chemical pathways responsible for the formation of CS2 remain poorly understood. Here, we use TOI-6894 b, a temperate gas giant with evidence for CS2, as a test case for one-dimensional photochemical kinetic-transport modeling and sensitivity analyses of CS2 chemistry. We show that CS2 is produced through coupled thermochemical and photochemical processes involving CH4 and H2S as the primary carbon and sulfur reservoirs, with S2 photolysis driving disequilibrium sulfur chemistry. Our models provide a physically consistent explanation for the observed CS2 feature in TOI-6894 b. Extending our analysis to gas giant exoplanets spanning a wide range of Teq, we find that CS2 abundance peaks in temperate to warm atmospheres (Teq ~ 500 - 700 K), and declines toward both lower and higher temperatures. This temperature dependence provides a unified framework for interpreting current CS2 observations, accounting for reported detections in temperate to warm planets and the lack of detections in colder and hotter giant exoplanets. Our results establish CS2 as a complementary probe of sulfur inventories and atmospheric metallicity in cool gas giant exoplanets
Versions
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BibTeX
@misc{yang2026photochemical,
title = {{Photochemical Production of CS2 in Temperate-to-Warm Gas Giant Exoplanet Atmospheres}},
author = {Jeehyun Yang and Vighnesh Nagpal and Michael Zhang and Qiao Xue and Eliza M. -R. Kempton and Jacob L. Bean and Michael R. Line and Jonathan J. Fortney and Peter Gao and Matthew C. Nixon and Caroline Piaulet-Ghorayeb and Kevin B. Stevenson and Madison Brady and Joost P. Wardenier and Luis Welbanks and Jean-Michel Désert and Guangwei Fu and Vivien Parmentier and Diana Powell},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2606.23820},
eprint = {2606.23820},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.23820},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Photochemical Production of CS2 in Temperate-to-Warm Gas Giant Exoplanet Atmospheres
AU - Jeehyun Yang
AU - Vighnesh Nagpal
AU - Michael Zhang
AU - Qiao Xue
AU - Eliza M. -R. Kempton
AU - Jacob L. Bean
AU - Michael R. Line
AU - Jonathan J. Fortney
AU - Peter Gao
AU - Matthew C. Nixon
AU - Caroline Piaulet-Ghorayeb
AU - Kevin B. Stevenson
AU - Madison Brady
AU - Joost P. Wardenier
AU - Luis Welbanks
AU - Jean-Michel Désert
AU - Guangwei Fu
AU - Vivien Parmentier
AU - Diana Powell
PY - 2026
DA - 2026/08/31
PB - arXiv
DO - 10.48550/arxiv.2606.23820
UR - https://arxiv.org/abs/2606.23820
AB - Sulfur chemistry has emerged as an important probe of exoplanet atmospheres in the JWST era, although observational constraints have thus far been largely limited to SO2 and H2S in warm and hot exoplanets. Recent JWST observations have revealed CS2 in several cooler gas-giant exoplanets, yielding a new tracer of sulfur chemistry. However, the detailed chemical pathways responsible for the formation of CS2 remain poorly understood. Here, we use TOI-6894 b, a temperate gas giant with evidence for CS2, as a test case for one-dimensional photochemical kinetic-transport modeling and sensitivity analyses of CS2 chemistry. We show that CS2 is produced through coupled thermochemical and photochemical processes involving CH4 and H2S as the primary carbon and sulfur reservoirs, with S2 photolysis driving disequilibrium sulfur chemistry. Our models provide a physically consistent explanation for the observed CS2 feature in TOI-6894 b. Extending our analysis to gas giant exoplanets spanning a wide range of Teq, we find that CS2 abundance peaks in temperate to warm atmospheres (Teq ~ 500 - 700 K), and declines toward both lower and higher temperatures. This temperature dependence provides a unified framework for interpreting current CS2 observations, accounting for reported detections in temperate to warm planets and the lack of detections in colder and hotter giant exoplanets. Our results establish CS2 as a complementary probe of sulfur inventories and atmospheric metallicity in cool gas giant exoplanets
ER -