Exoplanets, -moons, -comets

Photochemical CS2 Gas Detected On A 20-Myr-old Exoplanet

By Keith Cowing

Status Report

astro-ph.EP

June 3, 2026

Filed under atmosphere, Carbon disulfide, exoplanet, JWST, Photochemistry, Sun-like star, Transmission spectroscopy, V1298 Tau b, V1298 Tau e

Photochemical CS2 Gas Detected On A 20-Myr-old Exoplanet — Upper: Transit depths of V1298 Tau e as a function of wavelength, reduced with Eureka!. The blue and red curves show the best-fit transmission spectra from our free re- trieval with and without CS2, respectively. Including CS2 yields a decisive improvement in the Bayesian evidence (∆ ln Z = 33.2), corresponding to an 8.4σpreference. Lower: Absorption cross sections of the nine dominant molecular species included in our free retrieval and forward model. While a wider range of additional species were explored using POSEIDON opacity database, CS2 uniquely reproduces both the∼4.6–4.7 µm feature and the sharpened peak near ∼4.3 µm that cannot be explained by CO2 or CO alone. — astro-ph.EP

Probing the atmospheres of young exoplanets offers a powerful window into how planetary systems evolve and the physical and chemical processes that drive those early evolutions.

We present JWST/NIRSpec transmission spectroscopy of V1298 Tau e, a ∼20-Myr-old, ∼15-M_⊕ planet with a Jupiter-like radius orbiting a young Sun-like star.

We identified carbon disulfide (CS₂) in its atmosphere at >8σ significance based on spectral features between 4.3 and 4.7~μm. Photochemical forward models show that the inferred CS₂ abundance is physically plausible in an H/He-dominated atmosphere exposed to intense ultraviolet irradiation.

The atmosphere of V1298 Tau e is strikingly different from its nearest neighboring planet b, whose atmosphere shows SO₂ rather than CS₂. These observations demonstrate that even planets within the same system can occupy distinct photochemical regimes.

Our results further provide empirical evidence for complex sulfur photochemistry in exoplanet atmospheres in general and may also point to divergent formation or evolutionary pathways within the same planetary system.

Fei Dai, Erik Petigura, John Livingston, Nicholas Wogan, Sagnick Mukherjee, Zhecheng Hu, Ian J. M. Crossfield, James Owen, Kento Masuda

Comments: Manuscript under review. ArXiv posting was encouraged by the editor
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2606.00974 [astro-ph.EP] (or arXiv:2606.00974v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2606.0 0 974
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Submission history
From: Fei Dai
[v1] Sun, 31 May 2026 03:12:17 UTC (30,974 KB)
https://arxiv.org/abs/2606.00974

Astrobiology, Astrochemistry,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

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