Preprint: JWST spectra suggest carbon disulfide in atmosphere of young exoplanet V1298 Tau e

A new arXiv preprint reports that NASA’s James Webb Space Telescope detected carbon disulfide, or CS2, in the atmosphere of V1298 Tau e, a roughly 20 million-year-old exoplanet. In the paper’s abstract, the authors write, “We identified carbon disulfide (CS2) in its atmosphere at >8σ significance based on spectral features between 4.3 and 4.7 μm.” The paper, by Fei Dai and colleagues, was posted May 31 as arXiv:2606.00974 and is under review rather than peer-reviewed.

If confirmed, the result would mark a notable sign of sulfur photochemistry on a very young world. It would also strengthen the idea that planets forming and evolving in the same system can still end up with sharply different atmospheric chemistry, even early in their histories.

The study reports transmission spectroscopy observations with JWST’s Near-Infrared Spectrograph, or NIRSpec. That technique looks at starlight filtering through a planet’s atmosphere during a transit, allowing researchers to infer which gases may be present. In the abstract, the authors describe V1298 Tau e as an about 15-Earth-mass planet with a Jupiter-like radius orbiting a young Sun-like star. They say photochemical forward models show the inferred CS2 abundance is physically plausible in a hydrogen-helium-dominated atmosphere exposed to intense ultraviolet radiation.

The claimed detection matters in part because of what it suggests within the broader V1298 Tau system, a young multiplanet system often cited as about 20 to 30 million years old. A 2025 JWST preprint on nearby planet V1298 Tau b reported sulfur dioxide, or SO2, among its atmospheric signals. In the new paper, Dai and co-authors say V1298 Tau e instead shows CS2, not SO2. Their argument is that the contrast points to neighboring planets occupying distinct photochemical regimes despite sharing the same star.

That system-level comparison is part of what makes the new claim stand out. This is not being presented as the first reported CS2 signal in any exoplanet atmosphere; another 2026 preprint on WASP-80 b had already reported CS2. The novelty here is the youth of V1298 Tau e and the possibility of seeing sulfur chemistry diverge between sibling planets so early.

The finding also fits a broader trend in JWST-era exoplanet studies, which have begun to tease out more detailed chemistry, including sulfur-bearing molecules, from distant atmospheres. Young systems like V1298 Tau are especially useful because they offer a look at how planetary atmospheres behave early in their evolution.

Still, the new result should be treated cautiously. The arXiv page says, “Manuscript under review. ArXiv posting was encouraged by the editor.” V1298 Tau is a young, active star, and stellar activity can complicate the interpretation of transmission spectra. That makes independent confirmation especially important before the CS2 claim is treated as established.