KRONOS I: The 1 - 2.8 mu m JWST Transmission Spectrum of the 23 Myr V1298 Tau c
Matthew M. Murphy, Matthew C. Nixon, Adina D. Feinstein, Luis Welbanks, Girish M. Duvvuri, Saugata Barat, Benjamin V. Rackham, Darryl Z. Seligman, Michael Radica, Ian J. M. Crossfield, Kevin France, John H. Livingston, Jonathan Lunine, Rafael Luque, Catriona Murray, Sagnick Mukherjee, Biruk Nardos, Sydney Petz, Hinna Shivkumar
astro-ph.EP, astro-ph.SR
Submitted: 2026-06-02
Comments: Accepted for publication in The Astronomical Journal. 33 pages, 15 figures
Journal ref: AJ 172 66 (2026)
Code: https://github.com/radicamc/exoTEDRF
License: http://creativecommons.org/licenses/by/4.0/
The gist: While recent JWST observations of mature super-Earths and sub-Neptunes have frequently revealed featureless transmission spectra, their inflated progenitors offer a unique window into understanding
Terminology
Abstract
While recent JWST observations of mature super-Earths and sub-Neptunes have frequently revealed featureless transmission spectra, their inflated progenitors offer a unique window into understanding their primordial compositions. As part of the Keys to Revealing the Origin and Nature Of sub-neptune Systems (KRONOS) JWST program, we present the NIRISS/SOSS transmission spectrum of V1298 Tau c, a about 23 Myr super-Earth progenitor orbiting a young Solar analog. We detect H 2 O in V1298 Tau c's atmosphere with a 10 volume mixing ratio of-1.83+0.68-0.77, but no additional molecules from these data alone. We find consistent results for the planetary atmospheric properties in both retrievals with and without informed priors on stellar heterogeneities based on the observed stellar spectrum. We infer an atmospheric metallicity [O/H] of 14.8+56.0-12.28 times the solar value. This metallicity is similar to literature measurements for other young planets, including its massive outer companion V1298 Tau b. In contrast, this measured metallicity is systematically lower than the metallicities of mature planets of similar mass and temperature. Altogether, these results provide tentative but growing evidence that the exoplanet mass--metallicity relation evolves with planetary age.
Sources
- JWST Reveals CH$_4$, CO$_2$, and H$_2$O in a Metal-rich Miscible Atmosphere on a Two-Earth-Radius Exoplanet
- The Pandora SmallSat: A Low-Cost, High Impact Mission to Study Exoplanets and Their Host Stars
- Combined Exoplanet Mass and Atmospheric Characterization for Accelerated Exoplanetology
- What's in Your Transit? Towards Reliably Getting $5\times$ More Science from Exoplanet Transit Data
- KRONOS II: Solar-like Umbra and Penumbra Properties on the Young Sun V1298~Tau
- Unlocking HST's Stellar Treasure Trove: Stellar Activity Minima for HAT-P-11 Offer Prime Windows for Transmission Spectroscopy
- Oxygen left behind: Atmospheric Enrichment due to Fractionation in Sub-Neptunes using BOREAS
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