![Illustration of the TRAPPIST-1 system and the most recent JWST constraints on planetary atmospheres. Planet size and distance roughly to scale. - [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/08/veiled.png?fit=1200%2C782&ssl=1)
[astro-ph.EP] The TRAPPIST-1 system offers seven terrestrial exoplanets with tight orbits and large radii ratios to the host star.
If an atmosphere exists, transmission spectroscopy can be used to detect specific atmospheric features. Predictions of the atmospheric detectability of the TRAPPIST-1 planets prior to the launch of JWST assumed pristine stellar surfaces.
However, initial JWST observations of the TRAPPIST-1 planets demonstrate that stellar contamination from unocculted active regions imparts significantly stronger spectral features than any planetary atmospheres. Here, we evaluate the atmospheric detectability of the habitable zone planet TRAPPIST-1f using atmospheric retrievals accounting for stellar contamination.
We model a transmission spectrum given a CO2-rich, habitable atmospheric model, and we include a “worst case” stellar contamination spectrum. We then perform atmospheric retrievals on simulated JWST observations with MIRI LRS (5-15 𝜇m) and NIRSpec PRISM (0.6-5.3 𝜇m), assuming accurate starspot spectral models.
We find that NIRSpec observations alone achieve similar results as MIRI and NIRSpec together. We find ∼10 transits obtains strong evidence (B>150) for CO2, and ∼50 transits finds weak evidence (B>3) for CH4.
We could not retrieve evidence of H2O with up to 100 simulated transits with both instruments. Many challenges remain to accurately account for stellar contamination for ultra-cool M-dwarfs in atmospheric retrievals, and our results show that, while evidence for a CO2-rich atmosphere around TRAPPIST-1f can be found with a short JWST program, other prominent atmospheric signatures can only be disentangled from strong stellar features with more observation time than previous studies have indicated.
Harper Rosenthal, Lisa Kaltenegger, Ryan J. MacDonald, Rebecca Payne, Elijah Mullens
Comments: 15 pages, 8 figures, in review by MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2608.06207 [astro-ph.EP] (or arXiv:2608.06207v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2608.06207
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Submission history
From: Harper Rosenthal
[v1] Thu, 6 Aug 2026 16:01:11 UTC (743 KB)
https://arxiv.org/abs/2608.06207
Astrobiology,
