<div><p>The first JWST observations of TRAPPIST-1 c showed a secondary eclipse depth of 421±94 ppm at 15 µm, which is consistent with a bare rock surface or a thin, O 2 -dominated, low CO 2 atmosphere (Zieba et al. 2023).</p><p>Here, we further explore potential atmospheres for TRAPPIST-1 c by comparing the observed secondary eclipse depth to synthetic spectra of a broader range of plausible environments. To self-consistently incorporate the impact of photochemistry and atmospheric composition on atmospheric thermal structure and predicted eclipse depth, we use a two-column climate model coupled to a photochemical model, and simulate O 2 -dominated, Venus-like, and steam atmospheres. We find that a broader suite of plausible atmospheric compositions are also consistent with the data. For lower pressure atmospheres (0.1 bar), our O 2 -CO 2 atmospheres produce eclipse depths within 1σ of the data, consistent with the modeling results of Zieba et al. (2023). However, for higherpressure atmospheres, our models produce different temperature-pressure profiles and are less pessimistic, with 1-10 bar O 2 , 100 ppm CO 2 models within 2.0-2.2σ of the measured secondary eclipse depth, and up to 0.5% CO 2 within 2.9σ. Venus-like atmospheres are still unlikely. For thin O 2 atmospheres of 0.1 bar with a low abundance of CO 2 (∼100 ppm), up to 10% water vapor can be present and still provide an eclipse depth within 1σ of the data. We compared the TRAPPIST-1 c data to modeled steam atmospheres of ≤ 3 bar, which are 1.7-1.8σ from the data and not conclusively ruled out. More data will be required to discriminate between possible atmospheres, or to more definitively support the bare rock hypothesis.</p></div>< Réduire