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Potential Atmospheric Compositions of TRAPPIST-1 c constrained by JWST/MIRI Observations

Presentation #627.10 in the session Planetary Atmospheres - Theory.

Published onApr 03, 2024
Potential Atmospheric Compositions of TRAPPIST-1 c constrained by JWST/MIRI Observations

Published and ongoing 12 and 15 μm observations by the James Webb Space Telescope (JWST) of the TRAPPIST-1 planets (e.g. Greene et al. 2023, Zieba et al. 2023) present the first opportunity to characterize the planetary environment and potential atmospheres of these Earth-sized planets. JWST observations of TRAPPIST-1 c, which has Venus-like insolation, show a secondary eclipse depth of 421±94 ppm at 15 μm, which was first shown to be consistent with a bare rock surface or a thin, O2-dominated, low CO2 atmosphere (Zieba et al. 2023). Here, we explore a broader range of potential atmospheres for TRAPPIST-1 c and compare the observed secondary eclipse depth to synthetic spectra of plausible environments. To incorporate the impact of photochemistry and atmospheric composition on atmospheric thermal structure and predicted eclipse depth, we use a two-column (day-night) climate model coupled to a photochemical model to produce atmospheres that are self-consistent with the host star spectrum. We simulate O2-dominated, Venus-like, and steam atmospheres, and find that a broader suite of atmospheres are consistent with the data. For lower pressure atmospheres (0.1 bar), our O2-CO2 atmospheres produce eclipse depths within 1σ of the data, consistent with the modeling results of Zieba et al. (2023). However, for higher-pressure atmospheres, our models produce different temperature-pressure profiles and are less pessimistic; 1-10 bar O2 models with 100 ppm CO2 are within ~2σ of the measured secondary eclipse depth, and up to 0.5% CO2 are within 3σ. Venus-like atmospheres are still unlikely. For thin O2 atmospheres of 0.1 bar with a low abundance of CO2 (~100 ppm), up to 10% water vapor can be present and still provide an eclipse depth within 1σ of the data. Modeled steam atmospheres of ≤ 3 bar fit the data within 1.7-1.8σ and are not conclusively ruled out. We will also present preliminary modeling efforts on additional data for TRAPPIST-1 b and c, including phase curves which have just been obtained in GO 3077. This modeling will include other environmental archetypes, such as airless worlds and hazy and SO2-rich atmospheres, to further assess JWST observations of TRAPPIST-1 b and c. This work was supported by the Virtual Planetary Laboratory Team, under NASA Grant No. 80NSSC19K0829.

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