James Webb Space Telescope Feed Post

Potential Atmospheric Compositions of TRAPPIST-1 c constrained by JWST/MIRI Observations at 15 μm Published: 8/11/2023 4:21:12 AM Updated: 8/11/2023 4:21:12 AM

Paper abstract: The first JWST observations of TRAPPIST-1 c showed a secondary eclipse depthof 421+/-94 ppm at 15 um, which is consistent with a bare rock surface or athin, O2-dominated, low CO2 atmosphere (Zieba et al. 2023). Here, we furtherexplore potential atmospheres for TRAPPIST-1 c by comparing the observedsecondary eclipse depth to synthetic spectra of a broader range of plausibleenvironments. To self-consistently incorporate the impact of photochemistry andatmospheric composition on atmospheric thermal structure and predicted eclipsedepth, we use a two-column climate model coupled to a photochemical model, andsimulate O2-dominated, Venus-like, and steam atmospheres. We find that abroader suite of plausible atmospheric compositions are also consistent withthe data. For lower pressure atmospheres (0.1 bar), our O2-CO2 atmospheresproduce eclipse depths within 1\sigma of the data, consistent with themodeling results of Zieba et al. (2023). However, for higher-pressureatmospheres, our models produce different temperature-pressure profiles and areless pessimistic, with 1-10 bar O2, 100 ppm CO2 models within 2.0-2.2\sigmaof the measured secondary eclipse depth, and up to 0.5% CO2 within 2.9\sigma.Venus-like atmospheres are still unlikely. For thin O2 atmospheres of 0.1 barwith a low abundance of CO2 (~100 ppm), up to 10% water vapor can bepresent and still provide an eclipse depth within 1\sigma of the data. Wecompared the TRAPPIST-1 c data to modeled steam atmospheres of <= 3 bar,which are 1.7-1.8\sigma from the data and not conclusively ruled out. Moredata will be required to discriminate between possible atmospheres, or to moredefinitively support the bare rock hypothesis.