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Arxiv: JWST Thermal Emission of the Terrestrial Exoplanet GJ 1132b Published: 8/23/2024 10:20:15 PM Updated: 8/23/2024 10:20:15 PM

Paper abstract: We present thermal emission measurements of GJ 1132b spanning 5--12 umobtained with the Mid-Infrared Instrument Low-Resolution Spectrometer(MIRI/LRS) on the James Webb Space Telescope (JWST). GJ 1132b is an M-dwarfrocky planet with Teq=584 K and an orbital period of 1.6 days. We measure awhite-light secondary eclipse depth of 140+/-17 ppm, which corresponds to adayside brightness temperature of Tp,dayside= 709+/-31 K using improved starand planet parameters. This measured temperature is only 1 sigma below themaximum possible dayside temperature of a bare rock (i.e., assuming a zeroalbedo planet with no heat redistribution, Tmax = 746+14/-11 K). The emissionspectrum is consistent with a featureless blackbody, which agrees with a widerange of possible surface compositions. By comparing forward models to thedayside emission spectrum, we rule out Earth-thickness (P ~ 1 bar) atmosphereswith at least 1% H2O, atmospheres of any modeled thickness (10^-4 -- 10^2 bar)that contain at least 1% CO2, and thick, Venus-like atmospheres (P>~100 bar)with at least 1 ppm CO2 or H2O. We therefore conclude that GJ 1132b likely doesnot have a significant atmosphere. This finding supports the concept of auniversal 'Cosmic Shoreline' given the high level of bolometric and XUVirradiation received by the planet.