HyDRo: Atmospheric Retrieval of Rocky Exoplanets in Thermal Emission

Abstract

Emission spectroscopy is a promising technique to observe atmospheres of rocky exoplanets, probing both their chemistry and thermal profiles. We present y o, an atmospheric retrieval framework for thermal emission spectra of rocky exoplanets.y o does not make prior assumptions about the background atmospheric composition, and can therefore be used to interpret spectra of secondary atmospheres with unknown compositions. We use y o to assess the chemical constraints which can be placed on rocky exoplanet atmospheres using JWST. Firstly, we identify the best currently-known rocky exoplanet candidates for spectroscopic observations in thermal emission with JWST, finding > 30 known rocky exoplanets whose thermal emission will be detectable by JWST/MIRI in fewer than 10 eclipses at 𝑅 ∼ 10. We then consider the observations required to characterise the atmospheres of three promising rocky exoplanets across the ∼400-800 K equilibrium temperature range: Trappist-1 b, GJ 1132 b, and LHS 3844 b. Considering a range of CO 2 -to H 2 O-rich atmospheric compositions, we find that as few as 8 eclipses of LHS 3844 b or GJ 1132 b with MIRI will be able to place important constraints on the chemical compositions of their atmospheres. This includes confident detections of CO 2 and H 2 O in the case of a cloud-free CO 2 -rich composition, besides ruling out a bare rock scenario. Similarly, 30 eclipses of Trappist-1 b with MIRI/LRS can allow detections of a cloud-free CO 2 -rich or CO 2 -H 2 O atmosphere. y o will allow important atmospheric constraints for rocky exoplanets using JWST observations, providing clues about their geochemical environments.