Princeton University Extrasolar Planet Discussion Group

With the advent of JWST, the need for detailed chemical and photochemical models of exoplanet atmospheres has increased. Traditionally, building reaction networks required manually tracking species and reactions, a process that is both time-consuming and prone to errors, often limited to specific conditions. We introduce an automated approach using a computer-aided chemical reaction network generator combined with 1D photochemical kinetic-transport modeling, applied to various exoplanet atmospheres from hot Jupiters to temperate sub-Neptunes.

Applying this new framework to temperate sub-Neptunes reveals that the atmospheric CO2/CH4 ratio can infer the deep interior H2O/H2 ratio. Applying this to recent JWST observations, we suggest that K2-18 b likely has an interior with 50% water enrichment, indicating significant ice accretion during its formation. Conversely, our model suggests that TOI-270 d’s interior is about 25% water, consistent with a metallicity exceeding 100x solar metallicity. Additionally, our models identify carbonyl sulfide (OCS) and sulfur dioxide (SO2) as key indicators for temperate sub-Neptunes with at least 10% water content.

As a future study, investigating extensive sulfur (photo)chemistry will be crucial. This research should combine ab-initio calculations with experimental measurements, enabling a cross-disciplinary characterization of exoplanet atmospheres.