A Comparison of Simulated JWST Observations Derived from Equilibrium and Non-Equilibrium Chemistry Models of Giant Exoplanets

TL;DR

This study investigates whether JWST can detect differences between equilibrium and disequilibrium chemistry in exoplanet atmospheres by simulating spectra of three diverse planets and analyzing the observability of chemical disequilibrium effects.

Contribution

It introduces a combined modeling approach linking disequilibrium chemistry with radiative transfer to assess observability of chemical differences in exoplanet atmospheres using JWST.

Findings

Differences due to disequilibrium are most significant between 4-5 μm.

WASP-80b-like planets show detectable disequilibrium effects with one JWST eclipse.

GJ 436b-like planets require multiple eclipses and low metallicity for detection.

Abstract

We aim to see if the difference between equilibrium and disequilibrium chemistry is observable in the atmospheres of transiting planets by the James Webb Space Telescope (JWST). We perform a case study comparing the dayside emission spectra of three planets like HD 189733b, WASP-80b, and GJ436b, in and out of chemical equilibrium at two metallicities each. These three planets were chosen because they span a large range of planetary masses and equilibrium temperatures, from hot and Jupiter-sized to warm and Neptune-sized. We link the one-dimensional disequilibrium chemistry model from Venot et al. (2012) in which thermochemical kinetics, vertical transport, and photochemistry are taken into account, to the one-dimensional, pseudo line-by-line radiative transfer model, Pyrat Bay, developed especially for hot Jupiters, and then simulate JWST spectra using PandExo for comparing the effects of temperature, metallicity, and radius. We find the most significant differences from 4 to 5 $\mu$m due to disequilibrium from CO and CO$_{2}$ abundances, and also H$_{2}$O for select cases. Our case study shows a certain "sweet spot" of planetary mass, temperature, and metallicity where the difference between equilibrium and disequilibrium is observable. For a planet similar to WASP-80b, JWST's NIRSpec G395M can detect differences due to disequilibrium chemistry with one eclipse event. For a planet similar to GJ 436b, the observability of differences due to disequilibrium chemistry is possible at low metallicity given five eclipse events, but not possible at the higher metallicity.