Three-Dimensional Circulation Driving Chemical Disequilibrium in WASP-43b

Abstract

Spectral features in the observed spectra of exoplanets depend on the composition of their atmospheres. A good knowledge of the main atmospheric processes that drive the chemical distribution is therefore essential to interpret exoplanetary spectra. An atmosphere reaches chemical equilibrium if the rates of the forward and backward chemical reactions converge to the same value. However, there are atmospheric processes, such as atmospheric transport, that destabilize this equilibrium. In this work we study the changes in composition driven by a 3D wind field in WASP-43b using our Global Circulation Model, THOR. Our model uses validated temperature- and pressure-dependent chemical timescales that allow us to explore the disequilibrium chemistry of CO, CO$_2$, H$_2$O and CH$_4$. In WASP-43b the formation of the equatorial jet has an important impact in the chemical distribution of the different species across the atmosphere. At low latitudes the chemistry is longitudinally quenched, except for CO$_2$ at solar abundances. The polar vortexes have a distinct chemical distribution since these are regions with lower temperature and atmospheric mixing. Vertical and latitudinal mixing have a secondary impact in the chemical transport. We determine graphically the effect of disequilibrium on observed emission spectra. Our results do not show any significant differences in the emission spectra between the equilibrium and disequilibrium solutions for C/O = 0.5. However, if C/O is increased to 2.0, differences in the spectra due to the disequilibrium chemistry of CH$_4$ become non-negligible. In some spectral ranges the emission spectra can have more than 15$\%$ departures from the equilibrium solution.