The effect of metallicity on the atmospheres of exoplanets with fully coupled 3D hydrodynamics, equilibrium chemistry, and radiative transfer

TL;DR

This study uses advanced 3D simulations to explore how varying metallicity influences the atmospheric dynamics and thermal structure of GJ 1214b, emphasizing the critical role of opacities and radiative transfer.

Contribution

It introduces a coupled 3D GCM with a Gibbs energy minimisation scheme for chemical equilibrium, providing new insights into metallicity effects on exoplanet atmospheres.

Findings

Increased metallicity significantly alters atmospheric dynamics and temperature profiles.

Opacity effects dominate over molecular weight and heat capacity in influencing circulation.

Results are qualitatively consistent with previous studies but show quantitative differences.

Abstract

In this work we have performed a series of simulations of the atmosphere of GJ~1214b assuming different metallicities using the Met Office Unified Model (UM). The UM is a general circulation model (GCM) that solves the deep, non-hydrostatic equations of motion and uses a flexible and accurate radiative transfer scheme, based on the two-stream and correlated-$k$ approximations, to calculate the heating rates. In this work we consistently couple a well-tested Gibbs energy minimisation scheme to solve for the chemical equilibrium abundances locally in each grid cell for a general set of elemental abundances, further improving the flexibility and accuracy of the model. As the metallicity of the atmosphere is increased we find significant changes in the dynamical and thermal structure, with subsequent implications for the simulated phase curve. The trends that we find are qualitatively consistent with previous works, though with quantitative differences. We investigate in detail the effect of increasing the metallicity by splitting the mechanism into constituents, involving the mean molecular weight, the heat capacity and the opacities. We find the opacity effect to be the dominant mechanism in altering the circulation and thermal structure. This result highlights the importance of accurately computing the opacities and radiative transfer in 3D GCMs.