Chemical Kinetics on Extrasolar Planets

TL;DR

This paper reviews the role of chemical kinetics, including photochemistry and transport processes, in shaping the atmospheric composition of extrasolar planets, especially at temperatures below 2000 K.

Contribution

It provides a comprehensive review of disequilibrium processes like photochemistry and quenching in exoplanet atmospheres, highlighting their observational impacts.

Findings

Chemical kinetics significantly influences atmospheric composition below 2000 K.

Photochemistry and transport-induced quenching are key disequilibrium mechanisms.

Evidence for kinetic processes has been observed in exoplanet atmospheres.

Abstract

Chemical kinetics plays an important role in controlling the atmospheric composition of all planetary atmospheres, including those of extrasolar planets. For the hottest exoplanets, the composition can closely follow thermochemical-equilibrium predictions, at least in the visible and infrared photosphere at dayside (eclipse) conditions. However, for atmospheric temperatures < ~2000 K, and in the uppermost atmosphere at any temperature, chemical kinetics matters. The two key mechanisms by which kinetic processes drive an exoplanet atmosphere out of equilibrium are photochemistry and transport-induced quenching. We review these disequilibrium processes in detail, discuss observational consequences, and examine some of the current evidence for kinetic processes on extrasolar planets.