Atmospheric escape from exoplanets: recent observations and theoretical models

Abstract

The review aims to give an overview of atmospheric escape processes from exoplanets. I briefly discuss the physics of various escape processes responsible for atmospheric escape across different types of exoplanets. Transmission spectroscopy is one of the major workhorses to observe the escaping atmosphere from exoplanets. I discuss recent observations that established the fact that atmospheric escape is very common in exoplanets, especially during the early phase of their evolution when stellar high-energy radiation (X-ray and extreme ultraviolet, hence XUV) is strong. There are many theoretical efforts/models to understand atmospheric escape processes. Stellar radiation is one of the major drivers of atmospheric escape, but other stellar environments (e.g., stellar flares, stellar winds, stellar coronal mass ejections, and stellar magnetic field) also have control over how the escape process will be affected for a given property of exoplanet, as the planetary properties (e.g., gravity, thermal energy, magnetic field) plays an important role for atmospheric escape. I discuss all governing factors for the atmospheric escape process and corresponding theoretical models in detail. I also discuss how atmospheric escape plays a crucial role in the overall atmospheric evolution of exoplanets and can lead us to understand some features in recently observed exoplanet demographics.