Atmospheric Escape and the Evolution of Close-in Exoplanets

TL;DR

This paper reviews how intense stellar radiation causes atmospheric escape in close-in exoplanets, influencing their evolution, with recent models and observations highlighting the importance for lower-mass planets.

Contribution

It provides a comprehensive overview of hydrodynamic models and observational evidence for atmospheric escape, emphasizing its role in shaping exoplanet populations.

Findings

Atmospheric escape observed in hot Jupiters and super-Earths.

Hydrodynamic models incorporate radiative transfer and chemistry.

Escape significantly impacts lower-mass exoplanet evolution.

Abstract

Exoplanets with substantial Hydrogen/Helium atmospheres have been discovered in abundance, many residing extremely close to their parent stars. The extreme irradiation levels these atmospheres experience causes them to undergo hydrodynamic atmospheric escape. Ongoing atmospheric escape has been observed to be occurring in a few nearby exoplanet systems through transit spectroscopy both for hot Jupiters and lower-mass super-Earths/mini-Neptunes. Detailed hydrodynamic calculations that incorporate radiative transfer and ionization chemistry are now common in one-dimensional models, and multi-dimensional calculations that incorporate magnetic-fields and interactions with the interstellar environment are cutting edge. However, there remains very limited comparison between simulations and observations. While hot Jupiters experience atmospheric escape, the mass-loss rates are not high enough to affect their evolution. However, for lower mass planets atmospheric escape drives and controls their evolution, sculpting the exoplanet population we observe today.