Evaporation of extrasolar planets

TL;DR

This review discusses observational evidence and theoretical models of atmospheric evaporation in hot-Jupiters, highlighting how these processes influence planetary evolution and potential remnants.

Contribution

It synthesizes recent observational data and models to better understand atmospheric escape mechanisms in hot-Jupiters, including new insights from Lyman-alpha and MgII observations.

Findings

Extended atmospheres observed in hot-Jupiters like HD209458b.

Detection of oxygen and carbon at high altitudes constrains escape mechanisms.

Evaporation models suggest some planets may be remnants of former giants.

Abstract

This article presents a review on the observations and theoretical modeling of the evaporation of extrasolar planets. The observations and the resulting constraints on the upper atmosphere (thermosphere and exosphere) of the "hot-Jupiters". are described. The early observations of the first discovered transiting extrasolar planet, HD209458b, allowed the discovery that this planet has an extended atmosphere of escaping hydrogen. Subsequent observations showed the presence of oxygen and carbon at very high altitude. These observations give unique constraints on the escape rate and mechanism in the atmosphere of hot-Jupiters. The most recent Lyman-alpha HST observations of HD189733b and MgII observations of Wasp-12b allow for the first time comparison of the evaporation from different planets in different environments. Models to quantify the escape rate from the measured occultation depths, and an energy diagram to describe the evaporation state of hot-Jupiters are presented. Using this diagram, it is shown that few already known planets like GJ876d or CoRot-7b could be remnants of formerly giant planets.