Thermosphere and exosphere of Hot-Jupiters

TL;DR

This paper discusses observations and models of Hot-Jupiters' upper atmospheres, revealing atmospheric escape processes, composition, and potential planetary evolution, with comparative analysis of two different exoplanets.

Contribution

It provides new observational constraints on atmospheric escape mechanisms and introduces an energy diagram to assess evaporation states of Hot-Jupiters.

Findings

HD209458b has an extended, escaping hydrogen atmosphere.

Detection of oxygen and carbon at high altitudes.

Comparison of evaporation between HD209458b and HD189733b.

Abstract

Here we describe the observations and the resulting constraints on the upper atmosphere (thermosphere and exosphere) of the "Hot-Jupiters". In particular, observations and theoretical modeling of Hot-Jupiter evaporation are described. The observations allowed the discovery that the planet orbiting HD209458 has an extended atmosphere of escaping hydrogen and 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 these planets. The most recent Lyman-alpha HST observations of HD189733b allows for the first time to compare the evaporation from two 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 could be remnants of formerly giant planets.