Séminaire : Envelops and natures of close-in exoplanets : from hot-Jupiters to dusty remnants

Observations of exoplanets during the transit of their host star allow us to probe the structure and composition of their atmospheres. While the visible and infrared wavelength domains give access to low altitudes in the atmosphere, space-borne ultraviolet observations can reveal their highest atmospheric layers. Transit observations of strongly irradiated gaseous giants like HD209458b led to the detection of evaporation, when massive amounts of gas escape from the planet and form an extended exosphere shaped by interactions with the star.

Recently, the observation of a giant hydrogen exosphere around the warm Neptune GJ436b showed that much larger atmospheric signals can be retrieved from the upper atmosphere of moderately irradiated, lower-mass planets. This opens thrilling perspectives for the characterization of the many small planets that will be discovered in the coming decade, especially around M-dwarfs, by missions like TESS and PLATO. 

In this seminar, I will review the main results that were obtained from the observation and modeling of giant planets’ upper atmospheres, and I will show how such observations can help us to understand the nature, the formation and evolution of smaller exoplanets.