mercredi 14 septembre 2011, par David Ehrenreich (IPAG, Grenoble)
Mardi 18 octobre 2011 à 11h00 , Lieu : Salle de conférence du bât. 17
More than 600 extrasolar planets have been detected so far and an intense characterisation effort has been undertaken to unveil the atmospheric properties of some of these distant worlds seen in transit accross their stars. A large number of transiting exoplanets are found in extreme irradiation environments, very close to their stars, and the question arise of whether the atmospheres of these planets remain stable or get blown away. Atmospheric evaporation was observed in some hot giant exoplanets or "hot jupiters", but does not significantly alter the fate of these massive objects ( 300 Earth masses). Hot neptunes, on the other hand, are a class of exoplanets with typical masses around 20x Earth. They are the link between hot jupiters and super-earths (1 to10 Earth masses). It is surmised that the latters can be evaporation remnants, with atmospheres completely eroded by the extreme stellar irradiation. In this case, could hot neptunes be the progenitors of the hot rocky planets detected by the Corot and Kepler missions ? Detecting their extended atmospheres and measuring their mass loss rates and atmospheric heating efficiencies are key steps towards the understanding of the atmospheric dynamics and properties of low-mass exoplanets. After an introduction about planetary transits, I will review the results we have obtained with HST on the atmospheric evaporation of transiting exoplanets, on both observational and theoretical sides. I will finally discuss the prospects about atmospheric characterisation for Earth-size planets in more temperate - habitable - environments, and how the upcoming transit of Venus in June 2012 and the PLATO mission proposed to ESA could lead to a new era where atmospheric characterisation is common for hundreds of Earth-like exoplanets.
Seminar in french