Exo-Atmos

The discovery of extrasolar planets is a revolution in modern astrophysics which impacts not only our knowledge of planet formation and evolution, but also our understanding of the place of the Earth in the Universe. In this domain major advances have been made by using spectroscopic observations of transiting planets. Using this technique, we discovered an unexpected phenomenon : the evaporation of hot-Jupiters, and we made a detailed study of the atmosphere of the exoplanets HD209458b and HD189733b. Observations of transiting planets are now widely recognized as a powerful method to scrutinize the atmosphere of these exoplanets. The present “Exo-Atmos” programme is aimed at constraining both the extended upper atmosphere of evaporating planets, and the deeper atmosphere of a large variety of exoplanets, using transit spectroscopy observations. These objectives will be reached by two means: 1) We will observe with the best telescopes presently available: Very Large Telescope (VLT) and the Hubble Space Telescope (HST). 2) We will also enlarge the sample of planets for which atmosphere are detected and analysed. Indeed, we have obtained a large amount of time on the HST and the VLT telescopes to observe the atmospheres and evaporation of extrasolar planets. For instance, with 3 HST programs in 2012 we will observe a total of 10 planets (9 exoplanets + Venus as a benchmark). This will allow us to scrutinize the atmosphere of an unprecedented large sample of exoplanets, and will open the field of comparative exoplanetology. However, to obtain the best scientific return of these programs, a substantial financial support is required. Here we propose an ANR program to support this work. In addition to financial support for missions and equipment, we ask for 2 post-doctoral fellowships of 2 years, one for each of the two partners of the project. Finally, we ask for financial support for the acquisition of a powerful computer that will be dedicated to numerical simulations for the analysis and interpretation of HST spectroscopic observations, and modeling of the gas escape. These simulations will be designed to better constrain the structure, dynamics and composition of the atmospheres of planets observed by transit spectroscopy. In particular, a significant part of the CPU time will be dedicated to issues related to the evaporation of planets orbiting close to their star, an area in which our team has played a major role. Combined with the results of these simulations, the HST observations will allow to better constrain the escape rate and the evaporation mechanisms. At the end of this 3 year program "Exo-Atmos," we aim to better understand the atmosphere and evaporation of exoplanets.