Résumé / Abstract Journal-club_Doctorants

Journal-club Doctorants / Journal-club PhD students

« Are we alone in the Universe? »

Amélie Gressier
Institut d'Astrophysique de Paris (Paris, France)

Drake's equation provides a quantitative formula to this question and one of the many parameters involved is the fraction of planets on which life appears. We are quite far from being able to determine this probability, but studying the atmosphere of exoplanets is one way to get closer to a solution. The low mass planets are particularly interesting because they have no representatives in the solar system and yet they are the most numerous. Their nature (rocky, gaseous, ocean world) and their composition (water, carbon dioxide, ammonia) are difficult to constrain but could again shake up our knowledge of the solar system and planet formation.

Exoplanets detection is now routine with more than 4000 planets discovered, but atmospheric characterization is way more difficult and only a few percent’s have been studied. Transit and eclipse spectroscopy allow us to probe the planet's exosphere, where atmospheric escape takes place, down to deep layers and observe 3D effects of atmospheric circulation. Using Bayesian radiative transfer codes that include accurate molecular line-lists, we analyze HST observations and retrieve the atmospheric composition that causes the spectrum absorption in precise wavelength bands. As an example, we analyzed spatially scanned spectroscopic observations obtained with the G141 grism (1.125 - 1.650 µm) of the Wide Field Camera 3 (WFC3) on two Sub-Neptune planets. We found evidence of water vapor in both the planetary atmosphere with an abundance around 10^(-3) mixing ratio, using Iraclis pipeline and Tau-Rex 3. Low-mass planets will be interesting targets for upcoming telescopes such as JWST and ARIEL to highlight differences in atmospheric properties and better discriminate the transition between rocky and gaseous planets.
vendredi 15 mai 2020 - 16:00
Webinaire, Institut d'Astrophysique
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