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PhD Defense

Martin Turbet (LMD)

Title : Habitability of planets using numerical climate models. Application to extrasolar planets and early Mars."

Date and time : The 03-09-2018 at 14h00

Type : thèse

Université qui délivre le diplôme : Sorbonne Université

Location : Salle de conférence de l'UFR Terre, Environnement, Biodiversité de Sorbonne Université - Campus de Jussieu - 4 place Jussieu - Couloir 46-56, 2ème étage - 75005 Paris
Members of jury :

M. James KASTING (Penn State University), rapporteur
Mme Giovanna TINETTI (University College London), rapporteuseM. Jacques LE BOURLOT (LERMA), examinateur et président du jury
M. Jérémy LECONTE (Laboratoire d'Astrophysique de Bordeaux), examinateur
M. Emmanuel MARCQ (LATMOS), examinateur
M. Raymond PIERREHUMBERT (Oxford University), examinateur
Mme Ha TRAN (Laboratoire de Météorologie Dynamique), examinatrice
M. François FORGET (Laboratoire de Météorologie Dynamique), directeur de thèse

Summary :

Ancient rivers and lakes discovered on Mars. Numerous temperate, Earth-sized extrasolar planets detected around nearby stars. Thanks to ground and space-based telescope observations and Solar System exploration missions, we now have a fantastic playground to explore scientifically how prevalent life is in the Universe. The main goal of my thesis work is to better understand the conditions necessary for a planet to maintain liquid water - a primary building block for life - on its surface. Using sophisticated 3-D numerical climate models, as well as spectroscopic calculations and measurements, I conducted two major investigations during my thesis. First, I explored the environments of ancient Mars at multiple epochs in order to understand the conditions in which the enigmatic Martian rivers were carved. Apart from Earth, Mars is the only planet that has been habitable, but we don't know why. I showed that extreme events (outflow channel formation events, meteoritic impacts) that scarred the surface of Mars cannot by themselves explain the formation of these valley networks. Nonetheless, I showed that the presence of reducing greenhouse gases such as hydrogen and/or methane offers a promising alternative solution. Secondly, I studied the possible atmospheres of solid, temperate extrasolar planets, with a particular focus on those orbiting small stars such as Proxima Centauri and TRAPPIST-1. I showed that some of these planets have characteristics that are highly favourable to the presence of liquid water on their surface. This result is really promising as it will be soon become possible - as demonstrated in my thesis for Proxima b - to characterize the atmosphere of these planets with the future JWST (James Webb Space Telescope) and ELTs (Extremely Large Telescopes) astronomical observatories.

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