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David Dubois (LATMOS)

Titre : Ion, Neutral and Solid-State Chemistry in Titan's Atmosphere: An Experimental Approach

Date et heure : Le 01-10-2018 à 14h00

Type : thèse

Université qui délivre le diplôme : UVSQ

Lieu : Salle des thèses (2ème étage), Bâtiment d'Alembert, 7 boulevard d'Alembert, 78280 Guyancourt
Membres du jury :

Mme Nathalie CARRASCO, Université de Versailles-Saint-Quentin-en-Yvelines - Directrice de thèse

Mme Véronique VUITTON, Université de Grenoble Alpes - Rapporteure

M. Nicolas FRAY, Université Paris-Est Créteil Val-de-marne - Rapporteur

Mme Sandrine VINATIER, Observatoire de Paris-Meudon - Examinatrice

M. Francois LEBLANC, Université de Versailles-Saint-Quentin-en-Yvelines - Examinateur

M. Cyril SZOPA, Université de Versailles-Saint-Quentin-en-Yvelines - Examinateur

M. Murthy Gudipati, Jet Propulsion Laboratory - Invité

Résumé :

Titan, orbiting Saturn, is the only moon in the Solar System to possess its own dense and gravitationally-bound atmosphere, and is even larger than planet Mercury. Its rocky diameter is a mere 117 km shy of Ganymede’s. If we were to scoop up a 1 cm3 sample from Titan’s upper atmosphere, we would find two dominant molecules: molecular nitrogen N2 and methane CH4. Should we look a bit more carefully, we would find many neutral molecules and positive and negative ion compounds. These chemical species are the outcome of processes resulting from energetic radiation reaching Titan’s upper atmosphere, breaking apart the initial N2 and CH4. A cascade of subsequent reactions will trigger the formation of new more and more complex gas phase products. Eventually, these products mainly containing hydrogen, carbon and nitrogen will form large fractal aggregates composing the opaque haze enshrouding the surface of Titan. This haze is what gives Titan such a unique brownish hue. Most of the photochemically-produced volatiles will eventually condense in the lower atmosphere, where they may aggregate to form micrometer-sized icy particles and clouds. During my PhD, I have focused my studies on (i) the gas phase reactivity of aerosol precursors in experimental conditions analogous to Titan’s upper atmosphere, and (ii) the end of life of some of the products as they condense in the lower and colder atmosphere. I used two experiments to address these respective issues: the PAMPRE plasma reactor, located at LATMOS, UVSQ, Guyancourt, France, and the Acquabella chamber at the Jet Propulsion Laboratory, NASA-Caltech, Pasadena, USA. I present my work on the neutral-ion coupling reactivity as well as ice photochemistry resulting from irradiation in near-UV wavelengths.

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