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Theses

Study of Titan’s Upper and Lower Atmosphere: An Experimental Approach

David Dubois 1
1 IMPEC - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : Titan 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 gas phase products more and more complex. Eventually, these products mainly containing hydrogen, carbon and nitrogen will form large fractal aggregates composing the opaque haze en- shrouding 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 (Chapters 3 & 4), and (ii) the end of life of some of the products as they con- dense in the lower and colder atmosphere (Chapter 5). 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, California Institute of Technology, Pasadena, USA. In this manuscript, I present my work on the neutral and positive ion reactivity in the PAMPRE plasma discharge, as well as ice photochemistry results using laser irradiation in near-UV wavelengths.
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David Dubois. Study of Titan’s Upper and Lower Atmosphere: An Experimental Approach. Planetology. Université de Versailles Saint Quentin en Yvelines (UVSQ), France, 2018. English. ⟨tel-01925462v1⟩

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