Seminar by Audrey Chatain (LATMOS) – « Organic aerosols and methane clouds on Titan: combination of mission observations, laboratory experiments and climate models »

Titan, Saturn’s largest moon, is the only known moon with an atmosphere. It is in some ways very close to the Earth’s atmosphere, as it is mainly composed of N2, and reaches 1.5 bar at the surface. It is also quite exotic due to the presence of 5% CH4, which has important repercussions on Titan’s climate. First, the photodissociation of CH4 and N2 in the upper atmosphere starts a complex chemistry that leads to the formation of small organic solid aerosols. Secondly, at the cold temperatures of Titan’s lower atmosphere, the methane can condensate into ice or liquid, forming clouds, rain, rivers and lakes. To understand the complete interaction of methane with Titan’s climate, it is necessary to combine lab experiments to investigate the atmospheric chemistry and microphysics, and climate models to simulate at a larger scale their impact on the climate. The Cassini-Huygens mission gave insights and constraints on some observables that guide the lab and model works. Our results support the preparation of the future mission Dragonfly to Titan, by providing estimates for the surface composition and properties, and the weather expected at the landing site.