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Aerosols-plasma interaction in Titan’s ionosphere

Audrey Chatain 1, 2
1 IMPEC - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : The climatic system of Saturn’s moon Titan is governed by the intense production of organic aerosols in its upper atmosphere. This phenomenon also certainly happened on Earth at the beginning of life. These two points strongly motivate research on the formation and evolution processes of the aerosols in the atmosphere of Titan. The aerosols form and stay several weeks in the ionosphere, between ~900-1200 km of altitude. This atmospheric layer is ionized by UV solar rays and energetic particles coming from Saturn’s magnetosphere, forming a plasma with very reactive species: radicals, excited species, ions and electrons. In such an environment, the main question I tackle is how the organic aerosols interact with the plasma species.The phenomenon is simulated in the laboratory with a plasma setup developed on purpose: analogues of Titan aerosols are exposed to a N2-H2 plasma discharge. Both an evolution of the solid and the gas phase are observed. H and N atoms chemically interact with the aerosols. Then, hydrogen cyanide (HCN) and other organic molecules are ejected in the gas phase by ion sputtering. These results highlight an important contribution of heterogeneous processes in Titan’s upper atmosphere.My re-analysis of the Cassini Langmuir probe data revealed the presence of an unexpected electron population in the ionosphere, below 1200 km and on the day-side, where heavy ions are also detected. These electrons could be emitted by the aerosols, after collision with a photon, and/or heating by the active ion chemistry.
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Audrey Chatain. Aerosols-plasma interaction in Titan’s ionosphere. Astrophysics [astro-ph]. Université Paris-Saclay, 2020. English. ⟨NNT : 2020UPASV022⟩. ⟨tel-02971735⟩

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