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Physico-Chimie organique de l’atmosphère de Titan – CAT

Submission summary

1-Scientific background and objectives The physical and chemical properties of solid aerosols in planetary atmospheres, as well as their way of formation, remain today not well understood. However, the complex organic matter thus produced is of great interest for astrobiology, and these aerosols are crucial to understand the climate of these planets. Among the solar system bodies getting a dense atmosphere, Titan is of particular interest because its structure is similar to the Earth one. In the Titan's atmosphere, the gas to solid conversion is chemically generated, and induced by solar photons and energetic particles. Thanks to the Cassini-Huygens space mission, operational since 2005, numerous data can have been acquired on the atmosphere, revealing processes not predicted before the arrival of the mission. Despite the amazing progresses done thanks to these data, it remains today extremely difficult to precise the phycio-chemical mechanisms which generate the gas to solid conversion. This is due to the limitation of the data necessary to characterize these mechanisms, such as the knowledge of the chemical composition of the Titan's aerosols. For these reasons, laboratory simulations are necessary to characterise these processes. The objective of this project is to simulate and study the formation of the Titan's aerosols with a radio-frequency plasma, as well as the chemical and physical properties of the organic solid particles produced by this way. 2'Description of the project and methodology. The plasma used is a RF Capacitively Coupled Plasma. In this type of plasma, solid particles are maintained in levitation by electrostatic forces, and they grow in the gaseous phase without any surface interaction. This process is original because, up to now, tholins produced by plasma are deposited on solid substrate and their production and properties could be affected by the substrate. The RF plasma set up of the laboratory has to evolve in order to study in-situ the processes of formation of the solid particles. The aims of this project are the following: -the study of the physical and chemical properties of the organic solid particles produced; -the study of the gas composition during the particles formation and growth to understand the relationship between the two physical states; -the study of temperature conditions closer to the Titan's atmosphere one; - the development of a chemical model representative of the chemistry taking place in the upper atmosphere of Titan - the extension of all of this work to other solar system bodies, the giant planets In order to fulfill the objectives of this project, young scientists from LATMOS getting complementary competences in phydico-chemistry of the organic matter, physico-chemistry of the gaseous phase, and physico-chemistry of ionized media, associted together. This project however requires for the presence of a specialist of the reactive medium used to simulate the Titan's chemistry., asked in this project to be a post-doc. An evolution of the diagnostics of characterisation of the reactive medium is also required. This will be the addition of an IR spectroscope to the experimental set-up. 3'Expected results This project will give a significant progress in the understanding of the whole chemical chain of gas to organic solid particles conversion. This transition is important both for processes taking place in the Titan's atmosphere, but also for other planetary atmospheres (giant planets). The obtained results from in situ analysis of the plasma will be also useful for the interpretation of Cassini Huygens results. A best knowledge of Titan's aerosols and of its atmospheric chemistry is expected, especially by the modelling of the chemistry of its upper atmosphere.

Project coordinator

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

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Beginning and duration of the scientific project: - 0 Months

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