Aérosols atmosphériques de haute altitude

Atmospheric aerosols are present in many planetary environments, including the Earth and Saturn's largest satellite, Titan. With their varied physical and chemical properties, their presence influences various atmospheric processes. To understand their impact, we need to characterize their properties, using samples collected in the natural environment or synthesized through laboratory experiments. During my thesis, I was able to combine the experimental approach with instrumental development to study aerosols from Titan analogues and terrestrial stratospheric aerosols. Using a powder plasma reactor and a photochemical reactor, various aerosol productions were carried out to observe their optical properties, and the evolution of their morphology and chemical composition. Certain mechanisms of aerosol formation and growth were correlated with the kinetics of gaseous products derived from the gaseous mixture ionized in the experiments, and considered as potential precursors of solids. I was able to take part in the development of an atmospheric aerosol collector for ground-based stratospheric balloon-borne measurements.Les aérosols atmosphériques sont présents dans de nombreux environnements planétaires tels que la Terre et le plus grand satellite de Saturne, Titan. De part leurs aspects variés que ce soit au niveau de leurs propriétés physiques et chimiques, leurs présences influencent les différents processus atmosphériques. Pour comprendre leurs impacts, la caractérisation de leurs propriétés apportent les informations nécessaires, et peut se réaliser à partir d'échantillons collectés dans le milieu naturel ou synthétisé à l'aide d'expériences en laboratoire. Au cours de ma thèse, j'ai pu allier l'approche expérimentale et le développement instrumental pour étudier des aérosols d'analogues de Titan et les aérosols stratosphériques Terrestres. À l'aide d'un réacteur à plasma poudreux et d'un réacteur photochimique, différentes productions d'aérosols ont été réalisées pour observer leurs propriétés optiques, et l'évolution de leurs morphologie et composition chimique. Certains mécanismes de formation et de croissance de ces aérosols ont pu être corrélés à la cinétique de produits gazeux issus du mélange gazeux ionisé au sein des expériences, et considérés comme précurseurs potentiels des solides. J'ai pu participer au développement d'un collecteur d'aérosols atmosphériques pour la réalisation de campagne de mesures stratosphériques terrestres par ballon-sonde

Analogues of Titan's aerosols: the different steps of formation in a N₂-CH₄ plasma

International audienceObservations by the Cassini mission show the presence of aerosols in Titan's atmosphere. According to models, these aerosols should reside there during several years. A plasma reactor is used to simulate the production of aerosols in the upper atmosphere of Titan. Five productions of aerosols were carried out with different residence times in the plasma, corresponding to different stages of evolution. These analogues were then analyzed by electron microscopy and infrared spectroscopy. Our results show that aerosols undergo morphological evolution in time. They grow and start forming aggregates at a certain stage. In addition, we also observed evolutions of the chemical functions present in the aerosols of different formation times

Sediment transport by boiling seeping water: exploring effects of grainsize and atmospheric conditions

International audienceMany active and recently active surface processes on Mars have been controversially linked to the action of liquid water, yet the sediment transport capacity of water under martian environmental conditions is poorly understood. An understanding of the sediment transport capacity allows the amount of water required for any given landform to be back-calculated from its observed size/volume at the martian surface. Here we present a series of experiments where we explore the effects of grainsize, atmospheric pressure, humidity and temperature on the sediment transport capacity of seeping liquid water under martian conditions

Molecular hydrogen in CO₂-dominated atmospheres of terrestrial exoplanets : impact on the photochemical formation of water

International audienceAs for the rocky planets of the Solar System, the atmosphere of terrestrial exoplanets is affected by volcanic outgassing. Significant emissions of molecular hydrogen are expected in the early stage of their evolution. In the upper atmosphere, molecular hydrogen becomes photochemically active along with CO2. Laboratory experiments conducted highlight a significant formation of water which strongly depends on the concentration of molecular hydrogen

Molecular hydrogen in CO₂-dominated atmospheres of terrestrial exoplanets : impact on the photochemical formation of water

International audienceAs for the rocky planets of the Solar System, the atmosphere of terrestrial exoplanets is affected by volcanic outgassing. Significant emissions of molecular hydrogen are expected in the early stage of their evolution. In the upper atmosphere, molecular hydrogen becomes photochemically active along with CO2. Laboratory experiments conducted highlight a significant formation of water which strongly depends on the concentration of molecular hydrogen

Optical Constants of Titan's haze analogs particles from 3 to 10 μm

International audienc

Optical Constants of Titan's haze analogs particles from 3 to 10 μm

International audienc

Optical Constants of Titan's haze analogs particles from 3 to 10 μm

International audienc

An atmospheric origin for a HCN-derived polymer on Titan

International audienceTitan’s haze is strongly suspected to be an HCN-derived polymer, but despite the first in situ measurements by the ESA-Huygens space probe, its chemical composition and formation process remain largely unknown. To investigate this question, we simulated in the laboratory, the atmospheric haze for- mation process. We synthesized analogues of Titan’s haze, named Titan tholins, in an irradiated N2–CH4 gas mixture, mimicking Titan’s upper atmosphere chemistry. HCN was monitored in situ in the gas phase simultaneously with the formation and evolution of the haze particles. We show that HCN is produced as long as the particles are absent, and is then progressively consumed when the particles appear and grow. This work highlights HCN as an effective precursor of Titan’s haze and confirms the HCN-derived polymer nature of the haze