Étude des processus d'altération aqueuse et de maturation des surfaces par "space weathering" des astéroïdes primitifs en support aux futures missions spatiales de retour d'échantillons

Surface alteration processes on airless small bodies prevent the identification of primitive materials preserved since Solar System formation. Understanding how these modifications act on asteroids and change their spectra will provide a step toward better compositional interpretation of telescopic observations. This knowledge will also be valuable support for the forthcoming space missions planned to collect sample of primitive objects and bring it back to Earth. These asteroids are especially studied because they are thought to contain organic compounds and some water, key elements for life on Earth. Unaltered samples returns are crucial to precisely characterize these asteroids.Throughout my doctoral work, I studied these surface alterations -- also known as space weathering -- in order to propose a model of primitive surface maturation. I analysed spectral data from observations in the visible and near infrared ranges and find new evidence of space weathering on some specific primitive asteroid populations. Comparisons with meteorites are also made as asteroids are their parent bodies. A second approach performed in my work was to simulate space weathering effects in the laboratory using ion irradiation on meteorite samples. Such a global study on several carbonaceous chondrites had never been performed before. I show that the spectral changes are a function of initial composition. Space weathering studies must be pursued to decipher the physical, chemical and mineralogical changes it causes. I also investigated the aqueous alteration process among primitive Main Belt asteroids. Visible spectra of 600 objects were analysed to look for the absorption band indicating that liquid water had previously been present in this region of the Solar System. This study is the biggest statistical database for the aqueousalteration in the visible range. Together with recent dynamical models, these results allow us to understand the location of various compounds that originated at the time of planetary system formation and the evolution since that time.Les processus d'altération de surface des petits corps sans atmosphère empêchent l'identification des matériaux constituant ces témoins privilégiés des premières phases de la formation du Système solaire. Si comprendre comment ces modifications agissent sur les astéroïdes et transforment les spectres électromagnétiques de la lumière qu'ils envoient permettra de mieux interpréter les observations télescopiques, un autre enjeu actuellement est d'apporter un support d'exploitation des données des missions spatiales à destination d'objets primitifs. Ces astéroïdes en particulier intéressent la communauté scientifique puisqu'ils sont supposés contenir des matériaux carbonés et de l'eau, deux éléments essentiels à l'émergence de la vie sur Terre. Des retours d'échantillons sont précieux pour une caractérisation précise de ce type de corps, et la nécessité d'obtenir l'échantillon le moins altéré possible évidente.Durant cette thèse, j'ai étudié ces mécanismes de maturation -- appelés "space weathering" ou altération spatiale -- afin de proposer un modèle d'évolution des surfaces dites primitives. J'ai analysé des données spectroscopiques issues d'observations télescopiques dans les domaines de longueurs d'onde visible et proche infrarouge afin de mettre en évidence les effets de l'altération spatiale sur certaines populations d'astéroïdes primitifs. Des comparaisons avec les météorites, dont les astéroïdes sont les corps parents, sont également menées. Une seconde approche de la thématique a été faite via un travail expérimental pour simuler l'altération spatiale en laboratoire par irradiation ionique sur des échantillons météoritiques. Une étude complète sur plusieurs chondrites carbonées n'avait jusqu'alors jamais été proposée, et je montre que la réponse spectrale de telles surfaces aux irradiations est dépendante de la composition initiale. Les recherches sur l'altération spatiale doivent être poursuivies pour déchiffrer les modifications physiques, chimiques et minéralogiques qui s'en suivent.Un autre mécanisme dit d'altération aqueuse a été investigué parmi les astéroïdes primitifs de la Ceinture principale. Avec un total de 600 objets, cette étude constitue la plus importante base statistique de détection des indices spectroscopiques dans le domaine de longueurs d'onde visible de la présence d'eau liquide dans cette région du Système solaire. Combinés aux récents modèles dynamiques, ces résultats permettent de comprendre la répartition des divers éléments présents lors de la formation de notre système planétaire et quelle a été son évolution

ExoMars Raman Laser Spectrometer RLS, a tool for the potential recognition of wet target craters on Mars

In the present work, NIR, LIBS, Raman and XRD techniques have been complementarily used to carry out a comprehensive characterization of a terrestrial analogue selected from the Chesapeake Bay Impact Structure (CBIS). The obtained data clearly highlight the key role of Raman spectroscopy in the detection of minor and trace compounds, through which inferences about geological processes occurred in the CBIS can be extrapolated. Beside the use of commercial systems, further Raman analyses were performed by the Raman Laser Spectrometer (RLS) ExoMars Simulator. This instrument represents the most reliable tool to effectively predict the scientific capabilities of the ExoMars/Raman system that will be deployed on Mars in 2021. By emulating the analytical procedures and operational restrictions established by the ExoMars mission rover design, it was proved that the RLS ExoMars Simulator is able to detect the amorphization of quartz, which constitutes an analytical clue of the impact origin of craters. On the other hand, the detection of barite and siderite, compounds crystallizing under hydrothermal conditions, helps to indirectly confirm the presence of water in impact targets. Furthermore, the RLS ExoMars Simulator capability of performing smart molecular mappings was also evaluated. According to the obtained results, the algorithms developed for its operation provide a great analytical advantage over most of the automatic analysis systems employed by commercial Raman instruments, encouraging its application for many additional scientific and commercial purposes

Multiscale correlated analysis of the Aguas Zarcas CM chondrite

In this paper, we report the results of a campaign of measurements on four fragments of the CM Aguas Zarcas (AZ) meteorite, combining X‐ray computed tomography analysis and Fourier‐transform infrared (FT‐IR) spectroscopy. We estimated a petrologic type for our sampled CM lithology using the two independent techniques, and obtained a type CM2.5, in agreement with previous estimations. By comparing the Si‐O 10‐µm signature of the AZ average FT‐IR spectra with other well‐studied CMs, we place AZ in the context of aqueous alteration of CM parent bodies. Morphological characterization reveals that AZ has heterogeneous distribution of pores and a global porosity of 4.5 ± 0.5 vol%. We show that chondrules have a porosity of 6.3 ± 1 vol%. This larger porosity could be inherited due to various processes such as temperature variation during the chondrule formation and shocks or dissolution during aqueous alteration. Finally, we observed a correlation between 3D distributions of organic matter and mineral at micrometric scales, revealing a link between the abundance of organic matter and the presence of hydrated minerals. This supports the idea that aqueous alteration in AZ’s parent body played a major role in the evolution of the organic matter

Laboratory perspectives on sample returns from Hayabusa2 and OSIRIS-REx

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Irradiation of meteorites: decoding space weathering on low albedo asteroids

International audienceIn this presentation I will review the role of irradiation laboratory experiments on the understanding of space weathering and the interpretation of VNIR reflectance spectra of small bodies

More ion irradiated meteorites: expanding the space weathering view of dark asteroids

International audienceWe performed ion irradiation of dark meteorites as a simulation of slow solar wind irradiation of dark asteroid surfaces. As a follow-up of the reflectance spectroscopy study of several ion-irradiated carbonaceous chondrites from different petrologic groups (CO, CV, CM, CI, C2), we performed new ion irradiation of CK, CR, and CM meteorites to test composition effects. The results of these experiments are used to support current sample return missions Hayabusa2/JAXA and OSIRIS-REx/NASA

The Themis-Beagle families: clues into space weathering processes on primitive asteroids

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The Themis-Beagle families: clues into space weathering processes on primitive asteroids

International audienc

Aqueous and space weathering alteration processes on primitive asteroids: results from telescopic observations

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Aqueous and space weathering alteration processes on primitive asteroids: results from telescopic observations

International audienc