Etude de la diversité géochimique de la surface de Mars, à partir des données de spectrométrie X de la mission Mars Exploration Rover ; Modélisation de l'altération des roches martiennes

摘要

Since 2004, the twin rovers Spirit and Opportunity of the MER (Mars Exploration Rover) mission have been investigating their respective landing sites at Gusev Crater and Meridiani Planum. This PhD thesis deals with the analysis and the interpretation of the data from the APXS (Alpha-Particle X-ray Spectrometer) instrument located on the robotic arm of each rover and whose role is to determine the chemical composition of Martian rocks and soils by X-ray spectrometry. Thanks to their extraordinary longevity, Spirit and Opportunity have been able to reach distances several km from their initial landing sites and the APXS instruments have analyzed numerous samples, yielding clues about the role that water could have played in the Martian past. In a first time, I chose to investigate this diversity of samples thanks to a multidimensional analysis technique. This allowed me to perform a classification of samples and to highlight the petrogenetic relationships between rocks and soils from Gusev and Meridiani. I will present the main results obtained with this method and their connections with the spatial and stratigraphic organisation of the samples. Then I will show how these results led me to explore a numerical geochemical model of SO3 acid fog alteration of Martian basalts. I will describe the hypotheses of this model before comparing its results with MER data. We will finally see what are the implications about the geology of the sites of Gusev and Meridiani, and more generally about the geological history of Mars and the conditions that prevailed at its surface in the past.