Identifying Olivine Composition in Tyrrhena Terra, Mars, Using Orbital Mid-Infrared Data

Magnificent rock / Crater floors of melted Mars / Hold the olivine

Characterizing the Aqueous Geochemical History at Tyrrhena Terra, Mars

Tyrrhena Terra is an intriguing region of Mars extending from the southern part of Isidis Basin at the Libya Montes southward to Hellas Basin. Noachian and Hesperian basement rocks are covered by Syrtis lavas, especially in the northwestern part of Tyrrhena Terra and the surface is carved by craters and fluvial features. The central region is marked by the craters Jarry-Desloges, Owen, and Briault, and contains abundant Fe/Mg-rich phyllosilicates and olivine-bearing outcrops in Noachian-Hesperian terrain [1,2]. Many of the phyllosilicates in this region are located in crater ejecta and in central crater mounds, consistent with uplift of ancient materials, but some are present in dissected terrains. We are investigating the mineralogy and geology of this region through a coordinated study using TES, THEMIS, CRISM multispectral strips, CTX and HRSC imagery, and HRSC digital elevation models at a regional scale, as well as CRISM targeted images and HiRISE views of the surface at a closer scale. The phyllosilicate spectra across the central Tyrrhena Terra region (see attached figure) are most consistent with chlorite, Fe/Mg-smectite, and mixed smectite-chlorite. A few hydrated silica and zeolite outcrops are also present. This mineralogy is consistent with higher temperature processes than the primarily Fe/Mg-smectite and carbonate spectra observed in the Libya Montes region [3,4]. A few sites towards the east of our study site contain more Fe/Mg-smectite than chlorite and additional hydrated phases including sulfates, which likely represent a different formation environment. Ongoing investigations of the targeted CRISM images at the eastern part of this area are characterizing the stratigraphy of these aqueous units and their association with higher temperature units towards the west and smectite-carbonate units towards the north

Oxia Planum: The Landing Site for the ExoMars “Rosalind Franklin” Rover Mission: Geological Context and Prelanding Interpretation

The European Space Agency (ESA) and Roscosmos ExoMars mission will launch the “Rosalind Franklin” rover in 2022 for a landing on Mars in 2023.The goals of the mission are to search for signs of past and present life on Mars, investigate the water/geochemical environment as a function of depth in the shallow subsurface, and characterize the surface environment. To meet these scientific objectives while minimizing the risk for landing, a 5-year-long landing site selection process was conducted by ESA, during which eight candidate sites were down selected to one: Oxia Planum. Oxia Planum is a 200 km-wide low-relief terrain characterized by hydrous clay-bearing bedrock units located at the southwest margin of Arabia Terra. This region exhibits Noachian-aged terrains. We show in this study that the selected landing site has recorded at least two distinct aqueous environments, both of which occurred during the Noachian: (1) a first phase that led to the deposition and alteration of ∼100 m of layered clay-rich deposits and (2) a second phase of a fluviodeltaic system that postdates the widespread clay-rich layered unit. Rounded isolated buttes that overlie the clay-bearing unit may also be related to aqueous processes. Our study also details the formation of an unaltered mafic-rich dark resistant unit likely of Amazonian age that caps the other units and possibly originated from volcanism. Oxia Planum shows evidence for intense erosion from morphology (inverted features) and crater statistics. Due to these erosional processes, two types of Noachian sedimentary rocks are currently exposed. We also expect rocks at the surface to have been exposed to cosmic bombardment only recently, minimizing organic matter damage

Etude spectrale et géologique des phyllosilicates de Mars

La présence d eau liquide sur Mars est une question primordiale dans la recherche de milieux habitables extraterrestres. La planète nous a montré depuis les années 1970 des traces d écoulement d eau liquide. Depuis quelques années, nous cartographions des minéraux hydratés formés en grandes quantités par de l eau liquide : phyllosilicates, hydroxydes, sulfates... Le travail de ma thèse a consisté à étudier la minéralogie et la géologie de certaines régions, afin d essayer d y comprendre les conditions de formation de ces minéraux, et en particulier des phyllosilicates, grâce à l utilisation des données spectroscopiques, topographiques et d imagerie visible et infrarouge des sondes martiennes, et notamment d OMEGA et HRSC sur Mars Express. Les études des régions d Echus Chasma, de Terby Crater, de Tyrrhena Terra et de Mawrth Vallis ont révélé la corrélation des minéraux hydratés avec des roches parmi les plus anciennes de Mars. Les terrains finement stratifiés de la région de Mawrth Vallis nous montrent sur les données OMEGA la présence de divers phyllosilicates dans une unité épaisse de plusieurs centaines de mètres, et divisée en sous-unités de compositions différentes, marquant la complexité de l altération de ces terrains. Cette région est un des principaux témoins des environnements propices à la formation de phyllosilicates, qui ont dû être répandus à la surface de la planète au début de son histoire.The existence of liquid water on Mars is a fundamental question in the quest of habitability in extraterrestrial worlds. The planet showed since the 1970 s some liquid water flow features. For a few years, large quantities of hydrated minerals made by liquid water have been mapped: phyllosilicates, hydroxides, sulfates My thesis consisted in studying the mineralogy and geology of a few regions, to try to understand the conditions of formation of these minerals, thanks to the use of imagery, spectroscopy and topographic datasets of the martian probes, and especially OMEGA and HRSC on Mars Express. The study of the regions of Echus Chasma, Terby Crater, Tyrrhena Terra and Mawrth Vallis revealed the correlation between hydrated minerals and some of the oldest rocks on Mars. The finely layered terrains of the Mawrth Vallis region display on OMEGA data the presence of different phyllosilicates in a several hundreds meter thick unit, divided into sub-units of different compositions, indicating the complexity of the alteration of these terrains. This region is one of the main vestiges of the environments enabling the formation of phyllosilicates, which must have been widespread on the surface of the early Mars.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

The influence of bottom boundary layer hydrodynamics on sediment focusing in a contaminated bay

Understanding the dynamics and fate of particle bound contaminants is important for mitigating potential environmental, economic and health impacts linked to their presence. Vidy Bay, Lake Geneva (Switzerland), is contaminated due to the outfall and overflow from the wastewater treatment plant of the City of Lausanne. This study was designed to investigate the fate of particle-bound contaminants with the goal of providing a more complete picture of contaminant pathways within the bay and their potential spread to the main basin. This goal was achieved by investigating the sediment transport dynamics, using sediment traps and radionuclide tracers, and ascertaining how local bottom-boundary hydrodynamic conditions (temperature, turbidity, current velocity and direction) influence these dynamics. Results of the study indicated that sedimentation rates and lateral advections increased vertically with proximity to the lakebed and laterally with proximity to shore, indicating the presence of sediment focusing in the bay. Hydrodynamic measurements showed the persistent influence of a gyre within the bay, extending down to the lake bed, while just outside of the bay circulation was influenced by the seasonal patterns of the main basin. Calculated mean displacement distances in the bay indicated that suspended particles can travel similar to 3 km per month, which is 1.7 times the width of the Vidy Bay gyre. This results in a residence time of approximately 21 days for suspended particles, which is much greater than previously modelled results. The calculated mobility Shield parameter never exceeded the threshold shear stress needed for resuspension in deeper parts of the bay. In such, increased lateral advections to the bay are not likely due to local resuspension but rather external particle sources, such as main basin or shallow, littoral resuspensions. These external sources coupled with an increased residence time and decreased current velocity within the bay are the precipitating factors in sediment focusing. While the spread of contaminants from the bay may occur through the transport of fine suspended sediments in shallower zones of the bay (< 60 m) by longshore littoral currents, results suggest that particle-bound contaminants are likely to remain within the bay