Tyrrhena Terra: Hydrated Lobate Ejecta and Plains

Introduction: The Phyllosian period of Mars [1] displays rocks that are altered at different levels, containing phyllosilicates of various natures, revealing that liquid water played a strong role in their formation. However, debates currently exist to know if this alteration was conducted at the surface in concert with active hydrologic cycle, or in the subsurface in a hydrothermal or warm, wet crust environment. Here, we display new results in the Tyrrhena Terra region, which is of interest to address this issue. Tyrrhena Terra is located in cratered Noachian highlands in the southern hemisphere, south of Isidia Planitia and north of Hellas basin (Fig. 1). This region displays highland terrains partially dissected by fluvial valleys and several intercrater plains. This region was reported [2; 1; 3; 4] as one of the Martian region displaying outcrops rich in hydrated minerals, by the identification of a weak 1.9 μm absorption band on spectra acquired by OMEGA, the imaging spectrometer onboard Mars Express. In addition, CRISM observes phyllosilicates associated with crater ejecta blankets and in mounds and knobs on crater floors [5; 6].