Deep clays and surface weathering: two types of alteration on Mars

During the last decade, Martian Orbiters and Rover missions have provided new evidences of the ancient role of liquid water on Mars: we now have mineralogical detections to be added to the previous morphological observations. Liquid water is our most important tracer of a possible habitability of other planets and satellites. One of the discoveries concerns the phyllosilicates (e.g. clay minerals) which form by alteration of other rocks, over extant period of time, in the presence of liquid water. They have been detected and mapped from orbit by Mars Express (ESA) and Mars Reconnaissance Orbiter (NASA), and are driving the selection of landing sites on Mars for the future rover missions (Mars Science Laboratory, ExoMars...). Following the detection of these hydrated minerals, we need to understand the geological and climatological context of their formation, to constrain when water was present, how much and for how long, and the chemical environment at that time. I have been studying clay-bearing outcrops on Mars with many different datasets from the last 4 Martian orbiters. I will describe two very different types of environments were clays-bearing units formed, from kilometer depth to surface weathering.