The Earliest Aqueous, Habitable Environments on Mars: A View from Orbit

The emerging picture of Mars' first billion years includes diverse environments involving liquid water and chemical alteration. Clay, carbonate, chloride, and sulfate minerals have all been detected and mapped from orbit in coherent geologic units. When near-infrared spectroscopic detections of minerals from the orbiting CRISM imaging spectrometer are coupled with high-resolution images of morphology provided by orbiting cameras, distinctive aqueous, potentially habitable, environments can be identified, preserved in the geologic record. These include hydrothermal, near-surface weathering, and lacustrine settings. I will give a global overview of the most recent findings, delve into the details of transitions recorded in a few key stratigraphic sections, and discuss the evidence for the hypothesis that the most widespread and long-lived aqueous environments on early Mars were in the subsurface.