EXPLORING MARS’ EARLIEST AQUEOUS ENVIRONMENTS

The last fifteen years have marked a critical period in the exploration of Mars. Three NASA orbiters, one ESA orbiter, one lander and three rovers have collected images, measured composition, and monitored modern day weather and surface processes. Collectively, the datasets have enhanced understanding of Mars system science and the coupling of various planetary processes during Mars ‘evolution. Some of the most outstanding scientific advances relate to the question of whether Mars may be or have once been a habitable world, evaluated by studying the nature and prevalence of environments with liquid water over the planet’s geologic history. Liquid water is not stable today on the Mars surface, but a growing body of evidence points to possible episodic water availability in the form of recurring slope lineae during Martian late spring on equator-facing slopes of a few craters and scarps. Over timescales of hundreds of thousands to millions of years, changes in Mars’ obliquity result in profound changes in the location and stability of water ice reservoirs and atmospheric pressure. Moreover, the advent of high spatial and spectral resolution mineralogic data from orbit coupled with landed explorations by rovers have revealed a diverse and complex history during Mars’ first billion years, preserved in the rock record. Here, I will review some of the findings about the earliest environments on Mars, including evidence for subsurface hydrothermal systems, paleolakes, and groundwater-fed playa systems with pH’s varying from acidic to alkaline. Data from the orbiting hyperspectral imager CRISM and data from the rovers Spirit, Opportunity, and Curiosity will be discussed. Finally, I’ll describe how ongoing explorations of Earth geology (in the poles, deserts, mafic/ultramafic terrains) are used to inform our understanding of ancient Mars.