Mars Atmosphere History and Surface Interactions

A fundamental question about the surface of Mars is whether it was ever conducive to life in the past, which is related to the broader questions of how the planet’s atmosphere evolved over time and whether past climates supported widespread liquid water. Taken together, geochemical data and models support the view that much of the original atmospheric inventory was lost to space before about 3.5 billion years ago. It is widely believed that before this time the climate would have needed to be warmer in order to produce certain geological features, particularly valley networks, but exactly how the early atmosphere produced warmer conditions is still an open question. For the last 3.5 billion years, it is likely that Mars has been cold and dry so that geologically recent outflow channels and gullies were probably formed by fluid release mechanisms that have not depended upon a warm climate.