The planet Mars has engaged the curiosity of scientists and amateurs alike for centuries, but many aspects of its evolution remain poorly understood. In particular, Mars contains abundant evidence for erosion by liquid water 3-4 Ga, but due to the faintness of the young Sun, basic climate theory suggests its surface should have been extremely cold. Here I describe our recent progress on this important planetary science problem. Based on 3D climate modeling results, I describe how adiabatic cooling under a thicker CO2 atmosphere would have led to stabilization of snow and ice deposits in the highland regions where most surface aqueous alteration is recorded. I then show that bursts of reducing gases (H2 and CH4) outgassed into this atmosphere, would have led to intense intermittent warming on moderate (10^4 - 10^5 y) timescales. This scenario fits many aspects of the geologic record and will be amenable to further in-situ testing by the Mars 2020 rover. Finally, I will discuss some recent work we have done on the prospects for making Mars regionally habitable again in the future.
Robin Wordsworth / Harvard
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