The Geologic History Of Water On Mars
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Dr. Robert Craddock
Geologist
Smithsonian, National Air and Space Museum
Features such as valley networks and outflow channels suggest that at one time in the past Mars may have had liquid water on the surface. The interpretation has been that water was present for only a short time, outflow channels formed catastrophically, and the conditions necessary to support liquid water quickly died. Now, however, new analyses of lander and orbiter data are helping investigators to piece together a geologic history of water on Mars that suggests something that is much more complicated. The evidence indicates that initially there was a global arid climate capable of supporting rainfall while slowly eroding impact craters as they formed. Gradually these conditions improved where rainfall intensified and a sustained hydrologic cycle became possible, resulting in the formation of the valley networks. Perhaps the hydrologic cycle was supported by a northern ocean. Initiation of outflow channel formation may have begun when enough water from the atmosphere had infiltrated into the regolith to create the necessary hydraulic head. As Mars lost its primordial atmosphere, favorable conditions became more localized. Of course, this interpretation of the geology is controversial because of the "faint young sun paradox" and the failure of many climate models to create warmer surface environments on ancient Mars. However, new climate models may have resolved this problem. Are the empirical and theoretical data finally agreeing? Have we resolved the geologic history of water on Mars? What are some of the questions that remain? And what are some of the areas of research current graduate students may explore during their scientific careers to advance this topic?
Host: Dr. Jeffrey Andrews-Hanna