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T.L. Segura, A. Colaprete, O.B. Toon (LASP/University of Colorado)
The dendritic nature of the Martian valley networks, which date back 3.5-3.8 billion years, suggests that at some point in its history Mars possessed liquid water. The age of the valley networks coincides with the period of heavy bombardment in the solar system. One large (D > 50 km) impact to early Mars delivers enough energy (~ millions of megatons) to provide all the water that once filled the valley networks. An impact of this energy would completely vaporize both the impactor and a significant area of the target and would throw material into the upper atmosphere. On Earth, injection of water (both from the surface and the impacting body) into the atmosphere has a net warming effect, as water vapor is an efficient greenhouse gas. Mars also possesses water on its surface, in the solid phase, and thus we would expect the same phenomenon to occur there. In this research we explore the effects of a large impact on the Martian subsurface and atmospheric temperature profiles, how long such a perturbation would last, and whether the valley networks might have been formed as a result of a large impact. We use a 1-D radiative-convective greenhouse model coupled to a subsurface model to simulate the conditions after impact. Preliminary runs of our model show that Mars may have been kept above freezing for at least decades by the effects of a large impact.
The authors wish to thank the University of Colorado Astrobiology Program and NASA for support for this research.
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