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T.L. Segura, O.B. Toon (University of Colorado at Boulder), A. Colaprete, K. Zahnle (NASA-Ames Research Center)
The impacts of asteroids and comets of greater than 100 km in diameter have left more than thirty craters on Mars. Collisions of such large, energetic objects result in the production of meters thick global rock rain layers, that have temperatures in excess of 1600 K. These global rock melt layers warm the near-surface regolith of the planet considerably, melting subsurface water and keeping it above freezing for decades or even centuries. In addition, large impacts inject into the atmosphere a substantial amount of vaporized water, both from the impactor itself and from the target material on the planet, which will condense and precipitate out. We use a 1-dimensional radiative transfer code coupled to a time-marching finite-difference 1-dimensional subsurface model to calculate the evolution of the atmospheric, surface, and subsurface temperatures following the impact. The model is adjusted for early Martian conditions by reducing the solar constant to 75 its present value, and by increasing the post impact CO2 presssure to 150 mbar. The melted subsurface water, and the injected vaporized water will contribute to a global surface water layer meters or more in depth. The global water layer resulting from a large impact would form rivers and may be responsible for the observed valley networks on Mars.