Starting conditions for hydrothermal systems underneath Martian craters: Hydrocode modeling
E. Pierazzo, N.A. Artemieva, B.A. Ivanov, 2005. "Starting conditions for hydrothermal systems underneath Martian craters: Hydrocode modeling", Large Meteorite Impacts III, Thomas Kenkmann, Friedrich Hörz, Alex Deutsch
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Mars is the first place to look for any sign of present or past extraterrestrial life. Its surface shows many features indicative of the presence of surface and subsurface water, while impact cratering and volcanism have provided temporary and local surface heat sources throughout Mars' geologic history. In particular, impact-generated hydrothermal systems could have been some of the most favorable sites for the origin of life on Mars.
We present preliminary results of hydrocode simulations of impacts on Mars aimed at constraining the initial conditions for modeling the onset and evolution of a hydrothermal system on the red planet. Simulations of the early stages of impact cratering can identify the role of target composition and inhomogeneities in characterizing shock melting due to asteroidal and cometary impacts on the Martian surface. We find that cometary impacts produce significantly larger melt volumes than asteroidal impacts, thus affecting the thickness of the resulting melt sheet and its cooling history. The description of mixed targets is the main challenge of this study: unfortunately at this time, the lack of specific experimental data does not allow us to identify what is the best modeling approach (mixed cells versus mixed material equation of state) for mixed material targets. Modeling crater collapse is a necessary step to determine the final thermal state of the target underneath. We find that the combination of shock and plastic heating and the structural uplift of initially deeper strata create a water-bearing zone at depths where water is in the liquid stability field. In the central uplift, the high temperatures cause water to evaporate (steam-driven circulation). The simulations show that for a mid-sized crater (rim diameter around 30 km) the hydrothermal circulation is probably restricted to a “column” contained well within the final crater.