Sunday, January 31, 2016

Impacts by Comets and Asteroids Since the Noachian Probably NOT the Cause of Martian Atmospheric Loss

Scenarios of atmospheric mass evolution on Mars influenced by asteroid and comet impacts since the late Noachian


Pham et al


Early in its history, Mars probably had a denser atmosphere and higher surface temperatures to sustain the presence of stable liquid water or saline solution at the surface. Impacts by asteroids and comets could affect the atmospheric evolution of a planet, by removing part of its atmosphere and by delivering into it material and volatiles. In this study we investigate the atmospheric loss and delivery of volatiles between the end of the Noachian and present, with the help of a semi-analytic model. Our results suggest that impacts alone can hardly remove a significant amount of atmospheric mass over this period. Contribution of additional factors such as outgassing and non-thermal escape processes can not explain neither the presence of surface pressure larger than few hundreds of mbars 3.9 Gyr ago, unless parameter values outside of their expected range are considered. Based on extreme case scenarios, maximum surface pressures at the end of the Noachian, could be as much as 0.25 bar or 1.9 bar, with and without CO2 storage into carbonate reservoirs, respectively.

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