Comprehensive studies of the sputtering effects on CO2 atmospheres: Mars and Venus

The atmospheric loss rates related to the solar wind interactions with the weakly magnetized planets in the inner solar system are important for understanding their evolution histories. Besides photochemical mechanisms, sputtering by the re-impact of the heavy pick-up ions may play a key role, provided that their planetary fields were weak throughout much of their past. We use a 3D Monte Carlo model coupled to a molecular dynamic calculation to simulate the atmospheric sputtering effects due to pick-up O+ on CO2 atmospheres of Venus and Mars. The pick-up O+ precipitation distributions are obtained from a 3D Monte Carlo Pickup Ion Transport model, which includes the electromagnetic backgrounds from the 3D multi-species MHD simulations. The influences on the sputtering efficiencies due to different atmosphere and exosphere structures, the existence of the crustal fields at Mars, and the variation with the solar wind conditions at their heliocentric distances are examined for the two planets. The escape rates and the formation of hot coronae due to sputtering are compared in order to provide a comprehensive point of view on the sputtering efficiencies of these two terrestrial planets with CO2 atmospheres.