Impact degassing and atmospheric erosion on Venus, Earth, and Mars during the late accretion

Abstract

The atmospheres of the terrestrial planets are known to have been modified as a consequence of the impact degassing and atmospheric erosion during the late accretion. Despite the commonality of these processes, there are distinct gaps – roughly two orders of magnitude – between the abundances of noble gases and nitrogen in the present-day atmospheres on Venus, Earth, and Mars. The element partitioning on planetary surfaces is thought to be significantly different between the three planets ∼ 4 Ga: the runaway greenhouse on Venus, the carbon-silicate cycle and ocean formation on Earth, and the CO2-ice and H2O-ice formation on Mars. Consequences of element partitioning for the atmospheric evolution during the late accretion onto Venus, Earth, and Mars are investigated with a numerical model. We set upper limits to the partial pressures of CO2 and H2O on Earth and Mars, which corresponds to the state of phase equilibrium and carbon-silicate cycle. The final N2 mass shrinks by ∼ 40% and ∼ 15% for Earth and Mars, respectively. The effect of element partitioning is found to be insufficient to reproduce the gaps. For Venus, the survival of the primordial atmosphere through the late accretion may partially account for the present-day atmosphere. Whereas on Mars, the atmospheric escape due to solar extreme UV and wind may have also influenced the atmospheric evolution.