Dry Late Accretion inferred from Venus' coupled atmosphere and internal evolution

Abstract

The composition of meteoritic material delivered to the terrestrial planets after the end of core formation as late accretion remains contentious. Because the evolution of Venus' atmospheric composition is likely to be less intricate than the Earth's, we test implications of wet and dry late accretion compositions, using present-day Venus atmosphere measurements. Here we investigate the long-term evolution of Venus using self-consistent numerical models of global thermochemical mantle convection coupled with both an atmospheric evolution model and a late accretion N-body delivery model. Atmospheric escape is only able to remove a limited amount of water over the history of the planet. We show that late accretion of wet material exceeds this sink. CO2 and N2 contributions serve as additional constraints. A preferentially dry composition of the late accretion impactors is in agreement with observational data on H2O, CO2 and N2 in Venus' present-day atmosphere. Our study suggests that the late accreted material delivered to Venus was mostly dry enstatite chondrite, conforming to isotopic data available for Earth. Our preferred scenario indicates late accretion on Venus contained less than 2.5% wet carbonaceous chondrites. In this scenario, the majority of Venus' and Earth's water has been delivered during the main accretion phase.