Article révisé par les pairs
Résumé : It remains contentious whether the meteoritic material delivered to the terrestrial planets after the end of core formation was rich or poor in water and other volatiles. As Venus’s atmosphere has probably experienced less volatile recycling over its history than Earth’s, it may be possible to constrain the volatile delivery to the primitive Venusian atmosphere from the planet’s present-day atmospheric composition. Here we investigate the long-term evolution of Venus using self-consistent numerical simulations of global thermochemical mantle convection coupled with both an atmospheric evolution model and a late accretion N-body delivery model. We found that atmospheric escape is only able to remove a limited amount of water over the history of the planet, and that the late accretion of wet material exceeds this sink and would result in a present-day atmosphere that is too rich in volatiles. A preferentially dry composition of the late accretion impactors is most consistent with measurements of atmospheric H2O, CO2 and N2. Hence, we suggest that the late accreted material delivered to Venus was mostly dry enstatite chondrite, consistent with isotopic data for Earth, with less than 2.5% (by mass) wet carbonaceous chondrites. In this scenario, the majority of Venus’s and Earth’s water would have been delivered during the main accretion phase.

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