Early formation of a water ocean as a function of initial CO2 and H2O contents in a solidifying rocky planet

Abstract

We present a numerical model of a cooling magma ocean (MO) and the atmosphere degassing from it. The solidification of the MO leads to the enrichment of the silicate melt in volatiles, thus favoring degassing. Both reservoirs interact via heat and volatile exchange, where the volatiles are H2O and CO2. The aim of this model is to explore the influence of the atmosphere on the surface conditions after the MO stage, and especially the conditions required for the condensation of a water ocean to occur. For example, for an early Earth at 1 AU initially containing 1 Earth's water ocean mass, a water ocean could form for initial CO2 content as large as 1,000 bars. Moreover, a tenth of the actual Earth's water ocean mass would be sufficient to generate a water ocean on early Venus. Liquid water could also be present on the surface of the two exoplanets Trappist-1e and 1f. Comparing our results with other recent models, we discuss the relative influence of the model hypotheses, such as mantle composition, the treatment of the heat transfer in the atmosphere, and the treatment of the last stages of the MO solidification.