Early Formation of a Water Ocean as a Function of Initial CO₂ and H₂O Contents in a Solidifying Rocky Planet

Abstract

We present a model for the thermal evolution of Magma Ocean (MO) in interaction with a degassing atmosphere of H2O and CO2. The interior model is based on parameterized convection and is coupled to the atmospheric Model of Marcq et al. (2017, https://doi.org/10.1002/2016JE005224) through heat and volatiles. A new equation for the mass balance of volatiles is implemented, correcting Salvador et al. (2017, https://doi.org/10.1002/2017je005286). We found that the domain for water condensation is extended: for instance, depending on the cloud cover and resulting albedo, 0.13 Earth's ocean mass might be sufficient to form a water ocean on early Venus (instead of 0.3 MEO in Salvador et al. (2017, https://doi.org/10.1002/2017je005286)). Comparing our results with other recent models, we discuss the relative influence of the model hypotheses, such as mantle melting curves (which depend on mantle composition), the treatment of the atmosphere (e.g., gray or convective‐radiative) and the treatment of the last stages of the MO solidification (e.g., episodic resurfacing, stagnant lid…). We also apply our results to exoplanets. They suggest that liquid water might be present at the surface of Trappist‐1e and 1f, provided that those planets' volatile primitive contents were dominated by H2O and CO2.