The Role of Magma Oceans in Maintaining Surface Water on Rocky Planets Orbiting M-Dwarfs

Keavin Moore ( Université McGill )

Rocky planets orbiting M-dwarf stars are more abundant than those orbiting Sun-like stars. However, Earth-like planets orbiting M dwarfs ("M-Earths") are susceptible to lose significant water to space due to their closer orbits and enhanced irradiation compared to the Earth around the Sun. Emission in the X-ray and extreme ultraviolet (“XUV”) photodissociates water molecules and drives its loss to space. We aim to predict surface water inventories over time for various M-Earths with pure water vapour atmospheres, using a coupled model of magma oceans, deep-water cycling, and atmospheric loss. Our simulations begin from a global magma ocean phase concurrent with a runaway greenhouse phase, and although water is highly soluble within the magma ocean, atmospheric loss rates are high. Once the runaway greenhouse ends and the magma ocean solidifies, surface temperatures become modest; the loss rate decreases significantly, and we assume the M-Earth shifts into a plate-tectonics-driven deep-water cycling mode. We compare these results with a model which includes a long-lived basal magma ocean, which could exist below the solid mantle following solidification of the global magma ocean and slowly inject water into the overlying mantle for billions of years, potentially saving the M-Earth from desiccation. I will also briefly discuss my 3-month CRAQ-funded internship at the Freie Universität Berlin, where I collaborated with Lena Noack and her research group.