Keeping M-Earths Habitable in the Face of Atmospheric Loss by Sequestering Water in the Mantle
arXiv:2006.08514 · doi:10.1093/mnras/staa1796
Abstract
Water cycling between Earth's mantle and surface has previously been modelled and extrapolated to rocky exoplanets, but these studies neglected the host star. M-dwarf stars are more common than Sun-like stars and at least as likely to host temperate rocky planets (M-Earths). However, M dwarfs are active throughout their lifetimes; specifically, X-ray and extreme ultraviolet (XUV) radiation during their early evolution can cause rapid atmospheric loss on orbiting planets. The increasing bolometric flux reaching M-Earths leads to warmer, moister upper atmospheres, while XUV radiation can photodissociate water molecules and drive hydrogen and oxygen escape to space. Here, we present a coupled model of deep-water cycling and water loss to space on M-Earths to explore whether these planets can remain habitable despite their volatile evolution. We use a cycling parameterization accounting for the dependence of mantle degassing on seafloor pressure, the dependence of regassing on mantle temperature, and the effect of water on mantle viscosity and thermal evolution. We assume the M dwarf's XUV radiation decreases exponentially with time, and energy-limited water loss with 30% efficiency. We explore the effects of cycling and loss to space on planetary water inventories and water partitioning. Planet surfaces desiccated by loss can be rehydrated, provided there is sufficient water sequestered in the mantle to degas once loss rates diminish at later times. For a given water loss rate, the key parameter is the mantle overturn timescale at early times: if the mantle overturn timescale is longer than the loss timescale, then the planet is likely to keep some of its water.
10 pages, 4 figures, accepted for publication in MNRAS
References in corpus (14)
- Extreme Water Loss and Abiotic O Buildup On Planets Throughout the Habitable Zones of M Dwarfs
- The habitability of Proxima Centauri b. I. Irradiation, rotation and volatile inventory from formation to the present
- Alien Maps of an Ocean-Bearing World
- Abiotic oxygen-dominated atmospheres on terrestrial habitable zone planets
- Geodynamics and Rate of Volcanism on Massive Earth-like Planets
- Predictions of the atmospheric composition of GJ 1132b
- Oxygen fugacities of extrasolar rocks: Evidence for an Earth-like geochemistry of exoplanets
- Detecting Ocean Glint on Exoplanets Using Multiphase Mapping
- Explaining the variability of WD 1145+017 with simulations of asteroid tidal disruption
- The persistence of oceans on Earth-like planets: insights from the deep-water cycle
- An unbiased ALMA spectral survey of the LkCa 15 and MWC 480 protoplanetary disks
- Carbon cycling and interior evolution of water-covered plate tectonics and stagnant lid planets
- Binary star influence on post-main-sequence multi-planet stability
- Runaway climate cooling of ocean planets in the habitable zone: a consequence of seafloor weathering enhanced by melting of high-pressure ice