Water/Hycean Worlds & Oceanography

Water Evolution and Inventories of Super-Earths Orbiting Late M-Dwarfs

By Keith Cowing
Status Report
July 1, 2024
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Water Evolution and Inventories of Super-Earths Orbiting Late M-Dwarfs
Surface water regimes for terrestrial planets ranging from 0.1 MβŠ• to 10 MβŠ•. Each limit between regimes is explained in the text. Planets in either the waterworld, Earth-like, or Dune planet regime may be habitable, while desiccated surfaces are uninhabitable. The transition between surface water regimes depends weakly on planetary mass (cf. Cowan & Abbot 2014) — astro-ph.EP

Super-Earths orbiting M-dwarf stars may be the most common habitable planets in the Universe. However, their habitability is threatened by intense irradiation from their host stars, which drives the escape of water to space and can lead to surface desiccation.

We present simulation results of a box model of water cycling between interior and atmosphere and loss to space, for terrestrial planets of mass 1–8 MβŠ• orbiting in the habitable zone of a late M-dwarf. Energy-limited loss decreases with planetary mass, while diffusion-limited loss increases with mass.

Depending on where it orbits in the habitable zone, a 1 MβŠ• planet that starts with 3–8 Earth Oceans can end up with an Earth-like surface of oceans and exposed continents; for an 8 MβŠ• super-Earth, that range is 3–12 Earth Oceans. Planets initialized with more water end up as waterworlds with no exposed continents, while planets that start with less water have desiccated surfaces by 5 Gyr.

Since the mantles of terrestrial planets can hold much more water than is currently present in Earth’s atmosphere, none of our simulations result in Dune planets — such planets may be less common than previously thought. Further, more water becomes sequestered within the mantle for larger planets.

A super-Earth at the inner edge of the habitable zone tends to end up as either a waterworld or with a desiccated surface; only a narrow range of initial water inventory yields an Earth-like surface.

Keavin Moore, Benjamin David, Albert Yian Zhang, Nicolas B. Cowan

Comments: 12 pages, 5 figures; revisions submitted to The Astrophysical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2406.19923 [astro-ph.EP] (or arXiv:2406.19923v1 [astro-ph.EP] for this version)
Submission history
From: Keavin Moore
[v1] Fri, 28 Jun 2024 13:52:55 UTC (413 KB)
Astrobiology, Astrochemistry, Astrogeology,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) πŸ––πŸ»