Exoplanets & Exomoons

The Onset Of A Globally Ice-covered State For A Land Planet

By Keith Cowing
November 29, 2021
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The Onset Of A Globally Ice-covered State For A Land Planet
The meridionally averaged cloud fraction in the tropics (± 30º in latitude), the zonally averaged cloud radiative forcings and the albedos for cases of the meridionally concentrated surface water distributions with 90% S0. Two different water distributions are shown in upper row for 52 grid cells and lower row for 6 grid cells of the water pool region.

The climates of terrestrial planets with a small amount of water on their surface, called land planets, are significantly different from the climates of planets having a large amount of surface water.

Land planets have a higher runaway greenhouse threshold than aqua planets, which extends the inner edge of the habitable zone inward. Land planets also have the advantage of avoiding global freezing due to drier tropics, leading to a lower planetary albedo. In this study, we systematically investigate the complete freezing limit for various surface water distribution using a three-dimensional dynamic atmospheric model.

As in a previous study, we found that a land planet climate has dry tropics that result in less snow and fewer clouds. The complete freezing limit decreases from that for aqua planets (92% S0, where S0 is Earth’s present insolation) to that for land planets (77% S0) with an increasing dry area. Values for the complete freezing limit for zonally uniform surface water distributions are consistently lower than those for meridionally uniform surface water distribution. This is because the surface water distribution in the tropics in the meridionally uniform cases causes ice-albedo feedback until a planet lapses into the complete freezing state.

For a surface water distribution using the topographies of the terrestrial planets, the complete freezing limit has values near those for the meridionally uniform cases. Our results indicate that the water distribution is important for the onset of a global ice-covered state for Earth-like exoplanets.

T. Kodama, H. Genda, J. Leconte, A. Abe-Ouchi

Comments: 29 pages, 8 figures. Accepted for publication in Journal of Geophysical Research – Planets
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2111.12913 [astro-ph.EP] (or arXiv:2111.12913v1 [astro-ph.EP] for this version)
Submission history
From: Takanori Kodama
[v1] Thu, 25 Nov 2021 05:04:29 UTC (7,033 KB)

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) 🖖🏻