Habitable Zones & Global Climate

Redox State And Interior Structure Control On The Long-term Habitability Of Stagnant-lid Planets

By Keith Cowing
Press Release
January 10, 2023
Filed under , , , , , ,
Redox State And Interior Structure Control On The Long-term Habitability Of Stagnant-lid Planets
States of a stagnant-lid Earth as a function of the mantle oxygen fugacity. Each point represents a snapshot of the planetary evolution at a randomly selected planet age between 100 Myr and 8 Gyr. The colored points in panel a show the prevailing water phase at the surface as a function of the oxygen fugacity (fO2 ) and initial water content of the mantle (X 0 H2O ). The color background shows the area where the majority of neighboring data points share the same surface conditions. In panels b–d, points are colored according to the greenhouse gas that contributes most to surface heating. Panel b shows the surface temperature, panel c shows the total mass of outgassed water, and panel d shows the total mass of CO2 removed from the atmosphere via weathering. — astro-ph.EP

A major goal in the search for extraterrestrial life is the detection of liquid water on the surface of exoplanets.

On terrestrial planets, volcanic outgassing is a significant source of atmospheric and surface water and a major contributor to the long-term evolution of the atmosphere. The rate of volcanism depends on the interior evolution and on numerous feedback processes between atmosphere and interior, which continuously shape atmospheric composition, pressure, and temperature.

We present the results of a comprehensive 1D model of the coupled evolution of the interior and atmosphere of rocky exoplanets that combines central feedback processes between these two reservoirs. We carried out more than 280,000 simulations over a wide range of mantle redox states and volatile content, planetary masses, interior structures and orbital distances in order to robustly assess the emergence, accumulation and preservation of surface water on rocky planets.

To establish a conservative baseline of which types of planets can outgas and sustain water on their surface, we focus here on stagnant-lid planets. We find that only a narrow range of the mantle redox state around the iron-wüstite buffer allows forming atmospheres that lead to long-term habitable conditions. At oxidizing conditions similar to those of the Earth’s mantle, most stagnant-lid planets transition into a runaway greenhouse regime akin to Venus due to strong CO2 outgassing. At more reducing conditions, the amount of outgassed greenhouse gases is often too low to keep surface water from freezing.

In addition, Mercury-like planets with large metallic cores are able to sustain habitable conditions at an extended range of orbital distances as a result of lower volcanic activity.

Philipp Baumeister, Nicola Tosi, Caroline Brachmann, John Lee Grenfell, Lena Noack

Comments: 20 pages, 15 figures, submitted to Astronomy & Astrophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2301.03466 [astro-ph.EP] (or arXiv:2301.03466v1 [astro-ph.EP] for this version)
Submission history
From: Philipp Baumeister
[v1] Mon, 9 Jan 2023 16:01:55 UTC (24,385 KB)

SpaceRef co-founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.