Redox state and interior structure control on the long-term habitability of stagnant-lid planets

Abstract

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 \num{280000} 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 the formation of atmospheres that lead to long-term habitable conditions. At oxidizing conditions similar to those of the Earth's mantle, most stagnant-lid planets end up in a hothouse regime akin to Venus due to strong \ce{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.

23 pages, 18 figures, accepted for publication in Astronomy & Astrophysics

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• Habitable Zone and Atmosphere Retention Distance (HaZARD) Stellar-evolution-dependent loss models of secondary atmospheres
• Low 4.5 μm Dayside Emission Disfavors a Dark Bare-Rock scenario for the Hot Super-Earth TOI-431 b
• Geodynamics of super-Earth GJ 486b
• The influence of interior structure and thermal state on impact melt generation upon large impacts onto terrestrial planets
• The atmospheres of rocky exoplanets III. Using atmospheric spectra to constrain surface rock composition
• Evolution and Observable Properties of Rocky Planet Atmospheres
• The effect of a biosphere on the habitable timespan of stagnant-lid planets and implications for the atmospheric spectrum