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Ignan Earth’s: Habitability of Terrestrial Planets with Extreme Internal Heating

Presentation #629.03 in the session Habitability.

Published onApr 03, 2024
Ignan Earth’s: Habitability of Terrestrial Planets with Extreme Internal Heating

A prerequisite for long-term habitability is the geological cycling of material between the atmosphere and the mantle, causing negative feedbacks on the climate and allowing temperate conditions to persist for geologic time. This geological cycling is ultimately driven by internal heating. If the internal heating rate is too low, then the climate feedbacks cease to operate. Therefore, a lower limit of internal heating exists for habitability, but is there an upper limit? Is it possible for a rocky planet to have internal heating too high to maintain a habitable surface? An example of a world within our Solar System with significant internal heating is Jupiter’s moon Io, which has a surface heat flux of 2 W/m2 compared to the Earth’s 90 mW/m2. Io’s high internal heating rate is caused by tidal dissipation, a process that is expected to be significant for terrestrial planets in the habitable zones of M-dwarf stars. An ultimate upper limit to internal heating is the runaway greenhouse limit, when the combined stellar and internal heating of a planetary atmosphere reaches 300 W/m2. Even below this limit, such a planet must maintain a stable crust and a temperate climate to be habitable. We investigate the habitability of terrestrial planets with internal heating rates higher than that of Io and many orders of magnitude higher than that of the Earth. We demonstrate how the mantle will remain largely solid and thus support a stable crust despite the high internal heating. Finally, we simulate the carbonate-silicate cycle with a vertical tectonic regime (known as heat-pipe tectonics, expected to dominate in such worlds) for varying amounts of internal heating. We find Earth-mass planets with internal heating fluxes below 25 W/m2 produce average surface temperatures that Earth has experienced in its past (below 30 ⁰C), indicating a wide range of internal heating rates may be conducive with habitability. We will show climate-modeling results for variations in planet mass, ocean fraction and stellar insolation.

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