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Effects of Spin-Orbit Resonances and Tidal Heating on the Inner Edge of the Habitable Zone

Presentation #0505 in the session “From Stars to Planets to Atmospheres”.

Published onMar 17, 2021
Effects of Spin-Orbit Resonances and Tidal Heating on the Inner Edge of the Habitable Zone

Much attention has been given to the climate dynamics and habitable boundaries of synchronously rotating planets around low mass stars. However, other rotational states are possible, particularly when higher eccentricity orbits can be maintained in a system, including spin-orbit resonant configurations such as the 3:2 state of Mercury. Additionally, the oscillating strain on the planet as it moves from periastron to apoastron results in friction and the generation of tidal heating, which can be an important energy source around low mass stars. Here, we simulate the climate of ocean-covered planets near the inner edge of the habitable zone around M to solar stars with ROCKE-3D, and leverage the planetary evolution software package, VPLanet, to calculate tidal heating rates for Earth-sized planets orbiting 2600 K and 3000 K stars. This study is the first to use a 3-D General Circulation Model that implements tidal heating to investigate the habitable zone boundaries for multiple resonant states. We find that in the absence of tidal heating, the resonant state has little impact on the inner edge of the habitable zone, because for a given stellar flux, higher-order states tend to be warmer than synchronous rotators, but for a given temperature, have drier upper atmospheres. However, for the sampled planets where tidal heating can be strong, the rotational component of the heating implies a strong dependence of habitable conditions on the system evolution and rotational state of a planet. The dependence of tidal heating on distance from the stellar host implies heating increasing rapidly as incident stellar flux increases, resulting in a narrow habitable zone for the lowest mass star that is maintained at low values of stellar heating. We summarize these results and also compare ROCKE-3D to previously published simulations of the inner edge that used a modified version of the NCAR CAM4 model.

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