Tidal obliquity evolution of potentially habitable planets

By R. Heller, J. Leconte, Rory Barnes Leibniz Institute for Astrophysics Potsdam, DFG-funded GrK 1351, '. Lyon, U. Washington, Seattle, Virtual Planetary Laboratory, Usa. 2011

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Context. Stellar insolation has been used as the main constraint on a planet’s potential habitability. However, as more Earth-like planets are discovered around low-mass stars (LMSs), a re-examination of the role of tides on the habitability of exoplanets has begun. Those studies have yet to consider the misalignment between a planet’s rotational axis and the orbital plane normal, i.e. the planetary obliquity. Aims. This paper considers the constraints on habitability arising from tidal processes due to the planet’s spin orientation and rate. Since tidal processes are far from being understood we seek to understand differences between commonly used tidal models. Methods. We apply two equilibrium tide theories – a constant-phase-lag model and a constant-time-lag model – to compute the obliquity evolution of terrestrial planets orbiting in the habitable zones around LMSs. The time for the obliquity to decrease from an Earth-like obliquity of 23.5 ◦ to 5 ◦ , the “tilt erosion time”, is compared to the traditional insolation habitable zone (IHZ) in the parameter space spanned by the semi-major axis a, the eccentricity e, and the stellar mass Ms. We also compute tidal heating and equilibrium rotation caused by obliquity tides as further constraints on habitability. The Super-Earth Gl581 d and the planet candidate Gl581 g are studied as examples for these tidal processes.

Subfields: Astronomy and Astrophysics, Instrumentation, Microbiology

View Paper: https://www.semanticscholar.org/paper/d1d2e4e750f5c80fc4cd8a89c23332fe7f9304e4

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Citations in the corpus

GLIESE 581D IS THE FIRST DISCOVERED TERRESTRIAL-MASS EXOPLANET IN THE HABITABLE ZONE (2011, background): “In the Solar System, Rayleigh scattering reflects the bluer incoming starlight much more effectively, and hence a planet receiving the same flux as GJ581d would be uninhabitable for any CO2 pressure.”
Tidal locking of habitable exoplanets (2017, methodology): “The latter is a plausible initial condition from simulations of terrestrial planet formation (Kokubo and Ida 2007; Miguel and Brunini 2010). The HZ of Kopparapu et al. (2013) is shown as shading with the lighter gray representing empirical or optimistic limits, and the darker gray representing theor”
A dynamically-packed planetary system around GJ 667C with three super-Earths in its habitable zone (2013, background): “The timescale for these processes is a complex function of orbits, masses, radii and spins, (seee.g. Darwin 1880; Hut 1981; Ferraz-Mello et al. 2008; Leconte et al. 2010) but for super-Earths in the HZ of a∼ 0.3 M⊙ star, Heller et al. (2011) found that tidal locking should occur in 106–109 years.”
3D climate modeling of close-in land planets: Circulation patterns, climate moist bistability and habitability (2013, background): “…and which are either in a state of synchronous, pseudo-synchronous4, or resonant rotation with near zero obliquity (Goldreich & Peale 1966; Heller et al. 2011; Makarov et al. 2012), efficient and permanent cold traps present on the dark hemisphere or at the poles could irreversibly…”