Is there any way to avoid the tidal locking of a planet orbiting a red dwarf in the habitable zone?
For example, could a planet with a 90° obliquity and large moon avoid such a situation?
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Sign up to join this communityIs there any way to avoid the tidal locking of a planet orbiting a red dwarf in the habitable zone?
For example, could a planet with a 90° obliquity and large moon avoid such a situation?
Yes: It has a companion planet or an excessively large moon, with the two bodies orbiting their common center of mass (much like the Earth and the Moon). They could be tidally-locked to each other, but they cannot be tidally-locked to their star.
Leconte et al. (2015) suggested that the presence of an atmosphere could prevent or at least slow tidal locking. The star should exert two separate torques: one on the atmosphere and one on the solid body of the planet: $$T_a=-\frac{3}{2}K_ab_a(2\omega-2n),\quad T_g=-\frac{3}{2}K_gb_g(2\omega-2n)$$ where $$K_a\equiv\frac{3M_*R_p^3}{5\bar{\rho}a^3},\quad K_g\equiv\frac{GM_*R_p^5}{a^6}$$ for stellar mass $M_*$, planetary radius $R_p$, mean density $\rho$, semi-major axis $a$, mean motion $n$, rotation rate $\omega$, and response to torques $b_a$ and $b_g$. The two torques could be equal, and assuming that the atmosphere transfers some angular momentum to the surface of the planet, this could prevent tidal locking. There are several equilibria at which this could occur:
The more likely case is actually a spin-orbit resonance that is not 1:1 but a half odd multiple, like the 3:2 case of our own Mercury. Having eccentricity in the orbit encourages this situation.
I’ve been meaning to write this up on the Worldbuilding.SE but I have not re-found enough references. But see this video.