Why Is the Moon Synchronously Rotating

摘要

If the Moon's spin evolved from faster prograde rates, it could have been captured into a higher spin orbit resonance than the current 1:1 resonance. At the current value of orbital eccentricity, the probability of capture into the 3:2 resonance is as high as 0.6, but it strongly depends on the temperature and average viscosity of theMoon s interior. A warmer, less viscous Moon on a higher eccentricity orbit is even more easily captured into supersynchronous resonances. We discuss two likely scenarios for the present spin orbit state: a cold Moon on a low-eccentricity orbit and a retrograde initial rotation.