The Puzzle of Lunar Inclination

We are currently exploring two new solutions to the problem of lunar inclination. First involves 3:1 meanmotion resonance between the Moon and a smaller Earth satellite. Unlike Canup et al. (1999) who did not model inclinations, we find that the evolving moons preferentially enter an inclination resonance, exciting inclinations of both objects. We find that a second moonlet of 0.1 lunar masses can induce a 10-degree lunar inclination through thismechanism. Further evolution converts this inclination into eccentricity, so our scenario needs interaction with additional debris or impactors to break the resonance and "freeze" the lunar inclination. The other possible solution involves an early resonance between free core nutation of Earth and the Moon, exciting lunar inclination and changing the obliquity and spin rate of early Earth. We will present numerical simulations for both of these scenarios and discuss arguments for and against each of them.