  In the giant impact hypothesis for lunar origin, the Moon accreted from an
equatorial circum-terrestrial disk; however the current lunar orbital
inclination of 5 degrees requires a subsequent dynamical process that is still
debated. In addition, the giant impact theory has been challenged by the Moon's
unexpectedly Earth-like isotopic composition. Here, we show that tidal
dissipation due to lunar obliquity was an important effect during the Moon's
tidal evolution, and the past lunar inclination must have been very large,
defying theoretical explanations. We present a new tidal evolution model
starting with the Moon in an equatorial orbit around an initially
fast-spinning, high-obliquity Earth, which is a probable outcome of giant
impacts. Using numerical modeling, we show that the solar perturbations on the
Moon's orbit naturally induce a large lunar inclination and remove angular
momentum from the Earth-Moon system. Our tidal evolution model supports recent
high-angular momentum giant impact scenarios to explain the Moon's isotopic
composition and provides a new pathway to reach Earth's climatically favorable
low obliquity.
