~ 2-3RE) yields a lunar-sized
Moon. An initial disk mass of at least two-lunar masses is
implied by conservation of angular momentum, which dictates
that close to half the disk must be sacrificed to the Earth
in order for the remaining material to spread beyond the
Roche limit where accretion of the Moon can occur (
e.g., Ida et al. 1997). The collision time scale for
objects outside the Roche limit is typically much shorter
than the radiation-limited lifetime of the protolunar disk
(Thompson and Stevenson 1988), suggesting that a
newly-formed Moon may co-exist with its interior precursor
disk for a time interval O(102) years.
The Moon can dynamically couple to this disk through
resonant interactions. These can be quite powerful, and can
rapidly modify the orbital radius, eccentricity, and
inclination. It is likely that the disk torques are much
larger than those due to terrestrial tides, and thus control
the rate of early outward migration of the Moon. They may
also establish the intial conditions for the subsequent
tidal evolution of the Earth-Moon system (e.g.
Goldreich 1966, Touma and Wisdom 1994).
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