QUOTE (Myran @ Aug 9 2006, 09:14 AM)

QUOTE

In the work of Garrick-Bethell et al., the central issue is the Moon's own nonspherical shape, which, together with its orbit, lead the authors to an interesting conclusion about its past history: Its orbit around Earth in the distant past must have been much closer and also more eccentric than it is now. In fact, their optimum solutions locate the young Moon at a time 100 to 200 million years after its formation, when it was at a distance of some 24 to 27 Earth radii. At this time it would have passed through the 3:2 spin-orbit resonance, reminiscent of the present-day behavior of the planet Mercury, which rotates three times about its own axis for every two revolutions about the Sun. They show that the distance and eccentricity at this time would have been optimal for the bulge to "freeze" into the solidifying Moon, a fossil bulge we observe to this day. These results appear to dovetail in a reasonable way with the most viable contemporary theory of the Moon's own origin through a giant impact of a Mars-like object with Earth, from which debris the primordial Moon formed at some 4 Earth radii.