5 ms·

That is the type of theory that when you hear it sounds so plausible that it must be true.

• phkahler 12y ago
  >> That is the type of theory that when you hear it sounds so plausible that it must be true. But when 2 bodies of that size come together, and one of them splats onto the other, there is going to be a major change in rotation rate. There is no reason given for the resulting rotation rate to match the orbital period. I find that bothersome.
  • TheLoneWolfling 12y ago
    There is a potential reason: There is "drag" resulting from tides whenever a body is rotating faster or slower than the orbital period. (First approximation: actually there are weird things like orbital resonances. Mercury for example.) This drag becomes much more prevalent when the body is asymmetrical - say, when a large body just hit it. (Again: first approximation.) As such, one could conceivably say that the moon was rotating faster than it is now, and the impact slowed it down enough that the drag in the meantime was enough to tidally lock it to Earth sometime between the impact and now. (Or slower, and sped up. Same thing.) Although I don't know nearly enough to know how large the "window" would be of rotation rates that would tidally lock in the amount of time between the impact and now.