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On 2002-03-18 18:55, Donnie B. wrote:
I remember that when I was a kid I learned your out-then-back-in projection for tidal evolution,
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Well, it's not *my* out and back again model.
I don't see how slowing the system down further would cause the moon to come back in and speed up. Wait a minute.... the earth's tidal bulges lead the moon, increasing its angular momentum and causing it to move out and slow down. If the earth's bulges were to lag the moon, it would want to *decrease* the moon's angular momentum, causing it to move in and speed up. This would cause the earth to speed up again, because the time scale for earth-moon locking is so much shorter for earth-sun locking.
Okay. I'm convinced. :-)
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but I've recently read (wish I remembered where) that it's no longer expected to work that way. Possibly because it takes so long for the outbound leg that the sun does its red giant bit in the meantime, which seems likely to throw a monkey wrench into the whole scenario... but I don't know if that's the right explanation.
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Well that's *certainly* true. I don't know if that's the explanation you were thinking of, but it's definitely true.
Don Smith