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View Full Version : Couple of Questions about the Moon

CaptainToonces
2019-Mar-29, 04:17 PM
1. For how long has the moon's rotation been tidally locked to Earth, keeping the same side of it facing the Earth?

2. How much more likely is the "dark side" of the Moon (the side always facing away from Earth) to be struck by asteroids than the side facing Earth?

profloater
2019-Mar-29, 06:21 PM
there must be a slight effect in the shadowing of the near face by the Earth. So I guess a few more impacts might hit the far side. To estimate the tidal lock we need to know the initial spin rate and I do not know that.

Roger E. Moore
2019-Mar-29, 06:32 PM
Partial answer to #2, from NASA:

https://sservi.nasa.gov/?question=3318

ronin
2019-Mar-30, 12:19 AM
As for question 1, without knowing the initial rotation rate of the moon after it's formation it's very difficult to calculate.

Upper estimate of how long it would have taken according to https://astronomy.stackexchange.com/questions/1859/when-did-the-moon-stop is @16 million years, so in cosmic terms it's been tidally locked almost since it's creation.

WaxRubiks
2019-Mar-30, 05:01 AM
there must be a slight effect in the shadowing of the near face by the Earth. So I guess a few more impacts might hit the far side. To estimate the tidal lock we need to know the initial spin rate and I do not know that.

but for every potential collision object that Earth might shield the moon from, there might be a collision object that is swung around the Earth into the course of the moon...so it might be more complicated.

profloater
2019-Mar-30, 09:26 AM
but for every potential collision object that Earth might shield the moon from, there might be a collision object that is swung around the Earth into the course of the moon...so it might be more complicated.

complicated in minor detail but not in principle because a diverted object can also be directed toward the moon, it is only those that hit Earth that we can deduct from the arithmetic. Just as Jupiter is a sweeper that protects the inner planets.

StupendousMan
2019-Mar-30, 11:16 PM
A paper by Wang and Zhou (A&A, vol 594, p. 52, 2016) suggests that there should be no difference in the cratering rate on the Moon's near and far side .... but there should be a difference between its leading and trailing sides. There's a link to a PDF copy of the paper at the ADS entry for it: