What mechanism(s) prevented the gravitational effect of the earth on the moon from shattering the moon when it was closer to the earth than the Roche Limit some 4.5 billion years ago?


The leading theory for formation of the Moon is that a large object collided with the Earth and threw off a cloud of debris. This cloud then clumped together under it's own gravity to form the Moon. Simulations of the cloud show it formed outside the Roche limit - at around 1.3 times the Roche limit in fact.

So the Moon has never been closer to the Earth than the Roche limit.

  • $\begingroup$ thanks for your helpful reply and the link to the book. The mechanism is, so to speak, that the moon has been with the earth for a short enough period of time to have always remained outside the Roche Limit or that, if formed 4.5 billion years ago, it began its existence, again outside the Roche Limit and has been moving away from the earth ever since. $\endgroup$ – Ignor Ramus May 5 '15 at 17:43
  • $\begingroup$ @IgnorRamus: the Moon is roughly the same age as the Earth. It formed outside the Roche limit and has been outside the Roche limit ever since. $\endgroup$ – John Rennie May 5 '15 at 17:59
  • $\begingroup$ Given that the Moon was formed from a collision with the Earth, in one sense, it doesn't matter that it was formed at roughly the same time as the Earth or not. Or does it matter? Is there any evidence that the Moon's natal collision occurred shortly after the Earth was formed? $\endgroup$ – Ignor Ramus May 5 '15 at 18:26
  • $\begingroup$ @IgnorRamus: that needs to be a new question, thought you should Google around for theories describing the formation of the Moon to help you post a focussed question. $\endgroup$ – John Rennie May 6 '15 at 9:58

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