Where did the Moon come from?

If you pick up a textbook on astronomy, chances are that the origin of the Moon is ascribed to impact on the Earth by a large object, about the size of Mars. That is also the currently accepted view among non-specialists. But the impact hypothesis was never worked out or published completely.  We simply don't know if the hypothesis leads to the current Earth-Moon properties. On the other hand, starting with the present Moon and working backward in time guarantees success.  The only question is whether the initial conditions are reasonable.  We find that they are and are publishing that fact. The backward calculation is time-honored.  It was used first by Sir George Darwin in 1870 and since then by Harold Urey and Hannes Alfven, two Nobel-Prize winners, and other distinguished scientists. Darwin noted that the Moon raises tides on the Earth.  These tides, in turn, perturb the orbit of the Moon, causing it to move...(Read Full Post)
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