Where did the moon come from?

On Tue, 12 Dec 2000, you wrote:

> Where did the moon come from?

This is a good question, and a matter of some debate yet today!

The main key to the origin of the moon came from the rocks brought back by
Apollo astronauts. They found that the chemical make-up of the rocks on
the moon and those of the Earth are very similar. This means that the
Earth and the moon formed together somehow.

The leading theory for the formation of the moon is that a large object
about the size of Mars hit the Earth early in the history of the solar
system. The glancing blow blasted pieces of the Earth into orbit, where
they quickly (within a few days!) reassembled to form the moon. The rest
of the Mars-like object merged with the Earth. While this scenario sounds
far out, computer simulations show that it works very well in explaining
the known facts about the Earth-moon system.

Other theories for the formation of the moon include "co-formation," where
the Earth and moon formed together in the solar nebula, "capture," where
the moon was a large object careening through the early solar system and
was captured by the Earth, and "fission," where the early Earth was
spinning so rapidly that a hunk of the Earth was thrown off into space.

The following web site has a very nice explanation of the theories:
http://www.psi.edu/projects/moon/moon.html

I hope this helps! Thanks for writing.

Sincerely,
Kurtis Williams

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