02. Why do we have a Moon? (A K2S Question)

From The Space Library

We're very lucky that we have one. None of the other inner planets of the solar system are blessed with such a large companion, and it's thought to have played a vital role in the rise of life on Earth. There have been many theories as to how the Moon came to be in our orbit. Was it a wanderer from afar captured by the Earth's gravitational embrace? Did the gravity of a passing star pull it out like taffy from the Pacific Ocean side of the Earth? Was the Earth spinning so fast that it flung it off? Given how close the Moon's rocks and minerals seem to match those of Earth (just without any water whatsoever), it is generally, but not entirely, believed in the science community that back in the early years of our solar system, say the first couple of tens or hundreds of millions of years, the orbit of the Earth happened to coincide with that of an errant planetoid at least as big as Mars, which on impact sloshed off a large chunk of material into orbit, which coalesced into the Moon. This is commonly known as the big whack, or giant impactor theory. http://www.pbs.org/wgbh/nova/tothemoon/origins2.html (See CDROM) http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question38.html

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Answer provided by Thomas Matula, Ph.D. & Kenneth J. Murphy

Question and Answer extracted from the book Kids to Space - by Lonnie Schorer

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