A new theory put forward by Harvard scientists suggests the Moon was once part of the Earth that spun off after a giant collision with another body.
In a paper published on Wednesday in the journal Science, Sarah Stewart and Matija Ćuk said their theory would explain why the Earth and Moon have similar composition and chemistry.
The Earth was spinning much faster at the time the Moon was formed, and a day lasted only two to three hours, they said.
With the Earth spinning so quickly, a giant impact could have launched enough of the Earth’s material to form a moon, the scientists said in an explanation published on a Harvard website. http://www.fas.harvard.edu/~planets/sstewart/Moon.html