How did the moon come into existence?
Analysis of data from the Lunar Prospector spacecraft in 1999 backs the long existing theory that the Moon masses were ripped away from young Earth when an object the size of Mars ran into it. Parallels in the mineral composition of Earth and the Moon hint at a common origin. This similarity was already known. In the past, some scientists have translated this into an indication that Earth and the Moon had formed separately from the same cloud of rocks and dust.
The recent Lunar Prospector data shows however that the Moon has a small core that contains less than 4% of the Moon's total mass. Earth's iron core contains approximately 30% of the planet's mass. If Earth and the Moon had merely formed from the same blur of rocks and dust, the Moon would have a core comparable in proportion to Earth's, scientists claim. A much more liable thought is that a large body struck Earth, forcing a release of rocky matter from the outer shell into orbit, which collected to form the Moon.