The Moon has been circling the Earth for over four billion years, but where did it come from? In this video, Ralf Jaumann, planetary geologist at the German Aerospace Centre, DLR, discusses the four theories that could explain the origin of the Earth-Moon system. There are four theories about the origin of the Earth-Moon system. The first is that Earth captured a celestial body in its orbit. Another possibility is that a rapidly rotating Earth could have thrown material out to form the Moon around it. A third theory is that Earth and the Moon formed at the same time out of the same material. Today, most scientists believe the Moon is ‘Earth's child’–a large body collided with Earth, destroying our planet’s mantle and sending material into orbit from which the Moon formed. This ‘big splash’theory would explain why the Moon’s rocks are similar to those on Earth.