Moon formation. Artwork of the formation of the Moon in the early history of the solar system. At this time many protoplanets existed in the inner solar system, eventually colliding and coalescing to form the four remaining today. It is thought that one of these protoplanets collided with a young Earth (left), around 4.6 billion years ago, leading to the formation of the Moon (right). A mixture of terrestrial material and material from the colliding body would have been thrown into orbit around the Earth, later coalescing to form the Moon. Vaporisation during this process would explain why the Moon has a dearth of volatiles and an enrichment in high-boiling point materials.