Co-accretion formation of the Moon. Illustration of three stages (from left to right) in the co-accretion theory of the formation of the Moon. This theory states that the Moon and the Earth formed at the same time by accretion in the early Solar System. Current theory rejects this and states that the Moon formed following an impact event soon after the Earth formed. For a series of illustrations of moon formation theories, see images C047/7687 to C047/7698.