How the Moon formed is something astronomers have been wondering for ages. The best idea is that put forward by Bill Hartmann — an astronomer and fellow space artist — and Donald Davis. They assert that a massive protoplanet slammed into Earth just after it had formed, creating a ring of debris around the young planet. The Moon then formed later as the material in this disc clumped together. This picture shows the process in three stages. See also Lunar Naissance.