Scientists suggest the most likely theory is the collision theory. It states the Earth was hit by a planetesimal (a planetoid) and then Earth threw out a cloud of dust and gas. Gravity then formed the ring into a ball. The sister theory says the Earth and moon formed separately but close together in the Solar System. The fission theory states the rapidly spinning proto-Earth split off a chunk of magma and the blob of rock became the moon. The capture theory says the moon was a planetesimal (or planetoid) that the Earth captured.