Earth’s moon may be the product of many small moonlets that merged after multiple objects as big as Mars collided with Earth, leaving disks of planetary debris orbiting the planet, a new study suggests.
This idea that multiple impacts led to the moon’s birth challenges the most prevalent theory of lunar formation, which suggests that one giant impact led to the formation of the moon.
The new, multiple-impact hypothesis suggests that about 20 moon- to Mars-size objects struck the Earth, flinging debris from the planet into orbit. There, the debris formed disks around the Earth that looked somewhat like Saturn’s rings. Over centuries, debris in several disks accreted to form moonlets that migrated farther and farther from the Earth due to tidal interactions. Eventually, the moonlets settled at a distance known as the Hill radius, coalescing to form one big moon.