A new paper in the journal Nature challenges the leading explanation for the Moon’s formation. The predominant idea is that the Moon was created after a planetary body roughly the size of Mars collided with the early Earth. The debris it sent up later coalesced into the Moon. But researchers are now revisiting the largely discarded idea that a series of smaller impacts with the Earth may have collectively built the Moon.

Moon history

The giant impact hypothesis was first proposed in the 1970s. When computers became powerful enough, we found that it worked in simulations. A glancing blow from a Mars-sized planetesimal leads to a disc of material around the young Earth that, over time, coalesces into the Moon. And planetesimals were readily available in the early Solar System, flying around on weird orbits which made collisions with planets very probable.

In terms of its mass, angular momentum, and iron content, the Moon formed in these simulations was very similar to the real one we observe. But over the years, researchers kept running into difficulties with this model.