The leading explanation for how the Moon was born is that a world the size of Mars called Theia slammed into the young Earth and flung out the debris that became the Moon, and recent research suggests Theia itself never fully left, with two continent-sized blobs buried near our planet’s core possibly being the last remains of the world that struck us.

The leading account of where the Moon came from is a collision. Early in the Solar System’s history, a young planet roughly the size of Mars, given the name Theia, is thought to have struck the proto-Earth a glancing blow. The debris thrown into orbit gathered into the Moon. This is the giant-impact hypothesis, and […]