Two Impacts, Not Just One, May Have Formed the Moon
A study led by Professor Erik Asphaug suggests that the protoplanet most likely hit Earth twice. The first time, the impactor (dubbed "Theia") only glanced off Earth. Then, some hundreds of thousands of years later, it came back to deliver the final blow.
In this image, the proposed hit-and-run collision is simulated in 3D, shown about an hour after impact. Theia, the impactor, barely escapes the collision. A. Emsenhuber / University of Bern / University of Munich