According to the giant-impact hypothesis, the Moon was created during a collision between Earth and a large object about the size of Mars.

One leading idea is that gravitational tidal forces reshaped the moon's crust and made it lopsided. But the new theory builds on the "giant impact" model that explains the moon's creation.

The prevailing hypothesis is that the moon was formed from a giant impact event, when a Mars-sized object slammed into Earth.