Slow collision between lunar companions could solve moon mystery. Earth may have once had two moons, but one was destroyed in a slow-motion collision that left our current lunar orb lumpier on one side than the other, scientists say.

Did the Earth once have 2 moons?

Earth once had two moons, which merged in a slow-motion collision that took several hours to complete, researchers propose in Nature today. Both satellites would have formed from debris that was ejected when a Mars-size protoplanet smacked into Earth late in its formation period.

Do we have two moons?

The simple answer is that Earth has only one moon, which we call “the moon”. It is the largest and brightest object in the night sky, and the only solar system body besides Earth that humans have visited in our space exploration efforts.