The Earth Once Had Two Moons

This artist's rendering shows a simulation of a collision between the moon and a companion moon about 4 billion years ago. (Martin Jutzi and Erik Asphaug)

Two Moons Above Earth May Have Collided To Create One, Study Says -- L.A. Times

Scientists say such a collision could explain why the moon is lopsided and why its far side is covered with mountains.

Once upon a time, the sky above Earth may have held two moons — until they smashed into each other to create the lunar body we know today. Such a collision early in the solar system's history could explain why the moon is lopsided, and why its far side looks so different from the face we can see, according to a report in Thursday's edition of the journal Nature.

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