Earth Once Collided With Another Planet

The Moon exists because a Mars-sized planet slammed into the young Earth 4.5 billion years ago. This massive collision vaporized debris that eventually clumped together to form our lunar neighbor.

This lost planet, known as Theia, occupied a similar orbit to Earth before the catastrophic impact occurred. Scientists believe this event happened shortly after our solar system formed, when the Earth was still in its infancy. The name Theia is a nod to Greek mythology, as she was the mother of the goddess of the Moon. This theory explains why the Moon shares a chemical signature so similar to our own planet.