After the big bang, there might have been a "big splat." Astronomers believe the Earth once had two moons, until the smaller moon was pulled by gravity and into the larger one. This crash left behind the single, semi-lopsided moon that orbits our planet today. They proposed the theory in a presentation through a series of pictures depicting the collision, which would explain why the dark side of the moon has more craters and hills than the one that always faces Earth. "The physics is really surprisingly similar to a pie in the face," said the author of the study. They predict the collision took place 4.4 billion years ago, before there was life on Earth, and long before man could have waxed poetic about the lunar pair.