The big splat
Why is the far side of the moon so different than the one that faces the earth? That question has been challenging the best minds in science. Astronomers think they finally have the answer.
Just about 4.4 billion years ago, long before life formed on our planet, the earth had 2 moons. The smaller of the 2 was pulled into the gravity of its bigger brother and they collided. At 5,000 mph, it’s considered a low velocity crash that has been compared to getting “a pie in the face”.
This theory that’s being called “the big splat” explains why the dark side of the moon is so hilly and also why it’s slightly lopsided.
https://www.cbsnews.com/sacramento/news/new-theory-says-earth-had-two-moons/