system
Given the following post, respond as if you're commenting on Reddit:
human
Why are most of the large impact craters on the moon located on the side facing the Earth? Wouldn't the other side be less shielded?
gpt
There is a very big impact crater on the far side. Probably you meant lunar maria. They formed when impacts were big enough to break the lunar crust and reach the molten interior, so lava came out and later solidified in a relatively smoother and darker surface. The impact on the far side just created a big crater with no mare as the crust is thicker.

There are two theories about this. They do not contradict each other so they could even be both true.

One of them says that when the lunar maria formed, Earth was still hot and emitting lots of infrared. So the near side of the Moon was kept warmer, with a thinner solid crust.

Another theory is based on the giant impact hypothesis. Some background: A Mars-sized body (called Theia) is supposed to have impacted Earth at a relatively low speed. The collision created a disc of debris that eventually coalesced and formed the Moon.

Back to the maria: the other theory says that from this disc of debris it was actually *two moons* that formed. But since they were sharing the same orbit in an unstable configuration, eventually they crashed at a low speed and the smaller moon "pancaked" over the larger one, creating a thicker crust on that side. Then the Moon gradually became tidally locked and the thicker crust happened to be on the far side.