Why is the far side of the Moon so different from the side we see?

The Moon shows nearly the same face to Earth because it rotates once on its axis in the same time it orbits Earth, a state called tidal locking. But the far side is geologically different: it has much more heavily cratered terrain and far fewer of the dark basaltic plains, or maria, that dominate the near side. One leading reason is that the near side’s crust is thinner, so ancient lava could erupt more easily there. NASA’s Chang’e and Apollo-era data have helped map these asymmetries in greater detail.