
The Moon is like an aging boxer, its face scarred and distorted by a lifetime of powerful blows. In the boxer's case, those blows are delivered over the course of a few decades. In the case of the Moon, the punishment has been going on for billions of years, courtesy of comets and asteroids that carved out craters and piled up mountains all over the lunar surface. The very birth of the moon was violent: planetary scientists are pretty sure our companion world was created when a Mars-size object slammed into Earth and ripped off a Moon-size chunk.
Artist concept of GRAIL mission.
Much of our understanding of that violent history comes from rocks hauled back by the Apollo missions four decades ago. But the astronauts who gathered that...