Now a new analysis, using data from Nasa missions, suggests that the Moon could still be shrinking today. As it does, it is experiencing moonquakes along those thrust faults, with the rock shaking at the cliffs.

Scientists compare the process to the way a grape will gradually wrinkle up, adding lines as it cools and shrinks. But unlike a grape’s skin, the crust around the Moon cannot stretch and is instead brittle, making it break apart as the shrinking happens.

The faults form when the crust moves around, and one part of the crust is pushed up over another. They form unusual-looking cliffs that can be seen from the surface, standing tall and many miles long.