The Moon Has Shrunk About 50 Meters

The Moon is getting smaller. Its interior is cooling, and over the last several hundred million years the whole globe has contracted by about 50 meters (150 feet) in width.

The Moon’s crust is brittle, so it cannot flex the way a grape’s skin does as the grape dries into a raisin. It cracks instead. The cracks form thrust faults, where one slab of crust is pushed up over its neighbor and leaves a cliff-like scarp. The Lunar Reconnaissance Orbiter has photographed thousands of these scarps. Apollo-era seismometers recorded shallow moonquakes near them, some around magnitude 5, which shows the faults are still active today.