Did you think the moon was a dead and boring world? In recent years, we've discovered our closest large neighbor has so much more than we thought: a tenuous atmosphere, water ice, and even levitating dust. The most recent surprise? The moon has wrinkles. Not because it's old, but because it's shrinking.










How Is the Moon Shrinking?

The moon has moonquakes just like we have earthquakes, but the process is different. On Earth, huge sections of crust called tectonic plates slide against each other and create vibrations. But the moon is different.
The moon likely formed after a large, Mars-sized body smashed into Earth roughly 4.5 billion years ago. Over the eons, the pieces coalesced into the moon. As you can imagine, that collision generated a lot of heat. But that ancient heat is cooling, and as the whole moon cools down, its interior shrinks and its surface buckles.

In Mare Frigoris, this creates huge wrinkle ridges. The longest ones are roughly 250 miles (400 kilometers) long, or more than the distance between New York City and Washington, D.C. They also rise about 1,000 feet (333 meters) off the surface.
We can estimate the age of these ridges using "crater counting," or simply adding up the number of craters in a particular region. We know roughly how often objects hit the moon to generate these craters, but tectonic activity can cover them up over time. That means that by comparing the estimated collision rate to the actual number of craters present, scientists can have a rough idea of how old a region is. We also can see signs of craters "aging" — collecting debris from other impacts, for example. The moon might be old, gray, and wrinkled, but it's not dead yet.