Strictly speaking, there aren’t “earthquakes” on the moon, simply because the very definition of the word literally means “quakes on the earth.” However, putting aside lexicological hair-splitting, there are indeed quakes — “moonquakes,” as they’re called — on the moon. According to Space, we know this because of equipment left up there by the Apollo program. Specifically, a handful of seismographs left up there by the Apollo missions that landed humans on the moon have detected a couple of dozen quakes over the decades, ranging in intensity from 1.5 to 5.0 on the Richter scale.

This was something of a surprise to scientists. Though fault lines are clearly visible on the moon, scientists initially thought that it had cooled seismically hundreds of millions of years ago. Further, the Apollo equipment detected other rumblings of the lunar surface, possibly due to the gravitational pull on the moon by the Earth. Further, meteors hit the moon with considerable frequency due to the lack of an atmosphere, and Apollo-era equipment has picked up the seismic reverberations from those impacts as well.