The Moon is humanity’s nearest companion in our travels in space and the only celestial body that we have had the chance to actually visit. Still, despite its relative closeness and familiarity, our satellite continues to hold many interesting secrets. From its scientific strangeness to the many ways it affects our lives, the Moon is a mystery that is definitely worth a closer look.

5 Moonquakes

Despite being a dead hunk of rock with very little geological activity, the Moon is prone to shaking fits. These earthquake-like tremors are called moonquakes, and there are four different kinds of them.

The first three types—deep quakes, vibrations from meteorite impacts, and thermal quakes caused by the Sun’s heat—are relatively harmless. The fourth one, however, can be quite unpleasant.

These “shallow” moonquakes can register up to 5.5 on the Richter scale—enough to move large furniture around—and last for a remarkably long 10 minutes. According to NASA, these quakes also have the effect of making the Moon “ring like a bell.”

The frightening thing about moonquakes is that we have no real idea of what causes them. Earth’s earthquakes are usually caused by the movement of tectonic plates, but the Moon doesn’t have any active plate tectonics. Some researchers think they may have some link to Earth’s tidal activity, which is caused by the Moon’s pull. However, this theory is inconclusive, as the tidal forces affect the entirety of the Moon, but moonquakes are usually localized.