Although the moon looks quite spherical from the ground, it is flatter at its poles and wider at its equator, a trait known as an equatorial bulge. This characteristic is common; it’s usually caused by an object’s rotation around its axis. However, it’s been noted that the moon’s bulge is about 20 times larger than it should be given its rotational rate of once per month.

Outlined in a paper published this month in the journal Geophysical Research Letters, researchers at the University of