Editor’s Note: This article previously appeared in a different format as part of The Atlantic’s Notes section, retired in 2021.

Here I am. Again. @ISS lunar transit. Great shot, @ingallsimages! #YearInSpace #spacestation #moon #space #nasa

A photo posted by Scott Kelly (@stationcdrkelly) on

Poor moon. Covered in garbage and shrinking in size, all thanks to Earth.

Scientists noticed cracks in the lunar crust years ago, but it wasn't until recently that they figured out what was going on. Turns out “tidal forces of the Earth pulling on the moon, while small, generated enough stress to break the moon’s crust in the observed pattern,” as The New York Times reported this week. (The findings were reported in Geology in July.)

This isn’t so surprising. The gravitational pull of the tides does more than just buckle the moon’s observable crust, after all. Yesterday I wrote about the frequent deep-moonquakes that are caused by Earth’s tides.

The bigger question, when it comes to seismic activity on our lunar neighbor, is what’s causing the bigger moonquakes—ones that aren’t linked to the tides. Scientists know that they happen but still can't say exactly how, or where they originate.