Scientists discover the moon is shrinking, causing landslides and instability in lunar south pole

Earth's moon shrank more than 150 feet in circumference as its core gradually cooled over the last few hundred million years. In much the same way a grape wrinkles when it shrinks down to a raisin, the moon also develops creases as it shrinks. But unlike the flexible skin on a grape, the moon's surface is brittle, causing faults to form where sections of crust push against one another.

A team of scientists discovered evidence that this continuing shrinkage of the moon led to notable surface warping in its south polar region—including areas that NASA proposed for crewed Artemis III landings. Because fault formation caused by the moon's shrinking is often accompanied by seismic activity like moonquakes, locations near or within such fault zones could pose dangers to future human exploration efforts.

In a paper published in The Planetary Science Journal, the team linked a group of faults located in the moon's south polar region to one of the most powerful moonquakes recorded by Apollo seismometers over 50 years ago. Using models to simulate the stability of surface slopes in the region, the team found that some areas were particularly vulnerable to landslides from seismic shaking.

"Our modeling suggests that shallow moonquakes capable of producing strong ground shaking in the south polar region are possible from slip events on existing faults or the formation of new thrust faults," said the study's lead author Thomas R. Watters, a senior scientist emeritus in the National Air and Space Museum's Center for Earth and Planetary Studies.

"The global distribution of young thrust faults, their potential to be active and the potential to form new thrust faults from ongoing global contraction should be considered when planning the location and stability of permanent outposts on the moon."

Shallow moonquakes occur near the surface of the moon, just a hundred or so miles deep into the crust. Similar to earthquakes, shallow moonquakes are caused by faults in the moon's interior and can be strong enough to damage buildings, equipment and other human-made structures.

But unlike earthquakes, which tend to last only a few seconds or minutes, shallow moonquakes can last for hours and even a whole afternoon—like the magnitude 5 moonquake recorded by the Apollo Passive Seismic Network in the 1970s, which the research team connected to a group of faults detected by the Lunar Reconnaissance Orbiter more recently.

According to Nicholas Schmerr, a co-author of the paper and an associate professor of geology at the University of Maryland, this means that shallow moonquakes can devastate hypothetical human settlements on the moon.

"You can think of the moon's surface as being dry, grounded gravel and dust. Over billions of years, the surface has been hit by asteroids and comets, with the resulting angular fragments constantly getting ejected from the impacts," Schmerr explained.

"As a result, the reworked surface material can be micron-sized to boulder-sized, but all very loosely consolidated. Loose sediments make it very possible for shaking and landslides to occur."

The researchers continue to map out the moon and its seismic activity, hoping to identify more locations that may be dangerous for human exploration. NASA's Artemis missions, which are set to launch their first crewed flight in late 2024, ultimately hope to establish a long-term presence on the moon and eventually learn to live and work on another world through moon-based observatories, outposts and settlements.

"As we get closer to the crewed Artemis mission's launch date, it's important to keep our astronauts, our equipment and infrastructure as safe as possible," Schmerr said.

"This work is helping us prepare for what awaits us on the moon—whether that's engineering structures that can better withstand lunar seismic activity or protecting people from really dangerous zones."