Moon Shrinkage Causing Massive Quaking: What It Means for Space Exploration

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Swiss cheese moon? More like a raisin.

According to new data and images, the Earth’s moon is cooling, causing it to lose 150 feet in circumference over the past few hundred million years as it slowly shrinks like a grape into a raisin.

Discovery of the shrinkage was published in The Planetary Science Journal after a team of scientists linked a group of faults located on the moon’s south polar region to the most potent moonquakes recorded in the past 50 years. Between 1969 and 1977, researchers recorded 28 moonquakes ranging in magnitude from 1.5 to 5, had they been earthquakes. Moonquakes still occur today, with certain areas especially vulnerable to landslides and seismic shaking.

The shrinking, which has led to noticeable surface warping where NASA’s upcoming Artemis 3 mission—initially slated for 2024—plans to alight in 2026, could affect future moon exploration.

How Can the Moon Shrink?

Unlike a raisin, which has pliable skin, the moon’s surface is rigid yet fragile, so changing shape creates faults that rub against one another. These faults result in landforms called scarps, or stair-like cliffs, of which over 3,500 have been found since 2009. However, instead of dehydration, internal cooling within the moon’s core is causing the shrinkage. As the moon shrinks, fault lines appear. The result is moonquake activity that could jeopardize future landings.

“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, in a press release. “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.”

These moonquakes are severe and much like earthquakes. Shallow moonquakes occur about 100 miles into the moon’s crust, considered near the surface. Like earthquakes, moonquakes are strong enough to topple or damage buildings, equipment, or other human-made structures, the research team said. However, unlike earthquakes, which last seconds to minutes, moonquakes can last hours; the Apollo Passive Seismic Network once recorded a magnitude 5 moonquake that lasted an entire afternoon.

The Outlook for Human Moon Exploration

The moonquakes could make for a devastating outlook for future human colonization of 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,” said Nicholas Schmerr, co-author of the paper, in the press release. “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 research team will continue mapping out the moon and recording its seismic activity to identify alternative locations for human exploration. NASA’s Artemis missions hope to establish a long-term human presence on the moon and a way to live and work on another planet through trial and error on moon-based 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,” Mr. 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.”