Over the last few hundred million years, its circumference has reduced by more than 150 feet or almost 46 meters due to its cooling core.

This shrinkage causes the Moon's brittle surface to form faults as sections of crust collide, similar to a grape wrinkling into a raisin.

Scientists first hypothesized that the Moon was shrinking in 2010, after analyzing powerful moonquakes recorded by the Apollo mission over half a century ago.

In 2019, they realized that the Moon was still rocked by quakes and revised the initial data.

Last year, the Apollo Passive Seismic Network recorded one of the strongest moonquakes near the Moon’s south pole, events that are causing landslides and instability in that region.

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The new findings, detailed in a study published in the Planetary Science Journal this month, suggest that while the precise epicenter remains undetermined, the formation of faults often triggers seismic activity like moonquakes, posing risks to future human exploration.

"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," 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, was quoted as saying in a press release.

Models simulating surface slope stability indicated that some areas are particularly prone to landslides due to seismic shaking. Shallow moonquakes, occurring just a hundred or so miles deep, can be strong enough to damage buildings and equipment.

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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 NASA’s Lunar Reconnaissance Orbiter more recently.

Until now, moonquakes and landslides were not taken into consideration in future colonization plans. 

In practical terms, the news is particularly affecting the Artemis 3 lunar mission, which is planned for 2027. It will take two astronauts to land and stay on the surface of Earth’s natural satellite for a week. They will conduct scientific experiments including infrastructure testing and collect water ice samples.

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