The dark side of the (shrinking) moon: NASA missions could be at risk

The moon is shrinking − but it's nothing we need to worry about, scientists say in a new study.

The shrinkage is too small to have any effect on us down here on Earth, such as on eclipses, full moons or tidal cycles, study co-author Nicholas Schmerr of the University of Maryland told USA TODAY.

How small? Over the past few hundred million years, the moon has shrunk only about 150 feet in circumference as its core gradually cooled.

"Fortunately, as it shrinks, the mass of the moon doesn’t change, so it shouldn’t affect tidal cycles in any substantial way," Schmerr said. "Also, the radius change is so small and gradual that it will not have any meaningful effect on the appearance of eclipses or phases on the moon."

Moonquakes could be dangerous for astronauts

What is concerning is that the shrinking moon appears to cause moonquakes, which could be dangerous for any astronauts who might try to land or eventually live on the moon.

The shrinkage has "led to notable surface warping in its south polar region – including areas that NASA proposed for crewed Artemis III landings," according to a University of Maryland news release about the discovery.

The study, which was published last week in the journal Planetary Science, found that the hot inner core of the moon is slowly cooling, creating fault lines, or cracks, on the lunar surface as the moon contracts.

"There's a lot of activity that's going on in the moon," said Smithsonian Institution scientist emeritus Tom Watters, who led the study. "It's just something that we have to keep in mind when we're planning, especially, long-term outposts on the moon."

A landing site for future Artemis missions

The study looked specifically at the lunar south pole, a possible landing site for Artemis missions.

"We also knew from the Apollo seismic data that the most powerful moonquake, a shallow moonquake that was recorded by those seismometers, occurred near the south pole," Watters said.

Those quakes, Watters said, could make slopes in the same lunar region susceptible to landslides, also possibly endangering landing sites on the moon's surface.

Moonquakes could be severe, last longer than earthquakes

The moon's relatively lower gravitational pull could make a quake that would feel minor on Earth's surface multiply in intensity. "You're not as coupled to the surface on the moon as you are to the Earth," Watters said. "So even a magnitude 5 quake on the moon would feel much stronger than it would feel on the Earth."The gravitational difference could also make moonquakes last much longer. He said that even long-duration earthquakes last for only a couple of minutes. "On the moon, they can last for hours."Though moonquakes aren't likely to affect Artemis missions planned anytime soon, Watters said, missions aiming to establish a lunar outpost could be affected. "It's very unlikely that in a short-term mission like Artemis you're going to experience a moonquake," Watters said.

"But if we put a long-term outpost on the moon, then the probability becomes much greater that they're going to experience a strong moonquake."