Our lunar companion has slowly been shrinking, causing its surface to shrivel up like a prune and become more prone to dangerous moonquakes.
The moon has shrunk by around 150 feet in circumference over the past few million years as it's cooled. As a result, its surface has wrinkled and buckled like the skin of a dried fruit. Because of the brittleness of its surface, the moon has formed faults where its surface has warped, which may endanger future missions there.
These faults have been discovered in the moon's south polar region and have now been linked to a very powerful magnitude 5 moonquake recorded by Apollo seismometers in the 1970s, a new paper in The Planetary Science Journal reveals.
Moonquakes are caused by mechanisms similar to earthquakes as a result of faults in the crust slipping past each other. Moonquakes can last for much longer than earthquakes, often persisting for several hours, as seen in the powerful quake detected in the 1970s by the Apollo equipment. If a quake of this kind hit a lunar settlement, it could cause damage to structures and equipment and may trigger landslides that could be catastrophic.
Using models, the researchers discovered that this region is particularly in danger of moonquakes and resultant landslides. This may pose a major problem for future moon missions, as some of the most at-risk areas for these landslides include some proposed by NASA for crewed Artemis III landings because of the presence of water ice nearby.
"The main result of the study is we have found a likely source for the strongest shallow moonquake recorded by the Apollo seismometers with an epicenter near the south pole. That source is likely a young thrust fault," Thomas Watters, a geologist at the Smithsonian Institution and an author of the paper, told Newsweek.
"We also modeled the stability of slopes in the south polar region and found that there are surfaces in permanently shadowed regions that are [susceptible] to regolith landslides from even a light amount of seismic shaking," Watters said.
He continued: "There are young thrust faults within and near some of the Artemis III candidate landing regions. If a shallow moonquake like the one recorded by the Apollo seismometers occurs in the south polar region while robotic or Artemis III astronauts are on the surface, the seismic shaking could be disruptive to their activities."
Watters said that strong seismic shaking could trigger landslides in areas being explored and damage instruments on robotic landers. The real potential hazard is to long-term outposts located near young faults.
"Short-term missions like Artemis III are not likely a risk because strong shallow moonquakes are infrequent," he said.
"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," Nicholas Schmerr, a co-author of the paper and an associate professor of geology at the University of Maryland, said in a statement.
"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," he said.
The researchers hope to further explore how the moon's faults may affect its seismicity and how these might affect future lunar missions.
"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," he said.
Update 1/29/24, 11:51 a.m. ET: This story was updated with comments from geologist Thomas Watters.
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