COLLEGE PARK, Md. — Don’t adjust your telescope: If you feel like the moon seems smaller, you’re actually right. A new study, following up on earlier research that found the moon has shriveled as it’s cooled over time, shows that it’s still shrinking and experiencing so-called “moonquakes” in the process.
Scientists believe the moon was created some 4.5 billion years ago as the result of collisions from asteroids and meteors, but the collisions made its interior hot. As it eventually cooled off, it also shriveled — similar to how a grape shrivels when it becomes a raisin. The wrinkles we see on raisins are likened to stair-shaped cliffs that consequently formed on the moon’s surface, which experts say are called thrust faults.
Now researchers at the University of Maryland say quakes occurring from those faults have continued as the moon continues to shrink. The researchers, led by Nicholas Schmerr, an assistant professor of geology, analyzed massive quantities of seismic data from instruments placed on the moon’s surface by NASA’s Apollo missions in the 1960s and ’70s. The team created a new algorithm that gave the scientists more accurate epicenter locations for 28 moonquakes recorded between 1969 and 1977.
The research team superimposed the Apollo location data onto imagery taken by NASA’s Lunar Reconnaissance Orbiter (LRO), which revealed many thrust faults. Based on the moonquakes’ proximity to the thrust faults, the researchers found that at least eight of the quakes recorded were caused by tectonic activity, rather than asteroid impacts and quakes from the moon’s interior.
“We found that a number of the quakes recorded in the Apollo data happened very close to the faults seen in the LRO imagery,” Schmerr explains in a statement, adding that the LRO imagery also reveals physical evidence of recent fault movement, such as landslides and tumbled boulders. “It’s quite likely that the faults are still active today. You don’t often get to see active tectonics anywhere but Earth, so it’s very exciting to think these faults may still be producing moonquakes.”
The scientists say the moonquakes would be similar to an earthquake with a magnitude of 2 to 5.
Images taken by the LRO show more than 3,500 cliffs, or fault scarps, since 2009. Fresh tracks from boulder falls also support the theory of moonquakes, as do bright patches along the fault scraps where landslides appear to have occurred.
“For me, these findings emphasize that we need to go back to the moon,” adds Schmerr said. “We learned a lot from the Apollo missions, but they really only scratched the surface. With a larger network of modern seismometers, we could make huge strides in our understanding of the moon’s geology. This provides some very promising low-hanging fruit for science on a future mission to the moon.”
The study was published in the journal Nature Geoscience.