The Moon’s surface is likely still rippling with quakes, caused by stressors ranging from interior contraction to tidal pressures, according to a new study published on Monday in Nature Geoscience.
The moon is a mystery. Its formation is still technically theoretical, although most astronomers agree that it was formed by a Mars-sized object colliding with Earth billions of years ago. After that formation, its interior cooled and shrunk, causing seismic activity that researchers say might continue today, according to NASA.
Now, research from scientists at the University of Maryland again suggests that the Earth’s moon is still very alive. It’s possible that to this day, the Moon’s surface cracks and rumbles with moonquakes thanks to this shallow seismic activity. This is likely due to the moon’s interior contraction and other pressures, according to the study.
The researchers used modern algorithms to re-analyze imagery of the moon’s surface from NASA's Lunar Reconnaissance Orbiter (LRO) that’s been orbiting the moon for 10 years, and compared it to data gathered from instruments placed on the Moon during the Apollo missions in the 60s and 70s.
In 2010, the LRO found evidence of recent (for the Moon, anyway) seismic activity that might be associated with ongoing interior contraction associated with cooling. This new study expands on that research, using the Apollo seismographs to locate moonquake origins. The researchers examined how the moon’s distance from the Earth’s gravity stresses its surface, as well.
“The current stress state of the Moon is dominated by radial contraction from interior cooling,” the study authors wrote. “Superimposed on the compressional stresses from contraction are two components of tidal stress, orbital recession stress and diurnal stress.”
According to the study, some of the quakes on the Moon associated with seismic activity occurred “at or near peak compression, or closely before or after peak compressional stresses are reached.”
By looking at thrust faults—cliffs that form on the surface as the interior shrinks and cools—detected by LRO imagery, the researchers were able to pinpoint more accurate epicenter locations for 28 moonquakes that the Apollo-era instruments recorded on the surface between 1969 and 1977. Because they originated close to the faults, researchers determined that at least eight of those quakes were caused by tectonic activity on the moon, and not from asteroids or interior movement—activity that they say likely still occurs.
"The association of the shallow moonquakes with these recent faults suggests that the Moon may still be cooling and shrinking today albeit very slowly," Nicholas Schmerr, an assistant professor of geology at the University of Maryland, told me in an email.
"It's quite likely that the faults are still active today,” Schmerr, said in a press release. “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."
Recently-appointed NASA administrator Jim Bridenstine’s insists that humanity returns to the Moon “as fast as possible,” and Vice President Mike Pence’s obsession with moon exploration and is pushing NASA to get back there within the decade. Meanwhile, private companies like Jeff Bezos’ Blue Origins using moon colonization as a climate-change MacGuffin for capitalist pursuits. There’s a decent chance we’ll be back to the possibly-trembling lunar surface soon.
"For me, these findings emphasize that we need to go back to the Moon," 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."