The moon is still tectonically active and has “shriveled like a raisin” as its interior has cooled, according to a new analysis of imagery from the Apollo missions in the 1960s and 1970s, and from NASA’s Lunar Reconnaissance Orbiter (LRO).
A paper describing the work, “Shallow seismic activity and young thrust faults on the Moon,” was published in the journal Nature Geoscience yesterday, claims that the moon has gotten 150 ft. skinnier over the last several hundred million years.
Analysis by a team of researchers at the University of Maryland has identified thousands of cliffs, called thrust faults, on the moon’s surface. The research suggests that the moon is suffering from “moonquakes” along these faults and that our satellite may be shrinking.
The researchers identified the epicenters for 28 moonquakes recorded from 1969 to 1977 using data from seismic sensors left on the moon by NASA’s Apollo missions in the 1960s and 1970s.
What causes ‘moonquakes’?
Moonquakes could be caused by asteroid impacts or rumblings deep within the moon’s interior, but the researchers found that at least eight of the moonquakes probably resulted from tectonic plates moving along the thrust faults or fault scarps. It was discovered by superimposing the locations of the epicenters of the quakes onto photos of the thrust faults taken much more recently by the LRO. “Our analysis gives the first evidence that these faults are still active and likely producing moonquakes today as the Moon continues to gradually cool and shrink,” said Thomas Watters, senior scientist in the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum in Washington. “Some of these quakes can be fairly strong, around five on the Richter scale.”
Are they still going on?
There’s a bit of gap in the data (the Apollo instruments stopped gathering data in 1977), but the researchers suggest that the moon is probably still experiencing quakes now. “We found that a number of the quakes recorded in the Apollo data happened very close to the faults seen in the LRO imagery,” said Nicholas Schmerr, an assistant professor of geology at the University of Maryland, noting that the LRO imagery also shows physical evidence of geologically 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.”
What did Apollo astronauts do?
Astronauts placed five seismometers on the moon’s surface during all of the Apollo missions that landed on the moon – Apollo 11, 12, 14, 15 and 16. Although the Apollo 11 seismometer worked for just three weeks and captured nothing, the four others recorded 28 shallow moonquakes between —1969 and 1977. Those shallow moonquakes are exactly the kind produced by tectonic faults.
In 1972, Apollo 17 astronauts Eugene Cernan and Harrison Schmitt had to zig-zag their lunar rover up and over the cliff face of the Lee-Lincoln fault scarp in the Taurus-Littrow valley.
How did the researchers make this discovery?
The epicenters of eight of the 28 shallow quakes were found to be within 19 miles of faults visible in images from the Lunar Reconnaissance Orbiter, which has been orbiting and mapping the Moon or the last 10 years. So the faults were probably caused the quakes. The researchers also found that six of the eight quakes happened when the moon was at apogee, the furthest it gets from Earth in its slightly elliptical orbit (which causes a “micro-moon” as opposed to a “supermoon”). The effect of Earth’s gravity on the moon while at apogee causes extra stress on the moon’s crust, which makes moonquakes more likely. “We think it’s very likely that these eight quakes were produced by faults slipping as stress built up when the lunar crust was compressed by global contraction and tidal forces, indicating that the Apollo seismometers recorded the shrinking moon and the moon is still tectonically active,” said Thomas Watters, lead author of the research paper and senior scientist in the Center for Earth and Planetary Studies at the Smithsonian Institution in Washington.
Why this means we need to send astronauts back to the moon
“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. This provides some very promising low-hanging fruit for science on a future mission to the moon.”