NASA says that the moon is shrinking, which is resulting in Moonquakes

In a report published earlier today, NASA said that the moon is shrinking, which is resulting in Moonquakes.

NASA said that as the moon cooled over the last several hundred million years, it has shrunk about 50 meters in size. Much like the surface of a grape wrinkles as it becomes a raisin, the moon develops “wrinkles” as it shrinks as well. NASA explained that unlike a grape, the moon’s surface is brittle, which results in “thrust faults” where one section of the surface is pushed up over its neighboring part.

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Thomas Watters, who is a senior scientist in the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum in Washington, said “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. Some of these quakes can be fairly strong, around five on the Richter scale.”

This visualization of Lee Lincoln scarp is created from Lunar Reconnaissance Orbiter photographs and elevation mapping. The scarp is a low ridge or step about 80 meters high and running north-south through the western end of the Taurus-Littrow valley, the site of the Apollo 17 Moon landing. The scarp marks the location of a relatively young, low-angle thrust fault. The land west of the fault was forced up and over the eastern side as the lunar crust contracted. In a May 2019 paper published in Nature Geoscience, Thomas Watters and his coauthors provide evidence that this fault and others like it are still active and producing moonquakes today. Credits: NASA/Goddard/SVS/Ernie Wright

According to NASA:

Astronauts placed the instruments on the lunar surface during the Apollo 11, 12, 14, 15, and 16 missions. The Apollo 11 seismometer operated only for three weeks, but the four remaining recorded 28 shallow moonquakes – the type expected to be produced by these faults – from 1969 to 1977. The quakes ranged from about 2 to around 5 on the Richter scale.

Using the revised location estimates from the new algorithm, the team found that eight of the 28 shallow quakes were within 30 kilometers (18.6 miles) of faults visible in lunar images. This is close enough to tentatively attribute the quakes to the faults, since modeling by the team shows that this is the distance over which strong shaking is expected to occur, given the size of these fault scarps. Additionally, the new analysis found that six of the eight quakes happened when the Moon was at or near its apogee, the farthest point from Earth in its orbit. This is where additional tidal stress from Earth’s gravity causes a peak in the total stress, making slip-events along these faults more likely.

This prominent lunar lobate thrust fault scarp is one of thousands discovered in Lunar Reconnaissance Orbiter Camera (LROC) images. The fault scarp or cliff is like a stair-step in the lunar landscape (left-pointing white arrows) formed when the near-surface crust is pushed together, breaks, and is thrust upward along a fault as the Moon contracts. Boulder fields, patches of relatively high bright soil or regolith, are found on the scarp face and back scarp terrain (high side of the scarp, right-pointing arrows). Image LROC NAC frame M190844037LR. Credits: NASA/GSFC/Arizona State University/Smithsonian

“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 Watters. The researchers ran 10,000 simulations to calculate the chance of a coincidence producing that many quakes near the faults at the time of greatest stress. They found it is less than 4 percent. Additionally, while other events, such as meteoroid impacts, can produce quakes, they produce a different seismic signature than quakes made by fault slip events.

The Taurus-Littrow valley is the location of the Apollo 17 landing site (asterisk). Cutting across the valley, just above the landing site, is the Lee-Lincoln fault scarp. Movement on the fault was the likely source of numerous moonquakes that triggered events in the valley. 1) Large landslides on of slopes of South Massif draped relatively bright rocks and dust (regolith) on and over the Lee-Lincoln scarp. 2) Boulders rolled down the slopes of North Massif leaving tracks or narrow troughs in the regolith on the slopes of North Massif. 3) Landslides on southeastern slopes of the Sculptured Hills. Credits: NASA/GSFC/Arizona State University/Smithsonian

“It’s really remarkable to see how data from nearly 50 years ago and from the LRO mission has been combined to advance our understanding of the Moon while suggesting where future missions intent on studying the Moon’s interior processes should go,” said LRO Project Scientist John Keller of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.