Lunar tectonic activity likely arises because the moon is continuing to shrivel like a raisin as its interior cools and shrinks, the researchers said. Unlike the flexible skin on a grape, the Moon's surface crust is brittle, so it breaks as the Moon shrinks, forming "thrust faults" where one section of crust is pushed up over a neighboring part. These faults resemble small stair-shaped cliffs, or scarps, when seen from the. In 1972, Apollo 17 astronauts Eugene Cernan and Harrison Schmitt had to ascend one of these cliffs, the Lee-Lincoln fault scarp, by zig-zagging the lunar rover over it.
By combining information gathered by LRO and data from the various Apollo missions, researchers were able to "advance our understanding of the Moon while suggesting where future missions intent on studying the Moon's interior processes should go", according to LRO project scientist John Keller.
"This is exciting as it wasn't clear if the moon had already gone through this period billions of years ago and was tectonically dead, or if it was still active in the present", Schmerr said.
NASA says the moon isn't the only part of our solar system that is "shrinking with age", as planet Mercury has shrank more than the moon has.
For example, the Apollo missions detected about 11,000 moonquakes happening about 500 to 680 miles (800 to 1100 kilometers) beneath the lunar surface. They developed an algorithm that enabled them to get a more accurate location for the epicenters of each quake. Those missions even saw artificial moonquakes from the impacts of the spacecraft used to bring astronauts to the moon, Schmerr added.
Although the Apollo instruments recorded their last quake shortly before the instruments were retired in 1977, the researchers suggest that the moon is likely still experiencing quakes to this day.
These incredible findings were published today (May 13) in the journal Nature Geosciences.
A new analysis of Apollo-era quakes on the Moon reveal that our satellite is probably still tectonically active.
The moonquakes recorded aren't minor, they are "fairly strong, around five on the Richter scale".
The researchers also found that six of the eight quakes happened when the moon was at or near its apogee, the point in the moon's orbit when it is farthest from Earth. "These widely distributed stations made the Apollo network an ideal candidate for using sparse seismic network algorithms used on Earth where there aren't a lot of stations". The Lunar Reconnaissance Orbiter Camera (LROC) has captured over 3,500 images of the fault scarps on the lunar surface, which show boulders at the bottom of bright patches on the slopes of fault scarps or landslides. Over time, the lunar surface darkens due to weathering and radiation, so bright spots are areas where recent activity has exposed areas on the lunar surface.
"It's really remarkable to see how data from almost 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.