Study Finds Earth’s Moon Is Shrinking And Quaking

Pablo Tucker
May 14, 2019

Researchers re-analyzed seismic data they had from the moon to compare with the images gathered by the orbiter. The innermost planet Mercury boasts numerous thrust faults.

This means that the Apollo seismometers recorded the moon shrinking, the researchers said.

"It's a great testament to the continued benefits of the Apollo program that seismic data collected over 40 years ago is helping to confirm that the moon is likely tectonically active today", study lead author Thomas Watters, a planetary scientist at the National Air and Space Museum in Washington, said in a statement.

Astronauts have placed seismometers on the moon over a series of past missions. The Apollo 11 seismometer operated only for three weeks, but the four remaining instruments recorded 28 shallow moonquakes-the type produced by tectonic faults-from 1969 to 1977. A 5.5 to 6.0 magnitude quake can cause "slight damage to buildings and other structures".

By looking at the size and location of the tremors, the algorithm estimates the epicenter of the moonquakes.

As a result, researchers were able to "tentatively attribute" the recorded quakes to the faults.

The team also found that six of these moonquakes took place when the moon was at its farthest point from Earth.

For the first time, scientists have connected moon-quake data to the changing lunar landscape, showing that our satellite is tectonically active, according to the study published Monday in Nature Geoscience.

Our Moon is slowly shrinking, creating wrinkles on the surface and causing moonquakes, which were spotted by the NASA Lunar Reconnaissance Orbiter.

As the moon cools and gets smaller, its crust becomes brittle and breaks up: a bit like what happens to a grape as it dries out to become a raisin. Those missions even saw artificial moonquakes from the impacts of the spacecraft used to bring astronauts to the moon, Schmerr added. The scarps form when one section of the moon's crust (left-pointing arrows) is pushed up over an adjacent section (right-pointing arrows) as the moon's interior cools and shrinks. Analysis of the imagery shows that the lunar surface is covered in small, shallow, cliff-like features: faults. Some of these images show landslides or boulders at the bottom of relatively bright patches on the slopes of fault scarps or nearby terrain.

Those that appear brighter indicate freshly exposed rock, suggesting an event like a "moonquake". With almost a decade of LRO imagery already available and more on the way in the coming years, the team would like to compare pictures of specific fault regions from different times to look for fresh evidence of recent moonquakes.

"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. "We learned a lot from the Apollo missions, but they really only scratched the surface".

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