The Moon is cooling, shrinking and has moonquakes, Nasa finds

NASA calls for Apollo stories for 50th anniversary oral history

Shrinking Moon may be experiencing powerful quakes to this day

This is despite a general scientific rule that smaller rocky bodies cool down more rapidly, Watters says.

What's more, most of the Moonquakes occurred during times of the month when the tidal stresses between the Moon and Earth were at their greatest, which would make those faults more likely to slip and thus cause a quake.

Another Nasa project, the Lunar Reconnaissance Orbitor (LRO) spacecraft, has snapped thousands of images of the fault scarps on the moon since 2009, showing various landslides on the Moon's surface. However, the moon's surface crust is very brittle, and it breaks down as the moon shrinks, developing "thrust faults" where one area of crust is pushed up over a nearby part.

These moonquakes likely happen because the moon is quivering as it shrinks, researchers added.

The study of Apollo seismic data and analysis of more than 12,000 of the orbiter's photos were published Monday in the journal Nature Geoscience.

The researchers in the new study wanted to see if the shallow moonquakes that the Apollo missions detected were linked with faults on the lunar surface, and thus ongoing tectonic activity on the moon.

"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, in the statement. Mercury has enormous thrust faults - up to about 600 miles (1,000 kilometers) long and over a mile (3 kilometers) high - that are significantly larger relative to its size than those on the Moon, indicating it shrank much more than the Moon.

Now, new research has tracked the epicenters of each small moonquake, and found that eight of them could be traced to within 20 miles of so-called fault scarps.

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

The discovery of young faults less than 50 million years old by the LSO's camera in 2010 has been interpreted as evidence of lunar tectonic activity.

Other LRO fault images show fresh tracks from boulder falls, suggesting that quakes sent these boulders rolling down their cliff slopes. This rules out the possibility of asteroid impacts or rumblings from the moon's interior.

USA astronauts placed seismometers on the lunar surface during the Apollo 11, 12, 14, 15 and 16 missions, recording 28 shallow quakes up to nearly 5 magnitude, which is moderate strength.

Of the 8 moonquakes most recently recorded, 6 of them occurred at these times.

"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 Lunar Reconnaissance Orbiter (LRO) Project Scientist John Keller. "This provides some very promising low-hanging fruit for science on a future mission to the Moon".

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