The moon is shrinking — and may be generating “moonquakes” as a result

The moon is shrinking — and may be generating

May 14, 2019– Mary Greeley News – The interior of the moon has been cooling and as a result, has gotten about 150 feet “skinnier ” over the past several hundred million years — leading to a phenomenon known as “moonquakes,” NASA data suggests.

A survey of more than 12,000 images revealed that lunar basin Mare Frigoris near the Moon’s north pole — one of many vast basins long assumed to be dead sites from a geological point of view — has been cracking and shifting.

Unlike our planet, the Moon doesn’t have tectonic plates; instead, its tectonic activity occurs as it slowly loses heat from when it was formed 4.5 billion years ago.

The moon is shrinking — and may be generating

Similar to a grape’s skin when it shrinks into a raisin, the moon wrinkles as it gets smaller. And as it gets “skinner,” the moon actively generates moonquakes along the faults.

When the moon’s fragile crust breaks, it creates visible stair-step-like cliffs as parts of the crusts are pushed up and over one another. These faults, which are “high and extending for a few miles” on the surface, remain active and moving in response to the gradual reduction in size that the moon is undergoing.

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

The moon is shrinking — and may be generating

The data reported was recorded by the seismometer that was placed on the moon during five Apollo missions, and NASA’s Lunar Reconnaissance Orbiter captured 3,500 images.

A team of researchers led by NASA used a new algorithm to re-analyze data from seismometers placed on the moon during several Apollo missions from 1969 to 1977. They compared the data with more than 12,000 photos taken by NASA’s Lunar Reconnaissance Orbiter (LRO) since 2009 and determined the moon is 164 feet “skinnier” than it was in the early 1970s.

The LRO has imaged more than 3,500 of these fault scarps on the moon since 2009.

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The seismometers recorded 28 moonquakes ranging from 2 to 5 on the Richter scale between 1969 to 1977. The algorithm then allowed scientists to better pinpoint the epicenters of the quakes. They found that eight of those shallow quakes were located within 19 miles of thrust faults visible in LRO lunar images.

The moon is shrinking — and may be generating

The researchers also determined that six of the eight quakes linked to the thrust faults occurred when the moon was at its apogee, or at its farthest distance from the earth, where additional “tidal stress from Earth’s gravity causes a peak in the total stress on the moon’s crust.”

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“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,” Thomas Watters, senior scientist in the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum in Washington, said in a press release.

The research has led to more questions about what is happening as the moon ages. While the seismometers were retired in 1977, imagery capturing landslides and fallen boulders suggests moonquakes continue to occur. Future research can also help scientists understand what is occurring on other celestial bodies like the planet Mercury, which is also shrinking and has thousands of thrust faults.