Our Moon Is Getting Smaller


The Moon is shrinking as its interior cools and, in doing so, records earthquakes. A new NASA study shows that our moon has thinned by more than 50 meters in the last hundred million years.

Scientists have identified what they call “thrust cracks,” where a section of the Moon’s crust slides over a nearby part. These faults resemble small stepped cliffs, seen from the lunar surface, generally several dozen meters high and extending a few kilometers.

“Our analysis provides early evidence that these faults are still active and are likely producing moon tremors today as the Moon continues to cool and shrink gradually,” said Thomas Watters, Senior Scientist at the Center for Earth and Planetary. Studies of the Smithsonian’s National Air and Space Museum in Washington. “Some of these earthquakes can be quite strong, about five on the Richter scale.”

Moon Data Analyzed

Watters and his team analyzed the data of four seismometers placed on the moon by Apollo astronauts using an algorithm, which gave a better estimate of the location of moonquakes. The study was published May 13 in Nature Geoscience.

The astronauts placed the instruments on the lunar surface during the Apollo 11, 12, 14, 15 and 16 missions. The Apollo 11 seismometer only worked for three weeks, but the other four recorded 28 shallow moonquakes, from 1969 to 1977. The earthquakes ranged from 2 to 5 on the Richter scale.

According to NASA, astronauts Eugene Cernan and Harrison Smith had to zigzag with their lunar vehicle to cross the Lee Lincoln fault during the Apollo 17 mission in 1972.

Using the algorithm location estimates, the team found that the epicenter of 8 of the 28 earthquakes was within 30 kilometers of visible faults in the lunar images.

The surface of the Moon is rigid and cracks as it shrinks forming faults where one segment of the crust is pushed on top of another (NASA).

The team determined that 8 of the 28 movements occurred within about 18 miles of visible faults in the lunar images.

In addition, the new analysis revealed that six of the eight earthquakes occurred when the moon was at its peak or near its peak, the farthest point of the Earth in its orbit. This is where the extra tidal stresses due to the gravity of the Earth cause a peak in the total stress, which makes it more likely to slip events along these faults.

Reconnaissance Orbiter Plays Vital Role

Since taking office in 2009, NASA’s Lunar Reconnaissance Orbiter (LRO) has seized more than 3500 of these flaws.

“It is truly remarkable to see how the data from nearly 50 years ago and the LRO mission were combined to advance our understanding of the Moon while suggesting where future missions to study the inner processes of the Moon will take place. Moon should go, “said John Keller, LRO project researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

The Moon is not the only body in the solar system that shrinks with age. According to NASA, Mercury has “enormous faults” of up to 620 miles long and 2 miles high “significantly larger, relative to the size of the planet, than those of the Moon.”

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