Apparently the moon is shrinking because it’s tectonic plates are smashing together causing moonquakes


The moon shrinks? During its more than 4.5 billion years in space, it has slowly shrunk, researchers say. Over the last few hundred million years, the moon’s belt line has slimmed by approximately 150 feet.

moon shrinking, moon geology, moon tectonics, moonquakes
As the moon shrinks, the lunar surface is pushed together, forming hundreds of thrust faults, like the one photographed here by the Lunar Reconnaissance Orbiter Camera. Photo by NASA/GSFC/Arizona State University/Smithsonian

According to a new study, the moon’s contractions continue today, causing ongoing surface fracturing. These active fractures, or thrust faults, are responsible for moonquakes.

Some of these quakes can be fairly strong, around five on the Richter scale,” 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 news release.

The video below shows the Lee Lincoln scarp, a low ridge or step about 80 meters high and running north-south through the western end of the Taurus-Littrow valley, the site of the Apollo 17 Moon landing. The scarp marks the location of a relatively young, low-angle thrust fault. The land west of the fault was forced up and over the eastern side as the lunar crust contracted. New evidence show that this fault and others like it are still active and producing moonquakes today.

Using a new algorithm designed to pinpoint the origins of shallow rumblings produced by a sparse fault network, scientists analyzed the data collected by seismometers placed on the lunar surface during the Apollo missions.

The faults created by lunar shrinking take the form of stair-like cliffs. When scientists mapped the origins of the moonquakes recorded by the Apollo seismometers, they found eight of the 28 shallow quakes were within 18 miles of a visible lunar fault.

View of the Taurus-Littrow valley from the LRO spacecraft

This is a view of the Taurus-Littrow valley taken by NASA’s Lunar Reconnaissance Orbiter spacecraft. The valley was explored in 1972 by the Apollo 17 mission astronauts Eugene Cernan and Harrison Schmitt. They had to zig-zag their lunar rover up and over the cliff face of the Lee-Lincoln fault scarp that cuts across this valley.Credits: [NASA/GSFC/Arizona State University]

The new analysis, published this week in the journal Nature Geoscience, showed six of the eight quakes occurred when the moon was at its farthest point from Earth, its apogee, when tidal forces put additional stress on lunar faults.

Simulations determined the chance that coincidence could explain so many shallow quakes occurring near faults during periods of high stress was less than 4 percent.

Image of lunar lobate thrust fault scarp
This prominent lunar lobate thrust fault scarp is one of thousands discovered in Lunar Reconnaissance Orbiter Camera (LROC) images. The fault scarp or cliff is like a stair-step in the lunar landscape (left-pointing white arrows) formed when the near-surface crust is pushed together, breaks, and is thrust upward along a fault as the Moon contracts. Boulder fields, patches of relatively high bright soil or regolith, are found on the scarp face and back scarp terrain (high side of the scarp, right-pointing arrows). Image LROC NAC frame M190844037LR.Credits: NASA/GSFC/Arizona State University/Smithsonian

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 Watters.

Authors of the latest study plan to continue analyzing seismic data from the Apollo seismometers, as well as images of the moon’s faults, in hopes of uncovering additional evidence of recent moonquakes.

Evidence for moonquakes on Lee-Lincoln fault scarp
The Taurus-Littrow valley is the location of the Apollo 17 landing site (asterisk). Cutting across the valley, just above the landing site, is the Lee-Lincoln fault scarp. Movement on the fault was the likely source of numerous moonquakes that triggered events in the valley. 1) Large landslides on of slopes of South Massif draped relatively bright rocks and dust (regolith) on and over the Lee-Lincoln scarp. 2) Boulders rolled down the slopes of North Massif leaving tracks or narrow troughs in the regolith on the slopes of North Massif. 3) Landslides on southeastern slopes of the Sculptured Hills.Credits: NASA/GSFC/Arizona State University/Smithsonian

Establishing a new network of seismometers on the lunar surface should be a priority for human exploration of the Moon, both to learn more about the Moon’s interior and to determine how much of a hazard moonquakes present,” said Renee Weber, a planetary seismologist at NASA’s Marshall Space Flight Center.

Comprehension of tectonic and geology of the Moon is indeed of prime importance if we want to conquer the moon and and other nearby planets in the next few decades.

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[Nature, NASA,]

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