#^Scientists investigate moonquakes using Apollo 17 samples, LRO observations
While Earth and Mars are known for their intense surface quakes, other terrestrial bodies in our solar system also feature surface quakes — including the Moon. With NASA preparing to return humans to the lunar surface as part of the Artemis program, scientists and engineers are developing methods to investigate the nature and frequency of moonquakes.
Much like earthquakes, moonquakes occur along active fault lines on the lunar surface. These fault lines are cracks in the Moon’s crust that form due to the Moon’s shrinking as its interior slowly cools. As the Moon contracts from this shrinking, these cracks move suddenly, creating moonquakes.
During the Apollo missions to the lunar surface, astronauts deployed seismometers to measure moonquakes, and between 1969 and 1977, this network of seismometers recorded thousands of vibrations.
Moonquakes are rare and significantly weaker than earthquakes, with the most powerful moonquakes reaching magnitudes of around 5.0. With such small magnitudes, these moonquakes would likely pose little danger to astronauts completing missions lasting just several days. However, for long-term, multi-month missions, these moonquakes could significantly affect surface infrastructure.
While earthquakes last just a few seconds, moonquakes can last for several hours — long enough to tip over landers, collapse surface structures, and more.
The Taurus-Littrow valley, imaged by LRO. The Lee-Lincoln fault is seen cutting through the valley. The “X” denotes the Apollo 17 landing site. (Credit: NASA/ASU/Smithsonian)
“The hazard probability goes way up depending on how close your infrastructure is to an active fault,” said senior scientist emeritus Thomas Watters of the Smithsonian National Air & Space Museum in Washington. Watters also serves as a co-investigator on NASA’s Lunar Reconnaissance Orbiter (LRO) mission.
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Along with Nicholas Schmerr, a planetary seismologist at the University of Maryland, Watters developed a new method for investigating and estimating the intensity of moonquakes. The method involves analyzing dislodged boulders and landslides in an area where a moonquake is expected to have occurred.
Using data from LRO, which has orbited the Moon since 2009, Watters et al. have identified thousands of active faults along the lunar surface that may be regularly producing moonquakes. For their study, the scientists analyzed surface changes near the Lee-Lincoln fault in the Taurus-Littrow valley. The final Apollo mission to the lunar surface, Apollo 17, landed just four miles west of the fault in December 1972 and thoroughly explored the region surrounding the fault.
As mentioned, Watters and Schmerr study boulder movements and landslides to determine the location and intensity of moonquakes. According to observations of the environment around Lee-Lincoln, the scientists estimate that a magnitude 3.0 moonquake rattles the region once every 5.6 million years.
Computer simulation showing seismic waves emanating from the Lee-Lincoln fault. (Credit: Nicholas Schmerr)
“One of the things we’re learning from the Lee-Lincoln fault is that many similar faults have likely had multiple quakes spread out over millions of years. This means that they are potentially still active today and may keep generating more moonquakes in the future,” Schmerr said.
Watters et al. chose to study Lee-Lincoln due to Apollo 17’s extensive exploration of the region. During the mission, NASA astronauts Gene Cernan and Harrison Schmitt collected samples of boulders, which they brought back to Earth for study. After analyzing the rocks in labs, scientists were able to measure how the boulders’ internal chemistry changed due to exposure to cosmic radiation.
The amount of cosmic radiation in the rocks allowed scientists to ascertain how long the boulders had been sitting in one location and position. Knowing how long a boulder has been in one position helps determine the frequency and timing of moonquakes, as the boulders are shifted into different positions during the quakes.
Cernan and Schmitt collected boulders from the bases of two mountains in the Taurus-Littrow valley. Tracks behind the sampled boulders indicate that the boulders rolled downhill after being dislodged during a moonquake. Using the sizes of each boulder, Watters et al. were able to calculate how hard the ground had to have shaken for the boulders to be moved. This calculation subsequently allowed the team to determine the magnitude of the moonquake that freed them.
Astronaut Harrison Schmitt samples a boulder in the Taurus-Littrow valley. This boulder is believed to have been dislodged during a moonquake. (Credit: NASA/JSC/ASU)
Also present in Taurus-Littrow is evidence of a large landslide that deposited a variety of surface material onto the valley floor. As they did with the boulders, Watters et al. were able to estimate the magnitude of the moonquake that created the landslide.
Taking all of these measurements and calculations into account, the chances of a moonquake occurring during Apollo 17’s three-day surface mission were one in 20 million, according to an estimation by Watters and Schmerr. With NASA prioritizing the exploration of the Moon’s south polar region, they plan to apply their moonquake investigation method to faults near the south pole.
NASA plans to deploy additional seismometers on the Moon’s surface in the coming years. The Farside Seismic Suite, featuring two seismometers, will land in the Schrödinger basin on the far side of the Moon on a future Commercial Lunar Payload Services (CLPS) mission. The Lunar Environment Monitoring Station, which is co-led by Schmerr, is set to fly to the Moon’s south pole on NASA’s crewed Artemis III mission. These instruments and missions will help scientists like Watters and Schmerr further refine their methods for investigating moonquakes.
Watters and Schmerr reported their results in the Science Advances journal on July 30.(Lead image: NASA astronaut Harrison Schmidt walks near a boulder in the Taurus-Littrow valley during the Apollo 17 mission. Credit: NASA/JSC/ASU)
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Scientists investigate moonquakes using Apollo 17 samples, LRO observations appeared first on
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