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The moon slowly narrows over time, causing crustal wrinkles and moon tremors, according to NASA's Lunar Reconnaissance Orbiter photos.
Unlike the Earth, the Moon does not have tectonic plates. Instead, as the interior of the moon cooled in the last few hundred million years, the surface crumpled as it contracted. Unlike the supple skin of a grape that is reduced to grapes, the fragile crust of the moon breaks. This creates steep cliffs called thrust faults when part of the crust is pushed up and over another part close to the crust.
There are now thousands of cliffs scattered on the surface of the moon, a few miles long on average and several dozen meters high. Since 2009, the orbiter has photographed more than 3,500 of them. In 1972, Apollo 17 astronauts, Eugene Cernan and Harrison Schmitt, had to climb one of these cliffs, the Lee-Lincoln Fault, zigzagging against the lunar vehicle.
Today, the moon is "thinner" at 50 meters because of this process. And as it narrows, the moon is actively producing moonshells along the faults. The researchers reanalyzed the seismic data they had obtained from the moon to compare them to images collected by the orbiter.
Data from seismometers placed on the moon during Apollo 11, 12, 14, 15 and 16 missions revealed 28 moonquakes recorded between 1969 and 1977. The researchers compared the location of the epicentres of these earthquakes with imaging. orbital faults. At least eight earthquakes are due to activity along the faults. This excludes the possibility of asteroid impacts or rumblings from inside the moon.
This means that the Apollo seismometers recorded the narrowing of the moon, the researchers said. The study of Apollo seismic data and the analysis of more than 12,000 photos of the orbiter were published Monday in the journal Nature Geoscience.
"It's really remarkable to see how the data from almost 50 years ago and the [orbiter] The mission was combined to improve our understanding of the Moon while suggesting where future missions dedicated to the study of the inner processes of the Moon should go ", said John Keller in a statement, author of the study and scientist of the Moon. Lunar Reconnaissance Orbiter project at NASA's Goddard Space Flight Center.
Researchers believe that earthquakes still occur on the moon, which means it is actively changing.
"Our analysis provides the first evidence that these flaws are still active and are likely to produce moonshade today, as the Moon continues to cool and shrink gradually," said Thomas Watters, senior scientist at 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."
Some of the earthquakes also occurred at a point in the moon's orbit, farthest from Earth, indicating that tidal stress caused by the gravity of the Earth could have contributed to stress. on the crust of the moon.
"You often do not see active tectonics anywhere other than on Earth, so it's very exciting to think that these faults can still produce moonshares," said Nicholas Schmerr in an article, author and professor, and assistant geologist at the University of Maryland. Schmerr designed the algorithm that analyzed the Apollo data again.
The researchers noted further evidence on landslide and boulder photos at the bottom of the light plates, signaling recent activity. Over time, the lunar surface darkens due to inclement weather and radiation. The bright spots are therefore areas where recent activity has exposed areas on the lunar surface.
"For me, these results underscore the need to return to the moon," Schmerr said. "We learned a lot from the Apollo missions, but they only scratched the surface. With a larger network of modern seismometers, we could make enormous progress in our understanding of the geology of the moon. This gives very promising fruits for science during a future mission on the Moon. "
"The establishment of a new network of seismometers on the lunar surface should be a priority for the human exploration of the moon, both to learn more about the interior of the moon and to determine the magnitude of the moonquakes on the risks, "said Renee Weber, co-author of the study. and planetary seismologist at NASA's Marshall Space Flight Center, in a statement.
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