Due to gradual cooling, the Moon’s circumference has shrunk by more than 45 meters over the past hundreds of millions of years. Just as a grape wrinkles when it shrinks into a raisin, the moon also wrinkles. But unlike the flexible skin of a grape, the moon’s surface is brittle, causing fractures to form as pieces of the moon’s crust push against each other.
Scientists have now found evidence that the Moon’s shrinking size around its south pole has led to striking distortions in its surface. Because the formation of faults due to the shrinking Moon is often accompanied by seismic activity, such as moonquakes, locations near such fault zones could pose risks to future research missions.
In their paper, the scientists link a cluster of faults in the Moon’s south polar region to one of the strongest lunar earthquakes recorded by Apollo seismometers in more than fifty years. Using models to simulate the stability of slopes in the region, they found that some areas are particularly vulnerable to landslides due to seismic shocks.
Tremors that last for hours
On the surface of the moon, earthquakes regularly occur at a depth of only one hundred kilometers. Like earthquakes, these shallow lunar quakes are caused by faults in the moon’s interior and can be powerful enough to destroy buildings, equipment and other man-made structures. But unlike earthquakes, which usually end in a few seconds or minutes, shallow moonquakes can last for hours or even an entire afternoon.
According to the researchers, this means that shallow lunar quakes could have a devastating impact on any future manned bases on the Moon. “You can think of the moon’s surface as a layer of dry, packed gravel and dust,” said co-author Nicholas Schmer of the University of Maryland in the US. “Over billions of years, this surface has been exposed to numerous asteroids and comets, constantly throwing up sharp pieces of rock. As a result, the surface consists of loose sediments that are sensitive to tremors and landslides.