Scientists believe the moon’s shrinking is causing worrying lunar earthquakes

Research on lunar earthquakes dates back to the Apollo era. More than 50 years ago, astronauts placed seismometers on the near side of the moon’s surface to record shaking. The most powerful shallow earthquake occurred near the South Pole, near the landing site of NASA’s Artemis III mission, which will return people to the moon in 2027. The Moon’s south pole region is attractive because it contains permanently shadowed regions. It is speculated that water-based ice may be present.

In the new study, Watters and colleagues say the powerful earthquakes are linked to a series of currently seismically active faults that formed as the moon shrank. If an earthquake were to occur in the area, rocks and dust from surrounding craters could collapse, causing landslides.

Other researchers say they don’t yet have enough information to determine where it would be dangerous to land on the moon.

How the shrinking moon causes earthquakes

The moon’s shrinkage is measurable, but small. Over the past hundreds of millions of years, its circumference has shrunk by about 150 feet. Much of the contraction is caused by the natural cooling of the moon’s molten core. As the core cools, the moon’s surface contracts and accommodates the change in volume. As it contracted, parts of the Earth’s crust were pushed together, forming ridges known as thrust faults.

The Earth’s gravitational pull on the Moon also exerts forces and stresses on the Moon’s surface, helping these thrust faults form on the Moon.

Earth does not experience this same type of contraction. The molten core is also cooling, but the Earth’s crust is made up of a jigsaw puzzle of plates, unlike the moon, which has one plate. Energy from the Earth’s core moves these plates and is released through volcanic eruptions, Watters said.

The shrinking of the moon will have a negligible effect on Earth. For example, the occurrence of a solar eclipse does not change even if the size changes. Since its mass has not changed either, it has no particular effect on the Earth’s tides.

There’s no reason Earthlings will have to worry about the moon shrinking unless we move there.

“This idea should not deter anyone from exploring the moon’s south pole,” said Watters, a senior scientist emeritus at the National Air and Space Museum’s Center for Earth and Planetary Research. “But just to make sure you understand that it’s not a benign environment.”

As on Earth, these faults are often associated with seismic activity. Thrust faults can look like walls tens of meters high. It’s detectable, but it’s definitely not a mountain. Thanks to high-resolution images from NASA’s Lunar Reconnaissance Orbiter, thousands of small thrust faults have been discovered across the lunar surface. The fact that they remain on the surface rather than eroding away means they must be young and likely active, Watters said.

Once the thrust fault was identified in the images, team members reanalyzed data from the Apollo seismometer. Using an algorithm, they were able to narrow down the thrust faults that likely caused the lunar earthquake. They found that the largest earthquake (magnitude 5 on the Richter scale near the South Pole) was probably still associated with a mass of active faults.

“We know the moon is still hot and the interior is still cooling, so there’s no reason to believe they’re not active right now,” Watters said.

To determine the potential damage, the researchers modeled the surface slopes of the Antarctic region to see if any areas were susceptible to landslides caused by earthquake shaking. They found that some slopes in permanently shadowed areas, such as Shackleton Crater, one of the landing sites for NASA’s Artemis III mission, are highly susceptible to seismic activity. . Even the slightest shaking caused landslides along its steep walls.

“It’s not like a huge mass of material, but it’s still important enough that you don’t want to get close to it,” Watters said.

Lunar earthquakes differ from earthquakes in several important ways. On the Moon, they last much longer, sometimes several hours. Because the Moon’s gravity is weak, earthquakes are felt much more strongly than on Earth. Watters said even moderate shaking could cause it to stand up.

Geophysicist Allen Hasker, who was not involved in the study, said the study “provides further evidence that lunar earthquakes exist and that some of them may be relatively large.” The combination of the moon’s shrinkage and the gravitational pull from Earth “makes these moonquakes larger than we expected in advance.”

How earthquakes could affect future human visitation

Even large earthquakes do not occur very often. Hasker’s research estimates that shallow lunar earthquakes occur on average once every 100 days across the entire lunar surface. It would be very coincidental if an earthquake occurred for several days where the astronauts landed.

He said it’s important to prevent hazards when building outposts for people to visit and live on the moon, just as it’s important to strengthen buildings in earthquake-prone areas of California. He said it would be.

“Future lunar bases should be located far away from earthquake sources to avoid damage, or they should be built to withstand earthquake shaking,” said Hasker, a professor at the California Institute of Technology. “If we can map them, as we have done on Earth, we can avoid them.”

However, not everyone is convinced of this potential danger. Another study published in 2022 concludes that shallow lunar earthquakes from these thrusts are weaker than those described in this new study. It also won’t affect much of the moon, including most of the potential landing sites for Artemis III.

Senthil Kumar, author of the 2022 study, said despite the new study, “the position remains the same.” In fact, a new study points to “one of the rarest possibilities.”

“It is premature to assert such a risk scenario for the Artemis site. [which] The moon base could be destroyed,” said Kumar, a researcher at the National Geophysical Institute in Hyderabad, India.

He said that to make accurate risk assessments, the scientific community needs a deeper understanding of the local situation, the characteristics of potential lunar earthquake sources, and the conditions under which seismic motions propagate.

The best way to get these details is probably to go to the moon.