[ad_1]
Studies on lunar earthquakes date back to the Apollo era. More than 50 years ago, astronauts placed seismometers around the near side of the moon’s surface to record tremors. The most powerful shallow earthquake was located near the south pole, which is close to the landing sites for NASA’s Artemis III mission to send people back to the moon. potentially in 2027. The lunar south pole region is attractive because it contains permanently shadowed regions that some speculate could have water-based ice.
In a new study, Watters and his colleagues say that this powerful earthquake is related to a group of currently active seismic faults, which were created when the Moon shrank. Earthquakes in the area could trigger landslides of loose rock and dust from surrounding craters.
Other researchers say we still don’t have enough information to determine dangerous moon landing locations.
How a waning moon could cause earthquakes
The moon’s reduction has been measurable, but small. Its circumference has shrunk about 150 feet in the last few hundred million years. Much of the contraction is due to the natural cooling of our moon’s molten core. As the core cools, the moon’s surface contracts and adjusts to the change in volume. As it contracted, portions of the crust came together to form ridges known as thrust faults.
The Earth’s gravitational pull on the Moon also applies force to the lunar surface and adds tension, which helps form these thrust faults on the Moon.
The Earth does not experience this same type of contraction. Our molten core is also cooling, but the Earth’s crust is made up of a puzzle of tectonic plates, unlike the moon which has a single plate. Energy from the Earth’s core moves those plates or is released through volcanic eruptions, Watters said.
The shrinking of our Moon has negligible effects on Earth. Changing the size will not alter the occurrence of eclipses, for example. Its mass is also not changing, so the Earth’s tides are not affected differently either.
There is no reason Earthlings would have to worry about a shrinking moon unless we move there.
“The idea is not to discourage anyone from exploring the south pole of the Moon,” said Watters, a scientist emeritus at the Center for Earth and Planetary Studies at the National Air and Space Museum. “But just to make sure it’s understood that it’s not a benign environment.”
As on Earth, these faults are often associated with seismic activity. Thrust faults can appear as a wall tens of meters high: detectable but certainly not a mountain. Thousands of small thrust faults have been discovered across the Moon, thanks to high-resolution images from NASA’s Lunar Reconnaissance Orbiter. The fact that they remain on the surface, rather than being eroded into nonexistence, means they must be young and probably active, Watters said.
When they located the thrust faults in images, team members reanalyzed data from the Apollo seismometers. Using an algorithm, they were able to narrow down the thrust faults that likely triggered the moonquakes. They found that the largest earthquake, measuring 5 on the Richter scale near the south pole, was related to a group of faults probably still active.
“There is no reason to believe that they are not currently active because we know that the moon is still hot and its interior is still cooling,” Watters said.
To determine potential damage, the team modeled surface slopes in the south polar region to see if any areas were more susceptible to landslides due to seismic shaking. He found some slopes in permanently shadowed areas, such as Shackleton Crater, which is one of the possible landing sites for NASA’s Artemis III mission, which was very prone to seismic activity. Even a slight shaking caused landslides along its steep walls.
“It’s not like a huge mass of material, but it’s still significant enough that you don’t want to be near it,” Watters said.
Moonquakes differ from earthquakes in a few key ways. They can last much longer on the Moon, sometimes for hours. Due to the Moon’s weaker gravity, an earthquake will also be felt much stronger than on Earth. Even a moderate amount of shaking could cause one to lose balance, Watters said.
The study provides “more evidence that there are lunar earthquakes and some of them may be relatively large,” said geophysicist Allen Husker, who was not involved in the research. The combination of the Moon’s contraction and the Earth’s pull “combined to make these moonquakes larger than we would have imagined beforehand.”
How earthquakes could affect future human visits
Even if earthquakes are large, they do not occur very often. Husker’s research estimated that shallow moonquakes occur about once every 100 days on average across the lunar surface. It would be very fortuitous if an earthquake occurred right where the astronauts land for a few days.
He said it would be important to guard against danger in case people build an outpost to visit or even live on the moon, much like fortifying a building in earthquake-prone areas in California.
“Future lunar bases should be installed away from seismic sources to avoid damage or built to withstand seismic shocks,” said Husker, also a research professor at the California Institute of Technology. “If we can map them like we have on Earth, then we can avoid them.”
However, not everyone is convinced of this potential danger. An independent study published in 2022 concluded that shallow moonquakes coming from these thrust faults would be weaker than this new research describes. It also would not affect many areas of the moon, including most of the Artemis III landing site candidates.
Senthil Kumar, author of the 2022 study, said his “position remains the same” despite the new research. In fact, the new study presents “one of the strangest possibilities.”
“It is too early to advocate such danger scenarios for the Artemis sites, (which) could devastate the lunar base,” said Kumar, a researcher at the National Geophysical Research Institute in Hyderabad, India.
To make an accurate hazard assessment, he said, the scientific community needs a better understanding of local site conditions, the properties of potential moonquake sources, and the conditions that would propagate seismic ground motion.
Probably the best way to get some of those details is to go to the moon.