For hundreds of millions of years, our moon has been shrinking, like a fruit that slowly turns into a raisin. Now, scientists point out that this reduction in circumference has led to the occurrence of shallow moonquakes, some of which may be in the vicinity of NASA's planned human mission to the moon.
Many people generally think that the Moon is a geologically dead object, and that everything on the Moon never seems to change," said Lunar geologist Tom Waters. "But in fact, the Moon is an active celestial body. ”
The study of moonquakes dates back to the time of Apollo. More than 50 years ago, astronauts placed a ** instrument near the surface of the moon to record the tremors. The most intense shallow layer** occurs near the moon's south pole, near the landing site of NASA's planned Artemis III mission. The South Pole region of the Moon is of great concern because it contains permanently shadowed areas where some scientists speculate that water-based ice may be present.
In a new study, Waters and his team point out that these intense **s are linked to a group of faults that are still active today, which were formed during the shrinking of the Moon. According to their model, ** in the area could trigger loose rocks and dust from surrounding craters, leading to landslides.
Other researchers say we still lack enough information to identify dangerous sites for landing on the moon.
The shrinkage of the Moon is measurable, but by a small margin. Over the past few hundred million years, the diameter of the Moon has shrunk by about 150 feet. This contraction is mainly due to the natural cooling of the molten core inside the Moon. As the core cools, the lunar surface gradually shrinks and adapts to changes in volume. As it shrinks, parts of the Earth's crust are squeezed together, forming ridges called thrust faults.
The Earth's gravitational pull on the Moon also exerts pressure on the Moon's surface and increases the stress on the Earth's crust, which helps in the formation of these thrust faults.
But the Earth will not experience the same contraction as the Moon. Although our Earth's molten core is also cooling, the Earth's crust is made up of multiple tectonic plates, unlike just one plate like the Moon. Energy transmission in the Earth's core moves these plates, or is released through volcanic eruptions, Waters said.
The shrinkage of the Moon has little impact on the Earth. For example, changes in the size of the moon do not affect the occurrence of a solar eclipse. The mass of the Moon has not changed either, so the Earth's tides will not be affected.
People don't have to worry about the shrinkage of the moon unless we plan to move there, Waters said.
It's not about stopping people from exploring the moon's south pole," said Waters, a senior scientist at the National Air and Space Museum's Center for Earth and Planetary Studies. "But it's to make sure people understand that it's not a harmless environment. ”
Similar to Earth, these faults are often associated with activity. Thrust faults may look like walls tens of meters high and can be detected, but certainly not mountains. With high-resolution imagery from NASA's Lunar Reconnaissance Orbiter, thousands of small thrust faults have now been discovered on the Moon. Waters said they remain on the surface and have not been eroded, meaning they must be young and probably active.
In the image of locating thrust faults, study.
The team re-analyzed the data from the Apollo instrument. Through an algorithm, they were able to identify thrust faults that could cause moonquakes. They found that the largest Richter scale near the South Pole was associated with a group of faults that may still be active.
There's no reason to think they're inactive at the moment, because we know the moon is still hot and its interior is still cooling," Waters said.
To assess potential damage, the team modeled the surface slope of the Antarctic region to determine which areas were more susceptible to landslides triggered by **. They found that some slopes, especially in permanently shaded areas, such as the Shackleton Crater, one of the potential landing sites for NASA's Artemis III mission, are more prone to landslides than other areas. Even a slight shaking is enough to trigger a landslide on a steep wall.
It's not a lot of material, but it's still quite important, and you don't want to get close to it," Waters said.
Moonquakes differ from ** in several key ways. They may last longer on the moon, sometimes up to several hours. Since the Moon's gravitational pull is weaker, the ** on the Moon is also stronger than ** on Earth. Even a slight shake can make it difficult to stand up, Waters says.
The study provides "more evidence of the existence of moonquakes, some of which may be relatively large," said Alan Hasker, a geophysicist who was not involved in the study. The combination of the Moon's contraction and the gravitational pull from the Earth "makes these moonquakes more intense than we previously thought."
Although it can be intense, it doesn't happen very often. The Husk study estimates that a shallow moonquake occurs on average every 100 days across the lunar surface. It would be very rare if it happened in the place where the astronauts landed.
This danger becomes very important if we plan to build an outpost to explore or even inhabit the moon - like reinforcing buildings in **-prone areas," said Hasker, a researcher at the California Institute of Technology. "If we can make these maps like we do on Earth, then we can avoid this. ”
However, not everyone believes in this potential danger. In an independent study published in 2022, it was concluded that shallow moonquakes caused by these thrust faults would be weaker than the new study described. And this phenomenon will also not affect many regions of the moon, including most of the Artemis III mission landing site candidates.
Senhir Kumar, the author of the 2022 study, said his "position remains the same" despite the new research. In fact, what the new study raises is "one of the possibilities".
It's too early to talk about this dangerous situation at the Artemis site, [which] could destroy the moon base," said Kumar, a researcher at the National Geophysical Institute in Hyderabad, India.
In order to accurately assess the risk, he said, the scientific community needs to have a deeper understanding of local conditions on the ground, the characteristics of potential lunar hypocenters, and the propagation conditions of ** waves.
Probably the best way to get these details is to go straight to the moon.