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A region of the moon at the center of a new international space race because it may contain water ice may be less hospitable than once thought, new research has found.
Interest in the moon’s south pole surged last year, when India’s Chandrayaan-3 mission made the first successful soft landing in the area, just days after Russia’s Luna-25 spacecraft crashed en route to attempt the feat. same. NASA has chosen the region as a landing site for its Artemis III mission, which could mark the return of astronauts to the moon as early as 2026, and China also has plans to create future habitats there.
But now a NASA-funded study is ringing alarm bells: As the moon’s core gradually cools and contracts, its surface develops vibrations — like a grape shrinking into a raisin — that create “moonquakes” that will last hours, as well as landslides. . Like the rest of the natural surface of the satellite, the area of the south pole is the subject of so much interest in these seismic phenomena, which may pose a threat to human settlements and equipment in the future.
“This doesn’t scare anyone and it certainly won’t discourage exploration of that part of the moon’s south pole,” said the study’s lead author, Thomas R. Watters, senior scientist emeritus at the Earth Center of part of the National Air and Space Museum. and Planetary Studies, “but be aware that the moon is not this benign place where nothing is happening.”
Finding the source of the moon’s vibrations
The moon has shrunk by about 150 feet in circumference over the past few million years — a significant number in geological terms but too small to cause any ripple effect on Earth or tidal cycles, researchers say.
On the surface of the moon, however, it’s a different story. Despite appearances, the moon still has a hot interior, which makes it seismically active.
“There’s an outer core that’s molten and cooling out,” Watters said. “As it cools, the moon contracts, the volume of the interior changes and the crust has to adjust to that change – it’s a global contraction, which is also contributed by the Earth’s tidal forces.”
Because the surface of the moon is brittle, this pull generates cracks, which geologists call faults. “The moon is thought to be this geologically dead object that hasn’t happened for billions of years, but that couldn’t be further from the truth,” Watters said. “These faults are very young and things are happening. We have actually found landslides that occurred during the time the Lunar Reconnaissance Orbiter was in orbit around the moon.”
NASA’s Lunar Reconnaissance Orbiter, or LRO, was launched in 2009, and has been mapping the surface of the moon with a variety of instruments. In the new study, published on January 25 in The Planetary Science Journal , Watters and his colleagues used data collected by LRO to link powerful lunar tremors — detected by instruments left by Apollo astronauts more than 50 years ago ago — with a series of faults in the moon. south pole.
“We knew from the Apollo seismic experiment, which was four seismometers that operated over a period of about seven years, that there were these shallow moonquakes, but we didn’t really know what the source was,” Watters told him. “We also knew that most of the shallow moonquakes detected by the Apollo seismometers were located near the south pole. It became a detective story to try to find out what the source was, and these young defects turned out to be the best suspect.”
The strongest tremor recorded was a magnitude 5.0. On Earth, that would be considered moderate, but the moon’s lower center of gravity would be worse, Watters said.
“On Earth, you have a much stronger center of gravity that keeps you attached to the surface. On the moon, it’s much smaller, so even a little ground acceleration could pull you off your feet, if you’re walking along,” he said. “That kind of shaking can really start to throw things around in a low-G environment.”
Moonquake: Short-term vs. long-term implications
The results of the study will not affect the Artemis III landing region selection process, due to the scope and duration of the mission, according to study coauthor and NASA planetary scientist Renee Weber.
“This is because it is difficult to accurately estimate how often moonquakes occur in a given region, and like earthquakes, we cannot predict moonquakes,” Weber said. “Strong shallow lunar quakes are rare and pose a low risk to short-term missions to the lunar surface.”
NASA has identified 13 candidate Artemis III landing regions near the lunar south pole, she said, using criteria such as the ability to land safely in the region, the ability to meet science objectives, the availability of a launch window and conditions such as terrain, communications and lighting. . As part of the mission, two astronauts will spend about a week living and working on the surface of the moon.
However, Weber said that for a long-term human presence on the moon, the site selection process may indeed be a factor in geographic features such as proximity to tectonic features and terrain.
Like flashlights on the moon
Moonquakes could be a problem for future manned landing missions, said Yosio Nakamura, professor emeritus of geophysics at the University of Texas at Austin, who was among the researchers who looked at the data collected by the Apollo seismic stations. at the start.
However, Nakamura, who was not involved in the study, disagrees about the cause of the tremors, saying the Apollo data show the phenomena originates thousands of kilometers below the surface.
“We still don’t know what causes shallow moonquakes, but it’s not a strike-slip fault near the surface,” he said. “Whatever causes these tremors, it’s true that they could pose a threat to future landing missions, and we need more data about them.”
Regardless of the underlying cause, the potential danger of moonquakes to astronauts will be limited by the fact that – at least in the near future – humans will be on the moon for short periods of time, a few days at most , according to Allen Husker. , a research professor of geophysics at the California Institute of Technology who was also not involved in the study.
“There’s a small chance of a big moonquake while they’re there. However, it is good to know that these seismic sources (which cause the tremors) exist. They can be an opportunity to better study the moon as we do on Earth with earthquakes,” said Husker. “By the time there is an actual lunar base, we should have a much better idea of the actual seismic hazard for future missions.”
That sentiment is shared by Jeffrey Andrews-Hanna, an associate professor of planetary science at the University of Arizona, who also did not participate in the work. “Moonquakes are an incredible tool for doing science,” he said in an email. “They are like flashlights on the lunar interior that show us their structure to see. A study of lunar vibrations at the south pole will tell us more about the interior structure of the Moon as well as its activity today.”
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