The Moon is steadily shrinking, causing wrinkling on its surface and quakes, according to an analysis of imagery captured by NASA's Lunar Reconnaissance Orbiter (LRO) published Monday.
A survey of more than 12,000 images revealed that lunar basin Mare Frigoris near the Moon's north pole -- one of many vast basins long assumed to be dead sites from a geological point of view -- has been cracking and shifting.
Unlike our planet, the Moon doesn't have tectonic plates; instead, its tectonic activity occurs as it slowly loses heat from when it was formed 4.5 billion years ago.
This in turn causes its surface to wrinkle, similar to a grape that shrivels into a raisin.
Since the moon's crust is brittle, these forces cause its surface to break as the interior shrinks, resulting in so-called thrust faults, where one section of crust is pushed up over an adjacent section.
As a result, the Moon has become about 150 feet (50 metres) "skinnier" over the past several hundred million years.
The Apollo astronauts first began measuring seismic activity on the Moon in the 1960s and 1970s, finding the vast majority occurred deep in the body's interior while a smaller number were on its surface.
The analysis was published in Nature Geoscience and examined the shallow moonquakes recorded by the Apollo missions, establishing links between them and very young surface features.
"It's quite likely that the faults are still active today," said Nicholas Schmerr, an assistant professor of geology at the University of Maryland who co-authored the study.
"You don't often get to see active tectonics anywhere but Earth, so it's very exciting to think these faults may still be producing moonquakes."
NASA dubs 2024 Moon mission 'Artemis,' asks for $1.6 billion
NASA's next mission to the Moon will be called Artemis, the US space agency announced Monday, though it's still looking for the money to make the journey happen by its accelerated 2024 deadline.
In March, US President Donald Trump's administration moved the date for the next American lunar mission up by four years from its original goal of 2028 while pledging to get a female astronaut to the Moon's surface for the first time.
NASA Administrator Jim Bridenstine told reporters the agency would need an additional $1.6 billion to pay for the new ground and space vehicles needed to meet the deadline.
"This additional investment, I want to be clear, is a downpayment on NASA's efforts to land humans on the Moon by 2024," he said.
Bridenstine said the mission was named Artemis after the Greek mythological goddess of the Moon and twin sister to Apollo, namesake of the program that sent 12 American astronauts to the Moon between 1969 and 1972.
NASA's total annual budget is approximately $21.5 billion, and in the 2019 fiscal year, the agency spent about $4.5 billion on developing the Orion spacecraft, the Space Launch System (SLS) heavy rocket and a new lunar orbital mini-station, three elements essential to the Artemis mission.
But many experts and lawmakers are concerned that NASA cannot meet the accelerated deadline, especially given the major delays in development of the SLS, which is being built by aerospace giant Boeing.
Asked how much the new mission would cost in total, Bridenstine demurred, telling a reporter: "I would love to tell you that."