When you look at the night sky, you might not notice it.
But our moon is actually shrinking – and that could be catastrophic for NASA.
The moon is shrinking because its dense, metallic core is gradually cooling, according to a new study.
This causes the moon's surface to contract and become more brittle – and therefore more susceptible to seismic tremors, so-called “moonquakes”.
If these tremors cause landslides, they could pose a danger to NASA's Artemis astronauts after they finally land on the moon, University of Maryland scientists warn.
Earth's moon shrank by more than 150 feet in circumference as its core gradually cooled over the last few hundred million years. Pictured is the southern region of the Moon with blue boxes marking the planned locations of Artemis III's upcoming lunar landing. Magenta dots indicate possible epicenters of a very strong moonquake in the early 1970s
Why is the moon shrinking?
The moon is shrinking as it cools, a process that has been occurring since its formation nearly 4.5 billion years ago.
The moon is shrinking because its dense, metallic core is gradually cooling and contracting.
The moon folds as its interior cools and shrinks, much like a grape dries and becomes a raisin.
But unlike the flexible skin of a grape, the moon's crust is brittle, causing parts of the crust to press against each other.
The result is so-called “moonquakes” that could endanger manned lunar missions.
According to the team of experts, the moon has shrunk very gradually over the 4.4 billion years since its formation.
Its circumference has shrunk by more than 150 feet as its core has cooled over the last few hundred million years.
Much like a grape develops wrinkles as it shrinks into a raisin, the moon also develops wrinkles as it shrinks.
But unlike the flexible skin of a grape, the moon's surface is brittle, causing faults to form where parts of the crust butt against each other.
This causes the moonquakes – and could lead to landslides that endanger all lunar residents.
“As the launch date of the manned Artemis mission approaches, it is increasingly important to keep our astronauts, equipment and infrastructure as safe as possible,” said study author Nicholas Schmerr, a geologist at the University of Maryland.
“This work helps us prepare for what awaits us on the Moon – be it engineering structures that can better withstand seismic activity on the Moon or protecting people from truly dangerous zones.”
For their study, the scientists linked a group of faults in the moon's south polar region to one of the strongest moonquakes recorded by Apollo seismometers on March 13, 1973, dubbed the N9 event.
Using models to simulate the stability of surface slopes in the region, the team found that some areas were particularly vulnerable to landslides due to seismic shaking.
Scientists say moonquakes have happened before and could happen again. Here, arrows point to “scarps” – long structures that are thought to be tectonic in nature and the result of thrusting – at the moon's south pole
Pictured is part of the inner wall and floor of Shackleton Crater at the lunar south pole. Boulders (white arrows) indicate recent seismic tremors have occurred in the crater
Space agencies are generally interested in landing in the southern region of the moon (pictured) because of the abundance of water ice there
The experts say the moon's continued shrinkage has led to significant deformation of the surface in its south polar region.
In fact, the south of the moon is where the Artemis III mission is scheduled to land – the first mission to put humans on the moon in over 50 years.
Later in the Artemis program, probably after 2030, NASA wants to build a base camp in the south of the moon.
Space agencies are generally interested in landing in the southern lunar region because there is plenty of water ice there.
It could be a source of drinking water for lunar explorers and help cool equipment, or be broken down to produce hydrogen for fuel and oxygen for breathing.
But moonquakes and the resulting landslides can destroy the Artemis base camp, including buildings and infrastructure.
The study authors are concerned about shallow moonquakes (SMQs) that occur near the lunar surface, only about a hundred miles deep in the crust.
Artemis Base Camp: NASA plans to build a base camp in the southern lunar region by the end of this decade (artist's impression)
Artemis is the successor to NASA's Apollo program from the 1960s and 1970s. In this famous NASA photo, astronaut Buzz Aldrin Jr. poses for a photo next to the U.S. flag on the moon during the Apollo 11 mission on July 20, 1969
Similar to earthquakes on Earth, they can be powerful enough to damage buildings, equipment, and other man-made structures.
But unlike earthquakes, which typically only last a few seconds or minutes, shallow moonquakes can last for hours and even an entire afternoon.
Researchers will continue to map the moon and its seismic activity in hopes of identifying more places that could be dangerous to human exploration.
Although the next lunar landing was recently pushed back to 2026, that's still relatively early, especially considering we're still learning about our lunar neighbor.
“Slight seismic shaking may be enough to trigger regolith landslides,” the team warns in their paper published in the Planetary Science Journal.
“The potential for strong seismic events due to active thrust faults should be considered when preparing and locating permanent outposts and poses a possible threat to future robotic and human exploration of the Southern Polar Region.”
NASA plans to send a manned mission to Mars in the 2030s after the first landing on the moon
Mars has become the next big step for humanity's space exploration.
But before humans reach the Red Planet, astronauts will take a series of small steps and return to the moon for a year-long mission.
Details of a lunar orbit mission have been revealed as part of a timeline of events leading to missions to Mars in the 2030s.
Nasa outlined its four-step plan (pictured) at the Humans to Mars Summit in Washington DC yesterday, which will hopefully one day allow humans to visit Mars. This will require multiple missions to the Moon in the coming decades
In May 2017, Greg Williams, NASA's deputy associate administrator for policy and plans, outlined the space agency's four-stage plan that will hopefully one day allow humans to visit Mars, as well as the expected time frame.
Phases one and two involve multiple trips into lunar space to enable the construction of a habitat to serve as a residence for the trip.
The final piece of hardware delivered would be the actual Deep Space Transport vehicle, which would later be used to transport a crew to Mars.
And in 2027, a year-long simulation of life on Mars will be carried out.
Phases three and four will begin after 2030 and will include sustained crew expeditions to the Martian system and surface.