Rare new lunar crater shows how impacts remodel the moon's surface

From Earth, the moon appears to have barely changed for as long as humans have been gazing at it. But with the right equipment, they might notice a once-in-a-lifetime alteration: a brand new crater near the edge of the full moon.

"The moon is a very old body, as old as the Earth itself. When you observe the moon from a distance, you see that its surface is pockmarked with large impact craters that formed billions of years ago, and it's tempting to conclude that the lunar surface has essentially remained unchanged over time," said UCLA planetary scientist David Paige, the lead scientist of the Diviner Lunar Radiometer Experiment aboard NASA's Lunar Reconnaissance Orbiter (LRO).

But as described in two papers published in the journal Science Advances, scientists from UCLA and other institutions discovered a new stadium-sized crater that disturbed an area greater than expected.

► Read "A new 222-m lunar crater" and "New lunar crater reveals extensive distal regolith modification."

"During the last 17 years, NASA's Lunar Reconnaissance Orbiter has been orbiting the moon and has mapped it in much greater detail than previously possible. By carefully comparing images and thermal maps of the same regions obtained months and years apart, it's become clear that the moon's surface is slowly changing," said Paige.

The main causes of change on the moon are small meteoroid impacts that pepper the surface. These same objects also hit the Earth, but fortunately, most burn up in the Earth's atmosphere. The moon has no atmosphere to protect it, so small impact craters form on the moon constantly.

The vast majority of these objects are very small - too small to be detected even by LRO. However, there are occasional larger impacts, and when they occur, they represent a major scientific opportunity to learn more about impact cratering - a process rare to observe, but common to all planetary bodies on geologic timescales.

"We have a lot of detailed statistics for how often a crater of a certain size should form, and we know a crater of this size forms only once in a century," said UCLA doctoral student Tyler Horvath, who is a co-author of the "distal regolith" paper. "One of the exciting things about this discovery is that we're very lucky we have a spacecraft to observe it."

The recent impact occurred in the spring of 2024, forming an unusually large impact crater about 222 meters in diameter - roughly the size of two football fields. The new crater, named the McGetchin crater after pioneering lunar scientist Tom McGetchin, was first discovered by the LRO camera team earlier this year and is the largest new crater that has been identified since LRO observations began in 2009. Follow-up measurements by the Diviner instrument show that the effects of the collision extended more than 3 km from the point of impact.

"This means that lunar impacts can modify the surface over distances far beyond the crater itself. Better understanding the moon's changing landscape and surface properties is valuable for unraveling the moon's long-term history but also provides useful context for future lunar exploration, including NASA's Artemis program," said first author Tyler Powell, a researcher at the Johns Hopkins University Applied Physics Laboratory, who conducted part of this research as a doctoral student at UCLA.

Diviner makes maps of the surface temperature of the moon, and these maps show that nighttime surface temperatures in the extended impact zone became significantly cooler after the impact. Most of the moon's surface is covered with a thick layer of ultrafine dust generated by countless small impacts over billions of years. The colder temperatures, believed to be caused by ejected crater material churning and fluffing up the surrounding soil, which is known as regolith, indicate that the impacts disturb the lunar surface over a very wide area, according to the paper.

"We're now thinking of impacts as a way to garden the regolith - churning the sediments and putting stuff above that's usually below the surface," said Paige.

This new understanding of how the lunar surface evolves could help scientists better understand how valuable resources are distributed in the lunar soil, he said.

On Earth, we know that many big changes have happened over time because we can find fossils, observe sediments, take core samples and make other direct measurements of change. For the moon, we have only the observations we can make using telescopes and spacecraft like LRO, which remains in continuous orbit around the moon.

"By staying in orbit around the moon, it allows us to see evidence of change," said Paige. "We see change, but don't usually know how recently it happened. Here we see a crater that formed two years ago, so we know how it formed and how it is changing. This makes the new crater a very useful calibration point."