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Scientists have discovered a crater on the moon that’s bigger than the Roman Colosseum and is the result of a powerful impact two years ago that initially went undetected.
The steep-sided hole — 222 metres across and up to 43 metres deep — is the solar system’s biggest known impact crater carved out in recent times.
Such a large-scale event is estimated to occur only once every 132 years, researchers said, making this a treasure trove of information as NASA prepares to build a base for astronauts on the moon.
“This event constitutes a statistically rare, effectively once-in-a-lifetime observation,” the scientists wrote in one of two studies appearing on the subject Wednesday in the journal Science Advances.
NASA’s Lunar Reconnaissance Orbiter (LRO) spotted the crater on the moon’s near side in May 2024 soon after it was formed by an incoming fragment of an asteroid or comet. The moon strike escaped real-time detection by telescopes on Earth and in space.
LRO’s wide-angle images were not identified in the crush of data until August 2025. The spacecraft gathered more detailed pictures last fall, followed by confirmation of the discovery early this year.
The crater is named for the late Thomas McGetchin, a former director of Houston’s Lunar and Planetary Institute.
Like gardening
Pockmarked since ancient times, the moon bears some of the solar system’s largest impact craters, including one that stretches more than 2,400 kilometres across.
This latest impact churned the lunar surface for more than 100 kilometres. Dust and rocky soil were hurled away at a higher angle than expected, according to Mark Robinson, chief scientist for the LRO’s cameras who works at Intuitive Machines. Robinson was the lead author for one of the studies.
A separate study identified a seven-kilometre-wide cold spot around the new crater, consistent with a loosening of the moon’s topsoil. Co-author David Paige of the University of California, Los Angeles, likens it to gardening.
“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,” Paige said in a statement. (Regolith is the term for the loose, solid material on top of bedrock.)
The LRO’s numerous crater discoveries since its launch in 2009 show that the moon’s top two centimetres of soil is being overturned by ejected material every 80,000 years, faster than previously thought, according to Robinson.
Contrary to the popular belief that the Apollo moonwalkers’ dusty lunar footprints will last forever, they will “definitely be long gone in that time frame,” Robinson said in an email.
The next step is to calculate the risk of ejected crater material striking NASA’s planned moon base, he added.
“That information will help engineers harden structures so one won’t have to worry about damage, or maybe worry less.”
