Most candidate signals are false alarms triggered by shifts in shadows or lighting. Wagner usually verifies real impacts by searching for fuzzy rings around single-pixel bright points, which mark sprays of freshly thrown regolith. McGetchin looked nothing like those small features. Its debris pattern stretched across hundreds of pixels.

"It was by far the most obvious impact debris pattern I've ever seen in one of these images," Wagner said.

Follow-up images from LROC's Narrow-Angle Camera, which captures details at roughly 3 feet per pixel, let researchers measure the crater and study how the surroundings had changed.

Why is the Moon so cratered?

The Moon has no atmosphere capable of slowing incoming space rocks or burning them up. On Earth, most meteoroids disintegrate before reaching the ground. On the Moon, they hit at full speed.

For more than 17 years, LRO has circled the Moon in a pole-to-pole orbit about 60 miles above the surface. Its seven instruments map the terrain, measure surface composition, track temperatures, and monitor radiation.

During that time, researchers have confirmed at least 1,000 new impact craters and recorded about 100,000 additional surface changes from impacts and debris thrown outward during collisions. Scientists estimate that impacts large enough to leave craters above the smallest detection threshold (about 30 feet across) create roughly 140 new craters across the Moon each year.

What does the surrounding cold zone reveal?

After McGetchin's discovery, scientists turned LRO's thermal instrument, Diviner, toward the site. They expected the new crater to differ from its surroundings. They did not expect the surrounding area to differ so dramatically.

An area roughly 4 miles wide around the crater runs about 16 degrees Fahrenheit colder at night than nearby terrain. A second paper published September 16 in Science Advances reports the cause: the impact churned and loosened the lunar regolith, the layer of dust and broken rock that covers the surface.

The disturbance left the material less dense and less able to hold onto heat after sunset. The cold spot extends well beyond the crater rim, showing that a single major impact can reshape the lunar surface far past the crater itself. These changes could also affect future missions, since differences in regolith texture and density can influence how rover wheels grip the ground.

What limitations remain?

McGetchin is the biggest newly formed crater on record, not the biggest ever. Older features, including the 1-mile-wide Linné crater and the South Pole–Aitken basin, span far wider.

More detailed results about the impactor's size and energy are expected in a future paper. Researchers also caution that automated difference-detection methods yield hundreds of false positives per pass, which is why human review remains essential.