Geological Chronicle
Keeler is a large impact crater situated on the far side of the Moon, measuring 158.07 kilometers in diameter. Formed during the Early Imbrian epoch, it is one of the largest impact structures of that era. The crater adjoins the older walled plain Heaviside along its eastern edge, creating a straight rim segment where the two formations meet. Its northern perimeter bulges outward toward the north-northwest, while terraced shelves step down the inner walls of its southern half.
Within the crater, the smaller formation Planté occupies the eastern floor adjacent to the inner wall, while an interior ridge extends from near the midpoint toward the west-southwest. Spectroscopy of the central peaks reveals anorthosite with very low mafic abundance, alongside the infrared signature of pure crystalline plagioclase across the central peak, floor, and eastern rim.
Measurements by the electron reflectometer on the Lunar Prospector orbiter revealed that the impact site has undergone crustal demagnetization. A low magnetic anomaly sits at the center of Keeler and extends outward roughly one and a half crater diameters, a feature scientists attribute to shock demagnetization from the collision.
Before receiving its formal designation, the crater was cataloged simply as Crater 302. In 1970, the International Astronomical Union named the landmark in honor of American astronomer James Edward Keeler.