Geological Chronicle
Positioned in the eastern reaches of Mare Imbrium, Archimedes is the largest impact crater on the basin floor, measuring 83 kilometers across. Its terraced rim rises up to 2.1 kilometers above the surrounding basalt plains, with a prominent triangular promontory jutting 30 kilometers from its southeastern wall. Archimedes lacks a primary ray system of its own. Instead, faint streaks of bright material crossing its floor originate from the nearby Copernican impact that created the crater Autolycus.
The crater is a primary stratigraphic benchmark for the Upper Imbrian period. Its impact occurred after the excavation of the Imbrium basin roughly 3.85 billion years ago, but before the regional volcanic floods ceased. Subsequent eruptions of basaltic lava welled up through crustal fractures, submerging the interior. This inundation drowned the central peak and left a flat floor spanning more than 5,000 square kilometers, broken only by scattered micro-impacts.
Archimedes sits at the junction of several distinct geological formations. To the south rise the rugged highlands of Montes Archimedes, while the 150-kilometer rille network of Rimae Archimedes cuts through the lava plains of Palus Putredinis to the southeast. To the north-northwest, the isolated peaks of Montes Spitzbergen project through the mare, representing remnants of the Imbrium basin inner ring. To the east and northeast lie the craters Autolycus and Aristillus, enclosing the embayed mare region known as Sinus Lunicus.
The crater has a recorded place in lunar cartography and spaceflight history. Italian astronomer Giovanni Battista Riccioli named the crater in 1651 for the ancient Greek mathematician and engineer Archimedes of Syracuse, superseding earlier map names by Michael van Langren and Johannes Hevelius. On September 13, 1959, the Soviet probe Luna 2 crashed onto the plains between Archimedes and Autolycus, becoming the first human-made object to reach the lunar surface. Later orbital missions, including Apollo 15 and the Lunar Reconnaissance Orbiter, mapped the crater ramparts and surrounding volcanic rilles in high resolution.