Geological Chronicle
The Montes Apenninus form a continuous 600-kilometer mountain arc along the southeastern rim of the Mare Imbrium basin. The range begins west of the crater Eratosthenes and extends northeast to Promontorium Fresnel near the entrance to Mare Serenitatis. The Apennines formed during the colossal Imbrium impact roughly 3.85 billion years ago, when the collision fractured the lunar lithosphere and thrust massive crustal fault blocks upward in minutes. The resulting arc constitutes the uplifted southeastern rim of the multi-ring Imbrium impact basin.
The topography of the range is markedly asymmetric. Facing northwest toward the basaltic plains of Mare Imbrium, the mountains drop in steep escarpments that rise higher above their base than the Himalayas rise above the plains of northern India. To the southeast, the terrain transitions into gentler backslopes blanketed by thick sheets of impact debris known as the Fra Mauro Formation. Near the center of the chain, Mons Huygens reaches a relief of 5.4 kilometers above the mare floor, making it the tallest mountain mass on the lunar near side.
Other prominent peaks include Mons Bradley at 4.2 kilometers, Mons Ampere at 3.0 kilometers, and Mons Wolff at 3.5 kilometers. Near the northeastern terminus, Mons Hadley Delta rises 3.5 kilometers above the volcanic plain of Palus Putredinis, while adjacent Mons Hadley towers 4.2 kilometers over the plain. The steep frontal scarps expose ancient, stratified crust that was deeply buried before the basin excavation.
In July 1971, NASA targeted the Apennine front for the Apollo 15 mission, the first expedition equipped with the Lunar Roving Vehicle. Astronauts David Scott and James Irwin landed their lunar module Falcon on the plain between Mons Hadley and Rima Hadley, a 1.2-kilometer-wide, 370-meter-deep volcanic channel. While exploring the lower slopes of Mons Hadley Delta, Scott and Irwin recovered sample 15415, the celebrated Genesis Rock, a piece of 4.1-billion-year-old anorthosite that confirmed the existence of an early magma ocean in lunar history.