Geological Chronicle
Located in eastern Oceanus Procellarum south of the Montes Carpatus, Copernicus is a 96-kilometer impact crater that defines the youngest stratigraphic era in lunar history: the Copernican period. Excavated approximately 800 million years ago, likely during the collisional breakup of the parent asteroid of 495 Eulalia, Copernicus remains exceptionally well preserved because relatively few subsequent impacts have disturbed its structure.
The crater has a pronounced hexagonal outline shaped by pre-existing fault grids in the target crust. Its outer rampart slopes outward for 30 kilometers before merging into the surrounding basaltic plains. Inside, the rim drops 3.8 kilometers to the floor across three distinct terrace tiers formed by massive rotational slumping during the modification stage. High-resolution infrared spectroscopy from lunar orbiters identified exposures of pure crystalline plagioclase along the upper northern walls.
Unlike older lunar craters whose floors flooded with dark mare lavas, Copernicus retains its original impact-sculpted bedrock. A group of three central peaks rises up to 1.2 kilometers above the crater floor along an east-west axis. Spectral analysis indicates these peaks consist of magnesium-rich olivine brought up from the lower crust during central uplift rebound. The surrounding floor displays cracked impact-melt sheets and small volcanic or fluidized debris mounds.
Copernicus is famous for its 800-kilometer ray system, which blankets the mare surface with bright ejecta plumes and secondary crater chains that cross older rays from Kepler and Aristarchus. In November 1966, Lunar Orbiter 2 captured an oblique view across the crater interior that NASA scientists and news outlets termed the "Picture of the Century." Three years later, Apollo 12 astronauts collected ray ejecta samples from Oceanus Procellarum, enabling isotopic dating that confirmed the crater's roughly 800-million-year age.