Lunar Crater 'Copernicus' Beams its Rays This Week

By Gary A. Becker

StarWatch 886 for the week of Aug.  11

One of the great controversies about the moon prior to and during the Apollo program involved whether lunar craters were created through meteoritic impact or volcanism.  

Ground zero for the debate was a large 60-mile in diameter crater named Copernicus located on the edge of the Imbrium Basin. 

Here, features supported by both arguments could be made, but in the end, the impact theorists won the day; Copernicus was created by a large meteorite, perhaps 10 miles in diameter, which walloped the moon 800 million years ago.  

This impact site will be unveiled on Aug. 15 as the terminator, the boundary separating night and day, slowly sweeps past the crater. Observers using small telescopes can witness the debate itself.   

Copernicus was created by a meteorite, not the collapse of a giant volcano. Copernicus’ crater walls are terraced (stepped) showing that when the meteorite hit, the vibrations from impact cracked or faulted the crater walls.  The ground collapsed along the fault zones creating the stepped features of Copernicus’ ramparts.   

In the center of Copernicus, central peaks (mountains) formed. Central peaks are considered to be rebound features similar to the upward splash that is caused when a rock is thrown into water.  The impact occurred on a rocky surface and the “splash” became petrified in the lunar rock, forming numerous central mountains. Surrounding Copernicus are many sinuous channels that proponents of volcanism thought were areas where lava flowed.  

Impact supporters believed correctly that these arc-like features were formed from debris clumps thrown from the impact site.  As the moon waxes into its full phase by week’s end, Copernicus will display a brighter, prominent ray pattern created by the gardening of the soil from material ejected from the crater after the impact.