Rock spatial densities on the rims and interiors of a group of Copernicus secondary craters

Boulders larger than 2.2 m were studied on the rims and interior of 15 secondary craters of Copernicus Crater. The age of this Copernicus is 800 Ma, so that the age of its secondaries should be the same. This study continues the earlier work of Basilevsky et al. (2013, 2015b, 2018b) and Li et al. (2018), providing a possibility to verify our conclusions on the lifetime of boulders at this scale on the lunar surface. The investigation of the abundance of boulders inside the considered secondaries provided information on the evolution of the boulder populations on the crater inner slopes where their abundance is often higher than on the rims. Our study found that the lifetime of these boulders on the lunar surface is indeed only several hundred million years. The rock abundance inside some of the studied craters was found to be higher than on their rims. An analysis of these cases led to the conclusion that the observed higher abundance of the interior boulders is due to downslope material movement. This leads to the appearance of new boulders, which were not outcropped earlier, replacing those on the surface which have been destroyed. The study of boulders in the polar areas of the Moon, where the factor of the boulder thermal fatigue is different compared to other areas may be the next stage of our analysis on the evolution of the populations of boulders on the lunar surface.