We model the primary crater production of small primary craters on the Moon using the size-frequency distribution (SFD) observed for the annual flux of terrestrial fireballs with an appropriate velocity distribution for the Moon. We compare results from the model with crater counts conducted on the ejecta of North Ray crater which was selected for its relatively young age, constrained by cosmic ray exposure ages of Apollo 16 samples, to be ~50 Ma. A small, 0.1 km2, study area is used containing only craters D ≤ 22 m. We estimate an age of ~58 Ma consistent with lunar crater-count chronometry systems and other crater count studies. The fact that we reproduce a similar age using a small area with a limited range of diameters indicates that the cratering rate on average has been constant over this period and the craters must be predominately primary craters. This demonstrates that crater-count chronometry systems can, in principle, be applied to date young surfaces on the Moon using small diameter craters.
Using this model, we explore other young impact craters and compare modeled crater SFD’s with crater counts. Young craters are identified by high rock abundances derived from the Diviner Lunar Radiometer instrument on LRO. Studies have shown a clear relationship between Diviner-derived rock abundances and crater ages. This relationship is explored further. Initial counts have been conducted on a small region, 22 km2, of the ejecta blanket of Giordano Bruno crater, a 22 km diameter impact crater in the eastern hemisphere of the Moon (36° N, 103° E). This crater is possibly the youngest impact crater of its size and has high rock abundances on its proximal ejecta and interior. Our counts produce a crater SFD that falls between model SFD’s of a 1 My and 10 My surface, consistent with previous studies using larger craters and study areas. Counts were conducted on small areas of the ejecta blankets of two additional craters similar in size to Giordano Bruno, Moore F and Larmor Q. The observed crater SFD’s yielded ages 10 – 100 My with Moore F being the younger of the two, consistent with their observed rock abundances. The two SFD’s bracket the SFD of North Ray crater making Moore F < 58 Ma and Larmor Q > 58 Ma.