AS 16-4653 - Secondary Craters' Clusters

These 3 clusters of secondary craters (see arrows) are on the East flank of the larger crater Ptolemaeus near the center of the Moon's Near-Side. Each cluster has a ridged and hummocky appearance. The primary crater has not been identified in this case, but the configuration of the clusters tells us that it must be to the South of Ptolemaeus. Note that the South-facing side of each cluster is more sharply defined than the North-facing side.
This is a consequence of the oblique trajectory of impacting fragments that causes the ejecta of the secondary craters to be propelled away (down range) from the primary crater. Observations of manmade impact craters have shown that the individual fragments within a cluster of secondary debris strike the surface nearly simultaneously.
In the process, ejecta from one secondary collides and interferes with ejecta from adjacent craters, producing a ridged and hummocky surface.