Chandrayaan-1 observation of distant secondary craters of Copernicus exhibiting central mound morphology: Evidence for low velocity clustered impacts on the Moon

Analysis of the Chandrayaan-1 Terrain Mapping Camera image of a 20 km×27 km area in the Mare Imbrium region revealed a cluster of thousands of fresh and buried impact craters in the size range of 20–1300 m. A majority of the large fresh craters with diameter ranging from 160 to 1270 m exhibit near-circular mounds (30–335 m diameter and 10–40 m height) in the crater floor, and their size depends on the host crater size. The origin of this cluster of secondary craters may be traced to Copernicus crater, based on global lunar image and the analysis of Chandrayaan-1 Hyper Spectral Imager data. Our findings provide further evidence for secondary crater formation by low-velocity impact of a cloud of clustered fragments. The presence of central mounds can also distinguish the secondary craters from the primary craters and refine the chronology of lunar surface based on counting of small craters.

► A distal ray of Copernicus crater contains a cluster of thousands of secondary craters.
► Central mound bearing secondary craters are abundant and are deeper than regolith.
► Central mound craters were produced by low velocity clustered impacts.
► The crater clusters are spectrally similar to Copernicus crater ejecta.
► The central mound craters should be excluded from crater counting dating.