Fragments Delivered by Secondary Craters at the Chang'E‐4 Landing Site

The Chang'E‐4 landing site is depleted with boulders seen from both orbit and surface. However, the Yutu‐2 rover came across thousands of concreted fragments in and around an abnormally fresh crater that has more elevated northwestern rims. The origin of the fragments is crucial to resolve the provenances of surface materials detected by the rover. The lunar penetrating radar performed two in‐and‐out scans for the blocky ejecta, revealing that the subsurface materials have indistinguishable radar permittivity with the surrounding regolith. Forward modeling of electromagnetic wave propagation shows that the fragments were not an original component in the subsurface. This crater is among the several fresh craters photoed by the rover, and they are located in an eastern extension ray of the Zhinyu crater. The small craters are likely secondaries of Zhinyu, and the fragments contain a mixture of shattered projectiles and most likely compacted regolith clumps formed during the secondary impacts. Plain Language Summary The Chang'E‐4 landing site lacks boulders seen from both orbit and surface, but several abnormally fresh craters were encountered by the Yutu‐2 rover. The blocky rims and interiors are in sharp contrast with the heavily degraded crater population in the landing area. These craters are less than 3 m in diameter, and the fragments are less than 10 cm long and appear earthy in color. The origin of the fragments needs an explanation because it is the basis for the interpretation of data returned by both the lunar penetrating radar and reflectance spectrometer onboard the rover. At the ninth lunar day, the rover was carefully driven into the blocky ejecta deposits of such a crater, and ground‐penetrating radar detections were conducted. Radar measurements reveal that the physical properties beneath the blocky ejecta deposits are essentially the same with that of the surrounding regolith, and the observed fragments were not originated from the subsurface. The high spatial density, more pronounced northwestern rims, and colocation with an impact ray suggest that the small craters are most likely secondaries formed by the Zhinyu crater. The fragments are mainly formed by impact compaction of the preimpact target regolith, and the shattered secondaries‐forming projectiles are a minor component. Key Points Yutu‐2 encountered several abnormally fresh craters surrounded by blocky fragments Radar permittivity of the blocky ejecta is not distinct from nearby no