Crater size-frequency distributions. (a) Observed crater sizefrequency distributions by using a nested crater counting technique. Small craters were measured in a small region at the Chang’e-5 landing site (the blue polygon in Fig. 1c), and large craters were counted on the Chang’e-5 unit (the purple polygon in Fig. 1c). (b) SFD comparison. The SFD of Chang’e-5 was constructed from the SFDs of large craters mapped on a large area (the purple polygon in Fig. 1c), and smaller craters (blue) were mapped in a smaller region (the blue polygon in Fig. 1c) around the Chang’e-5 landing site. Error bars (1σ uncertainty) are given according to Poisson statistics. Both SFDs are considered completed for craters with diameters larger than 400 m.