Von Kármán crater (diameter = ~186 km), lying in the northwestern South Pole‐Aitken (SPA) basin, was formed in the pre‐Nectarian. The Von Kármán crater floor was subsequently flooded with one or several generations of mare basalts during the Imbrian period. Numerous subsequent impact craters in the surrounding region delivered ejecta to the floor, together forming a rich sample of the SPA basin and farside geologic history. We studied in details the targeted landing region (45.0–46.0°S, 176.4–178.8°E) of the 2018 Chinese lunar mission Chang'E‐4, within the Von Kármán crater. The topography of the landing region is generally flat at a baseline of ~60 m. Secondary craters and ejecta materials have covered most of the mare unit and can be traced back to at least four source craters (Finsen, Von Kármán L, Von Kármán L', and Antoniadi) based on preferential spatial orientations and crosscutting relationships. Extensive sinuous ridges and troughs are identified spatially related to Ba Jie crater (diameter = ~4 km). Reflectance spectral variations due to difference in both composition and physical properties are observed among the ejecta from various‐sized craters on the mare unit. The composition trends were used together with crater scaling relationships and estimates of regolith thickness to reconstruct the subsurface stratigraphy. The results reveal a complex geological history of the landing region and set the framework for the in situ measurements of the CE‐4 mission, which will provide unique insights into the compositions of farside mare basalt, SPA compositional zone including SPA compositional anomaly and Mg‐pyroxene annulus, regolith evolution, and the lunar space environment.

The unequal distribution of volcanic products between the Earth-facing lunar side and the farside is the result of a complex thermal history. To help unravel the dichotomy, for the first time a lunar landing mission (Chang’e-4, CE-4) has targeted the Moon’s farside landing on the floor of Von Kármán crater (VK) inside the South Pole-Aitken (SPA). We present the first deep subsurface stratigraphic structure based on data collected by the ground-penetrating radar (GPR) onboard the Yutu-2 rover during the initial nine months exploration phase. The radargram reveals several strata interfaces beneath the surveying path: buried ejecta is overlaid by at least four layers of distinct lava flows that probably occurred during the Imbrium Epoch, with thicknesses ranging from 12 m up to about 100 m, providing direct evidence of multiple lava-infilling events that occurred within the VK crater. The average loss tangent of mare basalts is estimated at 0.0040-0.0061.

Whether or not background secondary craters dominate populations of small impact craters on terrestrial bodies is a half‐century controversy. It has been suggested that small craters on some planetary bodies are dominated by background secondary craters based partly on the steepened slope of crater size‐frequency distribution (CSFD) toward small diameters, such as the less than ~1 km diameter crater population on the lunar mare. Here we show that topography degradation enlarges craters and increases CSFD slopes with time. When topography degradation is taken into account, for various‐aged crater populations, the observed steep CSFD at small diameters is uniformly consistent with an originally shallower CSFD, whose slope is undifferentiated from the CSFD slope estimated from near‐Earth objects and terrestrial bolides. The results show that the effect of topography degradation on CSFD is important in dating planetary surfaces, and the steepening of CSFD slopes is not necessarily caused by secondary cratering, but rather a natural consequence of topography degradation.

The upcoming lunar Chang'e‐5 mission is scheduled to land near Mons Rümker, in northern Oceanus Procellarum, and return samples with masses up to 2 kg from depths up to ~2 m. A clear understanding of the regolith components in the candidate landing region is crucial to both the selection of sampling sites and the interpretation of the geological affinities for the returned samples. We quantitatively estimate the abundance of distantly sourced particles (DSPs) in the regolith at the landing region using an updated ballistic sedimentation model. Our results suggest that older units have a higher abundance of DSPs. In the targeted landing area, the total abundance of DSPs on the surface of the regolith varies from approximately 12% to 20%, and most of the DSPs on the surface are ejecta from the Pythagoras (~5%) and/or Aristarchus (~7%) craters. The youngest geological unit, which is located in the easternmost sector of the landing region, possesses the least DSPs in the regolith. Therefore, sampling the eastern unit has a higher potential of revealing both the petrological characteristics and age of the youngest mare basalt, which are fundamentally important to improve both the lunar crater chronology and the understanding of late‐stage evolution of the Moon. Our results also indicate that the anorthositic material within the shallow regolith is most likely ejected from the Pythagoras and Aristarchus craters, which could further improve the understanding of lunar geology and chronology.

Partially buried craters on the Moon are those craters whose distal ejecta are covered by lava flows and where the crater rim crest still protrudes above the mare plain. Based on the difference in rim heights between a partially buried crater and an unburied crater, previous studies estimated the thicknesses of the lunar mare basalts. However, these studies did not consider the erosion of the crater rim height, which can result in an overestimate in the derived thickness. By using recent high‐resolution topographic data, we report a basalt thickness estimation method based on numerically modeling the topographic degradation of partially buried craters. We identified 661 buried craters over the lunar surface, and their spatial distribution suggests a preferential occurrence along the mare‐highland boundaries. An elevation model of fresh lunar craters was derived, and the topographic diffusion equation was used to model crater degradation. By modeling the formation, degradation, and flooding of partially buried craters, basalt thicknesses were estimated for 41 mare craters whose rims are completely exposed. The resulting mare basalt thicknesses vary from 33 to 455 m, with a median value of 105 m that is 95 m smaller than that derived when not considering crater degradation. The estimated eruption rate of lunar mare basalts is found to have peaked at 3.4 Ga and then decreased with time, indicating a progressive cooling of the lunar interior. As a by‐product from the crater degradation model, our results suggest that the topographic diffusivity of lunar craters increases with diameter.