Onsite radar shows what lies beneath: In more active periods of the Moon's history, volcanic eruptions created lava plains that formed layers of dark basalt. Without subsurface probing, we can only examine the most recent flows. After the soft landing of the Chang'E-3 spacecraft, Xiao et al. made penetrating radar measurements of the lunar crust with the Yutu rover. Several subsurface layers suggest multiple geologic processes at play throughout the crustal history, including multiple lava flows and the weathering-induced creation of dust and rocky debris. Science , this issue p. 1226

Remote sensing observations have shown that the far side of the Moon (lunar farside) has different geology and rock composition to those of the nearside, including the abundances of potassium, rare earth elements, and phosphorus (collectively known as KREEP). The Chang’e-6 (CE-6) spacecraft collected samples from the South Pole–Aitken (SPA) basin on the farside and brought them to Earth. We used lead-lead and rubidium-strontium isotope systems to date low-titanium basalt in a CE-6 sample, finding a consistent age of 2830 (±5) million years. We interpret this as the date of volcanism in SPA and incorporate it into lunar crater chronology. Strontium, neodymium, and lead isotopes indicate that the volcanic magma was from a lunar mantle source depleted in incompatible elements and containing almost no KREEP component.

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 Rümker region (41–45°N, 49–69°W) is located in northern Oceanus Procellarum of the Moon. Mons Rümker is the most distinctive geological feature in the area. The region is characterized by prolonged lunar volcanism (Late Imbrian Period to Eratosthenian Period), forming multiple geologic units in the area, including very low‐Ti to low‐Ti mare basalts, high‐Ti mare basalts, and volcanic complexes. Each geologic unit has distinct element composition and mineral assemblages. The Rümker region, overlying the Procellarum KREEP Terrain, was selected as the landing region for China's Chang'E‐5 lunar sample return mission. Prelanding analyses of the geologic context and scientific potential are reported in this contribution. We conducted detailed geological mapping using image, spectral, and altimetry data. Fourteen geological units were defined, a geologic map was constructed, and the geologic history was outlined. The western mare units (Im1, Im2, and Im3) are Imbrian‐aged (~3.4–3.5 Ga) representing the major stage of lunar mare eruptive volcanism. The eastern young mare units (Em3 and Em4; <2 Ga) are among the youngest mare basalts on the Moon. They have never been explored in situ or studied in the laboratory. We suggest that samples returned from the eastern mare unit (Em4) could answer many fundamental questions and that this unit should be listed as the top priority landing site for Chang'E‐5 sample return mission.

On 3 January 2019, the Chang'e‐4 (CE‐4) touched down on the Von Karman crater located inside the South Pole‐Aitken Basin, providing for the first time the opportunity for in situ measurements of the lunar regolith at the farside of the Moon. The CE‐4 ground penetrating radar reveals that fine‐grained regolith, coarse impact ejecta, and fractured bedrocks lie beneath the exploration path of the Yutu‐2 rover. The variations of regolith permittivity with depth and the radargrams indicate that the CE‐4 site has a fine‐grained regolith layer thickness of 11.1 m, which is about 1.3–3 times higher than the in situ measurement results at the Apollo and Chang'e‐3 (CE‐3) sites except for Apollo 16, possibly due to a faster weathering rate of ejecta deposits compared with coherent basalt substrates. The penetration depth of CE‐4 is about 2.85 times (in terms of round‐way delay) deeper than CE‐3, probably due to the differences in abundances of ilmenite and rocks in the regolith.

The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earth’s crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 × 10⁵ km³ of Earth’s crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 10⁶ years.