South Pole-Aitken Research Articles

The Lunar Regolith Thickness and Stratigraphy of the Chang’E-6 Landing Site

The Chang’E-6 (CE-6) mission successfully returned 1935.3 g of lunar soil samples from the Apollo basin within the South Pole–Aitken basin. One of its scientific objectives is to investigate the subsurface structure and regolith thickness at the landing site. Using remote sensing datasets, we estimated the regolith and basalt thicknesses at the landing site by employing the crater morphology method and crater excavation technique. A total of 53 concentric craters and 108 fresh craters with varying excavation depths were identified. Our results indicate that the regolith thickness at the CE-6 landing site ranges from 1.1 to 7.0 m, with an average thickness of 3.5 m. Beneath the regolith, the basalt layer consists of high-Ti basalt overlaying low-Ti basalt, with a total thickness of approximately 64 to 82 m, of which the high-Ti basalt layer accounts for about 22 to 30 m. Based on the local geological history, we proposed a stratigraphy at the CE-6 landing site. These findings provide valuable geological context for interpreting the Lunar Penetrating Radar data and analyzing the returned samples.

Evidence of a 4.33 billion year age for the Moon’s South Pole–Aitken basin

AbstractThe Moon’s farside South Pole–Aitken (SPA) basin is the largest and oldest visible impact basin in the inner Solar System. Determining the timing of this catastrophic event is key to understanding the onset of the lunar basin-forming epoch, with implications for understanding the impact bombardment history of the inner Solar System. Despite this, the formation age of the SPA basin remains poorly constrained. Here we show that the chemical composition of the lunar meteorite Northwest Africa 2995 is in good agreement with lithologies exposed within the southern region of the SPA basin. Radiometric dating of a range of mineral and rock components in Northwest Africa 2995 yielded consistent dates of ~4.32–4.33 billion years old. We interpret these dates as the age of SPA basin formation, inferring that this event occurred ~120 million years before the formation of the main cluster of lunar impact basins between ~4.2 Ga and 3.8 Ga. This weakens support for a narrow period of lunar late heavy impact bombardment and also implies that the earliest formed impact basins on the Moon (that is, >4.33–4.5 Ga old) were erased either by the SPA impact itself when its formation caused massive resurfacing of the lunar surface or through other geological processes.

Research on lunar regolith of the Chang'E-4 landing site: An automated analysis method based on deep learning framework

On January 3, 2019, the Chang'E-4 lander successfully landed within the Von Kármán crater, located in the South P ole-Aitken Basin (SPA) on the farside of the Moon (45.5°S, 177.6°E), marking the first soft landing on the lunar farside. The lander, equipped with the Lunar Penetrating Radar (LPR) system, aimed to provide insights into the structure and evolution of the Moon. Previous research often relied on manually identifying hyperbolic features to analyze the lunar shallow subsurface properties. This inefficient approach may lead to subjective biases, resulting in unstable outcomes. This research constructed an automatic analysis framework by integrating the Swin Transformer with a 3D velocity spectrum, which is then applied to analyze the properties of the Chang'E-4 LPR data. The experimental results indicate that the framework achieved a precision of 98.9 % and a recall of 96.7 % in hyperbolic feature identification, with an F1 of 0.9782 and AP of 94.8 %. Additionally, it has been experimentally validated that the framework can accurately invert hyperbolic features' two-way travel time and velocity. Finally, the framework is applied to analyze the lunar shallow subsurface structure and properties within the landing area of the Chang'E-4 mission.

Chandrayaan-3 landing site evolution by South Pole-Aitken basin and other impact craters

The Chandrayaan-3 mission with the Vikram-lander and the Pragyan rover landed in the high latitude highland region near the south pole of the Moon. The landing site is located ∼350 km from the South Pole-Aitken basin rim, an ancient and highly cratered terrain. This site has undergone the complex emplacement sequence of SPA basin ejecta followed by the nearby and distant impact basins and crater ejecta materials. To evaluate the source of individual basin and crater ejecta emplacement over this landing site, we carefully demarcated the nearby and distal basins and craters that could have contributed to the source regolith material. We found that the SPA basin is the major contributor, which deposited nearly ∼1400 m of ejecta materials, and 11 other basins deposited ∼580 m of ejecta. The other complex craters contributed up to ∼90 m of ejecta. Meanwhile, secondary craters of a few km in diameter located adjacent to the landing site contributed to ∼0.5 m ejecta, which are crucial target materials for the Pragyan rover insitu analysis. Pragyan rover images revealed the landing site is devoid of >1 m boulders along the traverse revealing typical highland terrain. The Pragyan rover Navcam and Orbital High Resolution Camera regional images revealed linear distal ejecta rays possibly from the distant impacts as insitu evidence of foreign material at the CH-3 landing site. We found a semi-circular, heavily degraded structure encompassed around the landing site, which is interpreted as a buried impact crater ∼160 km in diameter probably formed before the SPA basin. The erasure of pre-SPA basin craters is caused by both the direct burial by SPA basin ejecta, high seismic shaking during SPA formation, and then followed by various post-SPA craters and its associated some of the degradation processes. Overall, Chandrayaan-3 landed within an ancient region that hosts some of the most deeply excavated materials on the Moon.

Nature of the lunar far-side samples returned by the Chang'E-6 mission.

The Chang'E-6 (CE-6) mission successfully achieved return of the first samples from the far side of the Moon. The sampling site of CE-6 is located in the South Pole-Aitken (SPA) basin-the largest, deepest and oldest impact basin on the Moon. The 1935.3g of CE-6 lunar samples exhibit distinct characteristics compared with previous lunar samples. This study analyses the physical, mineralogical, petrographic and geochemical properties of CE-6 lunar scooped samples. The CE-6 soil has a significantly lower bulk density (0.983g/cm3) and true density (3.035g/cm3) than the Chang'E-5 (CE-5) samples. The grain size of the CE-6 soil exhibits a bimodal distribution, indicating a mixture of different compositions. Mineralogically, the CE-6 soil consists of 32.6% plagioclase (anorthite and bytownite), 19.7% augite, 10% pigeonite and 3.6% orthopyroxene, and with low content of olivine (0.5%) but high content of amorphous glass (29.4%). Geochemically, the bulk composition of CE-6 soil is rich in Al2O3 (14%) and CaO (12%) but low in FeO (17%), and trace elements of CE-6 soil such as K (∼630ppm), U (0.26ppm), Th (0.92ppm) and rare-earth elements are significantly lower than those of the lunar soils within the Procellarum KREEP Terrane. The local basalts are characterized by low-Ti (TiO2, 5.08%), low-Al (Al2O3 9.85%) and low-K (∼830ppm), features suggesting that the CE-6 soil is a mixture of local basalts and non-basaltic ejecta. The returned CE-6 sample contains diverse lithic fragments, including local mare basalt, breccia, agglutinate, glasses and leucocrate. These local mare basalts document the volcanic history of the lunar far side, while the non-basaltic fragments may offer critical insights into the lunar highland crust, SPA impact melts and potentially the deep lunar mantle, making these samples highly significant for scientific research.

Geological investigation of the lunar Apollo basin: From surface composition to interior structure

The Apollo basin, located in the northeastern part of the South Pole-Aitken (SPA) basin, represents one of the Moon's most significant geological features, offering profound insights into the lunar interior structure, the effects of the SPA impact, and the history of lunar crust evolution. This study presents an in-depth geological analysis of the Apollo basin region, revealing the distribution of rock types and compiling a comprehensive geologic map that correlates with the lithologic and geochemical properties of the area. Utilizing the characteristics and compositional provenance of the geologic units, we have constructed schematic cross-sections that elucidate the interior structure and stratigraphic evolution of the Apollo basin region. Despite excavations of the SPA and Apollo impacts, the anorthositic crust of this area was not entirely removed and has been uplifted to shallow depths, making it more susceptible to exposure by subsequent impacts. Additionally, upper mantle material, characterized by ultramafic, low-Ca pyroxene, was excavated by the SPA impact and is present in the impact melt/breccias of the Apollo basin. After the formation of the Apollo basin, multiple mare units were emplaced over a period potentially spanning ∼1.5 billion years, with the oldest of these maria being superposed by substantial postdating basin ejecta. The results of this study strengthen our understanding of the geology and evolution of the Apollo and SPA basins and offer valuable insights for interpreting the exploration and sample analysis results of the Chang'e-6 mission.

Lunar mantle composition and timing of overturn indicated by Mg# and mineralogy distributions across the South Pole-Aitken basin

The South Pole-Aitken (SPA) basin, excavating more than 100 km depth, must have exposed extensive lunar mantle materials, making it a promising location for sampling mantle material. To investigate the distribution of potential mantle materials across the SPA basin, we mapped the distribution of Mg# and major minerals contents using Moon Mineralogy Mapping data and radiative transfer modeling. We found that the potential mantle material exposed by SPA is Mg-rich orthopyroxenite, and we identified the locations of seven mantle candidate sites. The Chang'E-6 sample return site is located near mantle candidate sites within the Apollo basin, making it promising to return the first unambiguous mantle sample. Our Mg# and mineral mapping results show that the SPA ejecta is enriched in low-Ca pyroxene (LCP) with Mg#≥85, consistent with a post-overturn upper mantle composition. The enrichment of LCP in the SPA upper mantle may result from a low content of dunite or incomplete overturn.

Crustal-mantle layering deposits in the Von Kármán crater, South Pole-Aitken basin

Comprehending the properties of the Moon's crust and mantle materials is essential for decoding its interior. Whether the South Pole-Aitken (SPA) basin potentially excavated the upper mantle materials remains mysterious. The Chang'E Four Lunar Penetrating Radar (LPR) has provided an unprecedented opportunity to investigate the SPA basin in the Von Kármán (VK) crater. Utilizing a data-driven generative deep learning inversion algorithm, the subsurface physical properties along the Yutu-2 path were determined. 4 distinct deposit zones were discovered beneath the surface. All zones feature an upper low-permittivity (paleo-)regolith layer overlaying on a lower high-permittivity layer of rockier ejecta or basal basalt. Zone 1, an ejecta layer from the Finsen crater within the SPA Compositional Anomaly, has a bulk density (2.81±0.22g/cm3) denser than that of highland crust represented by materials originating from VKL and VKL' craters in the Mg-Pyroxene Annulus, which are present in Zones 2 and 3. This suggests the possible presence of mantle materials in Zone 1, providing the first diagnostic evidence that the SPA impact may have penetrated the upper lunar mantle.

Petrographic and geochemical analysis of lunar meteorite NWA 11788: Parallels with Luna 20 and the Apollo magnesian granulites

AbstractThe first in‐depth geochemical and petrological analyses of new lunar meteorite Northwest Africa (NWA) 11788 were conducted with the aim of better understanding the diversity of lunar rock types. Petrography, microcomputed tomography, electron probe microanalysis, and laser ablation inductively coupled plasma mass spectrometry were employed to analyze mineralogic/elemental makeup, petrologic profile, melt history, and inferred composition of the lunar mantle from which the crystals in this sample originated from. Geochemical maps of the lunar surface were generated to constrain potential lunar launch locations for NWA 11788. Potential launch locations are concentrated in the outer rims of impact basins on the lunar Eastern nearside limb (e.g., Crisium, Fecunditatis, Marginis, Smythii) and around the South Pole–Aitken Basin. Similarities in the major, minor, and trace element chemistry of NWA 11788 along with its potential launch locations suggest a petrogenetic relationship with regolith samples returned from the Luna 20 mission and the Apollo 16 and 17 magnesian granulites. Additionally, the results of this study add to the growing body of evidence that KREEP (potassium, rare earth elements, phosphorous)‐poor, Mg‐suite‐“like” lithologies are common in non‐Apollo‐type locales, that KREEP may not be required to generate lithologies like the Mg‐suite, and that KREEP is not globally distributed at present.

Extensive Intrusive Magmatism in the Lunar Farside Apollo and South Pole–Aitken Basins, Chang’e-6 Landing Site

Lunar igneous activities, including intrusive magmatism and extrusive volcanism, and their products contain significant information about the lunar interior and its thermal state. Their distribution is asymmetrical on the nearside and farside, reflecting the global dichotomy. Samples from the South Pole–Aitken (SPA) basin on the farside hold the key to disclosing the dichotomy conundrum and rebalancing the asymmetrical understandings of the Moon, in addition to previously returned nearside samples (Apollo, Luna, Chang’e-5). For the first time, the Chang’e-6 mission obtained ∼1935.5 g of lunar soils from the farside in the southern Apollo basin, northeast of SPA, opening a window to solve this long-standing question. However, compared with the well-known mare/cryptomare volcanism in SPA, intrusive activity has a much more obscure presence and origin, due to its unclear surface expression, thus impeding the ongoing Chang’e-6 sample analysis, which is therefore emphasized here. We found evidence that intrusive magmatism is extensive across SPA, including Mg-suite intrusions, floor-modified craters, and linear/ring dikes, consistent with its intermediate crustal thickness, where dike intrusion is favored. Intrusive magmatism is abundant in the Apollo basin, where Chang’e-6 landed. Two obscure craters were discovered (Apollo X and Q) with evidence for subsurface intrusions, strongly suggesting the intensive intrusion in the region. Plutonic materials are very likely to be obtained by Chang’e-6, especially the Mg-suite from the western peak ring of the Apollo basin that delivered and mixed in the soils by the Chaffee S crater, whose components might provide critical new insights into their petrogenesis, early lunar evolution, and the origin of dichotomy.

High-precision U-Pb zircon dating identifies a major magmatic event on the Moon at 4.338 Ga.

The Moon has had a complex history, with evidence of its primary crust formation obscured by later impacts. Existing U-Pb dates of >500 zircons from several locations on the lunar nearside reveal a pronounced age peak at 4.33 billion years (Ga), suggesting a major, potentially global magmatic event. However, the precision of existing geochronology is insufficient to determine whether this peak represents a brief event or a more protracted period of magmatism occurring over tens of millions of years. To improve the temporal resolution, we have analyzed Apollo 14, 15, and 17 zircons that were previously dated by ion microprobe at ~4.33 Ga using isotope dilution thermal ionization mass spectrometry. Concordant dates with sub-million-year uncertainty span ~4 million years from 4.338 to 4.334 Ga. Combined with Hf isotopic ratios and trace element concentrations, the data suggest zircon formation in a large impact melt sheet, possibly linked to the South Pole-Aitken basin.

The South Pole‐Aitken Basin: Constraints on Impact Excavation, Melt, and Ejecta

AbstractThe formation and evolution of the South Pole‐Aitken (SPA) basin is critical to relating large impact basin formation and modification to lunar geophysical evolution. Most prior models of the SPA impact were conducted in 2D, making it difficult to compare model output to the 3D crustal structure and ejecta distribution. In order to better constrain the parameters of the SPA impactor and the expected post impact distribution of crust and ejecta, we conducted numerical simulations of the SPA impact in 3D. We tested a wide range of impact parameters and constrained model results with recent geophysical data. We found the crustal structure of the SPA basin is best fit by an oblique impact (30–45°) of a 350–400 km diameter projectile impacting at 12–16 km/s. The impact excavated material from as deep as 80–120 km, and ejecta was deposited in a butterfly pattern with a forbidden region uprange of the impact.

Global Lunar Crater Density Using Buffered Nonsparseness Correction

The density of craters on a planetary surface directly relates to the age of the surface. As the surface ages, however, craters can be erased by subsequent large impacts via direct overprinting, known as geometric crater obliteration. Such counts become increasingly limited as surfaces become more heavily cratered. Techniques to infer the statistics of the regions obliterated by craters were developed in the past decade. Such techniques, however, have only been used for regional studies. Herein, we present a study of the global density of lunar impact craters ≥20 km in diameter using both traditional crater-counting and buffered nonsparseness correction (BNSC) crater-counting techniques. By comparing the measurements, we quantify the influence of geometric crater obliteration on the visible lunar crater record. Our results reveal that geometric crater obliteration erased up to three-fifths of craters ≥20 km in diameter that formed on the most ancient lunar terrains, whereas younger surfaces, like the Procellarum KREEP Terrane, show little to no evidence of such crater obliteration. The differences in derived crater densities highlight ancient surfaces in which the effects of geometric crater obliteration must be considered to characterize their cratering histories. Furthermore, our results identify the most heavily cratered area on the Moon, a region of the lunar highlands between Smythii basin and the South Pole–Aitken (SPA) basin (Smythii–SPA–Highlands); the number of impacts revealed by the BNSC technique for this region is consistent with estimates derived from the abundance of highly siderophile elements and from modeling crustal porosity.

Geological context of the Chang’e-6 landing area and implications for sample analysis

Research on returned samples can provide ground truth for the study of the geological evolution history of the Moon. However, previous missions all collected samples from the near side of the Moon, which is significantly different from the far side of the Moon in terms of the thickness of the lunar crust, magma activity, and composition. Therefore, the samples from the far side of the Moon are of great significance for a comprehensive understanding of the history of the Moon. China's Chang'e-6 (CE-6) probe has successfully landed on the lunar far side and will return samples in the coming days. With the precise location of the CE-6 landing site, a detailed analysis of the geological background is conducted in this research. The landing site of CE-6 is within the Apollo crater, which is inside the largest impact basin on the Moon, i.e., the South Pole-Aitken (SPA) basin. According to the numerical simulation of the formation process of the SPA basin, CE-6 landed at the edge of the SPA impact melting zone, which is presumably composed of impact melt of the lunar mantle. The Apollo crater subsequently excavated deep material again, which constitutes the basement of the CE-6 landing area. Later, erupted basalt covered these basement rocks, and they also constitute the main source of the CE-6 samples. Based on the dating method of crater size-frequency distribution, we find that the basalt is ∼2.50 Ga. The CE-6 samples also possibly contain basement rocks as excavated and ejected by craters, and they can provide crucial information for our understanding of lunar geological history along with the basalt samples.

Stratigraphic cross-sections, geologic history, and provenance of material at the candidate landing sites of the Artemis missions

From the scientific perspective, Artemis lunar missions focus on the south circumpolar region (SCR) mainly to investigate the existence and abundance of volatiles and to explore and sample ancient lunar deposits. The volatile distribution is primarily related to the cold traps in permanently shadowed regions, while the availability of ancient material is due to the proximity to the early lunar ∼2300 km diameter South Pole-Aitken (SPA) impact basin. One of the critical factors for future missions will be determining the geological structure and provenance (sources) of material at each candidate landing site, which can be predicted utilizing three-dimensional stratigraphic reconstructions of geological map units and crater ejecta deposits. This type of reconstruction permits a better understanding of candidate material that can be collected and analyzed at each site, and a ranking of landing sites can be formulated on this basis. Here, we present reconstructed geological cross-sections at Artemis landing sites using our recent SCR geological map and numerical modelling of crater ejecta thicknesses and their sequence.

A Catalogue of Impact Craters and Surface Age Analysis in the Chang’e-6 Landing Area

Chang’e-6 (CE-6) is the first sample-return mission from the lunar farside and will be launched in May of 2024. The landing area is in the south of the Apollo basin inside the South Pole Aitken basin. Statistics and analyses of impact craters in the landing area are essential to support safe landing and geologic studies. In particular, the crater size–frequency distribution information of the landing area is critical to understanding the provenance of the CE-6 lunar samples to be returned and can be used to verify and refine the lunar chronology model by combining with the radioisotope ages of the relevant samples. In this research, a digital orthophoto map (DOM) mosaic with resolution of 3 m/pixel of the CE-6 landing area was generated from the 743 Narrow Angle Camera of the Lunar Reconnaissance Orbiter Camera. Based on the DOM, craters were extracted by an automated method and checked manually. A total of 770,731 craters were extracted in the whole area of 246 km × 135 km, 511,484 craters of which were within the mare area. Systematic analyses of the crater distribution, completeness, spatial density, and depth-to-diameter ratio were conducted. Geologic model age estimation was carried out in the mare area that was divided into three geologic units according to the TiO2 abundance. The result showed that the east part of the mare had the oldest model age of μ3.27−0.045+0.036 Ga, and the middle part of the mare had the youngest model age of μ2.49−0.073+0.072 Ga. The crater catalogue and the surface model age analysis results were used to support topographic and geologic analyses of the pre-selected landing area of the CE-6 mission before the launch and will contribute to further scientific researches after the lunar samples are returned to Earth.

Geologic History of the Amundsen Crater Region Near the Lunar South Pole: Basis for Future Exploration

We provide the first detailed 1:100,000 scale geomorphologic map of the ∼100 km Amundsen crater region, which is of high scientific relevance for future exploration, e.g., NASA’s VIPER mission, the Artemis program, and the Chinese International Lunar Research Station. We investigated the complex geological history of the region before and after the formation of Amundsen crater on the rims of the South Pole–Aitken (SPA) and Amundsen–Ganswindt basins. We present a new Amundsen crater formation age of ∼4.04 Ga, which, in contrast to previously derived ages, is based on non-light-plains terrain. The estimated maximum excavation depth for Amundsen crater is ∼8 km, and elevated concentrations of FeO near the crater suggest that Amundsen may have redistributed SPA-derived materials. Plains materials of various kinds were observed both inside and outside Amundsen crater and are estimated to be up to 350 m thick and ∼3.8 Ga old. A less cratered, tens of meters thick mantling unit indicates a resurfacing event ∼3.7 Ga ago. We highlight five potential exploration sites that satisfy technical constraints (such as shallow slopes, solar illumination, and Earth visibility), provide materials that can be sampled, and are capable of addressing multiple science objectives. Due to its accessibility and traversability, combined with its geologic diversity, proximity of permanently shadowed regions for studying volatile processes, and ability to address multiple science objectives, we confirm and reinforce the Amundsen crater region as a high-priority landing and exploration site.

Long-lasting farside volcanism in the Apollo basin: Chang'e-6 landing site

A major lunar scientific question is the cause of the paucity of farside mare basalts. The South Pole-Aitken Basin (SPA) is the largest (2400×2050 km) and most ancient lunar impact basin. The Apollo peak-ring basin, the largest impact feature within the SPA, is located on its northeast edge in a transitional zone of crustal thickness and compositions. The Chang'e-6 (CE-6) mission, the first sample-return mission to the lunar farside, is targeted to land in the southern Apollo basin, sampling farside mare basalts with critical insights into early lunar evolution. In preparation for the CE-6 sample return, we conducted a comprehensive study of Apollo basin volcanism. We found that volcanic activity began in the Nectarian Period (∼4.05 Ga) (cryptomaria) and continued into the Eratosthenian Period (∼1.79 Ga). At least two Imbrian-aged episodes of eruptions occurred in the southern part of the Apollo basin where CE-6 is targeted to land. At ∼3.35 Ga, low-Ti (∼3.2 wt %) volcanism was active, and its products covered the entire low topographic region of the southern Apollo basin, between the inner and outer rings. Closely following its eruption at ∼3.07 Ga, high-Ti basalts (∼6.2 wt %) erupted close to the Chaffee S crater and flowed east with decreasing thickness until encountering proto-wrinkle ridges. In addition, volcanic activity in the region is significantly correlated with low crustal thickness, primarily thinned by the SPA and Apollo impact events. For regions of intermediate-thick crust (Oppenheimer crater), dikes stalled under the crater floor, spreading to form sills and a floor-fractured crater. For thin crust regions (Apollo basin interior), dikes erupted directly, forming extensive lava flows. In areas of thick highland crust, we see no evidence of extrusive activity or floor-fractured craters, suggesting that dikes there do not reach the surface and are intrusive. CE-6 samples returned from the unique geological setting will provide significant petrogenetic information to address further the paucity of farside mare basalts and the lunar nearside-farside dichotomy. To solve those scientific questions, the high-Ti mare region in south Apollo basin is recommended as the priority landing site.

Lunar Farside South Pole‐Aitken Basin Interior: Evidence for More Extensive Central Cryptomaria in the South Pole‐Aitken Compositional Anomaly (SPACA)

AbstractIn the central area of the South Pole‐Aitken (SPA) basin, an intermediate albedo, mafic compositional anomaly (SPA Compositional Anomaly, SPACA) has been documented by previous studies, but its origin remains uncertain. We conducted an investigation of stratigraphic units defined based on morphology and composition and their relative ages, and placed these in the context of basin topography and the observed sequence of geological events, all helping to distinguish between SPACA origins from: (a) SPA impact melt, (b) volcanism induced by the SPA event and (c) lunar cryptomaria. We conclude that SPACA represents extensive traditional cryptomare deposits overlying the SPA impact melt. We interpret the basin center to be filled with cryptomare deposits at least one km thick (>1 × 105 km3 in volume) with ages not younger than Early Imbrian. We attribute the relatively high albedo of SPACA to lateral mixing of ejecta from nearby highlands craters and basins, and conclude that the cryptomaria basalts are likely to be very similar to basalts on the nearside. Our findings imply a 0.5%–1.8% increase in the total volume of global lunar mare and cryptomare deposits. These results show that mare volcanism was common only in areas of thinnest crust on the lunar farside, a factor important in understanding lunar nearside‐farside asymmetries. Despite this significant increase in total cryptomare volume in the SPA basin center, SPA remains underfilled relative to nearside mascon basins. Return of mare basalts from the SPA region by Chang’E‐6 will help determine potential mantle source region differences and petrogenetic pathways.

Geologic context of Chang'e-6 candidate landing regions and potential non-mare materials in the returned samples

Our understanding of the lunar farside from orbital remote sensing is limited by the lack of ground-truth constraints from returned samples. China's Chang'e-6 (CE-6) mission plans to land at the southern rim of the Apollo basin in the South Pole-Aitken basin on the lunar farside and return ∼2 kg samples. In this study, we conduct analyses on the local geological context of the CE-6 candidate landing regions, with a focus on the non-mare ejecta. The CE-6 candidate landing region has been divided into three subunits. According to our analyses, the northeastern subunit is adjacent to the lowest elevation (and one of the highest excavation depth) of this region where the materials from the deepest crust may exist. The northwestern subunit is affected by the magnesian ejecta from young crater. Returning these non-mare ejecta will provide key insights into the magnesian lithologies that occurred in the lunar farside, whose petrogenesis is long debated. As for the southern light plains unit, a topographic positive feature (unofficially termed as Mons White) located at the west of the light plains is identified in this work. Three scenarios were proposed for its origin: (1) A volcanic complex built on special magmatism in the SPA basin; (2) Remnants of the central uplift of an ancient impact basin; (3) Target surface folded and uplifted by the Apollo basin impact event. Gradual lithological variations in the Mons White are discovered. The White crater has likely ejected materials with these gradual lithologies into the CE-6 candidate landing regions. The Orientale basin ejecta also exists on the light plains. These non-mare materials, if could be sampled by the CE-6 mission, will significantly help refine the lunar chronostratigraphic system from the pre-Nectarian/Aitkenian to the late Imbrian. Thus, we suggest that landing on the southern light plains will achieve the maximum scientific outcomes for the CE-6 mission, from a perspective of sample diversity.