Chang'E-1 Research Articles

Widespread Involvement of Low‐Abundance KREEP in the Mantle of Chang'e‐5 and Its Surrounding Units

ABSTRACTThe return of the young Chang'e‐5 (CE‐5) samples provide new insights into the lunar thermal evolution. In this study, we present a new type of exotic low‐Ti basalt in CE‐5 breccia, which has a magmatic equigranular texture with low Ti content and high Mg bulk composition and minerals. Low rare earth elements (REEs) imply that the clast was probably derived from a primitive source, which may originate from western ancient mare unit. Based on fractional crystallisation modelling, the exotic basalt source is considered as low‐Ti high‐Al, opposing the source of CE‐5 basalts. Our partial melting and REE modelling further imply that the addition of 8% plagioclase and only 1% KREEP contributes to the formation of this specific magma source. This low degree of KREEP involvement in mantle sources may be widespread in Chang'e‐5 terrane and its surrounding units, playing an important role in prolonging lunar magmatism.

Characterization of the Micro-Morphology and Compositional Distribution of Chang'e-5 Lunar Soil Mineral Surfaces Using TOF-SIMS.

The lunar soil samples returned by China's Chang'e-5 (CE-5) contain valuable information on geological evolutions on the Moon. Herein, by employing high-resolution time-of-flight secondary ion mass spectrometry (TOF-SIMS), five rock chip samples from the CE-5 lunar soil are characterized in-depth, which reveal micro-morphological and compositional features. From the elemental/molecular ion distribution images, minerals such as pyroxene, ilmenite, feldspar, K-rich glass, silica, and silicate minerals are identified, along with their occurrence states and distribution results. More importantly, uncommon vesicle-like patterns are probed via TOF-SIMS, which may not be captured by conventional electron microscopy. The possible origins of vesicles are also proposed. Hopefully, these discoveries will provide essential guidance for future investigations on the Moon and accelerate the application of TOF-SIMS in space exploration.

Lunar surface permittivity distribution along route of Yutu-2 rover

Abstract On January 3, 2019, Chang’E-4 (CE-4) landed in the Von Kármán crater within the South pole-Aitken Basin on the Moon’s farside. The lunar penetrating radar (LPR) onboard the Yutu-2 rover is the same as the Chang ‘E-3 mission, which can obtain information about the thickness and strutures of lunar regolith as well as upper crust along the excursion path. The permittivity of lunar material is one of the important parameters for interpreting radar data and can also be obtained by LPR. In this paper, we use the metal plate reflection method based on LPR data and panoramic camera (PC) data to estimate the relative permittivity distribution of 1373m route during the first 53 lunar days. We estimated an average relative permittivity of ~2.78, which is less than ~2.9 of Chang’E-3 (CE-3).

Atomic‐Level Structural Responses of Chang'e‐5 Ilmenite to Space Weathering

AbstractSpace weathering records provide insights to better understand the formation and evolution of the lunar regolith. Ilmenite has contrasting responses to different space weathering processes. However, the atomic‐scale structural modification of ilmenite induced using different space weathering processes remains poorly understood. Here, we investigate the effects of spacing weathering on lunar ilmenite grains returned from Chang'e‐5 (CE‐5) mission using a combination of transmission electron microscopy and thermodynamic modeling approaches. Experimental results show that melt shock induces the formation of twining structures and vein‐like Si‐Ca‐rich nanostructures in the outermost and sub‐outermost layers of ilmenite, respectively. In contrast, solar wind causes the formation of multilayered nanostructures surrounding the ilmenite grains. These structures are characterized by an outermost amorphous Si‐rich vapor deposited layer, a middle layer rich in titanium (Ti) oxides and zero‐valent iron (Fe0) nanoparticles, and an innermost layer hosting crystallographic orientation defect. The Ti oxides were identified as poorly crystallized anatase. Thermodynamic calculations indicate that the disruptive sputtering of solar wind and the reduction of hydrogen under lunar surface pressure conditions can promote ilmenite transformation into Fe0 and Ti oxides; nevertheless, the pressure increase associated with melt shock can lead to a rise in the decomposition temperature of ilmenite. In other words, solar wind irradiation plays a more significant role in promoting nanoparticle (such as anatase and Fe0) formation as compared to melt shock. Thus, unlike the chemical alteration of ilmenite induced by the solar wind irradiation, melt shock mainly causes physical changes in ilmenite grains.

Iron isotopes of Chang'e-5 soil and mineral components: Implications for post-eruption processes on lunar surface

Due to rapid magma cooling and extensive space weathering, significant disequilibrium crystallization and secondary modification widely occur in lunar mare basalt after its eruption on the lunar surface. In this study, we conducted bulk and in-situ Fe isotope analyses to investigate the post-eruption processes on Chang'e-5 (CE-5) samples. The CE-5 soil shows a minor elevation of δ56Fe value (∼0.05 ‰) relative to the CE-5 basalt clasts. Correlations between Ni and Cu contents with δ56Fe values suggest that the minor increase in the δ56Fe from the CE-5 basalt to soil primarily occurred during evaporation caused by meteorite impacts. Such isotopic variation between CE-5 basalt and soils is notably lower than what is observed for Apollo samples and reflects the low maturity of CE-5 soils. This is consistent with the low Is/FeO value constrained by magnetic approaches. Therefore, measuring the δ56Fe values of lunar soil is suitable to evaluate the degrees of maturity for lunar soils due to space weathering. In-situ analyses of δ56Fe reveal significant variations in different grains of olivine (δ56Fe: −0.57 to −0.17 ‰) and ilmenite (−0.06 to +0.42 ‰) and also in their interior (mainly for olivine). These δ56Fe variations in minerals can be ascribed to the disequilibrium crystallization of lava flow and fast cooling, which is consistent with conclusions based on petrologic observations such as its extensive differentiation and silicate liquid immiscibility. Therefore, the post-eruption processes on the lunar surface could lead to significant variations in isotopic compositions at different scales of basalts, which in turn record the history of late-stage magma evolution and space weathering on the lunar surface.

Analyzing strain localization of Chang'E-5 lunar regolith through discrete element analysis

The current understanding of the geotechnical behavior of lunar in-situ resources, particularly lunar regolith (LR), is significantly limited due to its scarcity. To address this gap, this research utilized the morphological characteristics of LR particles obtained from the Chang'E-5 (CE-5) mission to construct numerical simulants using the discrete element method (DEM). This approach was then employed to investigate the mechanical properties of LR. Firstly, high-definition lunar particle images from the CE-5 mission were selected to capture the morphological characteristics and grain size distribution. These morphological characteristics were linked with the rolling resistance parameter and incorporated into the three-dimensional (3D) micromechanical contact model. Additionally, a flexible boundary condition was employed in the triaxial simulation to ensure the evolution of strain localization. The relative particle translation gradient (RPTG) concept was utilized to capture the onset and development of strain localization during the shear process. The results indicated that the numerical lunar simulants can effectively reproduce the mechanical response of LR. Furthermore, at the particle scale, particle shape characteristics play a crucial role in particle rotation and translation during the shear process. This study may establish a foundation for lunar resource exploration and utilization techniques.

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.

Photometric Characteristics of Lunar Soils: Results from Spectral Analysis of Chang’E-5 In Situ Data Using Legendre Phase Function

China’s Chang’E-5 (CE-5) mission has successfully landed in the Northern Oceanus Procellarum of the Moon. Lunar mineralogical spectrometer (LMS), as one of the important payloads onboard CE-5 Lander–Ascender Combination, aims to study the physical and compositional properties of the landing area. This paper applies the Legendre phase function to correct the photometric effects on the LMS in situ spectra and reveal the photometric characteristic of the CE-5 landing area. LMS obtained the reflectance spectra in various geometric configurations by performing full-view scanning of the CE-5 landing area. By fitting these LMS spectral data, the parameters b=−0.29 and c=0.44 of the Legendre phase function were obtained. This indicates the strong forward scattering characteristic of the CE-5 landing area, which is similar to that of the Chang’E-4 (CE-4) landing area, and the side scattering is weaker than that of CE-4. In addition, we derived the FeO content of the landing area using the photometric-corrected LMS spectral data. Our results demonstrate that the estimated FeO content of the landing area is close to the laboratory measured data of the returned samples. The LMS in situ reflectance data will contribute to a better understanding of the physical and mineralogical properties of the CE-5 landing area.

Chang’E-5 In Situ Spectra Revealing Meter-scale Surface Temperature Distribution Characteristic of the Moon

The Lunar Mineral Spectrometer (LMS), on board the Chang’E-5 (CE-5) lander obtained the in situ spectra of the sampling area close to the Moon’s local noon. This provides an opportunity to investigate the meter-scale thermophysical properties and temperature distribution of the lunar surface. We established a new thermal correction method using the laboratory-measured spectra of CE-5 samples in this study. The surface temperature of the CE-5 sampling area was derived by applying this new method to LMS in situ data. The temperature of the flat lunar surface estimated by LMS is very close to that of Diviner data. The temperature estimated by Diviner probably represents the temperature characteristic of a flat lunar surface. The characteristic of meter-scale temperature distribution within the CE-5 sampling area was also discussed. This is essential to understanding the influence of the microscale landforms and roughness on the thermal and physical characteristics of the lunar surface.

Late-stage microstructures in Chang’E-5 basalt and implications for the evolution of lunar ferrobasalt

Abstract This study investigates silicate liquid immiscibility (SLI) microstructures in the Chang’E-5 (CE-5) lunar ferrobasalt sample, the youngest recovered mare basalt (ca. ~2.0 Ga). Employing advanced high-resolution imaging techniques and chemical analysis, we examined a subophitic fragment, revealing two distinct types of microstructures indicative of multi-stage SLI events. The first type is observed in the mesostasis pockets and exhibits both “sieve” and “maze” textures, where the Si-K rich glassy phases are interconnected with Fe-rich minerals, e.g., fayalite. This type of microstructure, similar to previous observations in Apollo and Luna samples, is the product of a stable SLI event. The second type is characterized by K-free but high-Si melt inclusions occurring as emulsions in the rims of plagioclase. The entrapment of these emulsions followed a metastable SLI event, with the Fe-rich liquids serving as precursors to subsequent stable SLI processes. Additionally, the Fe-rich droplets within the emulsions underwent coarsening via Ostwald ripening, a phenomenon in which smaller particles in solution dissolve and deposit on larger particles. Our simulation of this coarsening process suggests a duration of at least 15-32 days for the SLI processes, alongside a slow cooling rate (< 0.3 °C/hour) of the late-stage CE-5 lava. We propose that metastable SLI may have influenced the effusive signature of the CE-5 lava flow during its late-stage evolution. The metastable SLI process can potentially lead to the formation of various phases during the late-stage evolution of lunar ferrobasaltic magmas, thereby contributing to the diversity of lunar rock types.

Analysis of Thermal and Dielectric Loss Features of Lunar Regolith Considering Real‐Time Effect Solar Irradiance

AbstractSolar irradiance received at the lunar surface is crucial for interpreting brightness temperatures detected by orbiters and for understanding the thermal, physical, and dielectric properties of the lunar regolith. We developed a real‐time effect solar irradiance (ESI) model that accounts for the influence of surface relief and terrain shading. This model was integrated with a standard thermal model to examine ESI fluctuations and their impacts on the diurnal physical temperature variations. To assess the effects of spatial resolution, we selected four locations with significant ESI disparities for simulation, then compared lunar surface temperatures at various spatial scales, ranging from 20 m to 25 km. Utilizing brightness temperature data obtained from the Chang'E‐2 (CE‐2) microwave radiometer (MRM), we integrated the shallow physical temperature profiles with the radiative transfer equation to simulate brightness temperatures and determine dielectric loss at different frequencies. In the Von Kármán crater, the received ESI exhibits a cyclical pattern of approximately 18 years and areas with rugged topography may exhibit larger ESI variations (∼7%). We found that the spatial resolution of ESI has a minimal effect on the physical and brightness temperatures at resolutions of 10 km or coarser. At the shallow layer, the average dielectric loss values are 0.0128–0.0170, 0.0083–0.0110, 0.0055–0.0073, and 0.0061–0.0081 for the CE‐2 frequencies of 3, 7.8, 19.35, and 37 GHz, respectively. The integration of real‐time ESI modeling, thermal dynamics, radiative transfer equations, and observational data enhances our comprehension of the physical temperature profile and thermal characteristics of shallow regolith.

Petrological, chemical, and chronological study of breccias in the Chang'e‐5 soil

AbstractWe carried out a petrological, mineralogical, and geochemical study of fragmental and regolith breccia clasts separated from two Chang'e‐5 (CE‐5) soil samples, CE5C0000YJYX03501GP and CE5C0400, which provide an opportunity to investigate the compositional change of regolith at the landing site through time. Fragmental breccia CE‐5‐B3 contains a diverse range of basaltic clasts and basaltic mineral fragments, and some rare Mg‐suite‐like minerals. Regolith breccias CE‐5‐B006, CE‐5‐B007, CE‐5‐B010‐08, CE‐5‐B010‐09, CE‐5‐B011‐07, and CE‐5‐B016‐03 contain mare basaltic fragments, mare vitrophyric clasts, rare Mg‐rich fragments possibly derived from the Mg‐suite rocks, and impact‐derived glass spherules. Pb‐isotope data obtained for baddeleyite grains found both inside some of the basaltic clasts identified in breccia fragments and in the breccia matrices yield Pb/Pb dates similar to the 2 Ga crystallization age of the CE‐5 basalt fragments, extracted directly from the soil sample. Seventy‐four Pb isotope analyses of Ca‐phosphate grains also indicate that the majority of these grains have Pb/Pb dates of 2 Ga, suggesting that they originate from the CE‐5 basalts. In addition, a Pb–Pb isochron drawn through analyses of four Ca‐phosphates in breccia CE5‐B006 yielded an intercept corresponding to a date of 3871 ± 46 Ma, which is the best possible estimate of the formation age of these four grains. Electron probe microanalysis shows that the breccias contain components similar to CE‐5 mare basalt fragments extracted directly from the soil sample, implying that the fragmental and regolith breccia fragments are mostly composed of material sourced from the underlying basalts. The general absence of impact melt breccia clasts, along with the general lack of Fe–Ni metal and absence of added meteoritic debris all suggest that the regolith at the CE‐5 landing site is immature and dominated by material mixed together by small local impact cratering events. Trace element analyses show that the glass beads in the regolith breccias have a Th abundance of 4.06–5.28 μg g−1. This is similar to the Th content of the regolith above the Em4 unit at the landing site as measured from orbit, as well as the estimated bulk Th content of CE‐5 basalts, suggesting that Th of the local regolith is predominantly sourced from the underlying mare basalts, without significant Th addition from Th‐rich exotic clasts sourced from evolved lunar lithologies.

Multiple sources of water preserved in impact glasses from Chang'e-5 lunar soil.

The existence of molecular H2O and evolution of solar wind-derived water on the lunar surface remain controversial. We report that large amounts of OH and molecular H2O related to solar wind and other multiple sources are preserved in impact glasses from Chang'e-5 (CE5) lunar soil based on reflectance infrared spectroscopy and nanoscale secondary ion mass spectrometry analyses. The estimated water content contributed by impact glasses to CE5 lunar soil was ~72 ppm, including molecular H2O of up to 15 to 25 ppm. Our studies revealed that impact glasses are the main carrier of molecular H2O in lunar soils. Moreover, water in CE5 impact glasses provides a record of complex formation processes and multiple water sources, including water derived from solar wind, deposited by water-bearing meteorites/micrometeorites, and inherited from lunar indigenous water. Our study provides a better understanding of the evolution of surficial water on airless bodies and identifies potential source and storage pathways for water in the terrestrial planets.

Mapping the spatial distributions of oxide abundances and Mg# on the lunar surface using multi-source data and a new ensemble learning algorithm

The spatial distribution of oxide abundances and Mg# (Mg/(Mg + Fe)) on the lunar surface is of great significance for in-depth understanding the origin and evolution of the Moon. China's Chang’E−5 (CE-5) mission returned young lunar soils for the first time, providing a new ground truth for the inversion of oxide abundances. In this study, the relationship between multi-source remote sensing data (including Chang’E−1 Interference Imaging Spectrometer (CE-1 IIM) data and the new global Christiansen feature (CF) product, named IIM-CF data), and the abundances of six oxides (FeO, TiO2, MgO, SiO2, Al2O3 and CaO) measured at 40 lunar sampling sites including CE-5 were analyzed. The use of IIM-CF data as the input features of the selected inversion models for obtaining the abundances of oxides, and the oxide abundances measured at the 40 sampling sites were used as the ground truth. The models selected for this investigation contain three typical algorithms − random forest (RF), extreme gradient boosting (XGBoost) and partial least squares regression (PLSR), and a new method integrates RF, XGBoost and PLSR together named RXP was developed in this study. The modeling results of the abundances of the six oxides derived from the above four algorithms show that the RXP algorithm outperforms the other three algorithms. The distributions of the six oxides and Mg# on the lunar surface covering the range from 70° N to 70° S (70° N/S) with a resolution of about 200 m/pixel were generated using the proposed RXP algorithm. Our results indicate that, compared with the result of a single data source, the use of IIM-CF data improved the accuracy of the modeling of oxide abundances and Mg#. It is expected that the CE-5 samples can bring additional references to the studies of the inversion for the oxides of the lunar surface and deepen our understanding over this issue.

Young KREEP-like mare volcanism from Oceanus Procellarum

The Moon’s mare volcanism predominantly occurs within the Procellarum KREEP Terrane (PKT), which is widely thought to be associated with KREEP components within the lunar interior. The Chang’e-5 (CE-5) mission sampled a young (2 Ga) mare basalt Em4/P58 unit of northern Oceanus Procellarum. The geochemistry of the CE-5 mare basalt enables assessment of mantle source compositions which are essential to understand the thermo-chemical mechanism for prolonged volcanism during secular cooling of the Moon. Geochemical compositions of the CE-5 bulk soil, breccias, and basalt clasts from various depths within the drill core consistently display high concentrations of incompatible trace elements (ITE: ∼ 0.3 × high-K KREEP; ∼ 5 μg/g Th) with KREEP-like inter-element ratios, for example for La/Sm, Nb/Ta, and Zr/Y. Exotic impact ejecta, extensive magma differentiation (<70 % fractional crystallization) and significant assimilation of KREEP materials during magma transit and eruption cannot account for the ITE contents and ratios or radiogenic isotope compositions (e.g., εNdinitial of + 8 to + 9 and εHfinitial of + 40 to + 46) of the CE-5 basalts; instead, partial melting of their mantle source played a dominant role. The Chang’e-5 basalt is a chemically evolved low-Ti mare basalt (Mg# of ∼ 34) with enriched KREEP-like ITE compositions but high long-term time-integrated Sm/Nd and Lu/Hf ratios, which represent a hitherto unsampled type of mare basalt. It formed by melting of an augite-rich mantle source (late-stage magma ocean cumulates containing > 30–60 % augite, and little or no ilmenite), with a small amount of late-stage interstitial melt that resembles KREEP (∼1–1.5 modal %, equivalent to 0.2–0.3 μg/g Th in the mantle source). The voluminous mare basalts making up the Em4/P58 unit (>1500 km3) provide compelling evidence for large-scale, ITE enriched young mare magmatism within Oceanus Procellarum. In combination with remote sensing data and with the unique Th-rich Apollo 12 basalt fragment 12032,366–18 (impact ejecta likely from Oceanus Procellarum), this implies that significant portions of the FeO- and Th-rich mare regions of the western PKT may also have formed in a similar way.

High-pressure minerals and new lunar mineral changesite-(Y) in Chang’e-5 regolith

Forty-five years after the Apollo and Luna missions, China’s Chang’e-5 (CE-5) mission collected ∼1.73 kg of new lunar materials from one of the youngest basalt units on the Moon. The CE-5 lunar samples provide opportunities to address some key scientific questions related to the Moon, including the discovery of high-pressure silica polymorphs (seifertite and stishovite) and a new lunar mineral, changesite-(Y). Seifertite was found to be coexist with stishovite in a silica fragment from CE-5 lunar regolith. This is the first confirmed seifertite in returned lunar samples. Seifertite has two space group symmetries (Pnc2 and Pbcn) and formed from an α-cristobalite-like phase during “cold” compression during a shock event. The aftershock heating process changes some seifertite to stishovite. Thus, this silica fragment records different stages of an impact process, and the peak shock pressure is estimated to be ∼11 to 40 GPa, which is much lower than the pressure condition for coexistence of seifertite and stishovite on the phase diagram. Changesite-(Y), with ideal formula (Ca8Y)□Fe2+(PO4)7 (where □ denotes a vacancy) is the first new lunar mineral to be discovered in CE-5 regolith samples. This newly identified phosphate mineral is in the form of columnar crystals and was found in CE-5 basalt fragments. It contains high concentrations of Y and rare earth elements (REE), reaching up to ∼14 wt. % (Y,REE)2O3. The occurrence of changesite-(Y) marks the late-stage fractional crystallization processes of CE-5 basalts combined with silicate liquid immiscibility. These new findings demonstrate the significance of studies on high-pressure minerals in lunar materials and the special nature of lunar magmatic evolution.

Visible and near-infrared spectral results of Chang’E-5 surficial and subsurface soils

Aims. Studies on high-resolution and high-precision laboratory reflectance spectra of the Moon have historically been restricted to the analysis of old Apollo samples (&gt;3.0 Ga). In contrast, studies of young lunar soils have exclusively relied on the analysis of remote sensing spectra. In this study, we present the results of a laboratory spectral investigation of young lunar soils (~2.0 Ga) obtained by the Chang’E-5 (CE-5) mission. Methods. We analyzed surficial and subsurface soils collected through scooped and drilled sampling methods. The laboratory reflectance spectra of the CE-5 soils were compared with those of Apollo soils and orbital spectra. Two methods were employed for maturity inversion. The relationship between the UV-vis color and TiO2 content of young basalts was also investigated. Results. The CE-5 samples exhibit much fresher spectral features, including higher reflectance, deeper absorption depths, and a smaller visible and near-infrared continuum slope (VNCS), compared to pristine regolith. The subsurface soils sampled from a depth of approximately 10 cm exhibit a slightly fresher spectral feature compared to the surficial soils. Our comparison revealed a rapid rate of space weathering at the lunar surface compared to the vertical overturn. Compared to older iron-rich soils, the CE-5 soils have a larger reflectance but similar UV-vis ratios. The UV-vis ratio alone could not accurately predict the TiO2 content of all mare basalts. The CE-5 samples provide a new ground truth for estimating the TiO2 content of young lunar basalts, which have the largest uncertainty in TiO2 content, as estimated from spectral parameters. We find that the samples returned by the CE-5 mission represent disturbed soils and that they exhibit significantly fresher characteristics compared to pristine regolith, a fact that should be kept in mind when using samples as ground truth for remote sensing research.

Identification of Lunar Craters in the Chang’e-5 Landing Region Based on Kaguya TC Morning Map

Impact craters are extensively researched geological features that contribute to various aspects of lunar science, such as evaluating the model age, regolith thickness, etc. The method for identifying impact craters has gradually transitioned from manual counting to automated identification. Automatic crater detection based on the digital elevation model (DEM) is commonly used to detect larger craters. However, using only DEM has limitations in discerning smaller craters (diameter &lt; ~1 km). This study utilizes an improved Faster R-CNN algorithm and the Kaguya Terrain Camera (TC) morning map to detect small impact craters in the Chang’e-5 (CE-5) landing site. It uses model fusion to improve the precision of small crater identification. The results show a recall rate of 96.33% and a precision value of 90.19% for craters with diameters exceeding 200 m. The model found a total of 187,101 impact craters in the CE-5 region. The spatial distribution density of impact craters with diameters ranging from 100 m to 200 m is approximately 2.5706/km2. For craters with diameters ranging from 200 m to 1 km, the average spatial distribution density is about 0.9016/km2. By the unbiased impact crater density of chronological analysis, the model age of the Im2 and Em4 geological units in the CE-5 region is 3.78 Ga and 2.07 Ga, respectively.

Submicron spatial resolution Pb-Pb dating for the formation age of Chang'e-5 basalt

Chang'e-5 (CE-5) basalt, the youngest lunar basalt sample collected so far, is crucial for unraveling the mechanism of the prolonged volcanic activity on the Moon. To better understand the petrogenesis of this basalt, it is necessary to determine its eruption duration accurately. Previous Pb-Pb age measurements have yielded a wide range from 2040 Ma to 1963 Ma. This large range may be attributed to 80 million-year multi-eruption, analytical or interpretational biases from different laboratories, or disturbances in the U-Pb system. Here, we conducted sub-micron Pb-Pb dating on 25 Zr-rich mineral grains with various sizes (∼2 μm to 20 μm) from six CE-5 basalt fragments by a Cameca NanoSIMS 50L. After excluding anomalies caused by Pb enrichment, we obtained a weighted mean Pb-Pb age of 2059 ± 21 Ma and an isochron age of 2046 ± 29 Ma. By integrating all reported age data of the CE-5 basalt, we found inconsistencies in previous studies, probably due to analytical biases of insufficient spatial resolution, leading to the undetected presence of terrestrial common Pb. Isochron regression with a filtering process yields an age of 2031.1 ± 3.8 Ma, which we recommend as the best estimate of the formation age of the CE-5 basalt. This result suggests that all analyzed CE-5 basalt fragments have nearly the same crystallization age, indicating that the lava erupted in a very short period. Combined with previous studies on the mineralogy and geochemistry of the CE-5 basalt, this result contributes new insights into the volcanic history of the Moon.

Lunar Evolution in Light of the Chang'e-5 Returned Samples

The Chinese spacecraft Chang'e-5 (CE-5) landed on the northern Ocean Procellarum and returned 1,731 grams of regolith. The CE-5 regolith is composed mostly of fragments of basalt, impact glass, agglutinates, and mineral fragments. The basalts could be classified as of a low-Ti and highly fractionated type based on their TiO2 content of ∼5.3 wt% and Mg# of ∼28. Independent of petrographic texture, the CE-5 basalts have a uniform eruption age of 2,030 ± 4 Ma, demonstrating that the Moon remained volcanically active until at least ∼2.0 Ga. Although the CE-5 landing site lies within the so-called Procellarum KREEP [potassium (K), rare earth elements (REE), and phosphorus (P)] Terrane, neither the CE-5 basalts nor the mantle source regions of those basalts were enriched in KREEP components, such as incompatible elements, water, sulfur, or chlorine. Therefore, it would be a new and stimulating task in the future to look for the triggering mechanism of the young volcanism on the Moon. ▪The CE-5 spacecraft returned 1,731 grams of lunar regolith in December 2020. It was the first new lunar sample since the last collection in August 1976.▪CE-5 regolith is basaltic in chemical composition, with only ∼1% highland materials of anorthosite, Mg suite, alkali suite, and KREEP.▪The CE-5 basalt is low Ti and highly differentiated. It was extruded at ∼2.0 Ga, being the youngest lunar basalt identified so far from the Moon.▪The triggering mechanism of the ∼2.0 Ga lunar volcanism is not clearly understood because its mantle source was dry and contained low abundances of KREEP elements.