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Knowledge regarding the abundance and distribution of solar wind (SW)‐sourced water (OH/H2O) on the Moon in the shallow subsurface remains limited. Here, we report the NanoSIMS measurements of H abundances and D/H ratios on soil grains from three deepest sections of the Chang'E‐5 drill core sampled at depths of 0.45–0.8 m. High water contents of 0.13–1.3 wt.% are present on approximately half of the grain surfaces (topmost ∼100 nm), comparable to the values of Chang'E‐5 scooped soils. The extremely low δD values (as low as −995‰) and negative correlations between δD and water contents indicate that SW implantation is an important source of water beneath the lunar surface. The results are indicative of homogeneous distribution of SW‐derived water in the vertical direction, providing compelling evidence for the well‐mixed nature of the lunar regolith. Moreover, the findings demonstrate that the shallow subsurface regolith of the Moon contains a considerable amount of water. Plain Language Summary: Recently, China's Chang'E‐5 mission targeted a higher latitude on the Moon than previous Apollo and Luna missions, and brought back scooped and drilled samples to the Earth. These new soil samples provide an opportunity to investigate the distribution, abundance, and origin(s) of water in Moon's middle latitude. Here, we focus on using the NanoSIMS technique to analyze water content on soil near‐surface regions to understand whether the solar wind (SW)‐derived water could be preserved after burial at depth. Our results show that more than half of the core soils have high water contents on the rims of grains, similar to those of the Chang'E‐5 scooped soils. This finding suggests that the SW remains an important source of water in the Moon's subsurface. Our work provides direct evidence that the lunar regolith below the surface contains considerable water from SW implantation. This type of water could be a promising water resource in future exploration. Key Points: More than half of the soils from the single drill core have high water contents and low D/H ratios below the surfaceThe solar wind (SW)‐derived water could be preserved for hundreds of millions of years if buried at depthLunar regolith from the drill core contains considerable water from SW implantation, which is much more accessible [ABSTRACT FROM AUTHOR]

Mars' surface is characterized by a weathered layer of regolith and exposed rock exposures that are the results of long‐term geological processes. The Mars Rover Penetrating Radar (RoPeR) on board the Zhurong rover of China's first Mars mission (Tianwen‐1) has been investigating the fine structure and dielectric properties of the martian regolith in the southern Utopia Planitia. The permittivity of the regolith within 5 m of the landing zone is 3.6−2.0+3.1 ${3.6}_{-2.0}^{+3.1}$, and the average loss tangent is 0.0174−0.0053+0.0053 ${0.0174}_{-0.0053}^{+0.0053}$. The high lossy parameter suggests the possible cause for the missing subsurface reflectors in the landing region detected by either in‐situ radar or orbiter radars. The permittivity distribution map has been derived to show permittivity varying with depth and location. The high dispersion of both permittivity and loss tangent values along the traverse path indicates relatively heterogeneous material distribution on the landing site compared to an airless body such as the Moon. Plain Language Summary: A layer of regolith covers the surface of Mars, which is the result of geologic processes that occurred over millions to billions of years. Compared to the observations from satellites, the Zhurong rover of China's first Mars mission (Tianwen‐1) had a closer look at the properties of the regolith layer in the explored region within southern Utopia Planitia. There is evidence that the exposed materials might be related to aqueous activities. Local landforms on the surface suggest the possible presence of buried volatiles, like water ice. The radar instrument (RoPeR) on board the rover can expose subsurface structures and the dielectric properties of the regolith layer at high‐resolution, to assess their composition. The loss tangent results suggest that water ice is not the main component of the local martian regolith at some depth. The scattering distribution of radar profile along the traveling path and heterogeneous subsurface features show more diverse surface processes and weaker space weathering effects on Mars than those on the airless Moon. Key Points: The dielectric properties of martian regolith at the Tianwen‐1 landing site suggest that water ice is not the dominant componentThe radar image and permittivity and loss tangent distribution maps show a high heterogeneity of subsurface materialsCompared to the lunar regolith, the martian regolith shows more diverse surface processes and weaker space weathering effects [ABSTRACT FROM AUTHOR]

In the original hypothesis of ice in lunar polar cold traps, it was presumed that meteoritic water acquired by the lunar surface would be concentrated in cold traps by exospheric lateral transport. That supposition is proven to be false by the absence of evidence of exospheric water in data obtained by the neutral mass spectrometer on the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft. The upper limit for exospheric water at the lunar surface, ∼3 molecules cm−3, is deficient by several orders of magnitude in accounting for transport of the present influx of meteoritic water to cold traps. The proffered process for removal of meteoritic water from the lunar regolith is solar wind sputter. This LADEE result does not rule out the possibly of past impulsive exospheric events like cometary impacts but does place a rigid constraint on the modern day water cycling. Plain Language Summary: Whether vast deposits of water ice have accumulated in lunar polar cold traps may hinge on an unproven hypothesis that water acquired from meteor impacts and possibly other sources is moved to polar cold traps by the dynamic transport process of the lunar exosphere (a rarefied, collisionless atmosphere). Movement of exospheric molecules over the lunar surface is a two‐dimensional random walk process in which the steps are random segments of ballistic trajectories that begin with thermal desorption from soil grains and end with adsorption at distances measured in hundreds of kilometers. Obviously, trajectories that end in cold traps must create ice deposits. However, the upper bound for exospheric water derived here from data collected in 2013–2014 by the neutral mass spectrometer on the Lunar Atmosphere and Dust Environment Explorer spacecraft, about three molecules/cc, pales in comparison to the concentration of ∼15,000 molecules/cc needed to sequester the meteoritic water influx. The only pragmatic conclusion is that the hypothesis for water ice accumulation at the poles due to exospheric transport is false. This conclusion forces the question of the fate of water that accretes on the lunar surface. Key Points: The upper limit for water in the lunar exosphere is ∼3 molecules/ccThe lunar exosphere does not transport meteoritic water to polar cold trapsLunar regolith is arid [ABSTRACT FROM AUTHOR]

The porosity of the upper layers of regolith is key to the interaction of an airless planetary body with precipitating radiation, but it remains difficult to characterize. One of the effects that is governed by regolith properties is Energetic Neutral Atom (ENA) emission in the form of reflected and neutralized solar wind protons. We simulate this process for the surface of the Moon by implementing a regolith grain stacking in the ion‐solid‐interaction software SDTrimSP‐3D, finding that proton reflection significantly depends on the regolith porosity. Via comparison with ENA measurements by Chandrayaan‐1, we derive a globally averaged porosity of the uppermost regolith layers of 0.85−0.14+0.15 $0.8{5}_{-0.14}^{+0.15}$. These results indicate a highly porous, fairy‐castle‐like nature of the upper lunar regolith, as well as its importance for the interaction with impacting ions. Our simulations further outline the possibility of future regolith studies with ENA measurements, for example, by the BepiColombo mission to Mercury. Plain Language Summary: The Moon's surface is covered with regolith, a soil made up of stacked grains. Properties of this regolith influence how the Moon interacts with its environment. One example of such an effect are impact by charged particles emitted from the Sun called the "solar wind." We now present simulations of the reflection of such particles from the surface of the Moon, taking into account the grain structure of the regolith. We only find an agreement between the simulations and spacecraft measurements of reflected solar wind particles for very loosely stacked grains. Overall, the amount of reflected particles significantly depends on the structure of the regolith. Our simulations predict that 85% of the volume in the regolith is made up of empty space between grains. These results thus show how measurements of reflected particles can be applied for studying soil properties of the Moon, as well as other planetary bodies such as Mercury. Key Points: Reflection of solar wind protons from lunar regolith is simulated with SDTrimSP‐3DA precise agreement with spacecraft measurements of energetic neutral atom emission is only found for highly porous regolith structuresA lunar regolith porosity of 0.85−0.14+0.15 $0.8{5}_{-0.14}^{+0.15}$ is derived from solar wind proton reflection, which could also be applied to other airless bodies [ABSTRACT FROM AUTHOR]

This paper provides analyses to quantify the maturity of regolith within 24 m depth using a novel polarimetric attributes analysis of lunar penetrating radar (LPR) data. The results demonstrate that LPR signals were mainly from subsurface rock fragments of different sizes and were rarely from strata interfaces. The averages and ranges of maturities for the near‐surface (0–2 m), the fine‐grained regolith (2–12 m), and the coarse‐grained ejecta (12–24 m) are 68.98% (0%–99.82%), 82.61% (41.52%–96.56%), and 72.33% (5.91%–96.66%), respectively. Local regions with anomalously low maturities on the lunar surface may be due to the dense materials formed by local impacts or the rock fragments from distal impacts; a newly discovered sandwich structure with low maturity at a depth between 12 and 18 m is formed by the heterogeneous weathering in a paleo‐crater. Based on these new insights, we infer a heterogeneous weathering process of the regolith. Plain Language Summary: The entire lunar surface is considered to be covered by a layer of regolith. The study of regolith weathering degree almost focused on the near‐surface because the traditional techniques cannot detect the regolith at large depths. The Chang'E‐4 lunar penetrating radar (LPR) can detect the regolith structure within dozens of meters depth. However, previous publication of LPR results only use the macro layering model to interpret the regolith structure. This study innovatively extracts new properties from the LPR data acquired while the rover was turning and estimated the quantitative maturity of regolith within ∼24 m depth at lunar farside. We found that the LPR can mainly detect the subsurface rock fragments that survived weathering and rarely the interfaces of strata because the materials of different strata are mixed at interfaces and make it gradational. Our results also reveal the spatial difference of weathering in the regolith. We investigate the formations and material compositions of several interesting regions with unusual weathering degrees. Based on these new insights, we establish a model to illustrate the weathering process of the regolith at the CE‐4 landing site. Key Points: We quantify the maturity of the lunar regolith within 24 m depth by analyzing the lunar penetrating radar (LPR) data acquired during the rover turningsLPR signals were mainly from subsurface rock fragments of different sizes and were rarely from strata interfacesInferring the heterogeneous weathering process by comprehensively investigating the regions with anomalous maturities in the regolith [ABSTRACT FROM AUTHOR]

High‐pressure minerals in impact ejecta quantify shock conditions and provide clues for provenance analysis. The sampling site of Chang'E‐5 may contain distal ejecta, which is critical for constraining the impact events and interpreting the constitution of the target geological units. Here, we report a silica fragment consisting of seifertite, stishovite, α‐cristobalite‐like phase, and silica glass in Chang'E‐5 regolith. Both seifertite and stishovite formed via solid‐state transformation mechanism, in which seifertite formed by transition from α‐cristobalite upon pressure loading whereas stishovite may form from seifertite when postshock temperature was significant during pressure release. The coexistence of seifertite and stishovite suggests that their host rock has experienced a peak shock pressure of 11–40 GPa and records different stages of the impact process. Crater size calculation revealed that the host rock of stishovite and seifertite could have been transported from distant craters, confirming the retention of distal ejecta in Chang'E‐5 landing site. Plain Language Summary: Seifertite and stishovite, the two high‐pressure polymorphs of silica, are discovered in the lunar regolith returned by Chang'E‐5 mission. This is the very first confirmed existence of seifertite in returned lunar samples, which is the evidence that Chang'E‐5 regolith contains impact ejecta from distant craters as suggested by the remote sensing data. The presence of these two high‐pressure minerals indicates that their host rock has experienced a peak shock pressure of 11–40 GPa. Crater size calculation model suggests that formation of impact craters with 3–32 km in diameter is capable to generate high‐pressure condition for the formation of seifertite and stishovite. Four distant craters (Mairan G, Aristarchus, Harpalus, and Copernicus crater) that contributed to the impact ejecta material in Chang'E‐5 landing site are the possible candidate source crater of host rock of seifertite and stishovite. This study emphasizes the significance of studies on lunar high‐pressure minerals. Key Points: Two high‐pressure minerals seifertite and stishovite are identified in Chang'E‐5 lunar regolith for the first timeThe coexisting seifertite and stishovite suggests a peak shock pressure of 11–40 GPa and their host rock delivering from distant cratersThis study emphasizes the retention of distal ejecta in Chang'E‐5 landing site and the importance of studying lunar high‐pressure minerals [ABSTRACT FROM AUTHOR]

Micrometeorite impacts and solar wind irradiation, the dominant space weathering (SW) processes, largely modified compositions and microtexture of soil materials on the Moon. Here, we report the SW characteristics of the Chang'e‐5 lunar soils from mid‐high latitude (43.06°N). All mineral phases exposed on the surface of a single basalt clast have a vapor deposit layer, whereas the textures of the solar wind irradiation‐damaged zone are dependent on the host mineral species. Nanophase Fe (npFe0) particles are spherical in the amorphized zone of pyroxenes, elongated in ilmenite, and irregular on the jagged surface of iron sulfide, but not found in Fe‐poor merrillite. Vesicles were found in the damaged zone of ilmenite and merrillite, but with different shapes. The observations were compared to Apollo samples and demonstrate no significant altitude‐dependent effects on the SW, which is important for decoding the reflectance spectra of the Moon. Plain Language Summary: The lunar surface has been suffering intense meteorite impacts and solar wind irradiation for billions of years, which heavily modifies its physical properties, chemical compositions and mineralogical features, and in turn, the optical reflectance spectra of the Moon. The meteorite impacts are random events, but the intensity of solar wind irradiation is latitude dependent. However, all Apollo and Luna missions landed in a narrow and low range of lunar latitude. The Chang'e‐5 (CE‐5) mission returned lunar soil samples from a middle latitude (43.06°N), providing unique samples for study of lunar space weathering (SW). In this paper, we report the SW features of various minerals from a single basaltic clast of the CE‐5 sample. Our observations reveal phase‐dependent effects on the SW. Furthermore, the CE‐5 lunar soil shows no significant differences from those of Apollo samples, suggestive of little latitude‐dependent effects on lunar SW. Key Points: The space weathering (SW) characteristics of lunar soils returned by Chang'e‐5 landing at the mid‐high latitude site are reportedMicroscopic textures of SW depend on mineral species but show no relationship with the latitude of sampling siteThe SW products by micrometeorite impacts and solar wind irradiation are distinguished [ABSTRACT FROM AUTHOR]

The Moon's bright albedo markings, known as swirls, are defined by broad, bright, on‐swirl areas separated by darker off‐swirl lanes. Their formation mechanism has long been debated and is key for understanding the processing of the lunar surface, the mobility of the lunar soil particles, and the effects of the space environment on planetary surfaces. Here we present, for the first time, evidence that these features do not necessarily cross the surface without regard to topography or local terrain. Within portions of Mare Ingenii on the lunar far‐side, brighter on‐swirl areas have statistically lower mean elevations than adjacent, darker, off‐swirl lanes. These topographic characteristics provide constraints on the plausible formation mechanisms for the swirls in Mare Ingenii, which in turn provide insight into lunar soil migration and evolution. We believe this correlation with topography argues for highly mobile dust transport across the lunar surface. Plain Language Summary: The formation of the bright and dark swirling patterns on the lunar surface involves multiple processes. Until now these patterns, known as swirls, have seemingly crossed the surface without regard to elevation differences. We show the first evidence that this lack of correlation is not true for all swirls. Two regions in Mare Ingenii with swirls display a correlation with topography, where the bulk elevation in the bright regions is lower than the bulk elevation in the dark regions. These differences are apparent in meter‐scale resolution topographical data. For swirls, dust transport is the process most affected by elevation changes and we now re‐examine the role of dust mobility across the lunar surface in the context of this new discovery. Key Points: Meter‐scale topographical differences are seen between on‐swirl and off‐swirl areas in regions of Mare IngeniiTopographic correlations suggest dust migration is involved in lunar swirl formationSwirl formation is the result of multiple processes [ABSTRACT FROM AUTHOR]

Surface‐correlated nanophase iron particles (npFe0) alter the reflectance spectrum characteristics of airless bodies, thus making it an essential aspect of studying space weathering. Vapor deposition has been the only strongly proven npFe0 formation mechanism owing to the long exposure time of Apollo samples, whereas other formation mechanisms remain questioned. Newly returned younger Chang'E‐5 samples provide an opportunity to study the incipient formation mechanism of npFe0. Here, we combined transmission electron microscopy and electron energy loss spectroscopy to characterize the microscopic features of Chang'E‐5 olivine rims. The uppermost layer of these grains exhibits the simultaneous coexistence of npFe0 with Si‐rich material overlying an Mg‐rich layer, as well as numerous irregular vesicles containing oxygen‐rich (SiO and O2) components embedded in the npFe0. These microscopic features collectively suggest subsolidus olivine decomposition during (micro)impact‐induced fragmentation or local heating processes, which may be the essential agent to alter the reflectance spectrum of airless bodies. Plain Language Summary: Airless bodies experienced a space weathering modification to form the nanophase iron particles (npFe0) that would alter the reflectance spectrum. However, the formation mechanism of npFe0 remains controversial due to the lack of less‐exposed lunar samples to study the incipient information about npFe0 formation, except for the widely accepted vapor deposition origin. Our study is based on the younger Chang'E‐5 samples and report the first strong evidence of unique vesicular npFe0 produced by olivine decomposition under subsolidus conditions, which may be the first effect contributing to npFe0 formation on the lunar surface. This formation mechanism will shed light on the npFe0 production and further broaden the perspective of impact effects beyond the Moon and deepen the current understanding of unexplored celestial bodies using remote sensing. Key Points: Subsolidus fayalitic olivine decomposition forming unique vesicular nanophase iron particles in Chang'E‐5 soils was confirmedNanophase iron particles in the uppermost olivine layer are embedded with numerous vesicles containing possible O2 or SiO componentUnique microstructural features on fayalitic olivine rims shed light on the diversity of space weathering effects on the lunar surface [ABSTRACT FROM AUTHOR]

The growth of lunar regolith over time affects surface rock abundance, because larger, less frequent impacts are needed to penetrate thicker regolith developed on older surfaces and excavate rocks. On younger surfaces with thinner regolith, smaller, more frequent impacts are sufficient to excavate rocks. We quantify the correlation between observed rock abundances and age on the lunar surface by comparing Diviner rock abundance data to the surface ages of intercrater parts on the maria. Our observations show the expected negative correlation between age and rock abundance. The commonality of nonzero rock abundance values on ancient surfaces, combined with a simple Monte Carlo model of the rock excavation process, suggest that rocks reexcavated from the regolith volume contribute to the presently observed rock population on the lunar surface. The half‐life of meter‐scale surface rocks most consistent with our observations is 80 ± 20 Myr. Plain Language Summary: The lunar surface is covered by regolith, which includes particles ranging in size from dust to boulders. Past work has suggested that regolith is meters to tens‐of‐meters thick, with average thickness increasing with terrain age. At least in the maria, beneath the regolith is fragmental bedrock. When impacts large enough to penetrate the regolith occur, boulders from this underlying bedrock are excavated onto the surface. Excavating boulders is expected to be more difficult where the regolith is thicker, because thicker regolith limits the ability of craters to eject material from the underlying fragmental bedrock. This implies larger and rarer impacts are needed to excavate rocks on older terrain. We tested this idea by comparing the rock abundance data from the Diviner Lunar Radiometer Experiment on the Lunar Reconnaissance Orbiter spacecraft with previously obtained crater statistics for part of the maria, excluding the area within and immediately adjacent to D ≥ 1 km craters. We show that older maria have, on average, lower fractional rock abundances, consistent with a thicker regolith on older surfaces influencing rock excavation. Rocks excavated from within the regolith are necessary to be consistent with the continued presence of nonzero rock abundance on old terrains. Key Points: Crater frequency and age of mare units are inversely correlated with rock abundance, consistent with regolith thickening over timeOn old surfaces with thick regolith, the median rock abundance is nonzero, consistent with reexcavation of rocks from within the regolithThe half‐life of meter‐scale surface rocks as derived in the work presented here is 80 ± 20 Myr [ABSTRACT FROM AUTHOR]

The photometric properties of the uppermost lunar regolith are used in the spectroscopic study. China's Chang'E‐5 (CE‐5) mission successfully landed in the Northern Oceanus Procellarum of the Moon, carrying the scientific payload lunar mineralogical spectrometer (LMS). LMS performed full‐view scanning and obtained the reflectance spectra in various geometric configurations. The photometric properties, including the single‐scattering albedo ω and two parameters of the Henyey‐Greenstein phase function (b, c), were derived. Our modeling results showed weak backward scattering and strong forward scattering properties of the regolith at the CE‐5 landing site. Meanwhile, the asymmetry parameter (−b×c) $(-b\times c)$ indicates that CE‐5 regolith has weaker forward scattering than the Apollo lunar soil samples and the regolith at the Chang'E‐4 landing site. The derived Hapke parameters can be used for comparison with that of the returned lunar sample, supporting further studies of lunar spectroscopy, and can be the ground truth of the CE‐5 landing area. Plain Language Summary: The in‐situ mineral compositions of the lunar regolith can be retrieved using spectral observations with known photometric properties of the lunar surface. The lunar mineralogical spectrometer installed on the Chang'E‐5 lander conducted in‐situ full‐view scanning, and obtained many spectral data. We derived a photometric function using these data to study the properties of the regolith. These findings can be compared to the measured value of the lunar returned samples of CE‐5 to support future spectroscopy research and provide a better understanding of the mineralogical information at the CE‐5 landing area. Key Points: The photometric properties of the lunar regolith are revealed by in‐situ spectrum data from the Chang'E‐5 Lunar Mineralogical SpectrometerThe derived photometric parameters contribute to a better understanding of the properties of the regolith on the near side of the moonThe forward scattering was dominant in the landing site, consistent with the compositions of the lunar samples returned from the Chang'E‐5 [ABSTRACT FROM AUTHOR]

Small crater morphology method has been used extensively in lunar regolith thickness estimation. However, topographic degradation can change crater morphology and thus bias regolith thickness estimation. In this study, we first developed a shape model for small fresh craters with normal, central mound, flat‐bottomed, and concentric geometry. We then simulated their degradation processes by using a topographic diffusion model. Simulation results show that as a small crater degrades, its morphology changes from concentric/central mound to flat‐bottomed, from flat‐bottomed to normal, and from normal to invisible, depending on its initial morphology. Upon the time a crater becomes invisible, its diameter can be enlarged by a factor of ∼70%. We proposed a revised small crater morphology method and applied it to the Apollo 11 and 14 landing sites. Our revised method permits a more accurate estimate of regolith thickness, and our results are helpful in understanding the evolution of the Moon's surface. Plain Language Summary: On the Moon's surface, small impact craters generally exhibit four typical morphologic types: normal, central mound, flat‐bottomed, and concentric. Laboratory impact experiments show that morphology of small craters depends primarily on the thickness of the regolith layer. With the high‐resolution optical images acquired from recent missions, the small crater morphology method has been used extensively to estimate regolith thickness, which can provide critical information for the evolution of lunar surface. However, topography erosion by subsequent micrometeorite bombardments can change the morphology of impact craters, especially for small ones, preventing an accurate estimation of regolith thickness. In this study, we investigated the degradation effect on lunar regolith thickness estimation using small crater morphology method. We first designed an elevation profile model for small fresh craters with different geometry, and then simulated crater degradation processes by using a topographic diffusion model. These simulations give a quantitative measure on the changes in diameter and morphology of a small crater as it degrades. We further proposed a revised small crater morphology method for lunar regolith thickness estimation and applied it to the Apollo 11 and 14 landing sites, and the results are in good agreement with the estimates from small fresh craters only. Key Points: A new shape model of small fresh lunar craters with normal, central mound, flat‐bottomed, and concentric geometry is constructedDegradation effect on morphology of small craters and regolith thickness estimation is studied using a topographic diffusion modelThe small crater morphology method for regolith thickness estimation is revised and applied to the Apollo 11 and 14 landing sites [ABSTRACT FROM AUTHOR]

Chang'e‐5 successfully returned ∼1,731 g of lunar samples on December 17, 2020. We systematically studied the morphology and morphometry of craters surrounding the Chang'e‐5 site based on high‐resolution images. A key ejecta source crater database was produced, incorporating their morphometrical parameters, excavation depth, target rock types, and ages from either crater counting, crater morphology or degradation methods. We found that (a) the regolith at the Chang'e‐5 site is ∼4–6 m thick, (b) ejecta are primarily from five proximal craters, including Xu Guangqi, dominantly with ages <200 Ma; (c) distal materials are mainly from Harpalus, Copernicus, Aristarchus, and Mairan G craters; (d) the drill samples are likely to be mainly from Impact Crater (IC)‐261 and IC‐265 particles at the top and the contribution of Xu Guangqi increases with depth; (e) the ejecta of Xu Guangqi would buried preexisting materials but probably overturned by postimpacts. Plain Language Summary: The Chang'e‐5 mission, China's first lunar sample‐return mission, successfully landed on the Moon on December 1, 2020, at 43.06°N, 51.92°W, and returned 1,731 g of lunar soil samples. Because of the potentially large contribution from local impact craters to the collected samples, we conducted this research to study these craters based on high‐resolution orbital data. Our results support the hypothesis that local craters are the major ejecta sources, mainly from Impact Crater (IC)‐259, IC‐261, IC‐265, IC‐266, and Xu Guangqi crater. Of these, Xu Guangqi is the most critical ejecta source crater and Chang'e‐5 landed on its ejecta deposit. Its ejecta would bury preexisting materials, such as those from distant craters Harpalus, Copernicus, Aristarchus, and Mairan G, but subsequent craters may redistribute buried materials again, and represented in the regolith sampled by Chang'e‐5. Key Points: An impact crater database surrounding the Chang'e‐5 site was producedCrater ages are constrained either by CSFD or crater morphology or degradation methodsEjecta are mainly from local craters, delivered by Copernican‐aged (>200 Ma) craters [ABSTRACT FROM AUTHOR]

The surface slope and roughness of the Moon have been investigated extensively over a wide baseline range except millimeter to decimeter scales. In this study, we present for the first time millimeter‐to decimeter‐scale surface slope and roughness of the Moon at China's Chang'e‐4 landing regions (∼20 m across) using the Digital Terrain Model (DTM) with a resolution of 5 mm/pixel. The bidirectional slope at the 7 mm scale can be larger than 40° with a median value of ∼10°. The root‐mean‐square (RMS) height within a window size of 125 mm varies from ∼1 mm to ∼18 mm with a median value of ∼4 mm. Both the bidirectional slope and RMS height show scale‐dependent behaviors and the parameter of scale dependence, the Hurst exponent, is ∼0.6–0.85. We also synthesized the bidirectional slope at baseline from micrometer to kilometer, showing that bidirectional slope decreases from ∼60° at micrometer to ∼1° at a kilometer. At millimeter‐scale, surface roughness is mainly controlled by small impact craters, rocks, and regolith properties. Our roughness results not only bridge the gap in understanding surface roughness from traditional topographic data sets to radar and thermal observations, but also provide valuable information about lunar regolith characteristics, and small‐scale geological processes. Plain Language Summary: The roughness of a planetary body quantitively describes terrain surface topographic undulation at a horizontal scale and is widely used in geological and geomorphological studies. Roughness is an important parameter in radar observations due to its modulation of radar wave behaviors. Lunar surface roughness at a wide baseline range has been investigated before, but not in the baseline range of millimeter to decimeter. The Panoramic Camera onboard the Yutu‐2 rover collected millimeter‐scale resolution stereo images over China's Chang'e‐4 landing region. We generated a 5 mm/pixel resolution DTM covering an area of ∼20 m wide and then calculated three roughness parameters. We found that small impact craters, rocks, and regolith properties are the controlling factors affecting the millimeter‐scale roughness of the lunar surface. Combining with previous roughness results, we obtained lunar surface roughness versus baseline at scales ranging from micrometer to kilometer, which can be applied in a variety of studies. Key Points: We investigated millimeter to decimeter scale topographic roughness of the Moon in the Chang'e‐4 exploration region of ∼20 m wideThe median bidirectional slope is ∼10° at 7 mm scale and the median RMS height is ∼4 mm at 125 mm window size, and both show scale dependent behaviorsSmall impact craters, rocks, and regolith properties mainly affect millimeter‐scale topographic roughness of the Moon [ABSTRACT FROM AUTHOR]

The current paper investigates the shallow layers of the lunar regolith at the Chang'E‐4 landing site. Four layers between 0 and 10 m were identified using lunar penetrating radar. Based on these outputs, a revised stratigraphic model is suggested for the post‐Imbrian ejecta at the Von Kármán crater. The layers were previously unseen due to the smooth boundaries between them. The revised model was inferred using an advanced hyperbola‐fitting scheme. Applying conventional hyperbola‐fitting to non‐homogeneous media results in errors and inaccuracies that are often wrongly assumed to be negligible. We propose a novel hyperbola‐fitting scheme that is, not constrained to homogeneous media and can be applied subject to any arbitrary one‐dimensional permittivity distribution. Via this approach, we can estimate the permittivity profile of an investigated area and detect layered structures that were previously transparent to electromagnetic waves due to the gradational dielectric properties at their interfaces. Plain Language Summary: The landing site of Chang'E‐4 is at the Von Kármán (VK) crater at the South Pole‐Aitken (SPA) basin. The SPA basin is the oldest and biggest basin on the Moon created at the early stages of its evolution by an impact that is, believed to have penetrated the lunar crust and uplifted materials from the top mantle. Understanding the geology and stratigraphy of the SPA basin can help us understand cratering processes and shed light on the evolution of the Moon. To that extent, ground penetrating radar (GPR) has been added to the payload of Yutu‐2 to investigate the stratigraphy of the Chang'E‐4 landing site. One drawback of GPR is that conventional processing methods fail to detect layers with smooth boundaries between them. Consequently, GPR data might give the false impression that an area is relatively homogenous, while in fact it might consist of numerous gradational layers representing a much more complex geological history. In the current paper, a novel interpretation tool is described, capable of detecting smooth transitions between layers. The proposed methodology revealed a previously unseen layered structure for the first ∼10 m of the VK crater. Key Points: We suggest a novel hyperbola‐fitting technique that assumes an arbitrary permittivity distribution with respect to depthThe proposed method is used to map the lunar regolith at the Chang'E‐4 landing siteA layered structure is revealed at the first 10 meters. A new stratigraphic model is suggested for the Von Kármán crater [ABSTRACT FROM AUTHOR]

Space weathering processes form submicroscopic metallic iron particles that are optically active, darkening and reddening the lunar surface over time. The optical effects of these particles depend on their size; nanophase iron darkens and reddens, while microphase iron darkens without reddening. Using available Kaguya Multiband Imager parameter maps believed to estimate submicroscopic iron abundance, we investigate trends that may be associated with abundance of nanophase and microphase iron near dated lunar craters. We observe that nanophase iron is strongly correlated with crater age, while microphase iron exhibits a weaker correlation. We present models for the highlands nanophase and microphase iron accumulation rates from 100 ka to 1 Ga. Our observations suggest that highlands nanophase iron abundance is a direct result of space weathering exposure, while highlands microphase iron abundance is likely influenced by lunar source materials or stochastic impact‐delivery mechanisms. Plain Language Summary: The Moon, Mercury, and asteroids lack protective atmospheres and slowly darken over time due to their exposure to space. We call this darkening process space weathering. Apollo samples returned from the Moon show that space weathering produces tiny iron particles that range in size from nanometers to micrometers. We use orbital lunar maps of nanophase and microphase iron content to better understand how quickly space weathering occurs on the Moon. We first find the iron content of young lunar soils deposited by large impact events, then use the age of each impact crater to see how much iron accumulates in different lengths of time. We find that nanophase iron accumulates predictably over time due to space weathering. In contrast, microphase iron accumulates less predictably, possibly because it exists in the lunar soil initially, or is delivered to the Moon by crater‐forming impacts. This work helps us understand how the surface of the Moon weathers over time and how space weathering might work elsewhere in the Solar System. Key Points: We model nanophase and microphase iron accumulation rates using published parameter maps and crater agesHighlands nanophase iron is negligible at 100 ka and accumulates at ∼0.05 wt% ln (Ma)−1 until ∼1 GaHighlands microphase iron is enhanced by 100 ka and less correlated with age, possibly due to variable abundances in lunar source materials [ABSTRACT FROM AUTHOR]

Accurate assessments of surface temperatures on the Moon are important for understanding the physical properties of the lunar surface regolith and thermal effects on the reflectance spectra beyond 2 μm. The local time resolved spectral measurements of the same region were used to estimate the surface temperature at the Chang'E‐4 landing site. The results show that the surface temperatures at the landing site at lunar local time 14:28–14:41 are 346 ± 8 K. The spectral absorptions at ∼2 μm of the lunar surface are overestimated without sufficient thermal removal, and consequently may have resulted in overestimation of pyroxene and/or glasses at the landing site. The results play a foundation for correcting thermal effects of reflectance data that will be acquired by Chang'E‐5 and ‐6 and possible other future Chang'E missions. Plain Language Summary: Surface temperature is an important physical parameter of the lunar surface and it reflects the thermal state of the lunar regolith. Though some orbital observations have been conducted to measure the surface temperature, the in situ detections are very limited. We derived the surface temperature at the Chang'E‐4 landing site using the in situ spectral measurements acquired at different local time. In addition, we found that the thermal contributions on reflectance would induce significant errors on estimating pyroxene and/or glass abundances. The thermal correction model is critical for removing thermal contributions from reflectance data that will be acquired by Chang'E‐5 and ‐6. Key Points: We modeled the thermal effect of the near infrared reflectance spectra acquired by the Yutu‐2 rover near the Chang'E‐4 landing siteOur model results suggest that thermal emissions at the Chang'E‐4 landing site could substantially alter the reflectance spectra beyond 2 μmThis work plays a foundation for correcting thermal effects of infrared reflectance spectra that will be acquired by Chang'E‐5/6 missions [ABSTRACT FROM AUTHOR]

Shock‐lithification is a fundamental process of making rocks from fine‐grained and porous regoliths on the surface of the Moon. Previous investigations have constrained potential shock pressures during shock‐lithification based on experimental and numerical simulations. However, pressure and temperature conditions during shock‐lithification have not been directly inferred from natural lunar breccias. Here, we report the discovery of widespread tissintite in strongly shock‐lithified lunar meteorites, accompanied occasionally by Si‐rich corundum and coesite. The coexistence of tissintite and coesite and the absence of stishovite in molten regions indicate a shock pressure of 4–8 GPa, which might be the pressure boundary between weak and strong shock‐lithification. Meanwhile, the presence of Si‐rich corundum imposes a temperature constraint of ∼2,300 K for the intergranular melts. This temperature constraint has profound significance for interpreting the behaviors of volatile and moderately volatile elements and remanent magnetization records during strongly shock‐lithification of lunar breccias. Plain Language Summary: It is widely accepted that high‐speed impact makes lunar breccias from regolith on the Moon's surface. However, the detailed pressure and temperature conditions during strong shock lithification remain an open question due to complex properties and impact history of components in lunar breccias. In this study, we report the first discovery of tissintite, a high‐pressure mineral, and Si‐rich corundum in strongly shock‐lithified lunar breccias. Using the high‐pressure minerals in lunar breccias, we constrained the lower boundary (4–8 GPa) of shock pressure for strong shock lithification of lunar regoliths and the profound thermal effect. Key Points: We discovered tissintite, a high‐pressure mineral, in nine strongly shock‐lithified lunar brecciasWe discovered Si‐rich corundum in two strongly shock‐lithified lunar brecciasThe high‐pressure minerals provide constraints on the shock pressure and temperature during strong shock lithification of lunar regoliths [ABSTRACT FROM AUTHOR]

Lunar surface temperature variations provide key information about the thermophysical properties of the regolith. To date, temperatures have been measured using telescopes and orbiter instruments, providing information from mid‐infrared to long infrared (IR) wavelengths. Here, we report on temperature measurements in the short‐wavelength IR at centimeter scales observed in situ by the Chang'E‐4 rover. These local observations are an important complement to the existing large‐scale data. We show that even at 2.39 µm, where reflected radiation dominates the spectrum, thermal information can be retrieved from the data. The observed thermal radiances and derived temperatures depend on the observation geometry, specifically the relative azimuth angle between Sun and detector. This indicates that surface roughness on subresolution (millimeter) scales causes a non‐Lambertian radiation pattern of the emitted flux that is per definition independent of the observation angle. This behavior must be considered when deriving temperatures and thermal properties of lunar regolith. Plain Language Summary: The Chang'E‐4 spacecraft landed in the Von Kármán Crater in the Moon's South Pole‐Aitken Basin. A Visible and Near Infrared Spectrometer (VNIS) was carried on the "Yutu‐2" rover. The VNIS measured thermal emission on the surface of the Moon at short wavelengths and temperature variations at centimeter scales were retrieved during the first, second, and tenth day of rover operations on the lunar surface. These in situ observations are an important complement to the existing large‐scale measurements taken from orbit and reveal that the millimeter scale roughness plays an important role when deriving temperatures and physical properties of the lunar surface regolith. Key Points: The Chang'E‐4 VNIS observed the lunar surface in situ in the 0.45–2.4 μm wavelength rangeEmitted flux at centimeter scales is non‐Lambertian and depends on surface roughness and observation geometrySurface roughness as described by the bidirectional RMS slope was found to be 22°–24° [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are carried out to investigate dielectric breakdown of lunar regolith induced by space weather events and its potential effects on water ice formation on lunar surface. We find that dielectric breakdown can trigger the water formation process by breaking the chemical bonds of regolith grains and exposing the oxygen atoms to react with the hydrogen implanted by solar wind. In the permanently shadowed region, the water molecules formed become attached to regolith grains in the molecular structure of ice after the event. Thus, dielectric breakdown can also enable the preservation of water molecules by changing the hydrophobicity of regolith grains. Plain Language Summary: This study considers dielectric breakdown of lunar regolith induced by space weather events and presents the first molecular dynamics simulation study of the breakdown process and the relevant chemical reactions. We find that dielectric breakdown is a triggering mechanism for water formation on lunar surface. Dielectric breakdown also changes the hydrophobicity of the regolith grains and, thus, enables the preservation of the water molecules formed in the grain. Key Points: We report the first MD simulations of chemical reactions during lunar regolith dielectric breakdownDielectric breakdown breaks the chemical bonds of lunar regolith and triggers water formationDielectric breakdown changes hydrophobicity of regolith and enables preservation of water molecules [ABSTRACT FROM AUTHOR]

The dielectric permittivity is one of the most significant properties of lunar material. For the past decades, researchers have assumed or used an indirect density versus depth relation to constrain the subsurface permittivity on the Moon. On 3 January 2019, Chang'E‐4 (CE‐4) rover‐borne lunar penetrating radar (LPR) successfully landed on the Von Kármán crater on the Moon's farside. CE‐4 LPR is the first surface radar on the Moon's farside for exploring regolith thickness and geological structure. Numerous parabolic‐shaped diffractions (PSD), which indicate subsurface objects, are identified in LPR data. We estimate the permittivity of the first ~50 m at the landing region using these PSDs based on a hyperbolic fitting method. A best‐fit permittivity/density versus depth relation is obtained, and this relation could be used at different areas on the Moon. Plain Language Summary: Currently, rover‐deployed/spaceborne radar systems are frequently employed in lunar exploration. The depth and thickness of lunar subsurface structure observed from radar data are completely influenced by the dielectric properties of subsurface materials. The dielectric properties also provide vital clues on compositions and origin of subsurface materials. However, except the results measured with returned sample from lunar surface, we have no more information about dielectric properties of global and deeper lunar subsurface materials. In January, China's CE‐4 spacecraft softly landed on the farside of the Moon for the first time and released the lunar penetrating radar (LPR). In this study, we estimate the dielectric permittivity of the first ~50 m at the landing region with LPR data and propose a best‐fit permittivity/density versus depth relation which could be used at different areas on the Moon. Key Points: The permittivity of lunar subsurface materials at CE‐4 landing site is estimatedA best‐fit permittivity/density versus depth relation is obtainedThe obtained best‐fit relation can be used at different areas on the Moon [ABSTRACT FROM AUTHOR]

Chang'E‐4, with the Yutu‐2 rover, is the first lunar probe to successfully land and conduct a tour on the far side of the Moon from early 2019. We analyze the physical and mechanical characteristics of lunar soil through the in situ terrain data collected by the panoramic camera onboard the Yutu‐2 rover. With the slip ratio and wheel sinkage obtained by the derived Digital Orthophoto Map (DOM) and Digital Elevation Model (DEM), the mechanical parameters of lunar soil are derived from the slip‐sinkage model. These mechanical parameters and wheel size of the rover are used to obtain the pressure‐sinkage curves, which can estimate the lunar soil strength. The experimental results indicate that the soil strength at the Chang'E‐4 landing site is much higher than that at the Chang'E‐3 landing site. The discrepancies in lunar soil strength between the two landing sites may be related to the local surface topography and degree of space weathering. Plain Language Summary: The knowledge of the physical and mechanical characteristics of lunar soil is of fundamental importance because it is the basis for mineral resource exploration and engineering activity aimed at the construction of lunar bases. The Chang'E‐4 landing site is within the mare floor of the Von Kármán crater inside the South Pole‐Aitken (SPA) basin. The ejecta from the nearby impact craters has covered the Chang'E‐4 landing area. Besides, the lunar soil of the Chang'E‐4 landing area has been relatively mature. Here, a method of analyzing the characteristics of lunar soil is introduced to provide an opportunity to understand the physical and mechanical properties of the mature lunar soil at the Chang'E‐4 landing site. With the terrain data collected by the panoramic camera onboard the Yutu‐2 rover, we can get the relationship curve of the interaction between the rover wheels and lunar soil, such as the pressure‐sinkage curve. The pressure‐sinkage curves can intuitively reflect the discrepancies of lunar soil strength at the Chang'E‐4 and Chang'E‐3 landing sites, which may bear a big relationship to the local surface morphology and degree of space weathering. Key Points: The slip ratio can be estimated by Digital Orthophoto Map and the wheel sinkage can be derived from Digital Elevation ModelThe pressure‐sinkage curves can intuitively reflect the discrepancies of lunar soil strength at different landing sitesThe lunar soil strength at the Chang'E‐4 landing site nearby is higher than that at the Chang'E‐3 landing site [ABSTRACT FROM AUTHOR]

An exceedingly small number of high‐pressure polymorphs have been discovered in lunar samples. This situation does not seem to reconcile with the prolonged, intense bombardment of the lunar surface, which should produce suitable conditions for the formation of such polymorphs. Here we report the discovery of reidite, a high‐pressure polymorph of ZrSiO4 with scheelite structure in lunar meteorite Sayh al Uhaymir (SaU) 169. The reidite occurs mainly as lamellae hosted within zircon, likely corresponding to a deviatoric‐dominated transformation. The presence of reidite in the regolith portion of SaU 169 indicates a narrow temperature and pressure path constrained by the phase stability under low pressure and suggests heterogeneous shock features in the porous lunar regolith where the ambient temperature increases much higher than that in compact rocks. The inventory of high‐pressure polymorphs might be restricted by such unusual cooling processes lunar samples experienced. Plain Language Summary: The most striking phenomenon on the Moon's surface is the densely distributed impact craters. Asteroid impacts generate high pressure and temperature conditions, resulting in the formation of high‐pressure minerals. However, only few high‐pressure minerals have been discovered in very few lunar samples so far. In this study, we first discovered reidite, a high‐pressure polymorph of ZrSiO4, in the regolith portion of lunar meteorite Sayh al Uhaymir (SaU) 169. Previous research produced reidite by applying shock pressure of >30 GPa on zircon and found that it back‐transformed to zircon quickly at temperature of >1473 K under ambient pressure. Impact into porous lunar regolith will lead to a huge increase in ambient temperature. For a postshock temperature of <1473 K, the estimated average peak pressure should not have exceeded ~10 GPa. Therefore, we suggest that reidite formed in localized high‐pressure regions (>30 GPa) induced by an impact with an average peak pressure <10 GPa. In addition, shock‐induced high ambient temperature conditions in porous lunar regolith are not favorable for the preservation of most high‐pressure minerals, therefore might restrict the observation of high‐pressure minerals in lunar samples which were mostly derived from the porous regolith layer. Key Points: We discovered reidite, a high‐pressure polymorph of ZrSiO4, in the regolith breccia of lunar meteorite Sayh al Uhaymir 169The reidite could have formed under localized transient pressure spikes during initial stage of asteroid impact into porous lunar regolithHigh postshock temperature of porous lunar regolith likely inhibits the widespread preservation of high‐pressure polymorphs in lunar samples [ABSTRACT FROM AUTHOR]

Lunar mare regolith is traditionally thought to have formed by impact bombardment of newly emplaced coherent solidified basaltic lava. We use new models for initial emplacement of basalt magma to predict and map out thicknesses, surface topographies and internal structures of the fresh lava flows, and pyroclastic deposits that form the lunar mare regolith parent rock, or protolith. The range of basaltic eruption types produce widely varying initial conditions for regolith protolith, including (1) autoregolith, a fragmental meter‐thick surface deposit that forms upon eruption and mimics impact‐generated regolith in physical properties, (2) lava flows with significant near‐surface vesicularity and macroporosity, (3) magmatic foams, and (4) dense, vesicle‐poor flows. Each protolith has important implications for the subsequent growth, maturation, and regional variability of regolith deposits, suggesting wide spatial variations in the properties and thickness of regolith of similar age. Regolith may thus provide key insights into mare basalt protolith and its mode of emplacement. Plain Language Summary: Following recent studies of how lava eruptions are emplaced on the lunar surface, we show that solid basalt is only one of a wide range of starting conditions in the process of forming lunar soil (regolith). Gas present in the lavas during eruption also produced bubbles, foams, and explosive products, disrupting the lava and forming other starting conditions for mare soil parent material. Key Points: New basalt magma emplacement models explore fresh lava flows that form the lunar mare regolith parent rock, or protolithSome conditions predict immediate formation of a fragmental meter‐thick "autoregolith" that mimics impact‐generated regolithLava flows with significant near‐surface vesicularity, macroporosity, and magmatic foams will create nontraditional regolith growth rates [ABSTRACT FROM AUTHOR]

Global exosphere models of alkali gases surrounding Mercury and the Moon assume that the primary effect of the porous soil is to reduce the effective desorption rates. We demonstrate with a kinetic simulation that, following adsorption, the complicated structure of soils has two additional effects on the fate of previously released alkali atoms: (1) trapping of free atoms at lunar temperatures by microscopic shadows and inward diffusion, which becomes the primary sink mechanism, and (2) high‐energy barriers for thermal desorption compared to what would be retrieved from experiments on thin films or compacted pellets, especially when surface diffusion of adsorbates is considered. Lunar soils retain one fifth to two thirds of recycled adsorbates, depending on the assumed adsorbate mobility, photodesorption cross section, and soil thermal gradient. A transition from a retentive surface to full outgassing at T > 500 K will produce complex feedback mechanisms of alkali circulation at Mercury. Plain Language Summary: This paper seeks to understand physical processes that occur on mineral surfaces throughout the Solar System and which affect the atmospheres of Mercury and the Moon. When meteoroids and the solar wind impact the surface, they vaporize sodium and potassium atoms, some of which cannot escape the body's gravity and can populate the atmosphere with successive bounces until they are lost to space via ionization, react with the surface, or penetrate into the soil. We quantify the competition between evaporation and diffusion within the top 1 mm of the soil, which supports the atmosphere reservoir, by following test particle trajectories in soils simulated with a sphere packing code. The simulations provide empirically constrained insights about the longevity of these free atoms. These findings provide context for understanding observations from ground‐based telescopes, MESSENGER and LADEE observations, and laboratory experiments and pave the way for higher‐fidelity models of exospheres for these species. Key Points: We modeled processes occurring on very different timescales in the soil of Mercury and the MoonMicroscopic shadows trap up to half of the deposited sodium and potassium atoms at lunar temperaturesDesorption of previously trapped atoms at higher temperatures could induce additional feedback in Mercury sodium circulation models [ABSTRACT FROM AUTHOR]

The Chang'E‐4 (CE‐4) achieved the first successful soft landing on the floor of the Von Kármán crater located in the northeast of the South Pole‐Aitken (SPA) basin on the Moon. Here, through analysis and processing of the dual‐channel lunar penetrating radar (LPR) data, the shallow regolith structure and deep geological strata below the landing site are exposed. The high‐frequency data (CH‐2, 500 MHz) show that the Von Kármán crater underwent remodeling because of ejecta from multiple craters within a thickness of 40 m. Under the surface fine‐grained regolith, superpositions among these crater materials and mare basalt units establish shallow regolith stratigraphic sequences. The low‐frequency data (CH‐1, 60 MHz) show a deep stratigraphic structure to the depth of 360 m that indicates the previous geological evolution history of the Von Kármán crater. The LPR results provide an important scientific basis for understanding the geological history of the far side of the Moon. Plain Language Summary: The Chang'E‐4 (CE‐4) landed in the Von Kármán crater, which is located on the far side of the Moon. The lunar penetrating radar (LPR) loaded on the Yutu‐2 rover can be used to determine the shallow lunar regolith structure and deep geological strata of the Von Kármán crater. In this article, first, different processing procedures focused on the two channels of LPR data (CH‐1 and CH‐2) are designed, and clear radar images that can be used to explain the underground structure of the Von Kármán crater are obtained. The radar images are then combined with previous geological information to reveal the subsurface geological structure of the Von Kármán crater. The Von Kármán crater underwent various geological processes, including basaltic magmatism, ejecta coverage, and the interaction of volcanic eruptive clastics and lava. The regolith layer on the surface has a thickness of more than 10 m, and below the regolith layer is a multilayer formed by the ejecta material of surrounding impacts, which is as thick as more than 30 m. Underneath are three basalt magma covers. Key Points: The CH‐2 LPR data reveal that the landing site underwent remodeling because of ejecta from multiple craters within a thickness of 40 mThe CH‐1 LPR data provide the deep stratigraphic structure within 360 m, including more than three basalt magma activitiesThe LPR data demonstrate that the Von Kármán crater was landscaped by various geological processes [ABSTRACT FROM AUTHOR]

The Yutu‐2 rover of the Chang'E‐4 spacecraft observed many meter‐sized shallow pits fully covered with small fragments, distinct from the typical rock‐free impact craters with comparable sizes in the landing area. The unique morphology of the pits and the visible and near‐infrared spectra of the fragments suggest that the fragments are broken pieces of impact melt‐conglutinated regolith breccia projectiles, which were excavated from preexisting craters. The rareness of rock on the landing area surface suggests that the preexisting craters were probably small in size (e.g., <60 m in diameter), not large enough to penetrate the thick regolith (~12 m) and to excavate the beneath rock breccia and/or bedrock. The presence of the impact melts was confirmed by the glass‐like spectra of some fragments with unusually high albedo and blue‐green tint in the centers of the pits. These observations reveal the gardening and consolidating processes on the Moon. Plain Language Summary: There are very rare outcrops of bedrock on the lunar surface because the Moon is covered by the lunar regolith. The detailed formation processes of the lunar regolith are important for understanding the orbiting and landing exploration data, and for planning future sample return missions. The lunar rover Yutu‐2 discovered fragment‐filled pits and identified in situ impact glass in the fragments. The glass‐bearing and regolith‐like fragments were probably broken pieces of lunar regolith breccia projectiles, which were excavated from the consolidated bottom and walls of preexisting small craters within the lunar regolith (<12–15 m in thickness). These observations contribute to our understanding of the formation processes of the lunar regolith. Key Points: Unique fragment‐filled pits distinct from the meteorite impact craters were observed at the Chang'E‐4 landing siteImpact glass in the fragment‐filled pits was identified in situ for the first timeThe discoveries of the Yutu‐2 rover provide important evidence for the recycling of the lunar regolith [ABSTRACT FROM AUTHOR]

The visible and near‐infrared imaging spectrometer on board the Yutu‐2 rover of Chang'E‐4 mission has conducted 2 sets of spectrophotometric measurements at two sites on its 10th lunar day. At each site, the reflectance spectra were measured on the same lunar regolith at different geometric configurations. The experiments reveal an increasing trend of the spectral reddening effect with the increasing phase angles, which may cause significant uncertainties on interpreting the maturity of the lunar regolith. Furthermore, the phase angles have significant effects on the 2‐μm band center and the 1‐μm band depth of the spectra, consequently on the estimation of mineral composition of the regolith. Finally, the derived average Hapke parameters using the in situ spectrophotometric measurements provide important ground‐truth for remote sensing observations. Plain Language Summary: Olivine, pyroxenes and plagioclase, the major constituent minerals of the surface of the Moon, have diagnostic absorption features in their visible and near‐infrared reflectance spectra. These features, including the wavelength position of the absorption band center and the depth of the absorption band, can be used to identify the mineralogy of the observed surface. The slope of the reflectance spectral curve is another feature that can be used to describe the degree of how the surface materials interact with space environment. The Yutu‐2 rover on board the China's Chang'E‐4 mission has been equipped with a visible to near‐infrared spectrometer, to carry out in situ spectral measurements at varied illumination and azimuth angles. These measurements provided us an excellent chance to study the effects of measurement angles on these spectral features, which can help us better understand the mineralogical information of lunar surface. Key Points: In situ spectrophotometric measurements by Chang'E‐4 Yutu‐2 rover show viewing geometry may affect band centers and depth of the spectraPhase reddening coupled with space weathering effects on the spectra may cause significant uncertainties on interpreting the maturity of lunar regolithThe derived Hapke parameters from the in situ spectrophotometric measurements provide ground truth for both in situ and orbital observations [ABSTRACT FROM AUTHOR]

The Chang'E‐4 landing site is depleted with boulders seen from both orbit and surface. However, the Yutu‐2 rover came across thousands of concreted fragments in and around an abnormally fresh crater that has more elevated northwestern rims. The origin of the fragments is crucial to resolve the provenances of surface materials detected by the rover. The lunar penetrating radar performed two in‐and‐out scans for the blocky ejecta, revealing that the subsurface materials have indistinguishable radar permittivity with the surrounding regolith. Forward modeling of electromagnetic wave propagation shows that the fragments were not an original component in the subsurface. This crater is among the several fresh craters photoed by the rover, and they are located in an eastern extension ray of the Zhinyu crater. The small craters are likely secondaries of Zhinyu, and the fragments contain a mixture of shattered projectiles and most likely compacted regolith clumps formed during the secondary impacts. Plain Language Summary: The Chang'E‐4 landing site lacks boulders seen from both orbit and surface, but several abnormally fresh craters were encountered by the Yutu‐2 rover. The blocky rims and interiors are in sharp contrast with the heavily degraded crater population in the landing area. These craters are less than 3 m in diameter, and the fragments are less than 10 cm long and appear earthy in color. The origin of the fragments needs an explanation because it is the basis for the interpretation of data returned by both the lunar penetrating radar and reflectance spectrometer onboard the rover. At the ninth lunar day, the rover was carefully driven into the blocky ejecta deposits of such a crater, and ground‐penetrating radar detections were conducted. Radar measurements reveal that the physical properties beneath the blocky ejecta deposits are essentially the same with that of the surrounding regolith, and the observed fragments were not originated from the subsurface. The high spatial density, more pronounced northwestern rims, and colocation with an impact ray suggest that the small craters are most likely secondaries formed by the Zhinyu crater. The fragments are mainly formed by impact compaction of the preimpact target regolith, and the shattered secondaries‐forming projectiles are a minor component. Key Points: Yutu‐2 encountered several abnormally fresh craters surrounded by blocky fragmentsRadar permittivity of the blocky ejecta is not distinct from nearby normal regolithThe small craters are likely secondaries, and impact compaction occurred in regolith [ABSTRACT FROM AUTHOR]

Earth's present dipolar magnetic field extends into the interplanetary space and interacts with the solar wind, forming a magnetosphere filled up with charged particles mostly originating from the Earth's atmosphere. In the elongated tail of the magnetosphere, the particles were observed to move either Earthward or tailward at different locations, even outside the Moon's orbit. We hypothesize that the lunar soil, on both the nearside and farside, should have been impacted by these particles during the geological history, and the impact was controlled by the size and morphology of the magnetosphere. We predict that the farside soil could also have the features similar to those in the nearside soil, e.g., 15N‐enrichment. Furthermore, we may infer the evolution of the magnetosphere and atmosphere by examining the implanted particles in the lunar soil from both sides. This hypothesis could provide an alternative way to study the evolution of Earth's dynamo and atmosphere. Key Points: The configuration of ancient geomagnetic field could be inferred from lunar soilBoth nearside and farside lunar soil might have recorded Earth's volatilesThe farside soil was impacted by ~100 km/s atmospheric ions for 3.5 billion years [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: CE‐4 is the first craft in history to land on the lunar farside. Its rover is equipped with a ground‐penetrating radar (GPR), the same as the one mounted on the CE‐3 rover, which uses pulses of electromagnetic energy to reveal the subsurface structure and properties, especially useful to study the lunar soil layer ("regolith") that mantles most of the lunar surface. The results from the GPR show that the thickness of the regolith at the CE‐4 site is 1.3–3 times higher than the in situ measurements at the Apollo 11,12,14,15, 17, and CE‐3 sites even though the ages of the surfaces of Apollo 11 and Apollo 17 are thought to be comparable with that of the CE‐4 site. It implies a faster regolith growth speed at the CE‐4 site. The mineral mix of the surface materials at the CE‐4 site is different from that at the CE‐3: this results in less radar signal attenuation, thus increasing the detection limit up to the depth of 35 m, 2.85 times deeper than the CE‐3. Key Points: The LPR measurements at the CE‐4 landing site reveal that the shallow structure comprises of fine‐grained regolith, coarse impact ejecta, and fractured bedrocksThe CE‐4 landing site has a thicker regolith layer (~11 m) compared with the CE‐3, hinting at a longer weathering historyA lower abundance of ilmenite and rocks in the regolith at the CE‐4 site allows 2.85 times the penetration depth compared with CE‐3 site [ABSTRACT FROM AUTHOR]

In spite of great scientific and engineering interests in lunar exploration, natural dust activity near the Moon surface remains unclear. According to distinct reflectance features of lunar rocks and regolith observed by Chang'E‐3 mission, long‐term dust activity near a young surface is quantified with a new method. We found that a dust deposition upper line on rocks is about 28 cm above the ground. Below this line, the quantity of dust deposits becomes smaller as the altitude ascends, whereas above the line, no visible or only negligible amount of dust is distributed on the rocks. This dust distribution pattern could be explained by dust electrostatic levitation process. The results indicate distinctively weak long‐term dust activity near the young surface and suggest possible selection of geologically young regions as landing sites or lunar bases to minimize the effect of dust grains. Key Points: Chang'E‐3 observations show long‐term deposition upper line on rocks about 28 cm above the ground nearbyThis hight indicates the probable electrostatic levitation altitudes of most lofted grains in this areaThe results imply distinctively weak long‐term dust activity near the young surface at this site [ABSTRACT FROM AUTHOR]

Data from the Lunar Reconnaissance Orbiter Lyman Alpha Mapping Project and Diviner are consistent with surface water on the Moon varying in abundance with both terrain type and local time/temperature. A thermal desorption model including latitudinally varying desorption activation energy reproduces the observations. We interpret the observed variability in spectral slopes as water molecules in the uppermost lunar regolith (<1% of a monolayer) thermally adsorbing and desorbing from grains depending upon the local temperature and availability of chemisorption sites. The Lyman Alpha Mapping Project data also demonstrate that in the Earth's magnetotail, where the solar wind source of protons is absent, a decrease in H2O on the surface is not observed. This rules out a steady state process involving a prompt solar wind source and favors a migration mechanism for the distribution of adsorbed water on the Moon. Plain Language Summary: Data from the Lunar Reconnaissance Orbiter's UV spectrograph are used to measure the signature of a partial monolayer of water on the top surface of the lunar regolith. The diurnally varying signature is interpreted as water molecules thermally desorbing close to local noon each day, when the surface temperature reaches a maximum value. These measurements represent the first time the UV absorption signature has been used to detect water on a rocky airless body, and are the only set of data currently providing diurnal coverage of lunar hydration. Key Points: Variations in FUV spectra are attributed to a partial monolayer of water thermally adsorbing and desorbing, controlled mainly by temperatureHighlands regions are more hydrated than mare regions, likely due to greater numbers of activation sites on the grainsNo significant difference in hydration level is observed when the Moon is in the magnetotail compared to when it is out of the magnetotail [ABSTRACT FROM AUTHOR]

We have invented a new method for detecting solar particle events using data from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO). Using a simple function of the total particle detection rates from four of CRaTER's six detectors, we can precisely identify solar energetic particle event periods in the CRaTER data archive. During solar quiet periods we map the distribution of a mare‐associated mixture of elements in the lunar regolith using this new method. The new map of the moon probably reflects an as‐yet unknown combination of lunar albedo protons, neutrons, and gamma rays, and most closely resembles Lunar Prospector maps of gamma rays characteristic of thorium and iron. This result will lead to multiple follow‐up studies of lunar albedo particles and may also contribute to the study of diurnally varying hydrogenation of the lunar regolith. Key Points: The CRaTER instrument on LRO can detect and quantify small solar particle events with a simple new analysis techniqueOur new lunar map of albedo radiation resembles gamma ray maps from Lunar ProspectorFollow‐up studies will investigate contributions from neutrons, protons, and gamma rays, and signatures of hydrogen in lunar regolith [ABSTRACT FROM AUTHOR]