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To quantify fluorine (F) evolution during lunar magma ocean (LMO) crystallization, high-pressure, high-temperature experiments have been conducted to determine mineral-melt partitioning of F for lunar minerals (plagioclase, orthopyroxene and ilmenite). Results constrain the F abundance in the magma ocean to 21–41 ppm at the time crust-forming plagioclase started crystallizing. Forward modeling shows that 352–703 ppm F would remain in the final 1 % of magma toward the end of magma ocean solidification. This range overlaps that inferred for the urKREEP reservoir (660 ppm). Taking into account model uncertainties, from the perspective of F abundances the urKREEP reservoir can be formed at 98.9–99.5% LMO solidification, with negligible loss of F from the Moon since the onset of crust formation. Backward modeling from initial crust-forming plagioclase, an initial LMO would contain 4.2–8.5 ppm F, which is consistent with estimates of the lunar primitive mantle F content derived from melt inclusions in Apollo samples. This finding is consistent with previous suggestions that the bulk silicate Moon is depleted in F relative to the bulk silicate Earth (which contains ∼25 ppm F). A BSE-like initial LMO would yield a magma containing 122 ppm F at the onset of crust formation, significantly higher than our calculated 21–41 ppm F. Fluorine depletion could have occurred by degassing during the early LMO stages (between the onset of LMO crystallization and first crust formation), and/or prior to the LMO stage (e.g., depletion during the giant impact or vapor drainage in the protolunar disk), but seems to have ended by the time the crust started forming. [ABSTRACT FROM AUTHOR]

After its formation, the Moon is widely believed to have possessed a deep, global magma ocean. As it cooled, an anorthositic crust formed, floating atop this magma ocean and acting as an insulating blanket. As well as forming the Moon, the Moon‐forming giant impact also released more than a lunar mass of debris into heliocentric orbit. Reimpacting debris subjected the newly formed Moon to an extremely intense bombardment. We have conducted a suite of impact simulations for a range of conditions representative of this early period. We find that impact outcomes can be divided into four regimes and construct scaling relations for the transitions between these regimes and size of impact features. Exposure of liquid magma to the surface is generally more efficient than previously assumed, implying significant shortening of the solidification time of the Lunar Magma Ocean. Comparison with work on icy satellites also suggests that penetration of a solid crust overlying liquid is a relatively universal process with weak dependence on target material properties. Plain Language Summary: The Moon is believed to have formed in a giant impact between Earth and another planet‐sized body. After formation, the Moon was very hot and likely had a deep layer of magma. As the magma cooled and solidified, some of the solid minerals floated to the surface, creating an insulating blanket. As well as forming the Moon, the giant impact released over a Moon's mass of debris into orbit around the Sun, some of which returned to hit the young Moon. We ran computer simulations to understand what happens to the solid crust when debris hits it. We find that these impacts can be divided into four types and developed equations relating the size of the scar produced to impact energy and crust thickness. Creating a hole in the crust makes it a less effective insulating blanket, allowing heat out faster. We find that impacts more easily produce holes than previously assumed, so the magma should have cooled faster. Icy satellites are similar in structure having a solid ice layer with water underneath, and comparing with previous work, we suggest that how easy it is to puncture the solid layer does not depend much on what it is made out of. Key Points: Impacts into crusts overlying magma can be divided into four outcomes ranging from classical crater‐forming to complete penetrationWe derived impact energy scaling relations for the transitions between regimes and size of impact featuresPenetration of the early lunar crust would have been extensive—reimpacting debris substantially decreased magma ocean solidification time [ABSTRACT FROM AUTHOR]

Eleven isobaric experimental series simulate the fractional crystallization of 1,150 km deep lunar magma ocean. Crystallization begins at 1,850°C with olivine (to 32 per cent solidified, pcs), followed at 1,600°C by olivine + opx ± Cr‐spinel (to 62 pcs), at 1,210°C cpx + plagioclase ± olivine ± Ti‐spinel (to 97 pcs) and at 1,060°C quartz + cpx + plagioclase + Ti‐spinel, leaving 1.8 wt% residual magma that crystallizes minor K‐feldspar and apatite in addition. Melt compositions remain near 45 wt% SiO2, while FeO increases from 11 to 26 wt%, TiO2 peaks at 4 wt% at Ti‐spinel saturation. The available experimental liquid lines of descent yield an overall fractional crystallization sequence of olivine→opx→cpx + plagioclase→quartz→FeTi‐oxide. Plagioclase appears concomitantly with cpx, a result of the low magma ocean floor pressures (≤1 GPa) after 66%–76% of olivine + opx‐fractionation. A few wt% of FeTi‐oxides form mostly once the quartz + plagioclase + cpx‐cotectic is reached, cumulate densities remain ≤3,740 kg/m3. Scaled to a full magma ocean, plagioclase appears at 210–120 km depth, mainly as a function of bulk Al2O3. As buoyancy driven plagioclase‐cpx separation is likely limited, these depths may correspond to the primordial lunar crustal thickness. Allowing for complete plagioclase flotation to the quartz + plagioclase + cpx + FeTi‐oxide ± olivine cotectic yields 95–70 km primordial crust of anorthosite and quartz‐gabbro, far in excess of the 35–50 km observed. This supports an overturn of primordial layers, remelting of dense gabbroic cumulates in the harzburgitic cumulate mantle leading to further mixing and differentiation. We posit that such complex density induced convection led to a lunar marble cake mantle with primitive and fairly evolved reprocessed cumulates next to each other. Plain Language Summary: Upon its accretion the Moon was likely completely molten, forming a global magma ocean. This study experimentally simulates the crystallization of this magma ocean and constrains the resulting mineral cumulate layers, the initial temperature distribution, and the nature of the original lunar crust. Overall this crust was 2–5 times thicker than observed nowadays, supporting that post‐magma ocean convection has removed the larger part of this in some layers quite dense crust. The down‐slumping crust remelts in the hot deeper lunar mantle, leading to a second generation of magmatism explaining part of the available lunar samples. Key Points: Crystallization of a full Moon magma ocean defines the initial selenothermOur and previous results yield >95–70 km primordial crust, at least twice the modern value, requiring reprocessing through lunar overturnSlumping dense crust remelts in the cumulative harzburgitic mantle, adding further diversification to a lunar marble‐cake mantle [ABSTRACT FROM AUTHOR]

The ferroan anorthosite suite (FAS) represents the only direct sampling of the lunar magma ocean (LMO) and potentially contains information on the earliest history of the Moon. Apollo 16 FAS sample 60025 is extremely important for understanding early lunar evolution, but unraveling this information is complicated. For example, 60025 has two distinct Sm‐Nd crystallization ages that in themselves encapsulate the complicated history of this sample, along with the cataclastic and heterogeneous textures exhibited. Here, we present new in situ major and trace element plagioclase and pyroxene data gathered from five thin sections of 60025 that highlight such complexities. Trace element data are used to derive equilibrium liquids and while many of the minerals analyzed here are consistent with derivation from the LMO, there are also a significant number of plagioclase and pyroxene crystals that crystallized from magmas inconsistent with current models of LMO evolution. Integration of Sm‐Nd isotopic data with the elemental data reported here indicate a nonchondritic LMO is possible and we confirm that 60025 is a polymict lunar breccia containing differently sourced material. Plain Language Summary: The age of the lunar crust has previously been estimated by analyzing samples such as Apollo 16 Ferroan Anorthosite Suite (FAS) sample 60025. This sample and other members of this suite are considered to provide unique insight into the earliest evolution history of the Moon shortly after its formation. Constraining the ages of FAS samples has proven to be difficult and has yielded seemingly contradictory results with 60025 in particular, producing two distinct crystallization ages using the Sm‐Nd isotopic system. Here, we examine the individualcomponents of 60025 to better understand the formation history of this sample on a mineral to mineral scale. Using in situ analysis techniques and applying these data to models of lunar evolution, we have determined that this sample represents a mixture of rock types, some consistent with derivation from the LMO, while others are not. Combined with its multiple reported literature ages, we have determined that this sample better represents a lunar breccia rather than a pristine sample of the original lunar crust as previously thought. As such, interpretations of any ages reported from analysis of this sample require careful consideration. Key Points: Textures of ferroan anorthosites returned by Apollo display intense post‐crystallization reworkingFerroan anorthosite 60025 contains material inconsistent with models of lunar magma ocean productsThe multiple Sm‐Nd ages reported for this sample relate to sampling of multiple lithologies [ABSTRACT FROM AUTHOR]

We examined the global distribution and geological context of lunar sites where olivine‐ and plagioclase‐rich materials co‐exist. These sites are areas showing plagioclase‐rich spectra adjacent to areas showing olivine‐rich spectra, and they extend over several hundreds of meters on the lunar surface. From an analysis of the high‐spatial‐resolution data obtained from the SELENE (Kaguya) multiband imager, we identified 14 co‐existing occurrences among 49 olivine‐rich sites located around large impact basins. We found that the co‐existing occurrences are limited to a few sites among the olivine‐rich sites in the Moscoviense, Crisium, and Imbrium basins, while six of seven olivine‐rich sites in the Schrödinger basin show co‐existing occurrence. The geological features between the co‐existing occurrences and the olivine‐rich sites without plagioclase‐rich materials showed no clear difference, but both types of site are found at fresh geological features located around the peak rings of impact basins. These results may suggest that the co‐existing occurrences are closely related to the material heterogeneity of the peak ring regions. The heterogeneity could be formed by mixing of the olivine‐rich mantle and the anorthosite‐rich crust during impact basin formation, or it might be a reflection of the compositional heterogeneity of the lunar lower crust. For future sample return missions, the detailed information on the co‐existing occurrences presented here might be useful for a sampling strategy to select a "one‐stop" site that provides important information for the overall characterization of lunar mantle and crustal materials. Plain Language Summary: The surroundings of several impact basins on the lunar surface are known to contain olivine‐rich sites that are dominated by olivine‐rich spectra. Some of these olivine‐rich sites co‐exist with plagioclase‐rich (purest anorthosite) materials, which are adjacent to the olivine‐rich materials. The detailed study of these co‐existing occurrences would provide critical constraints on the structure, composition, and evolution of the lunar crust and upper mantle. In this study, we examined the global distribution and geological context of co‐existing occurrences based on the analysis of the high‐spatial‐resolution data obtained from the SELENE (Kaguya) multiband imager. Our results showed that the locations of co‐existing occurrences are limited to fresh geological features around the peak rings of impact basins, and their spatial distributions are sporadic along the peak rings, suggesting material heterogeneity in these regions. The heterogeneity could be due to mixing of the olivine‐rich mantle and anorthositic crust during the formation of the impact basins, or it may reflect a compositional heterogeneity of deep‐seated materials in the lower crust. For future sample return missions, the detailed information on co‐existing occurrences given here will be useful for a selecting a "one‐stop" sampling site to better characterize the lunar mantle and crustal materials. Key Points: We examined the global distribution and geological context of sites where olivine‐ and plagioclase‐rich materials co‐existWe identified 14 co‐existing occurrences among 49 olivine‐rich sites located around large impact basinsThe presence of co‐existing occurrences may indicate material heterogeneity in the peak rings of impact basins [ABSTRACT FROM AUTHOR]

Classical fractional crystallization scenarios of early lunar evolution suggest crustal formation by the flotation of light anorthite minerals from a liquid magma ocean. However, this model is challenged by the >200 $ > 200$ Myr age range of primitive ferroan anorthosites, their concordance with Mg‐suite magmatism and by the compositional diversity observed in lunar anorthosites. Here, we propose a new model of slushy magma ocean crystallization in which crystals remain suspended in the lunar interior and crust formation only begins once a critical crystal content is reached. Thereafter crustal formation occurs by buoyant melt extraction and magmatism. The mixture viscosity strongly depends on temperature and solid fraction driving the development of a surface stagnant lid where enhanced solidification and buoyant ascent of melt lead to an anorthite‐enriched crust. This model explains lunar anorthosites heterogeneity and suggests a crustal formation timescale of 100s Ma, reconciling anorthosite ages with an early age of the Moon. Plain Language Summary: The discovery of primitive lunar anorthosites by the Apollo 11 mission was surprising. Their global distribution and purity suggested flotation of anorthite crystals over a liquid magma ocean. Flotation theory elegantly explains early formation of the Highlands and the Procellarum KREEP terrane composition, interpreted as the residual liquid from crystallization, enriched in incompatible elements. Since then, many lunar meteorites have been analyzed and the lunar surface has been studied remotely. Lunar anorthosites appear more heterogenous in composition than suggested by ferroan anorthosite samples only, contradicting the classical flotation scenario where the liquid ocean is the common source of all anorthosites. The ∼300 Ma age range for ferroan anorthosites also appears difficult to reconcile with a mostly liquid ocean. A reevaluation of the magma ocean solidification history thus seems necessary. In the low lunar gravity, efficient crystal‐liquid separation may be difficult to achieve. Here, we investigate the case where a slushy crystal suspension persists throughout magma ocean solidification and the crust instead forms by extraction of melts enriched in an anorthite component. Crustal magmatism then produced the lunar anorthosites, explaining their observed diversity. The crust formation timescale is several hundreds of million years, matching the observed age range of lunar anorthosites. Key Points: We consider the cooling of a slushy lunar magma oceanCrust formation occurs by liquid extraction over hundreds of millions of yearsThis model can explain both the chronology and diversity of lunar crustal rocks [ABSTRACT FROM AUTHOR]

We present a method to determine local gravity fields for the Moon using Gravity Recovery and Interior Laboratory (GRAIL) data. We express gravity as gridded gravity anomalies on a sphere, and we estimate adjustments to a background global start model expressed in spherical harmonics. We processed GRAIL Ka‐band range‐rate data with a short‐arc approach, using only data over the area of interest. We determine our gravity solutions using neighbor smoothing constraints. We divided the entire Moon into 12 regions and 2 polar caps, with a resolution of 0.15°×0.15° (which is equivalent to degree and order 1199 in spherical harmonics), and determined the optimal smoothing parameter for each area by comparing localized correlations between gravity and topography for each solution set. Our selected areas share nodes with surrounding areas and they are overlapping. To mitigate boundary effects, we patch the solutions together by symmetrically omitting the boundary parts of overlapping solutions. Our new solution has been iterated, and it has improved correlations with topography when compared to a fully iterated global model. Our method requires fewer resources, and can easily handle regionally varying resolution or constraints. The smooth model describes small‐scale features clearly, and can be used in local studies of the structure of the lunar crust. Plain Language Summary: The gravity field of a planet depends on the density distribution in its interior, and as such, improved knowledge of the gravity field can help in determining the interior structure of the planet. Here, we have analyzed the data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to make local maps of the Moon's gravity field. Standard analysis of GRAIL data has focused on determining global models of the Moon's gravity field, partly because the tools of geophysics that are used to study the Moon's interior make use of such models, which are expressed in what are called spherical harmonics. However, if the data coverage is varying geographically, spherical harmonics are more difficult to determine precisely. We have applied a local method that can more readily handle variations in data coverage. We divided the Moon into 14 separate regions, and determined the optimal solution for each. We evaluated each solution by comparing it with the Moon's topography. GRAIL found that gravity and topography are highly correlated on the Moon, which we will leverage to independently evaluate our solution. We then patched together our separate maps into one global map. Our new model has improved correlations with topography when compared with a standard global model, but it takes fewer computational resources to make. Together with the easy way to handle geographically varying data coverage, this makes our method and model a good alternative to standard models. Our new model is smooth and has a resolution of 0.15°×0.15° (which is 4.5 km by 4.5 km at the equator) and can be used to study the structure of the Moon's crust at small scales. Key Points: We determine 14 local gravity field solutions covering the entire Moon using GRAIL intersatellite range‐rate dataWe patch the local solutions into a global map, which shows no seams, minimizing boundary effectsOur solution has improved correlations between gravity and topography compared to standard global solutions, with less computational effort [ABSTRACT FROM AUTHOR]

Abstract We present a method to determine local gravity fields for the Moon using Gravity Recovery and Interior Laboratory (GRAIL) data. We express gravity as gridded gravity anomalies on a sphere, and we estimate adjustments to a background global start model expressed in spherical harmonics. We processed GRAIL Ka‐band range‐rate data with a short‐arc approach, using only data over the area of interest. We determine our gravity solutions using neighbor smoothing constraints. We divided the entire Moon into 12 regions and 2 polar caps, with a resolution of 0.15°×0.15° (which is equivalent to degree and order 1199 in spherical harmonics), and determined the optimal smoothing parameter for each area by comparing localized correlations between gravity and topography for each solution set. Our selected areas share nodes with surrounding areas and they are overlapping. To mitigate boundary effects, we patch the solutions together by symmetrically omitting the boundary parts of overlapping solutions. Our new solution has been iterated, and it has improved correlations with topography when compared to a fully iterated global model. Our method requires fewer resources, and can easily handle regionally varying resolution or constraints. The smooth model describes small‐scale features clearly, and can be used in local studies of the structure of the lunar crust.

Maps of plagioclase, olivine, and pyroxene at 1 km resolution are derived from a combination of data from the Diviner Lunar Radiometer on the Lunar Reconnaissance Orbiter and the Kaguya Multiband Imager. The Diviner instrument features three infrared bands designed to characterize a spectral feature of lunar soils that is sensitive to the average silica polymerization of the surface called the Christiansen Feature, which is directly sensitive to the presence of plagioclase, the dominant lunar silicate. Existing global mineral maps based on near‐IR data largely infer the presence of plagioclase from the bright mineral's effect on total reflectance, excepting in rare locations where the surface is nearly pure plagioclase and a weak feature in the plagioclase near‐IR spectrum can be relied upon. By integrating both wavelength regions we produced more robust estimates of the abundance of the three dominant minerals. In the process of this work, we also improved the removal of space weathering effects from Christiansen Feature maps, and showed that silica rich compositional anomalies could be reliably detected by decorrelating Christiansen Feature and FeO maps. New silica‐rich locations are reported as are the global abundances of the three major silicates. Plain Language Summary: One of the goals of remote sensing of the Moon is to produce maps of the minerals present on its surface. In this paper, we bring together two infrared spectroscopic data sets to create maps of the minerals plagioclase, pyroxene, and olivine at a resolution of 1 km. One of these infrared data sets defines the wavelength position of a spectral phenomenon called the Christiansen Feature that is sensitive to the presence of unusual silica‐rich minerals that indicate a relatively rare but widespread style of lunar volcanism. Using these new data, we find a few previously unrecognized silica‐rich exposures that extend the spatial range of these features. The Christiansen Feature is also sensitive to rare rock types that may represent outcrops of the lunar mantle at the surface of the Moon, and a promising candidate is revealed at the farside crater Titov. Key Points: The global abundance of plagioclase, pyroxene and olivine are presentedThe effects of space weathering on Christiansen Feature maps are removed with an improved algorithmNew silica‐rich locations are identified in the Oceanus Procellarum region [ABSTRACT FROM AUTHOR]

The Chang'E‐5 (CE‐5) mission returned a total of 1,731 g of lunar regolith from the northern Oceanus Procellarum (NOP). Despite that the CE‐5 landing site is covered by Eratosthenian‐aged mare basalts, non‐mare lithologies might also have been collected owing to the lateral mixing introduced by nearby craters. Here we employed FeO and thorium abundance data obtained by the Lunar Prospector Gamma Ray Spectrometer to investigate the chemical composition of the NOP region. Four major compositional groups (feldspathic highland materials, Imbrium basin ejecta, Aristarchus ejecta, and mare basalts) and several subgroups have been identified. Their corresponding geographical locations were constrained using an interactive scatter‐plot tool in ENVI® software. We also determined the first‐order mixing trends occurring within the NOP region as well as the CE‐5 landing site. Aristarchus crater may have contributed highly evolved materials to the CE‐5 site. Rock fragments derived from Aristarchus ejecta are important for the interpretation of magmatic differentiation and non‐mare volcanism on the Moon. We proposed that thorium enrichments of CE‐5 landing site are due to the geochemical nature of local mare basalts rather than impact mixing. Highland ejecta, along with mare basalts, would expand Apollo and Luna sample collection diversity. Plain Language Summary: The Chang'E‐5 (CE‐5) probe, the third phase of the Chinese Lunar Exploration Program launched in November 24, 2020. This mission collected 1,731 g of lunar regolith samples. The landing site of this mission is located within the northern Oceanus Procellarum (NOP) region. This region is dominated by basaltic lava flows and mare basalts should be the main components of the returned regolith samples. However, lunar impacts could transport materials laterally to large distances and modify the local compositions. In the present study, we employed FeO and thorium abundance data obtained by the Lunar Prospector Gamma Ray Spectrometer to investigate the chemical composition of the NOP. It was found that the mare plains in the CE‐5 landing site are contaminated with highland ejecta from nearby craters. Highland ejecta would expand Apollo and Luna sample collection diversity. Key Points: Highly evolved fragments from Aristarchus crater may be found in the Chang'E‐5 (CE‐5) regolith samplesThorium enrichments of Chang'E‐5 (CE‐5) landing site are due to the geochemical nature of local mare basalts rather than impact mixingThese non‐mare lithologies would expand the Apollo and Luna sample collection diversity [ABSTRACT FROM AUTHOR]

The impact melt that records the formation time of basins is essential for the understanding of the lunar bombardment history. To better understand melt distribution on the Moon, this study investigates mixing of melt by small impacts using a Monte Carlo numerical model. The obtained mixing behavior is then integrated into a larger scale model developed in previous work. While large impacts produce most of the melt volume in both the regolith and megaregolith, we find that the dominant source of melt near the surface is small impacts. Material in the top meter is affected mainly by impacts that form craters <5 km in diameter. In the uppermost 10 cm, melt with age <0.5 Ga is abundant; while as depth increases older melt is increasingly present. This may indicate that the excess of impact melt <0.5 Ga in lunar samples from the near surface is caused by the cumulative mixing of small impacts. A comparison of the age distribution of melt derived from craters of different sizes with that of impact glass constrains the size of spherule‐forming impacts. Our model is consistent with observations if most impact glass spherules from the near surface are produced by <100 m craters and >100 m craters do not contribute abundant spherules. The distribution of the datable melt with depth is also analyzed, which is essential for future sampling missions. Excavated materials of young and large craters (>100 m on highlands; >10 km on maria) appear to be the most fruitful targets. Plain Language Summary: Hypervelocity impact events on the Moon generate great energy that melts materials in the near‐surface. The generated melt products record the age of impact craters. The abundance of impact melts of different ages is therefore essential for our understanding of the lunar bombardment history. Most of the returned samples are derived from the near‐surface, where the material composition has been significantly affected by the frequent gardening of small impacts. Improving our understanding of how impact processes change the material composition is helpful for sample interpretations. Here, we build a numerical model to investigate this issue. The simulation results show that craters <100 m likely lead to the excess of datable impact melt <0.5 Ga that has been found in returned samples. In addition, we delineate the distribution of datable melt in various depths. It provides insight into future lunar missions aiming to collect melt that can be easier to date. We suggest that ejecta blankets of young and large craters (>100 m on highlands; >10 km on maria) would be the optimal targets. Key Points: A numerical model is developed to investigate the effect of small impact gardening on ancient melt in the lunar near‐surfaceGardening of craters <100 m in diameter likely lead to the excess of datable impact melt <0.5 Ga in lunar regolith samplesDistribution of radiometrically datable melt in the regolith and the megaregolith is analyzed [ABSTRACT FROM AUTHOR]

One of the most critical issues associated with the analysis of lunar seismic data is the intense scattering, which prevents precise seismic phase identifications, thereby resulting in poor constraints on the internal structure of the Moon. Although some studies estimated subsurface scattering properties from analyses of the Apollo seismic data, the properties have large uncertainties and are still open issues to be resolved to improve the inner structure model of the Moon. While the previous studies tried to constrain the scattering features within the lunar crust mainly from data analysis, this study estimated them from a numerical approach. We constrained the scattering properties near Apollo 12 landing site by conducting seismic wave propagation simulations under various parameter settings and comparing the synthetics with the data. As a result, we succeeded in reproducing seismic signals excited by the Apollo artificial impacts. This led to a constraint on the scattering properties, such as typical scale and thickness of heterogeneity, around the Apollo 12 landing site. The derived structure suggests that the intense scattering structure exists down to 20 km at the northern portion of the region of the Apollo 12 landing site, and to 10 km at the southern region from the landing site. In addition, our model requires a smaller P‐ and S‐wave velocity ratio (1.2–1.4) compared with those conventionally considered (>1.73). This implies a dry and porous environment consistent with laboratory measurements of terrestrial samples and reasonable with the generalized lunar environment. Plain Language Summary: A long‐duration and spindle shape characterizes the lunar seismic signals observed by the Apollo seismometers. The moonquakes typically last for 1 or 2 h, and the shape of the seismic wave reflects the internal environment of the Moon. From previous studies, these characteristics are estimated to be due to the subsurface fractured structure resultant from the continuous meteoroid impacts over a long period. Generally, it is required to precisely read seismic phases, like P or S, to determine a planetary inner structure. However, for the lunar case, it becomes more difficult to pick up the precise information because almost all phases are covered with intense seismic scattering, resulting in large uncertainties in the lunar internal structure. Therefore, it is paramount to reveal the scattering structure for a better understanding of the lunar seismic features and the inner structure. This study constrains the subsurface scattering structure around Apollo 12 landing site by modeling the Apollo seismic waves using numerical simulation of seismic wave propagation. Our simulations for various inner structure settings resulted in reproducing the Apollo seismic records very well, leading to constraining the scattering structure around the Apollo 12 landing site. Key Points: We simulated impact‐induced seismic waves on the Moon considering both scattering effects due to topography and subsurface heterogeneityTwo different scales of heterogeneity result in better modeling of the scattering structure of the upper lunar crustSignificant scattering structure is present around the Apollo 12 landing site down to 10‐20 km depth [ABSTRACT FROM AUTHOR]

In this work, we examine variations in the mantle uplift associated with large lunar impact craters and basins between major terranes. This study is based on Bouguer gravity anomalies of 100–650‐km diameter impact craters using Gravity Recovery and Interior Laboratory (GRAIL) observations and the Lunar Orbiter Laser Altimeter (LOLA) crater database. The Bouguer gravity anomalies of 324 large impact craters analyzed herein are primarily controlled by the uplifted crust‐mantle (Moho) interface in the central region of these impact craters, while postimpact mare deposits that represent ∼25%–35% of the postimpact deposit column also contribute to the gravity anomalies of mare craters. The central uplift of the Moho interface is primarily controlled by impact energy and increases to ∼ 30 km for a 650‐km diameter crater. Analyses of nonmare craters in the Feldspathic Highlands Terrane (FHT) with varied crustal thickness (Tc) reveal that the onset crater diameter (Dmin) with an uplifted Moho interface is dependent on the local Tc: Dmin ∼ 150 + 1.3Tc (in a unit of km). This equation also provides a quantification of the depth‐dependent attenuation of impact‐induced structural uplift, using the Moho uplift as a proxy for the structural uplift. The Moho uplift of large craters in the South Pole‐Aitken (SPA) Terrane is not statistically different from the FHT craters, consistent with limited overall thermal difference between these two terranes and compensational thermal effects at crater collapse and viscoelastic relaxation stages. Plain Language Summary: Gravitational signatures of impact basins reveal notable mantle uplifts under the basin floor. The mantle uplift is significant for lunar basins with a crater diameter larger than ∼ 200 km and is one of the main characteristics for peak‐ring and multiring basins. The magnitude of the mantle uplift increases with impact energy, which also correlates with crater diameter. It has been suggested that the target properties, including the crustal thickness and thermal state, affect the crater mantle uplift as well. In this study, we find that increasing crustal thickness reduces basin mantle uplift. But there is no statistical difference between the mantle uplifts of impact basins formed in the highlands and those in the South Pole‐Aitken basin. We attribute this to limited thermal differences between the two terranes in the pre‐Nectarian period, which is consistent with the hypothesized early lunar thermal evolution and impact chronology. The compensational thermal effects at the transient crater collapse and viscoelastic relaxation stages also help explain this statistical indistinguishability. Key Points: The minimum crater diameter for which impacts result in mantle uplift is positively correlated with local crustal thicknessGravity signatures of mare craters suggest that the mare deposits account for ∼ 25%–35% of the thickness of postimpact depositsStatistical indistinguishability between the SPA and FHT craters provides an upper limit on the effect of thermal difference [ABSTRACT FROM AUTHOR]

Mineral abundance and Mg# (100× molar Mg/(Mg + Fe)) are significant in understanding the crustal composition and thermal history of the Moon. In this study, we derive a new set of optical constants for olivine, orthopyroxene, and clinopyroxene using radiative transfer equations that include soil porosity and the opposition effect. Based on the new optical constants, we develop a mineral abundance and Mg# unmixing model, and build a spectral library composed of mineral mixtures of plagioclase, olivine, low‐Ca pyroxene (LCP) and high‐Ca pyroxene (HCP), and Mg# ranging within 40–90. The accuracy of this model in estimating mineral abundance and chemistry is better than 3 vol% for olivine, LCP and HCP, better than 6 vol% for plagioclase, and better than 10 for Mg#. This model is validated using forward and inverse modeling. For the forward modeling, we reproduce the spectra of powdered pure minerals and Lunar Sample Characterization Consortium (LSCC) lunar soils, and the modeled spectra are consistent with those measured in the laboratory. For the inverse modeling, we determined mineral abundances and Mg# of 19 LSCC soil spectra by searching the best match to the spectral library. The modeled mineral abundances of LSCC soils are consistent with those measured by X‐ray digital imaging. We derived a global Mg# map using our model and Moon Mineralogy Mapper images, and our Mg# map shows a peak concentration at 70, consistent with that measured by the Lunar Prospector gamma‐ray spectrometer. Plain Language Summary: The abundances of lunar major minerals plagioclase, olivine and pyroxenes and the chemistry of the olivine and pyroxene as the ratio of magnesium to iron (expressed as Mg/(Mg + Fe)) are significant in understanding how the lunar crust was formed and evolved. Based on the spectral characteristics of major minerals of the Moon, we developed a model that can calculate the abundances of plagioclase, olivine, orthopyroxene, clinopyroxene and the magnesium to iron ratio from spectral data at high accuracies. This model has been tested using lunar soil with known composition and pure minerals with known chemistries. We modeled the spectra of powdered pure olivine and pyroxene minerals and lunar soils, and the modeled spectra are consistent with the measured ones. Mineral abundances calculated from lunar soil spectra using this model show consistent values with those measured in the laboratory. We applied this model to lunar global spectral data and derived a map of the magnesium to iron ratio, and this map shows values consistent with that measured by the Gamma‐Ray spectrometer on board a lunar satellite called Lunar Prospector. This model is useful in deriving high‐spatial resolution mineralogy and magnesium to iron ratio maps for studying lunar crustal and mantle composition. Key Points: We provide a new set of optical constants for olivine, orthopyroxene, and clinopyroxeneWe present a mineral abundance and Mg# unmixing model based on radiative transfer theoryMg# map derived from our model is consistent with that from the Lunar Prospector [ABSTRACT FROM AUTHOR]

A new large‐scale map of the lunar crustal magnetic field at 30 km altitude covering latitudes from 65°S to 65°N has been produced using high‐quality vector magnetometer data from two complementary polar orbital missions, Lunar Prospector and SELENE (Kaguya). The map has characteristics similar to those of previous maps but better resolves the shapes and distribution of weaker anomalies. The strongest group of anomalies is located on the northwest side of the South Pole‐Aitken basin approximately antipodal to the Imbrium basin. On the near side, both strong isolated anomalies and weaker elongated anomalies tend to lie along lines oriented radial to Imbrium. These include named anomalies such as Reiner Gamma, Hartwig, Descartes, Abel, and Airy. The statistical significance of this tendency for elongated anomalies is verified by Monte Carlo simulations. Great circle paths determined by end points of elongated anomaly groups and the locations of five individual strong anomalies converge within the inner rim of Imbrium and intersect within the Imbrium antipode zone. Statistically significant evidence for similar alignments northwest of the Orientale basin is also found. The observed distribution of anomalies on the near side and the location of the strongest anomaly group antipodal to Imbrium are consistent with the hypothesis that iron from the Imbrium impactor was mixed into ejecta that was inhomogeneously deposited downrange in groups aligned radial to the basin and concentrated antipodal to the basin. Plain Language Summary: The origin of crustal magnetic anomalies on airless silicate bodies like the Moon in the solar system is a fundamental unresolved problem of planetary science. Here, we report production of a new large‐scale map of the lunar crustal field that better resolves the shapes and distribution of weaker anomalies. The strongest group of anomalies is located on the south‐central far side approximately antipodal (diametrically opposite) to the Imbrium impact basin. On the near side, both strong isolated anomalies and weaker elongated anomalies tend to lie along lines oriented radial to Imbrium. These include named anomalies such as Reiner Gamma, Hartwig, Descartes, Abel, and Airy. The statistical significance of this tendency is verified by Monte Carlo simulations. Great circle paths determined by end points of elongated anomaly groups and the locations of strong isolated anomalies converge within the inner rim of Imbrium and intersect within the Imbrium antipode zone. The observed distribution of anomalies is consistent with the hypothesis that iron from the Imbrium impactor was mixed into ejecta that was inhomogeneously deposited downrange in groups aligned radial to the basin and concentrated antipodal to the basin. Key Points: A new large‐scale map of the lunar crustal magnetic field covering most latitudes at a constant altitude of 30 km has been produced.Anomalies on the near side tend to be aligned radial to the Imbrium impact basin; the strongest anomalies are located antipodal to Imbrium.These results are consistent with the idea that iron from the Imbrium impactor was mixed into ejecta deposited downrange & at the antipode. [ABSTRACT FROM AUTHOR]

A recent large‐scale map of the lunar crustal magnetic field is examined for the existence of magnetic anomalies internal to ringed impact basins. It is found that, of 25 basins with upper preNectarian and younger ages, 18 contain mapped internal anomalies with amplitudes of at least 1 nT at 30 km altitude. Of these, five are most confidently judged to contain intrinsic anomalies (i.e., anomalies located within the inner basin rims and originating at the times of basin formation): Crisium, Humboldtianum, Mendel‐Rydberg, Moscoviense, and Nectaris. Comparing the anomaly distributions with previous numerical simulations of the impact of iron‐rich planetesimals to form a large (SPA‐sized) basin, inferences are drawn about the likely trajectories of the impactors. Specifically, results suggest that impactor trajectories for these basins were within ∼45° of being vertical and tended to lie on average parallel to the lunar equatorial plane and the ecliptic plane. Inverse modeling of anomalies within these basins yields inferred directions of magnetization that are difficult to reconcile with the axial centered dipole hypothesis for the geometry of the internal lunar dynamo field: Paleomagnetic pole positions are widely scattered and, in agreement with a recent independent study, the two main anomalies within Crisium yield significantly different directions of magnetization. Plain Language Summary: Magnetic anomalies in lunar impact basins are especially important because the interiors of the basins cooled very slowly requiring a steady, long‐lived magnetizing field to impart magnetization. They are the best orbital evidence for a former internal lunar dynamo field. In this study, five basins are selected that most confidently contain internal anomalies that are intrinsic to the basin, i.e., located within the inner basin rims and originating at the times of basin formation. Assuming that these internal anomalies are due to magnetization of impact melt containing iron from the impactor that created the basins, comparisons are made with previous numerical simulations to constrain the trajectories of the impactors. Results suggest that the five impactor trajectories were within roughly 45 degrees of being vertical and tended to lie on average parallel to the lunar equatorial plane and the ecliptic plane. Inverse modeling of the anomalies yields inferred directions of magnetization that are difficult to reconcile with the hypothesis that the lunar dynamo field originated in the small metallic core. Possible explanations include that the core dynamo behaved unlike the current terrestrial dynamo or that the magnetizing field was instead due to dynamo generation in an early shallow magma ocean. Key Points: Based on a recent field map, five lunar impact basins containing magnetic anomalies dating from the time of basin formation are identifiedAssuming that these anomalies are due to impactor‐added iron, inferences are drawn about the trajectories of the basin‐forming impactorsInverse modeling of the anomalies yields results that are difficult to reconcile with the centered, axially aligned core dynamo hypothesis [ABSTRACT FROM AUTHOR]

The position of the vapor‐liquid dome and of the critical point determine the evolution of the outermost parts of the protolunar disk during cooling and condensation after the Giant Impact. The parts of the disk in supercritical or liquid state evolve as a single thermodynamic phase; when the thermal trajectory of the disk reaches the liquid‐vapor dome, gas and melt separate leading to heterogeneous convection and phase separation due to friction. Different layers of the proto‐Earth behaved differently during the Giant Impact depending on their constituent materials and initial thermodynamic conditions. Here we use first‐principles molecular dynamics to determine the position of the critical point for NaAlSi3O8 and KAlSi3O8 feldspars, major minerals of the Earth and Moon crusts. The variations of the pressure calculated at various volumes along isotherms yield the position of the critical points: 0.5–0.8 g cm−3 and 5500–6000 K range for the Na‐feldspar, 0.5–0.9 g cm−3 and 5000–5500 K range for the K‐feldspar. The simulations suggest that the vaporization is incongruent, with a degassing of O2 starting at 4000 K and gas component made mostly of free Na and K cations, O2, SiO and SiO2 species for densities below 1.5 g cm−3. The Hugoniot equations of state imply that low‐velocity impactors (<8.3 km s−1) would at most melt a cold feldspathic crust, whereas large impacts in molten crust would see temperatures raise up to 30000 K. Plain Language Summary: The Moon was formed after the cooling and aggregation of the debris disk produced by the Giant Impact between a small planet in formation and the early Earth. To understand completely this process of cooling and aggregation, we need thermodynamic information about the constituents of the disk, like the position of the liquid‐vapor dome and also of the critical point, located at the top of this dome. Here we use a technique called first‐principles molecular dynamics and based on quantum chemistry to perform computational experiments on NaAlSi3O8 and KAlSi3O8 feldspars, major minerals of the Earth and Moon crusts. We performed calculations of the fluids evolution at temperatures typical of those of the debris disk (from 2000 to 7000 K) and at densities covering the liquid‐gas transition for these temperatures. We find the position of the critical points: 0.5‐0.8 g cm−3 and 5500–6000 K range for the Na‐feldspar, 0.5–0.9 g cm−3 and 5000–5500 K range for the K‐feldspar. The simulations suggest that the liquid and the gas have different compositions, mainly due to a degassing of O2 starting at 4000 K, and free components like Na, K, O2, SiO, and SiO2, which go preferentially inside the gas phase. The behavior of liquid feldspars at high density shows also that impacts from a low‐velocity object would at most melt a cold crust, whereas impacts in molten crust would see temperatures raising up to 30000 K. Key Points: First‐principles molecular dynamics simulations of feldspars at low density and high temperatureFree Na, K, and O2, SiO, or SiO2 constitute the first gas when the vaporization startsThe critical point of alkali feldspars is between 0.5 and 0.9 g cm−3 and 5000–6000 K [ABSTRACT FROM AUTHOR]

The refilling of the lunar wake is facilitated by the wake ambipolar electric potential arising from the electron pressure gradient. Incident solar wind protons can be reflected by the lunar crustal magnetic fields and the lunar surface on the dayside and repicked up, entering the lunar wake due to their large gyroradii. This burst of positive charges can cause the lunar wake potential to be reduced by hundreds of volts. We utilize over 7 years of ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun) measurements to systematically investigate how the reflected protons affect the lunar wake potential structure when the Moon is immersed in the solar wind. RPs have a peak occurrence rate of ∼20% for downstream distances from the Moon at N×2πRg and a preference of high occurrence rates and high densities in the direction of the motional electric field of the solar wind. We show that reflected protons in the lunar wake can significantly change the electrostatic ambipolar potentials in the wake, leading in turn to the formation of field‐aligned, accelerated electron beams. Our case study also suggests a nonmonotonic field‐aligned potential structure in the presence of reflected protons in the wake. Lastly, our results show that when the reflected proton density is larger than ∼30% of the local proton density from refilling solar wind protons, the wake potential scales as the logarithmic density of reflected protons, which can be explained by the Boltzmann relation. Key Points: Reflected protons (RPs) have peak occurrence rates of ∼20% downstream of the Moon in the lunar wake at N×2πRgWe infer a nonmonotonic field‐aligned potential structure in the presence of reflected protons in the wake for the first timeWhen RP density is above ∼30% of local solar wind proton density, the wake potential scales as the logarithmic density of RPs [ABSTRACT FROM AUTHOR]

The petrogenetic models of the lunar crust are built on the returned Apollo and Luna samples collected from limited parts of the lunar nearside that are chemically unusual (i.e., material rich in K, Rare Earth Elements, and P [KREEP]) and not representative of the entire lunar lithologic suite. The lunar Mg‐suite is part of this sample collection and ubiquitously has geochemical characteristics indicating the involvement of KREEP in their petrogenesis and seemed to be linked to the Procellarum KREEP Terrain (PKT). However, it is unclear if KREEP is necessary for Mg‐suite magmatism or whether Mg‐suite magmatism was a global event that occurred without significant KREEP contribution, and thus, Mg‐suite rocks outside of the PKT region may exist without containing a significant KREEP signature. Here, we investigate lunar meteorite Northwest Africa (NWA) 10401, an anorthositic troctolitic breccia with a granulitic texture. NWA 10401 shares many characteristics of Apollo Mg‐suite rocks: both its bulk rock composition and alumina content, as well as its mineralogy and mineral chemistry, are more consistent with typical Apollo Mg‐suite rocks, rather than ferroan anorthosites. In addition, olivine‐spinel equilibria calculations indicate that NWA 10401 is consistent with being derived from a common parent to the Apollo Mg‐suite troctolites. However, despite these many shared characteristics, NWA 10401 is strongly depleted in REE, starkly separating it from the typical Apollo Mg‐suite of the PKT. This indicates that NWA 10401 (and pairs) could represent a Mg‐suite component outside the PKT, and thus, KREEP‐poor Mg‐suite magmatism may have been a global phenomenon on the Moon. Plain Language Summary: Theories of the formation and evolution of the Moon's crust were built upon the returned Apollo and Luna samples that were collected from small areas of the Moon's nearside (the side that always faces Earth). These areas are now known to be chemically unusual and contain rocks that are rich in K, Rare Earth Elements (REE), and P, called KREEP. The lunar magnesian‐suite, or Mg‐suite, is part of this sample collection and represents a series of ancient rocks formed from slow cooling magmas that formed immediately after the end of magma ocean crystallization. Samples of this Mg‐suite always have chemical characteristics that indicate the involvement of KREEP in their formation, and they seemed to be linked to the Procellarum KREEP Terrain (PKT) on the Moon. However, it is unclear if (1) KREEP is needed for the formation of Mg‐suite magmatism, and thus, if Mg‐suite magmatism is limited to the geographically restricted PKT area, or (2) whether Mg‐suite magmatism was a global event that occurred without significant KREEP contribution. In this case, KREEP is simply a contamination in the Mg‐suite rocks. If (2) is true, Mg‐suite rocks outside of the PKT area on the Moon should be KREEP poor. In this study, we investigate the lunar feldspar‐rich meteorite called Northwest Africa (NWA) 10401 from the lunar highlands. Calculations indicate that NWA 10401 was produced by similar magmas that also produced the Apollo Mg‐suite troctolites. In addition, NWA 10401 shares all the characteristics of Mg‐suite rocks from the Apollo collection, except it is strongly depleted in REE. This indicates that NWA 10401 could represent a Mg‐suite rock that comes from an area other than the PKT, and thus, KREEP‐poor Mg‐suite magmatism may have been a global event on the Moon. Key Points: NWA 10401 records the highest known bulk Mg# of feldspathic lunar meteorites, with a value of 82NWA 10401 seems consistent with being derived from a common parent to the troctolites from the Apollo Mg‐suite but is KREEP poor based on major and trace element of mineral grains and bulk compositionsNWA 10401 could represent a KREEP‐poor Mg‐suite component outside the PKT indicating that Mg‐suite magmatism was not driven by KREEP and may have been a global occurrence [ABSTRACT FROM AUTHOR]

We present our latest high‐resolution lunar gravity field model of degree and order 1200 in spherical harmonics using Gravity Recovery and Interior Laboratory (GRAIL) data. In addition to a model with the standard spectral Kaula regularization constraint, we determine models by applying a constraint based on topography called rank‐minus‐one (RM1). The new models using this RM1 constraint have high correlations with topography over the entire degree range by design. The RM1 models allow the determination of apparent crustal densities at all spatial scales (called effective density) covered by the model, whereas the Kaula‐constrained model can only be used globally up to spherical harmonic degree 700. We find that the effective density spectrum has a smaller slope for the high degrees when compared to the medium degrees. We interpret this as indicative of a global average surface density, as opposed to an ever‐decreasing effective density as one approaches the surface. We use the RM1 models to derive maps of lateral and vertical density variations in the lunar crust. These models allow us to increase the resolution of this analysis compared to previous studies, by increasing the degree range over which to fit theoretical models of vertical density variations, and by decreasing the size of the spherical caps used in a localized analysis. Several regions on the Moon, such as South Pole‐Aitken and Mare Orientale, are distinct from their surroundings in terms of surface densities. The RM1 models are especially valuable in (localized) spectral studies of the structure of the lunar crust. Plain Language Summary: The Gravity Recovery and Interior Laboratory (GRAIL) mission was designed to investigate the Moon's interior structure and advance the knowledge of its history of heat flow by mapping the Moon's variations in its gravity field to high precision. We present new models of the Moon's gravity field (with a resolution of 4.5 km by 4.5 km at the Moon's equator), where we have used information of the Moon's topography. With such models, we can investigate the structure of the crust at all spatial scales, whereas standard models can only be used globally up to lower resolution (on average, 8 km by 8 km at the most). We find indications for a global average surface density, and we present maps of the lateral and vertical density structure of the Moon. Several regions, such as South Pole‐Aitken and Mare Orientale, stand out as having different surface densities from their surroundings. Owing to their high resolution and improved correlations with topography, our models will be especially useful in local studies of the structure of the Moon's crust. Key Points: We apply a special constraint based on topography to determine a high‐resolution lunar gravity field modelOur new model has high correlations with topography over its entire degree rangeWe derive maps for the vertical and lateral density structure of the Moon's crust at high resolution [ABSTRACT FROM AUTHOR]

We examined lithic breccias from the Apollo sample collection in order to identify ferroan anorthosite samples suitable for geochronology, and better define the age relationships between rocks of the lunar highlands. Clast 3A is a previously unstudied noritic anorthosite from Apollo 16 lithic breccia 60016 with textural evidence of slow subsolidus recrystallization. We estimate a cooling rate of ~10 °C/Myr and calculate a pyroxene solvus temperature of 1,100–1,000 °C. Pyroxene exsolution lamellae (1–3 μm) indicate that the last stage of cooling was rapid at ~0.2 °C/year, typical of rates observed in thick ejecta blankets. We calculate concordant ages from the 147Sm‐143Nd, 146Sm‐142Nd, Rb‐Sr, and Ar‐Ar isotopic systems of 4,302 ± 28, 4,296 + 39/−53, 4,275 ± 38, and 4,311 ± 31 Ma, respectively, with a weighted average of 4,304 ± 12 Ma. The closure temperature of the Sm‐Nd system is ~855 ± 14 °C, whereas the closure temperature of the Ar‐Ar system is 275 ± 25 °C. Cooling from 855 to 275 °C at 10 °C/Myr should result in an age difference between the two isotopic systems of ~60 Myr. The concordant Sm‐Nd, Rb‐Sr, and Ar‐Ar ages imply that they record the time the rock was excavated by a large impact from the midcrust. The ages clearly predate various late accretion scenarios in which an uptick in impacts at 3.8 Ga is preceded by a period of relative quiescence between 4.4 and ~4.1 Ga, and instead are consistent with decreasing accretion rates following the formation of the Moon. Plain Language Summary: We investigated a previously unexamined Apollo 16 ferroan anorthosite rock to study the timing of the formation of the lunar crust. Ferroan anorthosites are important because they are thought to be the oldest formed part of the lunar crust. Using three different isotopic geochronology methods, we determined that this rock (Clast 3A) is approximately 4.3 billion years old. The age is slightly younger than all but one recently dated ferroan anorthosite rock. The geology and textures of Clast 3A indicate that it formed deep within the lunar crust. The different dating methods record the age of the rock different temperatures. The Sm‐Nd clock records the time when the rock cooled below about 855 °C, and the Ar‐Ar clock records a temperature of about 275 °C. Identical ages determined from the two isotopic systems indicate that the rock experienced rapid cooling from above 855 °C to below about 275 °C. It appears that Clast 3A formed deep within the crust, but was then excavated 4.3 billion years ago by a massive cratering event. This implies that large basin forming impact events occurred on the Moon early in its history and not just around 3.8 billion years ago during the Late Heavy Bombardment. Key Points: Several different radiometric systems provide common ages of approximately 4.3 Ga for the previously unstudied Apollo 16 Anorthosite Clast 60016,3ALunar anorthosite Clast 60016,3A provides evidence for a basin‐forming impact at approximately 4.3 GaThis has implications on the timing of the Late Accretion [ABSTRACT FROM AUTHOR]

In this study, the micromechanical interparticle contact behavior of "De NoArtri" (DNA‐1A) grains is investigated, which is a lunar regolith simulant, using a custom‐built micromechanical loading apparatus, and the results on the DNA‐1A are compared with Ottawa sand which is a standard quartz soil. Material characterization is performed through several techniques. Based on microhardness intender and surface profiler analyses, it was found that the DNA‐1A grains had lower values of hardness and higher values of surface roughness compared to Ottawa sand grains. In normal contact micromechanical tests, the results showed that the DNA‐1A had softer behavior compared with Ottawa sand grains and that cumulative plastic displacements were observed for the DNA‐1A simulant during cyclic compression, whereas for Ottawa sand grains elastic displacements were dominant in the cyclic sequences. In tangential contact micromechanical tests, it was shown that the interparticle friction values of DNA‐1A were much greater than that of Ottawa sand grains, which was attributed to the softer contact response and greater roughness of the DNA‐1A grains. Widely used theoretical models both in normal and tangential directions were fitted to the experimental data to obtain representative parameters, which can be useful as input in numerical analyses which use the discrete element method. Plain Language Summary: Lunar regolith simulants comprise natural soils found on Earth or artificially created materials which mimic the properties of the real lunar surface soil. Understanding the behavior of these simulants can help researchers to prepare for further explorations and settling of facilities on the Moon. In this study, an attempt is made to examine in the laboratory the behavior of the lunar regolith simulant "De NoArtri" (DNA‐1A), and the results are compared with a standard soil of quartz grains to understand the differences and obtain insights into the properties of the lunar simulant. The behavior of regolith simulant is compared with Ottawa sand grains to understand the differences between these two materials in terms of material properties as well as micromechanical behavior. This micromechanical behavior gives a fundamental understanding of the mechanical response of the material and can provide important parameters to be further utilized in computer simulations so that settling of facilities on the Moon surface can be designed safely. Key Points: The interface properties of DNA‐1A lunar regolith simulant and Ottawa sand were studied with an advanced grain‐scale apparatusDNA‐1A had much lower normal contact stiffness but higher interparticle friction angles compared with Ottawa sandAnalytical model by Yimsiri and Soga (2000, https://doi.org/10.1680/geot.2000.50.5.559) in the normal direction fits well the experimental curves for the entire span of displacements [ABSTRACT FROM AUTHOR]

Lunar cumulate mantle overturn has been proposed to explain the abundances of TiO2 and heat‐producing elements (U, Th, and K) in the source region of lunar basalts. Ilmenite‐bearing cumulates (IBCs) that were formed near the end of lunar magma ocean solidification are the driving force for overturn. IBCs are enriched with dense TiO2 and FeO contents and have lower viscosity and solidus than those of the underlying lunar cumulate mantle. We investigate the effects of temperature‐ and ilmenite‐dependent mantle rheology on the dynamic process of lunar cumulate mantle overturn and conditions for long‐wavelength downwellings of an IBC layer in a 3‐D spherical geometry. Our results show that the ilmenite‐induced rheological weakening is necessary to decouple the IBC layer from the top stagnant lid and facilitate overturn. Models with IBC viscosity derived from the experimental scaling can only produce short‐wavelength downwellings (spherical harmonic degree >3) and show an overturn timescale more than 100 Ma. A viscosity of the IBC layer at least 10−4 lower than that of the ambient mantle can produce the long‐wavelength (spherical harmonic degree ≤3) downwellings in ~10 Ma and even a hemispheric downwelling. Such low IBC viscosity requires additional weakening mechanisms, such as remelting or/and water enrichment. During the overturn, the cold downwellings displace upward the materials from hot lower mantle and produce partial melting in upper mantle, which may serve as a viable mechanism for early lunar magmatisms. The settling of cold downwellings on the core‐mantle boundary stimulates a transient high heat flux, which may contribute to generating an early lunar dynamo event. Key Points: A small viscosity of ilmenite‐bearing cumulates beneath the lunar crust is necessary to facilitate the overturn after the lunar magma oceanTo generate a hemispheric downwelling, additional weakening mechanisms other than low IBC viscosity are requiredThe overturn produces a large amount of melting and a transient high CMB heat flux [ABSTRACT FROM AUTHOR]

The megaregolith of the Moon is the upper region of the crust, which has been extensively fractured by intense impact bombardment. Little is known about the formation and evolution of the lunar megaregolith. Here we implement the Grady‐Kipp model for dynamic fragmentation into the iSALE shock physics code. This implementation allows us to directly simulate tensile in situ impact fragmentation of the lunar crust. We find that fragment sizes are weakly dependent on impactor size and impact velocity. For impactors 1 km in diameter or smaller, a hemispherical zone centered on the point of impact contains meter‐scale fragments. For an impactor 1 km in diameter this zone extends to depths of 20 km. At larger impactor sizes, overburden pressure inhibits fragmentation and only a near‐surface zone is fragmented. For a 10‐km‐diameter impactor, this surface zone extends to a depth of ~20 km and lateral distances ~300 km from the point of impact. This suggests that impactors from 1 to 10 km in diameter can efficiently fragment the entire lunar crust to depths of ~20 km, implying that much of the modern day megaregolith can be created by single impacts rather than by multiple large impact events. Plain Language Summary: The Moon's surface has experienced eons of bombardment by asteroid impacts. This bombardment is thought to have thoroughly shattered the lunar crust, the outermost layer of the Moon, to depths of 20 km or more. Despite this, the processes of fracturing and fragmentation during an asteroid impact have received little attention though. In this study, we simulated asteroid impacts and tracked how impacts shatter the lunar crust. We found that impacts break the lunar crust into roughly meter‐sized blocks. Impacts can break up the lunar crust down to approximately 20 km, and objects greater than 1 km in diameter are the most efficient at fragmenting the crust. This implies that the fragmented bedrock can be almost exclusively created by large‐scale high‐speed impacts and the lunar crust was thoroughly fractured early in its history. Similarly, impacts likely shattered the crust of the ancient Earth and Mars. Understanding how thoroughly fractured ancient planetary crusts are may help us determine if and when these environments became habitable. Key Points: Dynamic fragmentation has been included in an Eulerian hydrocode to study the development of megaregolith in the lunar highlandsImpacts substantially fragment the lunar crust down to tens of kilometers, limited only by overburden pressureLarge impactors considerably fragment the lunar crust hundreds of kilometers away from the point of contact and several kilometers deep [ABSTRACT FROM AUTHOR]

Highlights • A novel temperature measuring system for deep lunar regolith drilling exploration. • Measure the temperature of a rotating and penetrating drill to a depth of 2 m. • Succeed in measuring the temperature generated in drilling lunar regolith simulant. Abstract A novel temperature measuring system for deep lunar regolith drilling exploration is proposed herein. This system can be used to measure not only the temperature of a rotating and penetrating drill tool, but also the temperature of a lunar regolith simulant, to a maximum depth of 2 m inside a simulated lunar vacuum environment. This technique uses thermocouples and platinum resistors that are integrated into the drill tool and the lunar regolith simulant, respectively, and positioned as closely as possible to different measuring positions. To transmit and collect the temperature signals, a data condition system and a slip ring are specially incorporated to avoid wire wrapping and to transmit signals outside a vacuum environment. This system is shown to be successful in measuring the temperature generated in deep lunar regolith simulant drilling. The experimental results indicate the efficiency of this technique. [ABSTRACT FROM AUTHOR]

Abstract The innermost ring in impact basins exposes material originating from various depths, and can be used to study the composition of the lunar crust with depth. In this study, we conduct quantitative mineralogical analyses of the innermost ring in 13 lunar impact basins using reflectance data from the Kaguya Multiband Imager and radiative transfer modeling. We use results from recent hydrocode modeling to calculate the depth of origin of the material exposed by the innermost rings. We find that the most abundant rock type on the innermost ring of most basins is anorthosite. The mafic assemblages are dominated by olivine in some cases, but most often by pyroxene. The impact modeling suggests that the innermost ring material was excavated from a wide range of depths. Here we focus on two mean depths: a crustal component and a mantle component. The crustal component largely dominates the innermost ring material, and the mantle component is present on the innermost ring of 9 of the basins we studied. On these 9 rings, the abundance of low-calcium pyroxene decreases with the proportion of crustal component, suggesting a dominantly mantle origin. However, as we do not detect exposures of ultramafic material, such mantle material is possibly present at the sub-pixel scale (<62 m). This quantitative study reassesses the composition of the lunar crust and upper mantle, which is of great importance for understanding the formation of the Moon. Highlights • We conduct a quantitative mineral analysis of the inner ring of 13 impact basins. • We use radiative transfer modeling and near-infrared images at 60 m resolution. • Hydrocode impact modeling is used to link detected compositions to depths of origin. • The most abundant rock type on the innermost ring of most basins is anorthosite. • A small portion of the inner ring material of 9 basins may originate from the mantle. [ABSTRACT FROM AUTHOR]

Moon Mineralogy Mapper spectroscopic data were used to investigate the mineralogy of a selection of impact craters' central peaks or peak rings, in order to characterize the lunar crust‐mantle interface, and assess its lateral and vertical heterogeneity. The depth of origin of the craters' central peaks or peak rings was calculated using empirical equations, and compared to Gravity Recovery and Interior Laboratory crustal thickness models to select craters tapping within +10/−20 km of the crust‐mantle interface. Our results show that plagioclase is widely detected, including in craters allegedly sampling lower crustal to mantle material, except in central peaks where Low‐Calcium Pyroxene was detected. Olivine detections are scarce, and identified in material assumed to be derived from both above and below the crust‐mantle interface. Mineralogical detections in central peaks show that there is an evolution of the pyroxene composition with depth, that may correspond to the transition from the crust to the mantle. The correlation between High‐Calcium Pyroxene and some pyroxene‐dominated mixture spectra with the location of maria and cryptomaria hints at the existence of lateral heterogeneities as deep as the crust‐mantle interface. Plain Language Summary: This study surveys the mineralogy of 36 lunar impact craters scattered across the lunar surface. All these craters present a central peak or peak ring, inherited from the impact, where material from depth was brought up to the surface. According to our calculations, these craters should sample material originating from as deep as the interface between the crust and the mantle (+10/−20 km). We make use of visible near‐infrared spectroscopy (we investigate the light that is reflected from the lunar surface) in order to infer the central peaks compositions. We detected several minerals within the craters, including plagioclase, olivine, spinel, and pyroxene. An evolution of the composition of pyroxene (from High‐Calcium to Low‐Calcium) is observed with depth. We also demonstrate the presence of lateral heterogeneities within the crust and at the crust/mantle interface. Key Points: Plagioclase is widely detected in the central peaks of craters allegedly sampling the lower crust or mantle, except where LCP is observedLateral heterogeneities at the crust‐mantle interface and a pyroxene compositional evolution with depth (from HCP to LCP) were observedThis study's mineralogical observations support the GRAIL crustal thickness model 1 better than the model 3 [ABSTRACT FROM AUTHOR]

Multiring basins dominate the crustal structure, tectonics, and stratigraphy of the Moon. Understanding how these basins form is crucial for understanding the evolution of ancient planetary crusts. To understand how preimpact thermal structure and crustal thickness affect the formation of multiring basins, we simulate the formation of lunar basins and their rings under a range of target and impactor conditions. We find that ring locations, spacing, and offsets are sensitive to lunar thermal gradient (strength of the lithosphere), temperature of the deep lunar mantle (strength of the asthenosphere), and preimpact crustal thickness. We also explore the effect of impactor size on the formation of basin rings and reproduce the observed transition from peak‐ring basins to multiring basins and reproduced many observed aspects of ring spacing and location. Our results are in broad agreement with the ring tectonic theory for the formation of basin rings and also suggest that ring tectonic theory applies to the rim scarp of smaller peak‐ring basins. Plain Language Summary: The largest impact craters on the Moon are multiring basins that exhibit three or more topographic rings. Great volumes of material were ejected and redistributed during the formation of these 1,000‐km‐scale basins. Formation of these basins is the predominant process driving change of the lunar crust, the outermost layer of the Moon. Why large basins have multiple topographic rings and what they might tell us about the Moon remain poorly understood. Here we simulate the formation of these basins and their rings during an asteroid impact. We explore how thickness of the lunar crust, size of the impacting body, and interior temperature of the Moon affect the formation of basins and their rings. With well‐persevered multiring basins and an abundance of high‐quality gravity and topography data, the Moon is an ideal location to explore the formation of multiring basins. A better understanding of the formation of these basins will help us understand how similar basins may have affected the crusts of the Earth, Mars, Mercury, and Venus. Key Points: We simulate the formation of multiring basins exploring the effect of impactor size, target thermal structure, and crustal thicknessOur simulations reproduce observed trends in ring spacing including the transition from peak‐ring to multiring structuresOur results show that basin ring formation is quite sensitive to target thermal structure in general agreement with ring tectonic theory [ABSTRACT FROM AUTHOR]

We conducted a detailed photogeological analysis of the northern portion of the South Pole‐Aitken (SPA) basin (10–60°S, 125–175°W) and compiled a geological map (1:500,000 scale) of this region. Our new absolute model age for the Apollo basin, 3.98 + 0.04/−0.06 Ga, provides a lower age limit for the formation of the SPA basin. Some of the plains units in the study area were formed by distal ejecta from remote craters and basins. The characteristic concentrations of FeO and TiO2 of other plains are indicative of their volcanic origin. The oldest volcanic materials occur near the center of the SPA basin and have an Early Imbrian age of ~3.80 + 0.02/−0.02 Ga. Late Imbrian volcanic activity occurred in and around the Apollo basin. In total, the volcanic plains cover ~8% of the map area and cannot account for the extensive SPA iron signature. The sources of the signature are the oldest materials on the SPA floor (FeO ~11–14.5 wt%). In contrast, the ejecta composing the SPA rim are significantly poorer in FeO (<7.5 wt%). The signature could be related to the differentiation of the SPA impact melt. However, the spatial segregation of the ancient iron‐rich and iron‐poor materials suggests that the SPA iron signature predated the basin. Thus, the signature might be explained by a pre‐SPA lunar crust that was stratified with respect to the iron concentrations, so that the SPA impact excavated the upper, iron‐poorer portion of the crust to form the SPA rim and exposed the deeper, iron‐richer portion on the floor of the basin. Plain Language Summary: We conducted a geological analysis of the northern portion of the South Pole‐Aitken basin, which is the largest recognized and likely the oldest impact structure on the Moon. Results of our mapping efforts permitted the unraveling of the major sequence of impact and volcanic events that have shaped the basin throughout its evolution and resulted in the discovery of the oldest materials related to the basin formation. Analysis of the distribution and concentrations of iron and titanium in the materials of different age within the South Pole‐Aitken basin allows the characterization of the structure of the ancient lunar crust and mantle. These results introduce important constraints on the current models of the early evolution of the Moon. Key Points: A geological map of the northern portion of South Pole‐Aitken basin was madeConfirmed and potential volcanic materials make up ~8% of the basin floorThe pre‐SPA lunar crust was likely stratified with respect to iron [ABSTRACT FROM AUTHOR]

Based on Gravity Recovery and Interior Laboratory (GRAIL) observations and the Lunar Orbiter Laser Altimeter (LOLA) crater database, we constrain the spatial variations in the Moon's crustal porosity (ϕc) to a depth of several kilometers using the gravity anomalies of 4,864 midsized craters (those with a diameter of 20–100 km). For each crater, we estimated the local ϕc by quantifying the gravitational effects of impact‐induced porosity change and postimpact breccia infill. The crustal porosity model was uniquely determined assuming a global mean ϕc of 12%, although a trade‐off exists between the porosity of postimpact breccia infill and the (preimpact) crustal porosity that results in zero net porosity change underlying the crater floor. At this crustal porosity the effects of impact bulking and compaction compensate each other to yield zero crater residual Bouguer anomaly (RBA), when the effect of postimpact infill is excluded. For lower crustal porosities, bulking dominates to produce a negative RBA; for higher crustal porosities, compaction dominates to produce a positive RBA. Spatial kriging and statistical tests suggest lower‐than‐average ϕc in the western nearside maria and southern South Pole‐Aitken (SP‐A) basin, in contrast to higher‐than‐average values in the southwestern periphery of the nearside maria. Most of the large impact basins, presumably formed before the majority of the midsized craters we analyzed, show reduced porosities relative to their immediate surroundings. Plain Language Summary: Because the Moon lacks plate tectonics and surface erosion, its crustal structure has been preserved since the Late Heavy Bombardment ~3.9 billion years ago. The porosity structure of the lunar crust provides critical information on the early cratering history and the formation of major impact basins. Anomalously low crustal porosity implies the existence of relatively young volcanic deposits. In addition, the early porosity evolution of the Moon sheds lights on the origin of life as similar processing acting on the Earth created heat and pore space (as water conduits) to support life on Earth. This study uses 4,864 midsized craters as probes into the internal porosity structure of the lunar crust, which is one of the primary objectives of the Gravity Recovery and Interior Laboratory mission. For each midsized crater, we inverted the observed crater gravity signature for local crustal porosity. We then applied spatial statistical technique to map the regional‐scale variations in the crustal porosity and related the porosity variations with the major geologic units, including the nearside maria, highlands, South Pole‐Aitken basin, and other impact basins. This study shows that midsized craters are useful for detecting regional‐scale porosity structure that has long been established in the lunar evolution history. Key Points: Crater gravity anomalies are useful for constraining spatial variations in the crustal porosityWestern nearside maria and the southern South Pole‐Aitken (SP‐A) basin are associated with relatively low crustal porositySouthwestern periphery of the nearside maria and surroundings of most large impact basins show relatively high crustal porosity [ABSTRACT FROM AUTHOR]

We present crystallization experiments on silicate melt compositions related to the lunar magma ocean (LMO) and its evolution with cooling. Our approach aims at constraining the primordial internal differentiation of the Moon into mantle and crust. We used graphite capsules in piston cylinder (1.35–0.80 GPa) and internally-heated pressure vessels (<0.50 GPa), over 1580–1020 °C, and produced melt compositions using a stepwise approach that reproduces fractional crystallization. Using our new experimental dataset, we define phase equilibria and equations predicting the saturation of liquidus phases, magma temperature, and crystal/melt partitioning for major elements relevant for the crystallization of the LMO. These empirical expressions are then used in a forward model that predicts the liquid line of descent and crystallization products of a 600 km-thick magma ocean. Our results show that the effects of changes in the bulk composition on the sequence of crystallization are minor. Our experiments also show the crystallization of a silica phase at ca. 1080 °C and we suggest that this phase might have contributed to the building of the lower anorthositic crust. Calculation of crustal thickness clearly shows that a thin crust similar to that revealed by GRAIL cannot have been generated through solidification of whole Moon magma ocean. We discuss the role of magma ocean depth, trapped liquid fraction (with implication for the alumina budget in the mantle and the crust), and the efficiency of plagioclase flotation in producing the thin crust. We also constrain the potential range of pyroxene compositions that could be incorporated into the crust and show that delayed crustal building during ca. 4% LMO crystallization on the nearside of the Moon may explain the dichotomy for Mg-number. Finally, we show that the LMO can produce magnesian anorthosites during the first stages of plagioclase crystallization. [ABSTRACT FROM AUTHOR]

Abstract: This study presents the petrography, mineralogy, and bulk composition of lunar regolith breccia meteorite Northwest Africa (NWA) 7948. We identify a range of lunar lithologies including basaltic clasts (very low‐titanium and low‐titanium basalts), feldspathic lithologies (ferroan anorthosite, magnesian‐suite rock, and alkali suite), granulites, impact melt breccias (including crystalline impact melt breccias, clast‐bearing impact melt breccias, and glassy melt breccias), as well as regolith components (volcanic glass and impact glass). A compositionally unusual metal‐rich clast was also identified, which may represent an impact melt lithology sourced from a unique Mg‐suite parent rock. NWA 7948 has a mingled bulk rock composition (Al2O3 = 21.6 wt% and FeO = 9.4 wt%) and relatively low concentrations of incompatible trace elements (e.g., Th = 1.07 ppm and Sm = 2.99 ppm) compared with Apollo regolith breccias. Comparing the bulk composition of the meteorite with remotely sensed geochemical data sets suggests that the sample was derived from a region of the lunar surface distal from the nearside Th‐rich Procellarum KREEP Terrane. Our investigations suggest that it may have been ejected from a nearside highlands‐mare boundary (e.g., around Mare Crisium or Orientale) or a cryptomare region (e.g., Schickard‐Schiller or Mare smythii) or a farside highlands‐mare boundary (e.g., Mare Australe, Apollo basin in the South Pole–Aitken basin). The distinctive mineralogical and geochemical features of NWA 7948 suggest that the meteorite may represent lunar material that has not been reported before, and indicate that the lunar highlands exhibit wide geological diversity. [ABSTRACT FROM AUTHOR]

Abstract: Anorthosites that comprise the bulk of the lunar crust are believed to have formed during solidification of a lunar magma ocean (LMO) in which these rocks would have floated to the surface. This early flotation crust would have formed a thermal blanket over the remaining LMO, prolonging solidification. Geochronology of lunar anorthosites indicates a long timescale of LMO cooling, or remelting and recrystallization in one or more late events. To better interpret this geochronology, we model LMO solidification in a scenario where the Moon is being continuously bombarded by returning projectiles released from the Moon‐forming giant impact. More than one lunar mass of material escaped the Earth‐Moon system onto heliocentric orbits following the giant impact, much of it to come back on returning orbits for a period of 100 Myr. If large enough, these projectiles would have punctured holes in the nascent floatation crust of the Moon, exposing the LMO to space and causing more rapid cooling. We model these scenarios using a thermal evolution model of the Moon that allows for production (by cratering) and evolution (solidification and infill) of holes in the flotation crust that insulates the LMO. For effective hole production, solidification of the magma ocean can be significantly expedited, decreasing the cooling time by more than a factor of 5. If hole production is inefficient, but shock conversion of projectile kinetic energy to thermal energy is efficient, then LMO solidification can be somewhat prolonged, lengthening the cooling time by 50% or more. [ABSTRACT FROM AUTHOR]