Lunar Material Research Articles

Assessment of geotechnical properties of lunar soil simulant’s for lunar missions

Prototype-based experimental studies at the simulated environmental conditions are essential for the planned Chandrayaan missions of the Indian Space Research Organization (ISRO). A large quantity of lunar simulants was needed to prepare the lunar surface testbed, which cost more expensive to import. Therefore, the ISRO has intended to develop an indigenous new lunar simulant. All the available lunar soil simulants have been developed to mimic the actual lunar soil properties. Likewise, the new lunar soil simulant should mimic the properties of actual lunar soil. Hence, it is essential to examine the fidelity and properties of the existing lunar simulants with the actual lunar soil. This paper reviews the chemical composition, mineralogy, geotechnical and geomechanical properties of the past developed lunar simulants (mare and highland simulants) with actual lunar soils. Also, the review has provided an increased understanding of previous research on lunar soil development methods and materials used. Both mare and highland simulants discussed have variations with actual lunar soil; because the lunar simulants have been tested in the terrestrial environment, which can have significant effects on results. The variations between terrestrial simulants and lunar regolith and the related engineering implications are discussed.

An experimental investigation of F, Cl and H2O mineral-melt partitioning in a reduced, model lunar system

It is believed that the Moon formed following collision of a large planetesimal with the early Earth. Over the ∼4 Gyr since this event the Moon has been considerably less processed by geological activity than the Earth, and may provide a better record of processes and conditions in the early Earth-Moon system. There have been many studies of magmatic volatiles such as H, F, Cl, S and C in lunar materials. However, our ability to interpret variable volatile contents in the lunar sample suite is dependent on our understanding of volatile behaviour in lunar systems. This is currently constrained by limited experimental data. Here, we present the first experimental mineral-melt partitioning coefficients for F, Cl and H2O in a model lunar system under appropriately reduced conditions (log fO2 to IW-2.1, i.e. oxygen fugacity down to 2.1 log units below the Fe-FeO buffer). Data are consistent with structural incorporation of F, Cl and OH− in silicate melt, olivine and pyroxene under conditions of the lunar mantle. Oxygen fugacity has a limited effect on H2O speciation, and partitioning of H2O, F and Cl is instead largely dependent on mineral chemistry and melt structure. Partition coefficients are broadly consistent with a mantle source region for lunar volcanic products that is significantly depleted in F, Cl and H2O, and depleted in Cl relative to F and H2O, compared to the terrestrial mantle. Partitioning data are also used to model volatile redistribution during lunar magma ocean (LMO) crystallisation. The volatile content of lunar mantle cumulates is dependent upon proportion of trapped liquid during LMO solidification. However, differences in mineral-melt partitioning during LMO solidification can result in significant enrichment on F relative to Cl, and F relative to H2O, in cumulate phases relative to original LMO composition. As such, Cl depletion in lunar volcanic products may in part be a result of LMO solidification.

The spectral radiance of indirectly illuminated surfaces in regions of permanent shadow on the Moon

Regions of permanent shadow at the lunar poles have been suggested to host water ice and potentially other volatile compounds owing to their extremely low temperatures. Imaging in permanent shadow using indirect lighting from nearby topographic highs illuminated by the Sun has demonstrated the feasibility of optical remote sensing of permanent shadow surfaces, and a near-IR detection of water ice spectral features demonstrates the ability to collect usable spectroscopic data. The infrared emission of the lunar surface is largely in radiative equilibrium, so the temperature of surfaces in permanent shadow is driven by the intensity of the indirect illumination. This means that surfaces at very low temperatures, of high interest owing to their ability to trap and retain volatile compounds, will be the most challenging to measure.We provide estimates of indirect spectral radiance as a function of permanent shadow temperature from 400 nm to 14 μm using empirical data on permanent shadow temperature and broadband visible and near IR radiance, coupled with known reflectance properties of lunar materials. The relationships show there is ample radiance and photon radiance for reflectance imaging and spectroscopy from 400 nm to 8 μm at temperatures of regions of permanent shadow above 60K with appropriately designed instruments. Beyond 8 μm lunar spectral properties reduce the available radiance substantially, making reflectance observations challenging.

Dielectric Properties of Lunar Subsurface Materials

AbstractThe 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.

Lunar Surface and Buried Rock Abundance Retrieved from Chang’E-2 Microwave and Diviner Data

Abstract Microwave emission of the Moon, measured by the Chang’E-2 Microwave Radiometer (MRM), provides an effective way to understand the physical properties of lunar near-surface materials. The observed microwave brightness temperature is affected by near-surface temperatures, which are controlled by the surface albedo, roughness, regolith thermophysical properties, and the high thermal inertia and permittivity of both surface and buried rocks. In this study, we propose a rock model using thermal infrared measurements from the Lunar Reconnaissance Orbiter's (LRO) Diviner as surface temperature constraints. We then retrieve the volumetric rock abundance (RA) from nighttime MRM data at several rocky areas. Although our retrieved MRM RA cannot be compared to the rock concentration measured with LRO Camera images directly, there is a good agreement with Diviner-derived RA and radar observations. The extent of several geological units, including rocky craters, hummocky regions, and impact melts, agree well with the distribution of elevated rock concentration. Based on seven large craters with published model ages, we present an inverse correlation between rock concentration and crater age. The result shows that the rock concentration decreases with crater age rapidly within 1 Ga but declines slowly after that. These data are consistent with a short survival time for exposed rocks and a long lifetime for buried rocks that are shielded from lunar surface processes.

Radiation dose and its protection in the Moon from galactic cosmic rays and solar energetic particles: at the lunar surface and in a lava tube

The lunar surface is directly and continuously exposed to Galactic Cosmic ray (GCR) particles and Solar energetic particles (SEPs) due to the lack of atmosphere and lunar magnetic field. These charged particles interact with the lunar surface materials producing secondary radiations such as neutrons and gamma rays. In a departure from precise GCR and SEP data, we estimated the effective dose equivalent at the lunar surface and in a lunar lava tube in this paper by using PHITS, a Monte Carlo simulation tool. The effective dose equivalent due to GCR particles at the lunar surface reached 416.0 mSv yr−1 and that due to SEPs reached 2190 mSv/event. On the other hand, the vertical hole of the lava tube provides significant radiation protection. The exposure by GCR particles at the bottom of the vertical hole with a depth of 43 m was found to be below 30 mSv yr−1 while inside a horizontal lava tube, the value was less than 1 mSv yr−1 which is the reference value for human exposure on the Earth. We expect that the lunar holes will be useful components in the practical design of a lunar base to reduce radiation risk and to expand mission terms.

Lunar regolith and substructure at Chang’E-4 landing site in South Pole–Aitken basin

The South Pole–Aitken (SPA) basin is the oldest and largest impact structure on the Moon, and it gives particular insight on the lunar interior composition1–3. However, the surface of the SPA basin has been substantially modified by consequent impacts and basalt flooding. The exploration of the surficial material and the substructure of the SPA basin is one of the main scientific goals of the Chinese spacecraft Chang’E-4 that landed in the Von Karman crater inside the SPA basin4,5. Here we report the lunar penetrating radar profiles along the track of the lunar rover Yutu-2, which show a three-unit substructure at the landing site. The top unit consists of the ~12-m-thick lunar regolith and ~120 m multilayered ejecta that were delivered from several adjacent craters. The middle unit is the mare basalts filling the Von Karman crater. The lowest unit is another ejecta layer with a thickness of ≥200 m, likely from the Leibnitz crater. These discoveries fully support the local stratigraphy and geological explanation presented previously6. Our results reveal that the surface materials at the Chang’E-4 landing site are unambiguously dominated by the ejecta from the Finsen crater with a minor contribution from other neighbouring craters. The regolith measured by Yutu-2 is representative of the initial lunar deep interior materials, rather than the later erupted basalts. Three different layers can be distinguished in the first 500 metres of depth beneath the South Pole–Aitken basin on the Moon: a first layer made up by regolith and ejecta material from different craters, followed by a middle unit of mare basalts and finally a >200-m-thick layer of ejecta from the Leibnitz crater.

Profiling lunar dust dissolution in aqueous environments: The design concept

Published studies and internal NASA reports indicate that when native lunar dust is suspended in an aqueous solution a variety of metal and other ions are released. This release has implications for future lunar missions, ranging from effects on mission hardware, effects on life support systems, possible direct effects on human health, and effects on research experiments such as plant growth experiments, space biology experiments and any activities that may involve the use of water sourced from the lunar poles. Furthermore, such contaminants could become concentrated or chemically altered to a more hazardous form during a variety of lunar mission activities, including everything from space suit cleaning to lunar industrial materials extraction. The exact profile of the release of ions from lunar dust and the nature of the partially dissolved particles has not been explored. Any model of this dissolution must be based on an understanding of the unique micromorphology of lunar dust, including its glassy nature, agglutinate features, high surface area and the presence of small deposits of elemental iron (nanophase iron) located near the surface of the grain particles. Dust has a very high surface area available for interaction with water. For this reason, on first exposure to water, an immediate pulsed release of ions could occur, with more prolonged release taking place over months or years. The few studies that have been conducted previously have been limited in both the time scales examined and in the selection of ions that were measured. The proposed investigation is a comprehensive materials science investigation, using the most modern analytical tools to catalogue all metals given off from lunar dust in various aqueous solutions and their time profiles of release from the very short term to the very long term. The product of the proposed study will be a comprehensive database determined from NASA curated samples collected from the Apollo landing sites that can be applied to research in both living systems and non-living systems on the moon. The methods developed in the proposed study will also establish standards for analysis of lunar dust samples returned from future manned missions (Artemis and others) and future robotic missions. The knowledge gained from this basic materials science investigation will have broad impact on the design of engineered human safety and health systems.

Preservation of primordial signatures of water in highly-shocked ancient lunar rocks

Spurred by the discovery of water in lunar volcanic glasses about a decade ago, the accessory mineral apatite became the primary target to investigate the abundance and source of lunar water. This is due to its ability to contain significant amounts of OH in its structure, along with the widespread presence of apatite in lunar rocks. There is a general understanding that crustal cumulate rocks of the lunar magnesian (Mg) suite are better candidates for recording the original isotopic compositions of volatile elements in their parental melts compared to eruptive rocks, such as mare basalts. Consequently, water-bearing minerals in Mg-suite rocks are thought to be ideal candidates for discerning the primary hydrogen isotopic composition of water in the lunar interior. Mg-suite rocks and most other Apollo samples that were collected at the lunar surface display variable degrees of shock-deformation. In this study, we have investigated seven Apollo 17 Mg-suite samples that include troctolite, gabbro and norite lithologies, in order to understand if shock processes affected the water abundances and/or H isotopic composition of apatite. The measured water contents in apatite grains range from 31 to 964 ppm, with associated δD values varying between −535 ± 134‰ and +147 ± 194‰ (2σ). Considering the full dataset, there appears to be no correlation between H2O and δD of apatite and the level of shock each apatite grain has experienced. However, the lowest δD was recorded by individual, water-poor (<∼100 ppm H2O) apatite grains that are either directly in contact with an impact melt or in its proximity. Therefore, the low-δD signature of apatite could be a result of interactions with D-poor regolith (solar wind derived H), facilitated by shock-induced nanostructures that could have provided pathways for migration of volatiles. In contrast, in relatively water-rich apatites (>∼100 ppm H2O), regardless of the complexity of the shock-induced nanostructures, there appears to be no evidence of water-loss or alteration in their δD. The weighted average δD value of 24 such water-rich apatites is −192 ± 71‰, and, of all 36 analyzed spots is −209 ± 47‰, indistinguishable from that of other KREEPy lunar lithologies or the Earth's deep mantle. Despite experiencing variable degrees of shock-deformation at a later stage in lunar history, water-rich apatite in some of the earliest-formed lunar crustal material appears to retain the original isotopic signature of H in the Moon.

Complex Geophysical Investigations under Extreme P,T–Conditions at Zentralinstitut für Physik der Erde (ZIPE) (1970–1990)

The development of the geophysical high pressure research in the former German Democratic Republic (GDR) is described here. The GDR was a German state established in 1949 at the territory of the Soviet occupation zone. The different experimental investigations under extreme pressure and temperature conditions and their industrial applications, including the pilot manufacture of synthetic diamonds are explained. A review of the research topics pursued including experiments on lunar material and Earth core/mantle material is described.

Potassium isotopic composition of the Moon

The Moon is depleted in water and other volatiles compared to Earth and the bulk solar composition. Such depletion of volatile elements and the stable isotope fractionations of these elements can be used to better understand the origin and early differentiation history of the Moon. In this study, we focus on the moderately volatile element, potassium, and we report the K elemental abundances and isotopic compositions (δ41K relative to NIST SRM 3141a) for nineteen Apollo lunar rocks and lunar meteorites (twenty-two subsamples), spanning all major geochemical and petrologic types of lunar materials. The K isotopic compositions of low-Ti and high-Ti basalts are indistinguishable, providing a lunar basalt average δ41K of –0.07 ± 0.09‰ (2SD), which we also consider to be the best estimate of the lunar mantle and the bulk silicate Moon. The significant enrichment of K in its heavier isotopes in the bulk silicate Moon, compared with the bulk silicate Earth (δ41K = –0.48 ± 0.03‰), is consistent with previous analyses of K isotopes and other moderately volatile elements (e.g., Cl, Cu, Zn, Ga, and Rb). We also report analyses of K isotopes for lunar nonmare samples, which show large variations of K isotopic ratios compared to lunar basalts. We interpret this large K isotopic fractionation as the result of late-stage magma ocean degassing during urKREEP formation, which is also coupled with Cl isotope fractionation. Degassing of urKREEP likely triggered redistribution of K isotopes in the Moon, enriching the urKREEP reservoir in heavy K isotopes while implanting the light K isotopic signatures onto the lunar surface. This scenario suggests a heterogeneous distribution of K isotopes in the Moon as a consequence of its magmatic evolution.

EAC-1A: A novel large-volume lunar regolith simulant

The European Astronaut Centre (EAC) is currently constructing the European Lunar Exploration Laboratory (LUNA), a large training and operations facility to be located adjacent to EAC at the DLR (German Aerospace Centre) campus in Cologne, Germany. With an estimated representative lunar testbed area of approximately 660 m2, a large volume of lunar regolith simulant material is needed for this purpose. In this study, a basanitic sandy silt from a quarry located in the Siebengebirge Volcanic Field is evaluated as a large-volume source of material. The focus of this project has been to conduct a physical and chemical characterisation of the fine-grained material to be used in LUNA; the European Astronaut Centre lunar regolith simulant 1 (EAC-1 A). The physical characterisation tests undertaken include sphericity, density measurements, cohesion and static angle of repose, with mineralogical investigations via petrographical analysis with optical microscope and SEM, XRF, XRD and DSC measurements. The results of the EAC-1A tests are compared to published data on existing widely used lunar regolith simulants, namely JSC-1A, JSC-2A, NU-LHT-3M, DNA and FJS-1.

Petrography and chronology of lunar meteorite Northwest Africa 6950

Northwest Africa (NWA) 6950 is an olivine-gabbro lunar meteorite that has a distinctly different petrographic texture from other lunar basalts. In this contribution, we report the petrography, mineralogy, and U-Pb geochronology of baddeleyite and phosphate in this lunar meteorite and make a comparison with other NWA 773 paired meteorites. NWA 6950 consists mainly of coarse-grained olivine, pyroxene, and plagioclase, with minor ilmenite, chromite, troilite, baddeleyite, taenite, and apatite. The abundant rounded to euhedral olivine has a limited Fo ranging from 68 to 69. Pyroxenes include both augite and pigeonite, with a narrow range of Mg#=71–80, and composition, respectively, ${\rm~En}_{46\text{-}52}{\rm~Fs}_{12\text{-}16}{\rm~Wo}_{32\text{-}41}$ and ${\rm~En}_{58\text{-}68}{\rm~Fs}_{19\text{-}28}{\rm~Wo}_{7\text{-}20}$. Plagioclase is mainly anhedral, conforming to the crystal margins of olivine and pyroxene. The plagioclase grains are elongated and several hundreds of microns in length. Raman spectra shows that plagioclase has been transformed into maskelynite, which is very calcic (${\rm~An}_{87\text{-}95}$) with low sodium and very low potassium (${\rm~Ab}_{4\text{-}9}{\rm~Or}_{0.6\text{-}3.7}$). The weighted mean $^{207}{\rm~Pb}/^{206}{\rm~Pb}$ ages of baddeleyite and phosphate measured using a sensitive high resolution ion micro probe (SHRIMP II) are $3119\pm16$ Ma ($n=9$, MSWD = 2.5) (meansquared weighted deviates, MSWD) and $3119\pm18$ Ma ($n=15$, MSWD = 2.1), respectively, giving the crystallization age of the meteorite.NWA 6950 has similar mineral compositions, geochemical characteristics, and an almost identical age of crystallization to the magnesian gabbro of the NWA 773 clan. We conclude that NWA 6950 and NWA 773 are paired meteorites, which crystallize at ca. 3119 Ma, and represent magmatic activities in the KREEP (potassium (K), rare earth elements (REE) and phosphorus (P) rich lunar material) region of the Moon.

Dynamic Potential Sputtering of Lunar Analog Material by Solar Wind Ions

Abstract Pyroxenes ((Ca, Mg, Fe, Mn)2Si2O6) belong to the most abundant rock forming minerals that make up the surface of rocky planets and moons. Therefore, sputtering of pyroxenes by solar wind ions has to be considered as a very important process for modifying the surface of planetary bodies. This is increased due to potential sputtering by multiply charged ions; to quantify this effect, sputtering of wollastonite (CaSiO3) by He2+ ions was investigated. Thin films of CaSiO3 deposited on a quartz crystal microbalance were irradiated, allowing precise, in situ, real time sputtering yield measurements. Experimental results were compared with SDTrimSP simulations, which were improved by adapting the used input parameters. On freshly prepared surfaces, He2+ ions show a significant increase in sputtering, as compared to equally fast He+ ions. However, the yield decreases exponentially with fluence, reaching a lower steady state after sputtering of the first few monolayers. Experiments using Ar8+ ions show a similar behavior, which is qualitatively explained by a preferential depletion of surface oxygen due to potential sputtering. A corresponding quantitative model is applied, and the observed potential sputtering behaviors of both He and Ar are reproduced very well. The results of these calculations support the assumption that mainly O atoms are affected by potential sputtering. Based on our findings, we discuss the importance of potential sputtering for the solar wind eroding the lunar surface. Estimated concentration changes and sputtering yields are both in line with previous modeling for other materials, allowing a consistent perspective on the effects of solar wind potential sputtering.

Prediction of micrometeoroid damage to lunar construction materials using numerical modeling of hypervelocity impact events

The use of Lunar regolith for the creation of construction materials to build habitats and other infrastructure required for a Lunar base is an example of in situ resource utilization (ISRU), an important strategy for minimizing the launch mass associated with a NASA mission to the Moon. One class of solidified regolith, Biopolymer-bound Soil Composites (BSC), consists of regolith mixed with a small amount of biopolymer binding agent (10% w/w). This paper characterizes BSC's micrometeoroid impact performance using experimental and numerical methods. Micrometeoroids are a notable hazard of the Lunar environment and pose a challenging design consideration. A total of 17 hypervelocity impact experiments were conducted on BSC targets at NASA's White Sands Testing Facility. Numerical simulations of the hypervelocity impact experiments were carried out using CTH, a shock physics code developed by Sandia National Laboratories. Comparisons between the experimental craters and the simulation results indicate that there is good agreement between crater dimensions of the hypervelocity impact experiments and the CTH model. The CTH model developed in this paper provides (1) a damage prediction tool that allows for the necessary extrapolation of micrometeoroid impact velocities beyond what is experimentally achievable and into the velocity regime that is relevant for micrometeoroids and (2) a material design tool that is capable of varying material parameters computationally, ultimately allowing for the engineering and optimization of BSC's performance under impact loading.

A database of noble gases in lunar samples in preparation for mass spectrometry on the Moon

The lunar regolith provides a temporal archive of the evolution of the Moon and inner Solar System over the last ~4 billion years. During this time, noble gases have been trapped and produced within soils and rocks at the lunar surface. These noble gas concentrations can be used to unravel the history of lunar material and shed light on processes that have evolved the surface of the Moon through time. We have collected published noble gas data for a range of lunar samples including soils, regolith breccias, crystalline (e.g., mare basalts, anorthosite) and impact-melt rocks. The compilation includes noble gas concentrations and isotope ratios for He, Ne, Ar, Kr and Xe; trapped, cosmogenic and radiogenic isotopes; and cosmic ray exposure ages. We summarise the significance of these data, which can be used as a baseline for expected noble gas concentrations in a range of lunar samples, and provide a framework for future in situ noble gas measurements on the lunar surface.

Magmatic intrusion-related processes in the upper lunar crust: The role of country rock porosity/permeability in magmatic percolation and thermal annealing, and implications for gravity signatures

Shallow crustal country rock on the Moon is demonstrably more fractured and porous than deeper crustal bedrock, and Gravity Recovery and Interior Laboratory (GRAIL) mission gravity data have shown that deeper crustal bedrock is more porous than previously thought. This raises the question of how crustal porosity and permeability will influence the nature of magmatic dike intrusions in terms of: 1) the ability of intruding magma to inject into and occupy this pore space (shallow magmatic percolation), 2) the influence of the intruded magma on annealing of this porosity and permeability (thermal annealing) both 1 and 2 densify the country rock), and 3) the effect of crustal porosity on favoring sill formation as a function of depth in the lunar crust. We analyze quantitatively the emplacement of basaltic dikes and sills on the Moon and assess these three factors in the context of the most recent data on micro- and macro-scale porosity of lunar crustal materials. For the range of plausible micro/macro-scale porosity and permeability determined by crack widths (mm to cm) and open crack lateral continuity (mm to tens of cm), we find that 1) rapid conductive cooling of injected magma due to the very large surface area to volume ratio restricts magmatic percolation to very limited zones (extending for at most several tens of cm) adjacent to the ascending dike or intruded sill, even in the upper several hundred meters of the lunar crust; 2) the conductive heat loss from intruded dikes and sills results in a thermal wave decay rate that is predicted to limit the extent of intrusion-adjacent thermal annealing to less than ~6% of the thickness of the intruded body; 3) the extremely rapid rise rate of magma in dikes originating from sources in the lunar mantle disfavors the lateral migration of dikes to form sills in the crust, except in specific shallow crustal locations influenced by impact crater-related environments (e.g., floor-fractured craters). We conclude that, although magmatic percolation and thermal annealing in association with lunar mare basalt magmatic dike and sill emplacement should be taken into consideration in interpreting gravity signatures, the effects are likely to be minor compared with the density contrast of the solidified basaltic magmatic intrusion itself.

Lunar deep materials observed by Chang'e-4 rover

China's Chang'e-4 spacecraft achieved the first ever soft-landing within the South Pole-Aitken (SPA) basin on the farside of the Moon. The Chang'e-4 rover, named Yutu-2, made in-situ spectral observations on lunar regolith and a rock fragment at 11 locations during a nominal three-month mission period. The lunar regolith has a relative high olivine/pyroxene ratio, with the pyroxene being chiefly Mg-rich Low-Ca pyroxene (LCP). The rock fragment has a similar Mg-rich composition to that of the regolith. According to the surrounding topographic and geologic context, though originating from the lower base of a differentiated melt pool cannot be excluded here, the rover observed regolith and rock fragment are very likely to be lunar mantle materials excavated from nearby Finsen crater.

P-bearing olivines of lunar rocks: sources and localization in the lunar crust

Fragments of P-bearing olivine have been studied in lunar highland, mare and mingled meteorites and in «Apollo-14», «Luna-16, -20, -24» lunar samples. Olivine contains up to 0.5 wt.% P2O5 and has variable MG# number. It is associated with anorthite, pyroxene and accessory spinel group minerals, Ti and Zr oxides, phosphates, troilite and Fe-Ni metal. Three possible sources of P-bearing olivine were found in lunar material: 1) highland anorthositic-noritic-troctolitic rocks enriched in incompatible elements and thought to be related to high-Mg suite rocks: 2) late-stage products of mare basalts crystallization; 3) unusual olivine-orthopyroxene intergrowths either of meteoritic or lunar origin. Enrichment in incompatible elements may be resulted from both crystallization processes (source 2) and KREEP assimilation (sources 1 and 3). However following metasomatic processes can lead to some addition of phosphorus and other elements.&#x0D; The rarity of P-bearing olivines points either to the low abundance or local distribution of their sources in the lunar crust. Association with mare basalts specifies the highland-mare boundary. The presence of the evolved rocks in the studied breccias suggests possible connection of some sources with recently discovered granitic domes in Procellarum Ocean. That means the P-bearing sources are mainly localized on the visible side of the Moon.

Abundance of highly siderophile elements in lunar basalts controlled by iron sulfide melt

The Moon accreted meteoritic material towards the end of Solar System formation. Quantification of this late accretion requires an estimation of the abundance of highly siderophile, or iron-loving, elements in the lunar mantle. As lunar mantle samples are not available, estimates are derived from lunar basalt compositions, but the melting phase relations needed to derive the mantle composition are poorly constrained. Here we present sulfur solubility measurements from laboratory experiments, combined with thermodynamic calculations, which show that the lunar basalt source is likely to be saturated in a sulfur-poor, iron-rich sulfide melt that concentrates some highly siderophile elements more than others. We found that the observed range in the ratios of highly siderophile elements in primitive lunar basalts is much smaller than expected from residual sulfide control alone. Instead, the elemental ratios are consistent with mixing between primary sulfide-saturated melts and minute (<1%) amounts of lunar regolith that contain impact debris. Although the composition of some samples suggests a highly depleted lunar mantle, the exact level of depletion is unclear, because mixing trajectories overlap at the inferred level of regolith contamination. We conclude that the composition of the lunar mantle is veiled by regolith contamination of the lunar basalts. If so, highly siderophile element abundances in lunar mantle-derived materials cannot be used to determine the mass of material accreted late onto the Moon. The abundance of iron-loving elements in Moon rocks cannot indicate the amount of late accretion onto the Moon, according to experiments and thermodynamic calculations constraining the behaviour of these elements under lunar mantle conditions.