Hydrogen isotopes in lunar volcanic glasses and melt inclusions reveal a carbonaceous chondrite heritage

Lunar dichotomy in surface water storage of impact glass beads

Water is the one of most precious resources for planetary utilisation. Lunar nearside impact glass beads (IGBs) have been demonstrated to contain abundant solar wind-derived water (SW-H2O); however, little is known about its farside counterpart. Here, we report the water abundances and hydrogen isotope compositions and their distribution in farside IGBs collected by the Chang'e-6 mission to investigate the role of IGBs in the lunar surface water cycle. Farside IGBs are found to have water abundances of ~10-1,070 μg.g-1 with hydrogen isotopes (δD) ranging from -988‰ to >2000‰ and display typical SW-H2O hydration profiles. The SW-H2O hydration depths in farside IGBs are strikingly shallower than in nearside IGBs. Moreover, the hydration profiles are only found in mare IGBs, with none observed in non-mare IGBs, indicating that SW-H2O hydration in IGBs is likely composition dependent. These findings indicate that SW-H2O storage of IGBs exhibits a dichotomy distribution in lunar soils.

Water abundance in the lunar farside mantle

The water contents of the lunar interior record important clues for understanding the formation and subsequent thermochemical evolution of the Moon1. The Chang'e-6 (CE6) mission returned samples from the South Pole-Aitken impact basin of the lunar farside2-4, providing an opportunity to study the water contents of the farside mantle. Here we report the water abundances and hydrogen isotope compositions of apatite and melt inclusions from CE6 mare basalt, derived from partial melting of the lunar mantle. The parent magma of CE6 mare basalt is estimated to have a water abundance of 15-168 μg g-1 with a δD value of -123 ± 167‰. Our estimate of water abundance of 1-1.5 μg g-1 for the mantle source indicates that the farside mantle is potentially drier than its nearside counterpart. This contrast thus suggests that the distribution of water in the interior of the Moon may exhibit a hemispheric dichotomy similar to numerous surface features5. The new estimate for the lunar farside mantle represents a landmark for estimating the water abundance of the bulk silicate Moon, providing critical constraints on the giant impact origin hypothesis6-8 and the subsequent evolution of the Moon for which the role of water is central1,9.

Higher water content observed in smaller size fraction of Chang'e-5 lunar regolith samples

Water has been detected in lunar regolith, with multiple sources identified through the analysis of individual grains. However, the primary origin of water in the bulk lunar regolith remains uncertain. This study presents spectroscopic analyses of water content in sealed Chang'e-5 samples. These samples were sieved into various size fractions (bulk, <45 μm, and 45-355 μm) inside a glovebox filled with high-purity nitrogen. Results indicate a higher water content in the fine fractions (∼87 ± 11.9 ppm) than in bulk soil (∼37 ± 4.8 ppm) and coarse fractions (∼11 ± 1.5 ppm). This suggests that water is predominantly concentrated in the outermost rims of the regolith grains, and thus exhibits dependence on the surface volume ratio (also known as surface correlation), indicating solar wind is a primary source of lunar surface water. Laboratory, in-situ, and orbital results bridge sample analysis and remote sensing, offering a cohesive understanding of lunar surface water characteristics as represented by Chang'e-5. The discovery provides statistical evidence for the origin of water in lunar soil and can be considered representative of the lunar surface conditions. The water enrichment of the finest fraction suggests the feasibility of employing size sorting of lunar soils as a potential technological approach for water resource extraction in future lunar research stations.

Massive water production from lunar ilmenite through reaction with endogenous hydrogen

Finding water resources is a crucial objective of lunar missions. However, both hydroxyl (OH) and natural water (H2O) have been reported to be scarce on the Moon. We propose a potential method for obtaining water on the Moon through H2O formation via endogenous reactions in lunar regolith (LR), specifically through the reaction FeO/Fe2O3 + H → Fe + H2O. This process is demonstrated using LR samples brought back by the Chang'E-5 mission. FeO and Fe2O3 are lunar minerals containing Fe oxides. Hydrogen (H) retained in lunar minerals from the solar wind can be used to produce water. The results of this study reveal that 51-76 mg of H2O can be generated from 1 g of LR after melting at temperatures above 1,200 K. This amount is ∼10,000 times the naturally occurring OH and H2O on the Moon. Among the five primary minerals in LR returned by the Chang'E-5 mission, FeTiO3 ilmenite contains the highest amount of H, owing to its unique lattice structure with sub-nanometer tunnels. For the first time, in situ heating experiments using a transmission electron microscope reveal the concurrent formation of Fe crystals and H2O bubbles. Electron irradiation promotes the endogenous redox reaction, which is helpful for understanding the distribution of OH on the Moon. Our findings suggest that the hydrogen retained in LR is a significant resource for obtaining H2O on the Moon, which is helpful for establishing a scientific research station on the Moon.

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

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

Diverse glasses revealed from Chang'E-5 lunar regolith

Lunar glasses with different origins act as snapshots of their formation processes, providing a rich archive of the Moon's formation and evolution. Here, we reveal diverse glasses from Chang'E-5 (CE-5) lunar regolith, and clarify their physical origins of liquid quenching, vapor deposition and irradiation damage respectively. The series of quenched glasses, including rotation-featured particles, vesicular agglutinates and adhered melts, record multiple-scale impact events. Abundant micro-impact products, like micron- to nano-scale glass droplets or craters, highlight that the regolith is heavily reworked by frequent micrometeorite bombardment. Distinct from Apollo samples, the indigenous ultra-elongated glass fibers drawn from viscous melts and the widespread ultra-thin deposited amorphous rims without nanophase iron particles both indicate a relatively gentle impact environment at the CE-5 landing site. The clarification of multitype CE-5 glasses also provides a catalogue of diverse lunar glasses, meaning that more of the Moon's mysteries, recorded in glasses, could be deciphered in future.

Rapid transition from primary to secondary crust building on the Moon explained by mantle overturn

Geochronology indicates a rapid transition (tens of Myrs) from primary to secondary crust building on the Moon. The processes responsible for initiating secondary magmatism, however, remain in debate. Here we test the hypothesis that the earliest secondary crust (Mg-suite) formed as a direct consequence of density-driven mantle overturn, and advance 3D mantle convection models to quantify the resulting extent of lower mantle melting. Our modeling demonstrates that overturn of thin ilmenite-bearing cumulates ≤ 100 km triggers a rapid and short-lived episode of lower mantle melting which explains the key volume, geochronological, and spatial characteristics of early secondary crust building without contributions from other energy sources, namely KREEP (potassium, rare earth elements, phosphorus, radiogenic U, Th). Observations of globally distributed Mg-suite eliminate degree-1 overturn scenarios. We propose that gravitational instabilities in magma ocean cumulate piles are major driving forces for the onset of mantle convection and secondary crust building on differentiated bodies.

Degassing of early-formed planetesimals restricted water delivery to Earth

The timing of delivery and the types of body that contributed volatiles to the terrestrial planets remain highly debated1,2. For example, it is unknown if differentiated bodies, such as that responsible for the Moon-forming giant impact, could have delivered substantial volatiles3,4 or if smaller, undifferentiated objects were more probable vehicles of water delivery5-7. Here we show that the water contents of minerals in achondrite meteorites (mantles or crusts of differentiated planetesimals) from both the inner and outer portions of the early Solar System are ≤2 μg g-1 H2O. These are among the lowest values ever reported for extraterrestrial minerals. Our results demonstrate that differentiated planetesimals efficiently degassed before or during melting. This finding implies that substantial amounts of water could only have been delivered to Earth by means of unmelted material.

Nanoscale Secondary Ion Mass Spectrometry determination of the water content of staurolite

RATIONALE

Staurolite is an important mineral that can reveal much about metamorphic processes. For instance, it dominates the Fe-Mg exchange reactions in amphibolite-facies rocks between about 550 and 700°C, and can be also found at suprasolidus conditions. Staurolite contains a variable amount of OH in its structure, whose determination is a key petrological parameter. However, staurolite is often compositionally zoned, fine-grained, and may contain abundant inclusions. This makes conventional water analysis (e.g., Fourier transform infrared (FTIR) spectroscopy or by chemical titration) unsuitable. With its high sensitivity at high spatial resolution, Nanoscale Secondary Ion Mass Spectrometry (NanoSIMS) is potentially a valuable tool for determining water contents in staurolite. However a calibration with relevant standards covering a large range of water content is required to obtain accurate and reliable analyses, because matrix effects typically prevent direct quantification of water content by SIMS techniques.

METHODS

In this study, a calibration for NanoSIMS analyses of water content by using minerals with crystallographic structures comparable to that of staurolite (i.e., amphibole and kyanite, an inosilicate and a nesosilicate, respectively) has been developed.

RESULTS

Water measurements in an inclusion-free crystal from Pizzo Forno, Ticino, Switzerland, by FTIR spectroscopy (1.56 ± 0.14 wt% H₂ O) and by Elastic Recoil Detection Analysis (ERDA) (1.58 ± 0.15 wt% H₂ O) are consistent with NanoSIMS results (1.56 ± 0.04 wt% H₂ O).

CONCLUSIONS

This implies that our approach can accurately account for NanoSIMS matrix effects in the case of staurolite. With this calibration, it is now possible to investigate variations in water content at the microscale in metamorphic minerals exhibiting high spatial variability and/or very small size (few micrometers).

Indigenous noble gases in the Moon's interior

The origin of volatiles in the Moon's interior is debated. Scenarios range from inheritance through a Moon-forming disk or "synestia" to late accretion by meteorites or comets. Noble gases are excellent tracers of volatile origins. We report analyses of all noble gases in paired, unbrecciated lunar mare basalts and show that magmatic glasses therein contain indigenous noble gases including solar-type He and Ne. Assimilation of solar wind (SW)-bearing regolith by the basaltic melt or SW implantation into the basalts is excluded on the basis of the petrological context of the samples, as well as the lack of SW and "excess ⁴⁰Ar" in the magmatic minerals. The absence of chondritic primordial He and Ne signatures excludes exogenous contamination. We thus conclude that the Moon inherited indigenous noble gases from Earth's mantle by the Moon-forming impact and propose storage in the incompatible element-enriched ("KREEP") reservoir.

Lunar Mare Fecunditatis: A Science-Rich Region and a Concept Mission for Long-Distance Exploration

Mare Fecunditatis is a ~310,000 km2 flat basalt plain located in the low-latitude area of the Moon. Plenty of volcanic features (multiple episodes of mare basalts, sinuous rilles, lava tubes, pyroclastic deposits, domes, irregular mare patches (IMP), ring-moat dome structures (RMDS), floor-fractured craters), tectonic features (grabens and wrinkle ridges), impact-related features, and other features (swirls, pit craters) are identified in Mare Fecunditatis. An in-situ mission to Mare Fecunditatis is scientifically significant to better understand the lunar thermal histories and other questions. All previous in-situ and human missions (Apollo, Luna, Chang’E) were limited to small areas, and no traverse longer than 40 km has been made yet. With the development of technology, long-distance movement will be possible in the future on the lunar surface, providing opportunities to explore multiple sites at one mission with complete documentation of the regional geology. Eight high-value targets (pit crater, IMPs, RMDSs, young basalts, high-Al basalts, pyroclastic deposits, swirls, and fresh craters) were found in Mare Fecunditatis, and a ~1400 km-traverse in 5 years is proposed to explore them to solve the most fundamental lunar questions.

Abnormal (Hydroxy)proline Deuterium Content Redefines Hydrogen Chemical Mass

Analyzing the δ²H values in individual amino acids of proteins extracted from vertebrates, we unexpectedly found in some samples, notably bone collagen from seals, more than twice as much deuterium in proline and hydroxyproline residues than in seawater. This corresponds to at least 4 times higher δ²H than in any previously reported biogenic sample. We ruled out diet as a plausible mechanism for such anomalous enrichment. This finding puts into question the old adage that “you are what you eat”.

In situ detection of water on the Moon by the Chang'E-5 lander

We report analysis results of the reflectance spectra (0.48 to 3.2 μm) acquired by the Chang’E-5 lander, which provides vital context of the returned samples from the Northern Oceanus Procellarum of the Moon. We estimate up to 120 parts per million (ppm) of water (OH + H₂O) in the lunar regolith, which is mostly attributed to solar wind implantation. A light-colored and surface-pitted rock (named as CE5-Rock) is evident near the lander. The reflectance spectra suggest that CE5-Rock could be transported from an older basalt unit. CE5-Rock exhibits a stronger absorption, near 2.85 μm, than the surrounding regolith, with estimation of ~180 ppm of water if the model for estimating water content of regolith is applicable to rock samples, which may suggest an additional source from the lunar interior. The low water content of the regolith may suggest the degassing of mantle reservoir beneath the Chang’E-5 landing site.

A dry lunar mantle reservoir for young mare basalts of Chang'e-5

The distribution of water in the Moon's interior carries implications for the origin of the Moon1, the crystallization of the lunar magma ocean2 and the duration of lunar volcanism2. The Chang'e-5 mission returned some of the youngest mare basalt samples reported so far, dated at 2.0 billion years ago (Ga)3, from the northwestern Procellarum KREEP Terrane, providing a probe into the spatiotemporal evolution of lunar water. Here we report the water abundances and hydrogen isotope compositions of apatite and ilmenite-hosted melt inclusions from the Chang'e-5 basalts. We derive a maximum water abundance of 283 ± 22 μg g-1 and a deuterium/hydrogen ratio of (1.06 ± 0.25) × 10-4 for the parent magma. Accounting for low-degree partial melting of the depleted mantle followed by extensive magma fractional crystallization4, we estimate a maximum mantle water abundance of 1-5 μg g-1, suggesting that the Moon's youngest volcanism was not driven by abundant water in its mantle source. Such a modest water content for the Chang'e-5 basalt mantle source region is at the low end of the range estimated from mare basalts that erupted from around 4.0 Ga to 2.8 Ga (refs. 5,6), suggesting that the mantle source of the Chang'e-5 basalts had become dehydrated by 2.0 Ga through previous melt extraction from the Procellarum KREEP Terrane mantle during prolonged volcanic activity.

Highest resolution chemical imaging based on secondary ion mass spectrometry performed on the helium ion microscope

This paper is a review on the combination between Helium Ion Microscopy (HIM) and Secondary Ion Mass Spectrometry (SIMS), which is a recently developed technique that is of particular relevance in the context of the quest for high-resolution high-sensitivity nano-analytical solutions. We start by giving an overview on the HIM-SIMS concept and the underlying fundamental principles of both HIM and SIMS. We then present and discuss instrumental aspects of the HIM and SIMS techniques, highlighting the advantage of the integrated HIM-SIMS instrument. We give an overview on the performance characteristics of the HIM-SIMS technique, which is capable of producing elemental SIMS maps with lateral resolution below 20 nm, approaching the physical resolution limits, while maintaining a sub-nanometric resolution in the secondary electron microscopy mode. In addition, we showcase different strategies and methods allowing to take profit of both capabilities of the HIM-SIMS instrument (high-resolution imaging using secondary electrons and mass filtered secondary sons) in a correlative approach. Since its development HIM-SIMS has been successfully applied to a large variety of scientific and technological topics. Here, we will present and summarise recent applications of nanoscale imaging in materials research, life sciences and geology.

Conditions and extent of volatile loss from the Moon during formation of the Procellarum basin

Rocks from the lunar interior are depleted in moderately volatile elements (MVEs) compared to terrestrial rocks. Most MVEs are also enriched in their heavier isotopes compared to those in terrestrial rocks. Such elemental depletion and heavy isotope enrichments have been attributed to liquid-vapor exchange and vapor loss from the protolunar disk, incomplete accretion of MVEs during condensation of the Moon, and degassing of MVEs during lunar magma ocean crystallization. New Monte Carlo simulation results suggest that the lunar MVE depletion is consistent with evaporative loss at 1,670 ± 129 K and an oxygen fugacity +2.3 ± 2.1 log units above the fayalite-magnetite-quartz buffer. Here, we propose that these chemical and isotopic features could have resulted from the formation of the putative Procellarum basin early in the Moon's history, during which nearside magma ocean melts would have been exposed at the surface, allowing equilibration with any primitive atmosphere together with MVE loss and isotopic fractionation.

Large sulfur isotope fractionation in lunar volcanic glasses reveals the magmatic differentiation and degassing of the Moon

Sulfur isotope variations in mantle-derived lavas provide important constraints on the evolution of planetary bodies. Here, we report the first in situ measurements of sulfur isotope ratios dissolved in primitive volcanic glasses and olivine-hosted melt inclusions recovered from the Moon by the Apollo 15 and 17 missions. The new data reveal large variations in 34S/32S ratios, which positively correlates with sulfur and titanium contents within and between the distinct compositional groups of volcanic glasses analyzed. Our results uncover several magmatic events that fractionated the primordial sulfur isotope composition of the Moon: the segregation of the lunar core and the crystallization of the lunar magma ocean, which led to the formation of the heterogeneous sources of the lunar magmatism, followed by magma degassing during generation, transport, and eruption of the lunar lavas. Whether the Earth's and Moon's interiors share a common 34S/32S ratio remains a matter of debate.

Water on Mars: Insights from apatite in regolith breccia Northwest Africa 7034

Determining the source of planetary water from the hydrogen isotope compositions of crustal samples is complicated by the overprinting of isotopically diverse source material by geologic and atmospheric processes. As Mars has no plate tectonics, crustal material, which may have isotopically exchanged with the martian atmosphere, is not recycled into the mantle keeping the water reservoirs in the mantle and atmosphere mostly isolated, buffered by the crust. As the only known martian samples that are regolith breccias with a composition representative of the average crust of Mars, Northwest Africa (NWA) 7034 and its paired stones provide an important opportunity to investigate the water content and hydrogen isotope composition of the martian crust. In particular, apatites in distinct clasts as well as the brecciated matrix of NWA 7034 record a complex history including magmatic and impact processes, and exchange with crustal fluids.

Variations in color and reflectance on the surface of asteroid (101955) Bennu

Visible-wavelength color and reflectance provide information about the geologic history of planetary surfaces. Here we present multispectral images (0.44 to 0.89 micrometers) of near-Earth asteroid (101955) Bennu. The surface has variable colors overlain on a moderately blue global terrain. Two primary boulder types are distinguishable by their reflectance and texture. Space weathering of Bennu surface materials does not simply progress from red to blue (or vice versa). Instead, freshly exposed, redder surfaces initially brighten in the near-ultraviolet region (i.e., become bluer at shorter wavelengths), then brighten in the visible to near-infrared region, leading to Bennu's moderately blue average color. Craters indicate that the time scale of these color changes is ~10⁵ years. We attribute the reflectance and color variation to a combination of primordial heterogeneity and varying exposure ages.

The Cl isotope composition and halogen contents of Apollo-return samples

Lunar mare basalts are depleted in F and Cl by approximately an order of magnitude relative to mid-ocean ridge basalts and contain two Cl-bearing components with elevated isotopic compositions relative to the bulk-Earth value of ∼0‰. The first is a water-soluble chloride constituting 65 ± 10% of total Cl with δ³⁷Cl values averaging 3.0 ± 4.3‰. The second is structurally bound chloride with δ³⁷Cl values averaging 7.3 ± 3.5‰. These high and distinctly different isotopic values are inconsistent with equilibrium fractionation processes and instead suggest early and extensive degassing of an isotopically light vapor. No relationship is observed between F/Cl ratios and δ³⁷Cl values, which suggests that lunar halogen depletion largely resulted from the Moon-forming Giant Impact. The δ³⁷Cl values of apatite are generally higher than the structurally bound Cl, and ubiquitously higher than the calculated bulk δ³⁷Cl values of 4.1 ± 4.0‰. The apatite grains are not representative of the bulk rock, and instead record localized degassing during the final stages of lunar magma ocean (LMO) or later melt crystallization. The large variability in the δ³⁷Cl values of apatite within individual thin sections further supports this conclusion. While urKREEP (primeval KREEP [potassium/rare-earth elements/phosphorus]) has been proposed to be the source of the Moon's high Cl isotope values, the ferroan anorthosites (FANs) have the highest δ³⁷Cl values and have a positive correlation with Cl content, and yet do not contain apatite, nor evidence of a KREEP component. The high δ³⁷Cl values in this lithology are explained by the incorporation of a >30‰ HCl vapor from a highly evolved LMO.

KAGUYA observation of global emissions of indigenous carbon ions from the Moon

Carbon is a volatile element that has a considerable influence on the formation and evolution of planetary bodies, although it was previously believed to be depleted in the Moon. We present observations by the lunar orbiter KAGUYA of carbon ions emitted from the Moon. These emissions were distributed over almost the total lunar surface, but amounts were differed with respect to lunar geographical areas. The estimated emission fluxes to space were ~5.0 × 104 per square centimeter per second, which is greater than possible ongoing supplies from the solar wind and micrometeoroids. Our estimates demonstrate that indigenous carbon exists over the entire Moon, supporting the hypothesis of a carbon-containing Moon, where the carbon was embedded at its formation and/or was transported billions of years ago.

Isotopic evidence for volatile replenishment of the Moon during the Late Accretion

The traditional view of a dry, volatile-poor Moon has been challenged by the identification of water and other volatiles in lunar samples, but the volatile budget delivery time(s), source(s) and temporal evolution remain poorly constrained. Here we show that hydrogen and chlorine isotopic ratios in lunar apatite changed significantly during the Late Accretion (LA, 4.1-3.8 billion years ago). During this period, deuterium/hydrogen ratios in the Moon changed from initial carbonaceous-chondrite-like values to values consistent with an influx of ordinary-chondrite-like material and pre-LA elevated δ37Cl values drop towards lower chondrite-like values. Inferred pre-LA lunar interior water contents are significantly lower than pristine values suggesting degassing, followed by an increase during the LA. These trends are consistent with dynamic models of solar-system evolution, suggesting that the Moon's (and Earth's) initial volatiles were replenished ∼0.5 Ga after their formation, with their final budgets reflecting a mixture of sources and delivery times.

An extremely heavy chlorine reservoir in the Moon: Insights from the apatite in lunar meteorites

Chlorine, an extremely hydrophilic volatile element, provides important information regarding the origin of intrinsic volatiles in the Moon. Lunar apatite was found to have a wider spread of δ³⁷Cl (from -1 to +40‰ versus standard mean ocean chloride) than most terrestrial and chondritic ones (0 ± 0.5‰). However, the provenance of the elevated lunar δ³⁷Cl is still enigmatic. Here we report new isotopic data for H and Cl in apatite from three lunar meteorites and discuss possible mechanisms for Cl isotopic fractionation of the Moon. The apatite grain in Dhofar 458 has an average δ³⁷Cl value of +76‰, indicative of an extremely heavy Cl reservoir in the Moon. Volatile loss associated with the Moon-forming Giant Impact and the formation of lunar magma ocean could account for the large Cl isotopic fractionation of the Moon. The observed H₂O contents (220-5200 ppm), δD (-100 to +550‰) and δ³⁷Cl values (+3.8 - +81.1‰) in lunar apatite could be understood if late accretion of hydrous components were added to the Moon after the fractionation of Cl isotopes. The heterogeneous distribution of lunar Cl isotopes is probably resulted from complex lunar formation and differentiation processes.

Delivery of carbon, nitrogen, and sulfur to the silicate Earth by a giant impact

Earth's status as the only life-sustaining planet is a result of the timing and delivery mechanism of carbon (C), nitrogen (N), sulfur (S), and hydrogen (H). On the basis of their isotopic signatures, terrestrial volatiles are thought to have derived from carbonaceous chondrites, while the isotopic compositions of nonvolatile major and trace elements suggest that enstatite chondrite-like materials are the primary building blocks of Earth. However, the C/N ratio of the bulk silicate Earth (BSE) is superchondritic, which rules out volatile delivery by a chondritic late veneer. In addition, if delivered during the main phase of Earth's accretion, then, owing to the greater siderophile (metal loving) nature of C relative to N, core formation should have left behind a subchondritic C/N ratio in the BSE. Here, we present high pressure-temperature experiments to constrain the fate of mixed C-N-S volatiles during core-mantle segregation in the planetary embryo magma oceans and show that C becomes much less siderophile in N-bearing and S-rich alloys, while the siderophile character of N remains largely unaffected in the presence of S. Using the new data and inverse Monte Carlo simulations, we show that the impact of a Mars-sized planet, having minimal contributions from carbonaceous chondrite-like material and coinciding with the Moon-forming event, can be the source of major volatiles in the BSE.

Terrestrial exposure of a fresh Martian meteorite causes rapid changes in hydrogen isotopes and water concentrations

Determining the hydrogen isotopic compositions and H₂O contents of meteorites and their components is important for addressing key cosmochemical questions about the abundance and source(s) of water in planetary bodies. However, deconvolving the effects of terrestrial contamination from the indigenous hydrogen isotopic compositions of these extraterrestrial materials is not trivial, because chondrites and some achondrites show only small deviations from terrestrial values such that even minor contamination can mask the indigenous values. Here we assess the effects of terrestrial weathering and contamination on the hydrogen isotope ratios and H₂O contents of meteoritic minerals through monitored terrestrial weathering of Tissint, a recent Martian fall. Our findings reveal the rapidity with which this weathering affects nominally anhydrous phases in extraterrestrial materials, which illustrates the necessity of sampling the interiors of even relatively fresh meteorite falls and underlines the importance of sample return missions.

The delivery of water by impacts from planetary accretion to present

Dynamical models and observational evidence indicate that water-rich asteroids and comets deliver water to objects throughout the solar system, but the mechanisms by which this water is captured have been unclear. New experiments reveal that impact melts and breccias capture up to 30% of the water carried by carbonaceous chondrite-like projectiles under impact conditions typical of the main asteroid belt impact and the early phases of planet formation. This impactor-derived water resides in two distinct reservoirs: in impact melts and projectile survivors. Impact melt hosts the bulk of the delivered water. Entrapment of water within impact glasses and melt-bearing breccias is therefore a plausible source of hydration features associated with craters on the Moon and elsewhere in the solar system and likely contributed to the early accretion of water during planet formation.

Late-stage magmatic outgassing from a volatile-depleted Moon

The abundance of volatile elements and compounds, such as zinc, potassium, chlorine, and water, provide key evidence for how Earth and the Moon formed and evolved. Currently, evidence exists for a Moon depleted in volatile elements, as well as reservoirs within the Moon with volatile abundances like Earth's depleted upper mantle. Volatile depletion is consistent with catastrophic formation, such as a giant impact, whereas a Moon with Earth-like volatile abundances suggests preservation of these volatiles, or addition through late accretion. We show, using the "Rusty Rock" impact melt breccia, 66095, that volatile enrichment on the lunar surface occurred through vapor condensation. Isotopically light Zn (δ66Zn = -13.7‰), heavy Cl (δ37Cl = +15‰), and high U/Pb supports the origin of condensates from a volatile-poor internal source formed during thermomagmatic evolution of the Moon, with long-term depletion in incompatible Cl and Pb, and lesser depletion of more-compatible Zn. Leaching experiments on mare basalt 14053 demonstrate that isotopically light Zn condensates also occur on some mare basalts after their crystallization, confirming a volatile-depleted lunar interior source with homogeneous δ66Zn ≈ +1.4‰. Our results show that much of the lunar interior must be significantly depleted in volatile elements and compounds and that volatile-rich rocks on the lunar surface formed through vapor condensation. Volatiles detected by remote sensing on the surface of the Moon likely have a partially condensate origin from its interior.

Water on the surface of the Moon as seen by the Moon Mineralogy Mapper: Distribution, abundance, and origins

A new thermal correction model and experimentally validated relationships between absorption strength and water content have been used to construct the first global quantitative maps of lunar surface water derived from the Moon Mineralogy Mapper near-infrared reflectance data. We find that OH abundance increases as a function of latitude, approaching values of ~500 to 750 parts per million (ppm). Water content also increases with the degree of space weathering, consistent with the preferential retention of water originating from solar wind implantation during agglutinate formation. Anomalously high water contents indicative of interior magmatic sources are observed in several locations, but there is no global correlation between surface composition and water content. Surface water abundance can vary by ~200 ppm over a lunar day, and the upper meter of regolith may contain a total of ~1.2 × 10¹⁴ g of water averaged over the globe. Formation and migration of water toward cold traps may thus be a continuous process on the Moon and other airless bodies.

Gallium isotopic evidence for extensive volatile loss from the Moon during its formation

The distribution and isotopic composition of volatile elements in planetary materials holds a key to the characterization of the early solar system and the Moon's formation. The Moon and Earth are chemically and isotopically very similar. However, the Moon is highly depleted in volatile elements and the origin of this depletion is still debated. We present gallium isotopic and elemental measurements in a large set of lunar samples to constrain the origin of this volatile depletion. We show that while Ga has a geochemical behavior different from zinc, both elements show a systematic enrichment in the heavier isotopes in lunar mare basalts and Mg-suite rocks compared to the silicate Earth, pointing to a global-scale depletion event. On the other hand, the ferroan anorthosites are isotopically heterogeneous, suggesting a secondary distribution of Ga at the surface of the Moon by volatilization and condensation. The isotopic difference of Ga between Earth and the Moon and the isotopic heterogeneity of the crustal ferroan anorthosites suggest that the volatile depletion occurred following the giant impact and during the lunar magma ocean phase. These results point toward a Moon that has lost its volatile elements during a whole-scale evaporation event and that is now relatively dry compared to Earth.

D/H ratios of the inner Solar System

The original hydrogen isotope (D/H) ratios of different planetary bodies may indicate where each body formed in the Solar System. However, geological and atmospheric processes can alter these ratios through time. Over the past few decades, D/H ratios in meteorites from Vesta and Mars, as well as from S- and C-type asteroids, have been measured. The aim of this article is to bring together all previously published data from these bodies, as well as the Earth, in order to determine the original D/H ratio for each of these inner Solar System planetary bodies. Once all secondary processes have been stripped away, the inner Solar System appears to be relatively homogeneous in terms of water D/H, with the original water D/H ratios of Vesta, Mars, the Earth, and S- and C-type asteroids all falling between δD values of -100‰ and -590‰. This homogeneity is in accord with the 'Grand tack' model of Solar System formation, where giant planet migration causes the S- and C-type asteroids to be mixed within 1 AU to eventually form the terrestrial planets.This article is part of the themed issue 'The origin, history and role of water in the evolution of the inner Solar System'.

Early accretion of water and volatile elements to the inner Solar System: evidence from angrites

Inner Solar System bodies are depleted in volatile elements relative to chondrite meteorites, yet the source(s) and mechanism(s) of volatile-element depletion and/or enrichment are poorly constrained. The timing, mechanisms and quantities of volatile elements present in the early inner Solar System have vast implications for diverse processes, from planetary differentiation to the emergence of life. We report major, trace and volatile-element contents of a glass bead derived from the D'Orbigny angrite, the hydrogen isotopic composition of this glass bead and that of coexisting olivine and silicophosphates, and the 207Pb-206Pb age of the silicophosphates, 4568 ± 20 Ma. We use volatile saturation models to demonstrate that the angrite parent body must have been a major body in the early inner Solar System. We further show via mixing calculations that all inner Solar System bodies accreted volatile elements with carbonaceous chondrite H and N isotope signatures extremely early in Solar System history. Only a small portion (if any) of comets and gaseous nebular H species contributed to the volatile content of the inner Solar System bodies.This article is part of the themed issue 'The origin, history and role of water in the evolution of the inner Solar System'.

The origin of inner Solar System water

Of the potential volatile sources for the terrestrial planets, the CI and CM carbonaceous chondrites are closest to the planets' bulk H and N isotopic compositions. For the Earth, the addition of approximately 2-4 wt% of CI/CM material to a volatile-depleted proto-Earth can explain the abundances of many of the most volatile elements, although some solar-like material is also required. Two dynamical models of terrestrial planet formation predict that the carbonaceous chondrites formed either in the asteroid belt ('classical' model) or in the outer Solar System (5-15 AU in the Grand Tack model). To test these models, at present the H isotopes of water are the most promising indicators of formation location because they should have become increasingly D-rich with distance from the Sun. The estimated initial H isotopic compositions of water accreted by the CI, CM, CR and Tagish Lake carbonaceous chondrites were much more D-poor than measured outer Solar System objects. A similar pattern is seen for N isotopes. The D-poor compositions reflect incomplete re-equilibration with H2 in the inner Solar System, which is also consistent with the O isotopes of chondritic water. On balance, it seems that the carbonaceous chondrites and their water did not form very far out in the disc, almost certainly not beyond the orbit of Saturn when its moons formed (approx. 3-7 AU in the Grand Tack model) and possibly close to where they are found today.This article is part of the themed issue 'The origin, history and role of water in the evolution of the inner Solar System'.

On the Effect of Planetary Stable Isotope Compositions on Growth and Survival of Terrestrial Organisms

Isotopic compositions of reactants affect the rates of chemical and biochemical reactions. Usually it is assumed that heavy stable isotope enrichment leads to progressively slower reactions. Yet the effect of stable isotopes may be nonlinear, as exemplified by the "isotopic resonance" phenomenon. Since the isotopic compositions of other planets of Solar system, including Mars and Venus, are markedly different from terrestrial (e.g., deuterium content is ≈5 and ≈100 times higher, respectively), it is far from certain that terrestrial life will thrive in these isotopic conditions. Here we found that Martian deuterium content negatively affected survival of shrimp in semi-closed biosphere on a year-long time scale. Moreover, the bacterium Escherichia coli grows slower at Martian isotopic compositions and even slower at Venus's compositions. Thus, the biological impact of varying stable isotope compositions needs to be taken into account when planning interplanetary missions.

An asteroidal origin for water in the Moon

The Apollo-derived tenet of an anhydrous Moon has been contested following measurement of water in several lunar samples that require water to be present in the lunar interior. However, significant uncertainties exist regarding the flux, sources and timing of water delivery to the Moon. Here we address those fundamental issues by constraining the mass of water accreted to the Moon and modelling the relative proportions of asteroidal and cometary sources for water that are consistent with measured isotopic compositions of lunar samples. We determine that a combination of carbonaceous chondrite-type materials were responsible for the majority of water (and nitrogen) delivered to the Earth-Moon system. Crucially, we conclude that comets containing water enriched in deuterium contributed significantly <20% of the water in the Moon. Therefore, our work places important constraints on the types of objects impacting the Moon ∼4.5-4.3 billion years ago and on the origin of water in the inner Solar System.

The chlorine isotope fingerprint of the lunar magma ocean

The Moon contains chlorine that is isotopically unlike that of any other body yet studied in the Solar System, an observation that has been interpreted to support traditional models of the formation of a nominally hydrogen-free ("dry") Moon. We have analyzed abundances and isotopic compositions of Cl and H in lunar mare basalts, and find little evidence that anhydrous lava outgassing was important in generating chlorine isotope anomalies, because (37)Cl/(35)Cl ratios are not related to Cl abundance, H abundance, or D/H ratios in a manner consistent with the lava-outgassing hypothesis. Instead, (37)Cl/(35)Cl correlates positively with Cl abundance in apatite, as well as with whole-rock Th abundances and La/Lu ratios, suggesting that the high (37)Cl/(35)Cl in lunar basalts is inherited from urKREEP, the last dregs of the lunar magma ocean. These new data suggest that the high chlorine isotope ratios of lunar basalts result not from the degassing of their lavas but from degassing of the lunar magma ocean early in the Moon's history. Chlorine isotope variability is therefore an indicator of planetary magma ocean degassing, an important stage in the formation of terrestrial planets.

Extensive volatile loss during formation and differentiation of the Moon

Low estimated lunar volatile contents, compared with Earth, are a fundamental observation for Earth-Moon system formation and lunar evolution. Here we present zinc isotope and abundance data for lunar crustal rocks to constrain the abundance of volatiles during the final stages of lunar differentiation. We find that ferroan anorthosites are isotopically heterogeneous, with some samples exhibiting high δ(66)Zn, along with alkali and magnesian suite samples. Since the plutonic samples were formed in the lunar crust, they were not subjected to degassing into vacuum. Instead, their compositions are consistent with enrichment of the silicate portions of the Moon in the heavier Zn isotopes. Because of the difference in δ(66)Zn between bulk silicate Earth and lunar basalts and crustal rocks, the volatile loss likely occurred in two stages: during the proto-lunar disk stage, where a fraction of lunar volatiles accreted onto Earth, and from degassing of a differentiating lunar magma ocean, implying the possibility of isolated, volatile-rich regions in the Moon's interior.

Isotopic resonance hypothesis: experimental verification by Escherichia coli growth measurements

Isotopic composition of reactants affects the rates of chemical and biochemical reactions. As a rule, enrichment of heavy stable isotopes leads to progressively slower reactions. But the recent isotopic resonance hypothesis suggests that the dependence of the reaction rate upon the enrichment degree is not monotonous. Instead, at some “resonance” isotopic compositions, the kinetics increases, while at “off-resonance” compositions the same reactions progress slower. To test the predictions of this hypothesis for the elements C, H, N and O, we designed a precise (standard error ±0.05%) experiment that measures the parameters of bacterial growth in minimal media with varying isotopic composition. A number of predicted resonance conditions were tested, with significant enhancements in kinetics discovered at these conditions. The combined statistics extremely strongly supports the validity of the isotopic resonance phenomenon (p ≪ 10⁻¹⁵). This phenomenon has numerous implications for the origin of life studies and astrobiology, and possible applications in agriculture, biotechnology, medicine, chemistry and other areas.

The Moon as a recorder of organic evolution in the early solar system: a lunar regolith analog study

The organic record of Earth older than ∼3.8 Ga has been effectively erased. Some insight is provided to us by meteorites as well as remote and direct observations of asteroids and comets left over from the formation of the Solar System. These primitive objects provide a record of early chemical evolution and a sample of material that has been delivered to Earth's surface throughout the past 4.5 billion years. Yet an effective chronicle of organic evolution on all Solar System objects, including that on planetary surfaces, is more difficult to find. Fortunately, early Earth would not have been the only recipient of organic matter-containing objects in the early Solar System. For example, a recently proposed model suggests the possibility that volatiles, including organic material, remain archived in buried paleoregolith deposits intercalated with lava flows on the Moon. Where asteroids and comets allow the study of processes before planet formation, the lunar record could extend that chronicle to early biological evolution on the planets. In this study, we use selected free and polymeric organic materials to assess the hypothesis that organic matter can survive the effects of heating in the lunar regolith by overlying lava flows. Results indicate that the presence of lunar regolith simulant appears to promote polymerization and, therefore, preservation of organic matter. Once polymerized, the mineral-hosted newly formed organic network is relatively protected from further thermal degradation. Our findings reveal the thermal conditions under which preservation of organic matter on the Moon is viable.

Early solar system. Early accretion of water in the inner solar system from a carbonaceous chondrite-like source

Determining the origin of water and the timing of its accretion within the inner solar system is important for understanding the dynamics of planet formation. The timing of water accretion to the inner solar system also has implications for how and when life emerged on Earth. We report in situ measurements of the hydrogen isotopic composition of the mineral apatite in eucrite meteorites, whose parent body is the main-belt asteroid 4 Vesta. These measurements sample one of the oldest hydrogen reservoirs in the solar system and show that Vesta contains the same hydrogen isotopic composition as that of carbonaceous chondrites. Taking into account the old ages of eucrite meteorites and their similarity to Earth's isotopic ratios of hydrogen, carbon, and nitrogen, we demonstrate that these volatiles could have been added early to Earth, rather than gained during a late accretion event.

The negligible chondritic contribution in the lunar soils water

Recent data from Apollo samples demonstrate the presence of water in the lunar interior and at the surface, challenging previous assumption that the Moon was free of water. However, the source(s) of this water remains enigmatic. The external flux of particles and solid materials that reach the surface of the airless Moon constitute a hydrogen (H) surface reservoir that can be converted to water (or OH) during proton implantation in rocks or remobilization during magmatic events. Our original goal was thus to quantify the relative contributions to this H surface reservoir. To this end, we report NanoSIMS measurements of D/H and (7)Li/(6)Li ratios on agglutinates, volcanic glasses, and plagioclase grains from the Apollo sample collection. Clear correlations emerge between cosmogenic D and (6)Li revealing that almost all D is produced by spallation reactions both on the surface and in the interior of the grains. In grain interiors, no evidence of chondritic water has been found. This observation allows us to constrain the H isotopic ratio of hypothetical juvenile lunar water to δD ≤ -550‰. On the grain surface, the hydroxyl concentrations are significant and the D/H ratios indicate that they originate from solar wind implantation. The scattering distribution of the data around the theoretical D vs. (6)Li spallation correlation is compatible with a chondritic contribution <15%. In conclusion, (i) solar wind implantation is the major mechanism responsible for hydroxyls on the lunar surface, and (ii) the postulated chondritic lunar water is not retained in the regolith.

Understanding the origin and evolution of water in the Moon through lunar sample studies

A paradigm shift has recently occurred in our knowledge and understanding of water in the lunar interior. This has transpired principally through continued analysis of returned lunar samples using modern analytical instrumentation. While these recent studies have undoubtedly measured indigenous water in lunar samples they have also highlighted our current limitations and some future challenges that need to be overcome in order to fully understand the origin, distribution and evolution of water in the lunar interior. Another exciting recent development in the field of lunar science has been the unambiguous detection of water or water ice on the surface of the Moon through instruments flown on a number of orbiting spacecraft missions. Considered together, sample-based studies and those from orbit strongly suggest that the Moon is not an anhydrous planetary body, as previously believed. New observations and measurements support the possibility of a wet lunar interior and the presence of distinct reservoirs of water on the lunar surface. Furthermore, an approach combining measurements of water abundance in lunar samples and its hydrogen isotopic composition has proved to be of vital importance to fingerprint and elucidate processes and source(s) involved in giving rise to the lunar water inventory. A number of sources are likely to have contributed to the water inventory of the Moon ranging from primordial water to meteorite-derived water ice through to the water formed during the reaction of solar wind hydrogen with the lunar soil. Perhaps two of the most striking findings from these recent studies are the revelation that at least some portions of the lunar interior are as water-rich as some Mid-Ocean Ridge Basalt source regions on Earth and that the water in the Earth and the Moon probably share a common origin.

Lunar exploration: opening a window into the history and evolution of the inner Solar System

The lunar geological record contains a rich archive of the history of the inner Solar System, including information relevant to understanding the origin and evolution of the Earth-Moon system, the geological evolution of rocky planets, and our local cosmic environment. This paper provides a brief review of lunar exploration to-date and describes how future exploration initiatives will further advance our understanding of the origin and evolution of the Moon, the Earth-Moon system and of the Solar System more generally. It is concluded that further advances will require the placing of new scientific instruments on, and the return of additional samples from, the lunar surface. Some of these scientific objectives can be achieved robotically, for example by in situ geochemical and geophysical measurements and through carefully targeted sample return missions. However, in the longer term, we argue that lunar science would greatly benefit from renewed human operations on the surface of the Moon, such as would be facilitated by implementing the recently proposed Global Exploration Roadmap.

Planetary science. Analyzing Moon rocks

A better inventory of lunar volatiles will help improve our understanding of the origin and evolution of the Earth-Moon system. [Also see Report by Boyce et al. ]