Lunar Interior Research Articles

Volatile distributions in and on the Moon revealed by Cu and Fe isotopes in the ‘Rusty Rock’ 66095

The Apollo 16 ‘Rusty Rock’ impact melt breccia 66095 is a volatile-rich sample, with the volatiles inherited through vapor condensation from an internal lunar source formed during thermo-magmatic evolution of the Moon. We report Cu and Fe isotope data for 66095 and find that bulk-rocks, residues and acid leaches span a relatively limited range of compositions (3.0 ± 1.3 wt.% FeO [range = 2.0–4.8 wt.%], 5.4 ± 3.1 ppm Cu [range = 3–12 ppm], average δ56Fe of 0.15 ± 0.05‰ [weighted mean = 0.156‰] and δ65Cu of 0.72 ± 0.14‰ [weighted mean = 0.78‰]). In contrast to the extreme enrichment of the light isotopes of Zn and heavy isotopes of Cl in 66095, δ65Cu and δ56Fe in the sample lie within the previously reported range for lunar mare basalts (0.92 ± 0.16‰ and 0.12 ± 0.02‰, respectively). The lack of extreme isotopic fractionation for Cu and Fe isotopes reflects compositions inherent to 66095, with condensation of a cooling gas from impact-generated fumarolic activity at temperatures too low to lead to the condensation of Cu and Fe in the sample, but higher than required to condense Zn. Together with thermodynamic models, these constraints suggest that the gas condensed within 66095 between 700 and 900 °C (assuming a pressure of 10−6 and an fO2 of IW-2). That the Cu and Fe isotopic compositions of sample 66095 are within the range of mare basalts removes the need for an exotic, volatile-enriched source. The enrichment in Tl, Br, Cd, Sn, Zn, Pb, Rb, Cs, Ga, B, Cl, Li relative to Bi, Se, Te, Ge, Cu, Ag, Sb, Mn, P, Cr and Fe in the ‘Rusty Rock’ is consistent with volcanic outgassing models and indicates that 66095 likely formed distal from the original source of the gas. The volatile-rich character of 66095 is consistent with impact-generated fumarolic activity in the region of the Cayley Plains, demonstrating that volatile-rich rocks can occur on the lunar surface from outgassing of a volatile-poor lunar interior. The ‘Rusty Rock’ indicates that the lunar interior is significantly depleted in volatile elements and compounds and that volatile-rich surface rocks likely formed through vapor condensation. Remote sensing studies have detected volatiles on the lunar surface, attributing them dominantly to solar wind. Based on the ‘Rusty Rock’, some of these surface volatiles may also originate from the Moon’s interior.

1D geothermal inversion of the lunar deep interior temperature and heat production in the equatorial area

We present a study on lunar interior temperature and heat production by 1D geothermal inversion. With the layered structure and thermal state of the lunar interior reported by lunar seismic and magnetic sounding research, a forward modeling of deep temperature is given based on the theory of thermal conduction. Then, the particle swarm optimization (PSO) method is applied to implement the inversion of lunar interior heat production. A six-layer model is solved using a global heat flux of 12 mW/m2 and a near-surface temperature of 250 K. The inversion results show that the crust has an average heat production of approximately 210 nW/m3, the mantle has a depleted heat production varying from 3.7 to 8.1 nW/m3, and the heat production in the lunar core varies from 30 to 36 nW/m3. The distribution of heat production indicates that the present radioisotopes are mainly concentrated in the lunar crust. Different from previous estimates, the heat release in the lunar core may be considerable, similar to the average heat production in the Moon, implying that the residual heat from lunar accretion or radioactive decay is probably substantial; in contrast, perhaps the core was involved to a limit in the material exchange with the mantle. In addition, the obtained heat flux at the core-mantle boundary meets the value required for the core adiabatic process, indicating that the core convection may have stopped.

A petrologic study on the effect of mantle overturn: Implications for evolution of the lunar interior

Abstract Lunar mantle overturn caused by gravitational instability of the Fe-Ti rich KREEP layer (formed as the last 5% of a crystallizing magma ocean, and emplaced between the overlying anorthitic crust and the underlying lunar mantle) is a process that would introduce Fe-Ti enriched bodies deep inside the lunar interior. These chemical heterogeneities in the lunar mantle may be the source of the very Fe-Ti enriched near-primary Apollo basalts. Also, the Fe-Ti and KREEP enriched layer deep inside the Moon may be responsible for the 5–30% partial melt seismically detected close to the core-mantle boundary (CMB). This is assuming that the partial melt is neutrally buoyant at P-T conditions of the CMB. Here, we experimentally investigate the phase equilibria of the overturned Fe-Ti rich layer mixed with the mantle, at P-T conditions deep inside the lunar interior, focusing on the partial melt compositions formed. Our aim is to test (a) whether potential partial melt compositions formed near the CMB are neutrally buoyant with respect to the surrounding mantle, hence, stable; (b) if the partial melts formed within the lunar interior are positively buoyant and ascend, whether they can reproduce chemical characteristics of Apollo basalts. The densities calculated for the Fe-Ti rich partial melts from this study, using the physical parameters from previous studies, range from lower to higher values compared to that of the lunar mantle. This provides a basis for future investigations to experimentally constrain better the densities of these partial melts. Depending on the buoyancy of the partial melts, the following two scenarios are likely to happen. Firstly, if the partial melts are neutrally buoyant at the CMB, 5–30% partial melt would constrain the CMB temperatures between 1330(±1) and 1470(±19) °C. This can be used by future studies to derive the selenotherm better. Secondly, if the partial melts are positively buoyant, they should ascend and react with the mantle along their path. Upon reaching shallow depths below the crust, they may likely assimilate any Fe-Ti rich layer that was left over from the gravitational overturn, as well as undergo olivine fractionation upon pooling in a shallow magma chamber. We modeled assimilation-fractional crystallization of the partial melts using the Gibb’s-free minimization algorithm alphaMELTS. Our results show that reactive ascent of Fe-Ti rich partial melts through the lunar mantle and subsequent olivine fractionation in a shallow magma chamber is a promising way to evolve the melt compositions to converge with the lunar basalts better. Shallow level assimilation of Fe-Ti rich lithology post reactive-ascent through the mantle is also feasible, but only for low degrees of assimilation.

The participation of ilmenite-bearing cumulates in lunar mantle overturn

The ilmenite-bearing cumulates (IBC) formed from the solidification of the lunar magma ocean are thought to have significantly affected the long-term evolution of the lunar interior and surface. Their high density is considered to trigger Rayleigh–Taylor instabilities which allow them to sink into the solidified cumulates below and drive a large-scale overturn in the lunar mantle. Knowledge of how the IBC participate in the overturn is important for studying the early lunar dynamo, chemistry of surface volcanism, and the existence of present-day partial melt at the lunar core–mantle boundary. Despite early efforts to study this process as Rayleigh–Taylor instabilities, no dynamical models have quantified the degree of IBC sinking systematically. We have performed quantitative 2-D geodynamical simulations to measure the extent to which IBC participate in the overturn after their solidification, and tested the effect of a range of physical and chemical parameters. Our results show that IBC overturn most likely happened when the magma ocean had not yet fully solidified, with the residual melt decoupling the crust and IBC, resulting in 50–70% IBC sinking. Participation of the last dregs of remaining magma ocean melt is unlikely, leaving its high concentrations of radiogenic elements close to the surface. Our simulations further indicate that foundered IBC can stay relatively stable at the core–mantle boundary until the present day, at temperatures consistent with the presence of a partially molten zone in the deep mantle as inferred from geophysical data. 30–50% of the primary IBC remain at shallow depths throughout lunar history, enabling their assimilation by rising magma to form high-Ti basalts.

Origin of lunar Very High Potassium (VHK) basalts: A combination of endogenous and exogenous processes

Very high potassium or VHK basalts have been described from the Apollo 14 landing site at Fra Mauro on the lunar near side. Many of the known samples are clasts in polymict breccias with a few as <1 cm rocklets in the regolith samples. VHK basalts are distinct from the high-Al basalts that are more common at the Apollo 14 site in that they are enriched in the alkali/alkaline earth elements (e.g., K, Rb, Ba, etc.). The source of this enrichment was initially proposed to be through assimilation of granite by a crystallizing high-Al basaltic magma. However, with the discovery of more VHK basalt clasts from three Apollo 14 polymict breccias, the number of different AFC episodes and granite assimilants had to increase in order to explain the whole rock compositional diversity within the VHK basalt suite.New work completed on fourteen VHK basalts include Crystal Size Distributions (CSDs) and in-situ chemical analyses and element maps collected by electron probe microanalysis (EPMA). CSDs completed on three VHK basalt samples indicate that these basalts are not impact melts and represent endogenous melts of the lunar interior. Potassium Kα element maps reveal the spatial relationship between the K-rich material and the basalt clasts with attached breccia matrix if present. In-situ EPMA analyses have identified two distinct types of K-rich material: K-feldspar and K-rich glass. With these new data, an additional mechanism for an exogenic petrogenesis of VHK basalts is proposed that involves the impact process. VHK basalts can be divided into two groups based on density and viscosity. VHK-1 basalts formed when a hot impact ejecta covered the granite/felsite-rich matrix material containing high-Al basalt clasts. Heat from the impact ejecta partially melted and possibly evaporated nearby K-bearing materials, which then infiltrated and contaminated the high-Al clasts. VHK-2 basalts are consistent with the hypothesis of granite assimilation by a high-Al magma, as seen in the higher abundances of network-forming elements.

Volatile contents of the lunar interior

Volatile contents of the lunar interior

The New Moon: Major Advances in Lunar Science Enabled by Compositional Remote Sensing from Recent Missions

Volatile-bearing lunar surface and interior, giant magmatic-intrusion-laden near and far side, globally distributed layer of purest anorthosite (PAN) and discovery of Mg-Spinel anorthosite, a new rock type, represent just a sample of the brand new perspectives gained in lunar science in the last decade. An armada of missions sent by multiple nations and sophisticated analyses of the precious lunar samples have led to rapid evolution in the understanding of the Moon, leading to major new findings, including evidence for water in the lunar interior. Fundamental insights have been obtained about impact cratering, the crystallization of the lunar magma ocean and conditions during the origin of the Moon. The implications of this understanding go beyond the Moon and are therefore of key importance in solar system science. These new views of the Moon have challenged the previous understanding in multiple ways and are setting a new paradigm for lunar exploration in the coming decade both for science and resource exploration. Missions from India, China, Japan, South Korea, Russia and several private ventures promise continued exploration of the Moon in the coming years, which will further enrich the understanding of our closest neighbor. The Moon remains a key scientific destination, an active testbed for in-situ resource utilization (ISRU) activities, an outpost to study the universe and a future spaceport for supporting planetary missions.

Thermo-chemical constraints on the lunar bulk composition and the structure of a three-layer mantle

The main purpose of the present study is to evaluate the lunar bulk composition (BSM) and the composition of a three-layer mantle based on a joint inversion of lunar mass and moment of inertia, and the mantle seismic velocity profiles in combination with Gibbs free energy minimization. As an integral characteristic of the thermal state, the mean volume temperature Tmean of the lunar mantle controlling the mineral composition of the Moon was chosen. In terms of Tmean, all thermal models can be conditionally divided into “cold” ones with Tmean ∼ 690–860 °C and “hot” ones with Tmean ∼ 925–1075 °C. We find that irrespective of the thermal state, BSM is characterized by practically constant values of bulk FeO ∼ 12–13 wt% and Mg# 80–81.5, which indicates a significant difference in the composition of the silicate Earth (BSE) and its satellite. The FeO content of 11–14 wt% and Mg# 80–83 are approximately identical in the upper and lower mantle. The bulk SiO2 abundance depends little on the thermal state and ranges from 45 to 52 wt%, with probable concentrations of SiO2 being 50–55% in the upper mantle and 45–50 wt% in the lower mantle; orthopyroxene, and not olivine, is the predominant mineral of the upper mantle. On the contrary, the lunar abundance of alumina, depending on the thermal state, falls into two different groups. Cold models of BSM with a content of 3–4.6 wt% Al2O3 are comparable to those of BSE, whereas for hot models the bulk-alumina content can be in the range of 1.2–1.7 × BSE. The results indicate a tendency for a gradual increase in the alumina content with depth: from 1 to 2% in the upper mantle to 4–7 wt% Al2O3 in the lower mantle with an increasing amount of garnet. The composition of the middle mantle remains controversial, since it may partially overlap with the compositions of the overlying and underlying shells. Our simulation results show that a chemically stratified lunar interior is consistent with the observations and has similar concentrations of FeO and MgO but different concentrations of Al2O3 and SiO2 in different zones of the mantle. However, the question of the similarity and/or difference in the composition of the silicate Earth and its satellite with respect to the abundance of refractory elements, which is of fundamental importance for lunar geochemistry, remains unresolved and requires further research.

The Cassini State of the Moon's Inner Core

AbstractWe present a model of the precession dynamics of the Moon that comprises a fluid outer core and a solid inner core. We show that three Cassini states associated with the inner core exist. The tilt angle of the inner core in each of these states is determined by the ratio between the free inner core nutation frequency (ωficn) and the precession frequency Ωp=2π/18.6 year−1. All three Cassini states are possible if |ωficn|&gt;2π/16.4 year−1, but only one is possible otherwise. Assuming that the lowest energy state is favored, this transition marks a discontinuity in the tilt angle of the inner core, transiting from −33° to 17° as measured with respect to the mantle figure axis, where negative angles indicate a tilt toward the orbit normal. Possible Lunar interior density structures cover a range of ωficn, from approximately half to twice as large as Ωp, so the precise tilt angle of the inner core remains unknown, though it is likely large because Ωp is within the resonant band of ωficn. Adopting one specific density model, we suggest an inner core tilt of approximately −17°. Viscoelastic deformations within the inner core and melt and growth at the surface of a tilted inner core, both neglected in our model, should reduce this amplitude. If the inner core is larger than approximately 200 km, it may contribute by as much as a few thousandths of a degree on the observed mantle precession angle of 1.543°.

Preferred design and error analysis for the future dedicated deep-space Mars-SST satellite gravity mission

Because the precise measurement of the Martian gravitational field plays a significant role in the future Mars exploration program, the future dedicated Mars satellite-to-satellite tracking (Mars-SST) gravity mission in China is investigated in detail for producing the next generation of the Mars gravity field model with high accuracy. Firstly, a new semi-numerical synthetical error model of the cumulative Martian geoid height influenced by the major error sources of the space-borne instruments is precisely established and efficiently verified. Secondly, the deep space network in combination with the satellite-to-satellite tracking in the low-low (DSN-SST-LL) mode is a preferred design owing to the high precision determination of the gravity maps, the low technical complexity of the satellite system and the successful experiences with the Earth’s Gravity Recovery and Climate Experiment (GRACE) projects and the lunar Gravity Recovery and Interior Laboratory (GRAIL) program. Finally, the future twin Mars-SST satellites plan to adopt the optimal matching accuracy indices of the satellite-equipped sensors (e.g., $10^{-7}$ m/s in the inter-satellite range-rate from the interferometric laser ranging system (ILRS), 35 m in the orbital position tracked by the DSN and $3\times 10^{-11}$ m/s2 in the non-conservative force from the drag-free control system (DFCS)) and the preferred orbital parameters (e.g., the orbital altitude of $100\pm 50$ km and the inter-satellite range of $50\pm 10$ km).

Evidence for a sulfur-undersaturated lunar interior from the solubility of sulfur in lunar melts and sulfide-silicate partitioning of siderophile elements

Sulfur concentrations at sulfide saturation (SCSS) were determined for a range of low- to high-Ti lunar melt compositions (synthetic equivalents of Apollo 14 black and yellow glass, Apollo 15 green glass, Apollo 17 orange glass and a late-stage lunar magma ocean melt, containing between 0.2 and 25 wt.% TiO2) as a function of pressure (1–2.5 GPa) and temperature (1683–1883 K). For the same experiments, sulfide-silicate partition coefficients were derived for elements V, Cr, Mn, Co, Cu, Zn, Ga, Ge, As, Se, Mo, Sn, Sb, Te, W and Pb. The SCSS is a strong function of silicate melt composition, most notably FeO content. An increase in temperature increases the SCSS and an increase in pressure decreases the SCSS, both in agreement with previous work on terrestrial, lunar and martian compositions. Previously reported SCSS values for high-FeO melts were combined with the experimental data reported here to obtain a new predictive equation to calculate the SCSS for high-FeO lunar melt compositions. Calculated SCSS values, combined with previously estimated S contents of lunar low-Ti basalts and primitive pyroclastic glasses, suggest their source regions were not sulfide saturated. Even when correcting for the currently inferred maximum extent of S degassing during or after eruption, sample S abundances are still > 700 ppm lower than the calculated SCSS values for these compositions. To achieve sulfide saturation in the source regions of low-Ti basalts and lunar pyroclastic glasses, the extent of degassing of S in lunar magma would have to be orders of magnitude higher than currently thought, inconsistent with S isotopic and core-to-rim S diffusion profile data. The only lunar samples that could have experienced sulfide saturation are some of the more evolved A17 high-Ti basalts, if sulfides are Ni- and/or Cu rich.Sulfide saturation in the source regions of lunar melts is also inconsistent with the sulfide-silicate partitioning systematics of Ni, Co and Cu. Segregation of significant quantities of (non)-stoichiometric sulfides during fractional crystallization would result in far larger depletions of Ni, Co and Cu than observed, whereas trends in their abundances are more likely explained by olivine fractionation. The sulfide exhaustion of the lunar magma source regions agrees with previously proposed low S abundances in the lunar core and mantle, and by extension with relatively minor degassing of S during the Moon-forming event. Our results support the hypothesis that refractory chalcophile and highly siderophile element systematics of low-Ti basalts and pyroclastic glasses reflect the geochemical characteristics of their source regions, instead of indicating the presence of residual sulfides in the lunar interior.

Effects of multiscale phase-mixing and interior conductance in the lunar-like pickup ion plasma wake. First results from 3-D hybrid kinetic modeling

The study of multiscale pickup ion phase-mixing in the lunar plasma wake with a hybrid model is the main subject of our investigation in this paper. Photoionization and charge exchange of protons with the lunar exosphere are the ionization processes included in our model. The computational model includes the self-consistent dynamics of the light (H+ or H2+ and He+), and heavy (Na+) pickup ions. The electrons are considered as a fluid. The lunar interior is considered as a weakly conducting body. In this paper we considered for the first time the cumulative effect of heavy neutrals in the lunar exosphere (e.g., Al, Ar), an effect which was simulated with one species of Na+ but with a tenfold increase in total production rates. We find that various species produce various types of plasma tail in the lunar plasma wake. Specifically, Na+ and He+ pickup ions form a cycloid-like tail, whereas the H+ or H2+ pickup ions form a tail with a high density core and saw-like periodic structures in the flank region. The length of these structures varies from 1.5RM to 3.3RM depending on the value of gyroradius for H+ or H2+ pickup ions. The light pickup ions produce more symmetrical jump in the density and magnetic field at the Mach cone which is mainly controlled by the conductivity of the interior, an effect previously unappreciated. Although other pickup ion species had little effect on the nature of the interaction of the Moon with the solar wind, the global structure of the lunar tail in these simulations appeared quite different when the H2+ production rate was high.

Widespread distribution of OH/H2O on the lunar surface inferred from spectral data.

Remote sensing data from lunar orbiters have revealed spectral features consistent with the presence of OH or H2O on the lunar surface. Analyses of data from the Moon Mineralogy Mapper spectrometer onboard the Chandryaan-1 spacecraft have suggested that OH/H2O is recycled on diurnal timescales and persists only at high latitudes. However, the spatial distribution and temporal variability of the OH/H2O, as well as its source, remain uncertain. Here we incorporate a physics-based thermal correction into analysis of reflectance spectra from the Moon Mineralogy Mapper and find that prominent absorption features consistent with OH/H2O can be present at all latitudes, local times, and surface types examined. This suggests the widespread presence of OH/H2O on the lunar surface without significant diurnal migration. We suggest that the spectra are consistent with the production of OH in space weathered materials by the solar wind implantation of H+ and formation of OH at crystal defect sites, as opposed to H2O sourced from the lunar interior. Regardless of the specific composition or formation mechanism, we conclude that OH/H2O can be present on the Moon under thermal conditions more wide-ranging than previously recognized.

New high pressure experiments on sulfide saturation of high-FeO∗ basalts with variable TiO2 contents – Implications for the sulfur inventory of the lunar interior

In order to constrain sulfur concentration in intermediate to high-Ti mare basalts at sulfide saturation (SCSS), we experimentally equilibrated FeS melt and basaltic melt using a piston cylinder at 1.0–2.5 GPa and 1400–1600 °C, with two silicate compositions similar to high-Ti (Apollo 11: A11, ∼11.1 wt.% TiO2, 19.1 wt.% FeO∗, and 39.6 wt.% SiO2) and intermediate-Ti (Luna 16, ∼5 wt.% TiO2, 18.7 wt.% FeO∗, and 43.8 wt.% SiO2) mare basalts. Our experimental results show that SCSS increases with increasing temperature, and decreases with increasing pressure, which are similar to the results from previous experimental studies. SCSS in the A11 melt is systematically higher than that in the Luna 16 melt, which is likely due to higher FeO∗, and lower SiO2 and Al2O3 concentration in the former. Compared to the previously constructed SCSS models, including those designed for high-FeO∗ basalts, the SCSS values determined in this study are generally lower than the predicted values, with overprediction increasing with increasing melt TiO2 content. We attribute this to the lower SiO2 and Al2O3 concentration of the lunar magmas, which is beyond the calibration range of previous SCSS models, and also more abundant FeTiO3 complexes in our experimental melts that have higher TiO2 contents than previous models’ calibration range. The formation of FeTiO3 complexes lowers the activity of FeO∗, aFeO∗silicate melt, and therefore causes SCSS to decrease. To accommodate the unique lunar compositions, we have fitted a new SCSS model for basaltic melts of >5 wt.% FeO∗ and variable TiO2 contents. Using previous chalcophile element partitioning experiments that contained more complex Fe-Ni-S sulfide melts, we also derived an empirical correction that allows SCSS calculation for basalts where the equilibrium sulfides contain variable Ni contents of 10–50 wt.%. At the pressures and temperatures of multiple saturation points, SCSS of lunar magmas with compositions from picritic glasses, mare basalts, to young lunar meteorites vary from 2600 to 4800 ppm for basalt equilibration with a pure FeS melt and from 1400 to 2600 ppm for basalt equilibration with a Fe-rich sulfide melt containing 30 wt.% Ni. The measured S contents in these proposed near-primary lunar magmas are lower than the predicted SCSS at the conditions of their last equilibration with the lunar mantle, indicating no sulfide retention in the lunar mantle source during partial melting. Sulfide exhaustion during partial melting in the lunar mantle also supports the notion that the bulk silicate moon is depleted in highly siderophile elements. Based on the measured S contents and the estimated degree of melting, the estimated S contents for the mantle source of A15 green glass and A15 mare basalts is 10–23 ppm; for A17 orange glass is 25–62 ppm, for A12 mare basalts is 27–92 ppm, and for A11 basalt is 35–120 ppm. Consideration of SCSS decrease due to the presence of Ni in the sulfide melt does not change these mantle S abundance estimates for <30 wt.% Ni in the sulfide. The inferred S contents suggest that the lunar mantle is heterogeneous in terms of S. Although variable among different groups, the inferred S abundance of up to 120 ppm in the lunar mantle falls near the lower end of the S content of the depleted terrestrial mantle such as the MORB source.

Surface water on the Moon

Space Sciences Recent research has fueled debate regarding the abundance of water in the Moon's interior and its implications for lunar evolution, but surface water is known to occur in the lunar regolith. Using data from NASA's Moon Mineralogy Mapper—an imaging spectrometer that was included on India's first mission to the Moon, Chandrayaan-1—Li and Milliken present a globally comprehensive map of these deposits. The upper meter of the lunar regolith is estimated to contain roughly 0.1 petagrams of water. Higher latitudes have more water ice than lower latitudes. Most of the ice was implanted by solar wind, with some local input from the lunar interior. Sci. Adv. 10.1126/sciadv.1701471 (2017).

Olivine-bearing lithologies on the Moon: Constraints on origins and transport mechanisms from M3 spectroscopy, radiative transfer modeling, and GRAIL crustal thickness

High-resolution hyperspectral data from Chandrayaan-1’s Moon Mineralogy Mapper (M3) allow detection of olivine on the lunar surface. Olivine exposed at the surface may originate as mantle material or igneous products (intrusive or extrusive). Potential transport mechanisms include excavation of the mantle or lower crustal material by impacts that form basins and complex craters, differentiation of impact melt sheets, or magmatic emplacement of lavas, cumulates, or xenoliths. A sample of the lunar mantle, which has not been conclusively identified in the lunar sample collection, would yield fundamental new insights into the composition, structure, and evolution of the lunar interior. Olivine identified in remote spectral data is generally accepted to originate from the primary mantle, because abundant olivine is expected to exist in the mantle and lower crust, yet have sparse occurrences in the upper crust. In this study, we identified 111 M3 single-pixel spectra with characteristic absorption features consistent with olivine at Crisium, Nectaris, and Humorum basins and near the craters Roche and Tsiolkovsky. In an effort to determine the origins and transport mechanisms that led to these individual exposures, we estimated mineral abundances using radiative transfer modeling and examined crustal thickness estimates, topography and slope maps, and images from the Lunar Reconnaissance Orbiter Camera (LROC). At Crisium basin, where crustal thickness is near 0 km (Wieczorek et al., 2013), mantle olivine may have been exposed by basin-forming impact and deposited on the rim. Picard crater, which is superposed on the floor of Crisium, also exhibits potential mantle olivine in its ejecta. Within Nectaris basin, olivine exposures are confined to the rims of small craters on the mare, which are inferred to excavate a layer of olivine-rich mare basalt. Olivine occurrences on the rim of Humorum basin, including those located on a graben, are likely to be cumulates of shallow intrusions that were transported magmatically to the surface. Near Roche crater, olivine may have originated in shallow dikes that reached the subsurface and were exposed by impacts. In addition to verifying both known and previously unidentified olivine exposures, our combined geophysical, spectral, and radiative transfer modeling investigation has allowed identification of both igneous and mantle-derived olivine.

Volatile element loss during planetary magma ocean phases

Moderately volatile elements (MVE) are key tracers of volatile depletion in planetary bodies. Zinc is an especially useful MVE because of its generally elevated abundances in planetary basalts, relative to other MVE, and limited evidence for mass-dependent isotopic fractionation under high-temperature igneous processes. Compared with terrestrial basalts, which have δ66Zn values (per mille deviation of the 66Zn/64Zn ratio from the JMC-Lyon standard) similar to some chondrite meteorites (∼+0.3‰), lunar mare basalts yield a mean δ66Zn value of +1.4 ± 0.5‰ (2 st. dev.). Furthermore, mare basalts have average Zn concentrations ∼50 times lower than in typical terrestrial basaltic rocks. Late-stage lunar magmatic products, including ferroan anorthosite, Mg- and Alkali-suite rocks have even higher δ66Zn values (+3 to +6‰). Differences in Zn abundance and isotopic compositions between lunar and terrestrial rocks have previously been interpreted to reflect evaporative loss of Zn, either during the Earth–Moon forming Giant Impact, or in a lunar magma ocean (LMO) phase. To explore the mechanisms and processes under which volatile element loss may have occurred during a LMO phase, we developed models of Zn isotopic fractionation that are generally applicable to planetary magma oceans. Our objective was to identify conditions that would yield a δ66Zn signature of ∼+1.4‰ within the lunar mantle. For the sake of simplicity, we neglect possible Zn isotopic fractionation during the Giant Impact, and assumed a starting composition equal to the composition of the present-day terrestrial mantle, assuming both the Earth and Moon had zinc ‘consanguinity’ following their formation. We developed two models: the first simulates evaporative fractionation of Zn only prior to LMO mixing and crystallization; the second simulates continued evaporative fractionation of Zn that persists until ∼75% LMO crystallization. The first model yields a relatively homogenous bulk solid LMO δ66Zn value, while the second results in a stratification of δ66Zn values within the LMO sequence. Loss and/or isolation mechanisms for volatiles are critical to these models; hydrodynamic escape was not a dominant process, but loss of a nascent lunar atmosphere or separation of condensates into a proto-lunar crust are possible mechanisms by which volatiles could be separated from the lunar interior. The results do not preclude models that suggest a lunar volatile depletion episode related to the Giant Impact. Conversely, LMO models for volatile loss do not require loss of volatiles prior to lunar formation. Outgassing during planetary magma ocean phases likely played a profound role in setting the volatile inventories of planets, particularly for low mass bodies that experienced the greatest volatile loss. In turn, our results suggest that the initial compositions of planets that accreted from smaller, highly differentiated planetesimals were likely to be severely volatile depleted.

THE ADVANCEMENT OF LUNAR GRAVITY MODEL DUE TO THE DEVELOPMENT OF SPACE TRACKING TECHNIQUES

AbstractBased on the three modes of lunar spacecraft tracking techniques: Earth‐based tracking mode, high‐low satellite‐to‐satellite tracking mode and low‐low satellite‐to‐satellite tracking mode, the development of lunar gravity models could be divided into 4 stages. First, we introduce the principle, technical characteristics of the different tracking modes, and the representative gravity models, and then make comments on these models’ precision. Further, through the comparison of gravity anomaly precision, characteristics and orbit determination precision from different stages’ lunar gravity field models, we conclude that: the advancement of space tracking techniques has significantly improved the precision of lunar gravity model and effectively promotes the understanding of lunar interior structure and the reliability of lunar satellite orbit determination. Finally, we analyze the deficiency of current lunar gravity models and give a perspective of future space tracking techniques.

Origin and Evolution of Water in the Moon's Interior

Nearly forty years after the return of the first lunar samples to Earth, improvements in laboratory detection limits made possible the first definitive discovery of magmatic water in lunar volcanic samples. The intervening decade has seen an exponential increase in the amount of data on the abundance of magmatic water, and its hydrogen isotope composition, in various rock types recovered from the Moon. Here we review these data and describe how the abundance of water in the lunar interior places important constraints on models for the high-temperature origin and evolution of the Moon.

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.