Chang’E-5 samples reveal high water content in lunar minerals

Optical and Dielectrical Properties of Opal Water Content Determination Using Terahertz Time-Domain Spectroscopy

The optical and dielectric properties of opals with different water contents were investigated using terahertz time-domain spectroscopy. The refractive indices and absorption coefficients showed different trends due to the different water contents. The effective medium theory was used to extract the intrinsic dielectric permittivity of opal from opal-polytetrafluoroethylene mixtures. The extracted dielectric permittivities were fitted using a double Debye model to analyze the microscopic relaxation mechanism.

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.

Characterization of the Micro-Morphology and Compositional Distribution of Chang'e-5 Lunar Soil Mineral Surfaces Using TOF-SIMS

The lunar soil samples returned by China's Chang'e-5 (CE-5) contain valuable information on geological evolutions on the Moon. Herein, by employing high-resolution time-of-flight secondary ion mass spectrometry (TOF-SIMS), five rock chip samples from the CE-5 lunar soil are characterized in-depth, which reveal micro-morphological and compositional features. From the elemental/molecular ion distribution images, minerals such as pyroxene, ilmenite, feldspar, K-rich glass, silica, and silicate minerals are identified, along with their occurrence states and distribution results. More importantly, uncommon vesicle-like patterns are probed via TOF-SIMS, which may not be captured by conventional electron microscopy. The possible origins of vesicles are also proposed. Hopefully, these discoveries will provide essential guidance for future investigations on the Moon and accelerate the application of TOF-SIMS in space exploration.

Nanoscale characterization of space weathering in lunar samples

Nanoscale Fourier transform infrared (Nano-FTIR) imaging and spectroscopy correlated with photoluminescence measurements of lunar Apollo samples with different surface radiation exposure histories reveal distinct physical and chemical differences associated with space weathering effects. Analysis of two sample fragments: an ilmenite basalt (12016) and an impact melt breccia (15445) show evidence of intrinsic or delivered Nd3+ and an amorphous silica glass component on exterior surfaces, whereas intrinsic Cr3+ and/or trapped electron states are limited to interior surfaces. Spatially localized 1050 cm-1/935 cm-1 band ratios in Nano-FTIR hyperspectral maps may further reflect impact-induced shock nanostructures, while shifts in silicate band positions indicate accumulated radiation damage at the nanoscale from prolonged space weathering due to micrometeorites, solar wind, energetic x-rays and cosmic ray bombardment. Our observations demonstrate that space weathering alterations of the surface of lunar samples at the nanoscale may provide a mechanism to distinguish lunar samples of variable surface exposure age.

Exploring the lunar water cycle

The presence of water on the Moon has been indicated by various remote-sensing observations and analyses of returned samples. Several missions are planned to conduct new in situ research on the lunar surface to directly observe and characterize lunar water. A comprehensive characterization of the present forms of water, their abundance, spatial distribution, temporal variation, and possible origin is required to understand the lunar water cycle and the relevance of individual source and sink mechanisms and transformations between the involved volatile species. These processes extend over vastly different scales, and the governing parameters are often insufficiently constrained by experimental and observational data. Here, I present a brief overview of the current state of knowledge on the lunar water cycle, its relevance for lunar science and exploration, and some of the main challenges of modeling and future in situ analyses aiming to substantially advance the understanding of lunar water occurrences.

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.

Trace element detection in anhydrous minerals by micro-scale quantitative nuclear magnetic resonance spectroscopy

Nominally anhydrous minerals (NAMs) composing Earth's and planetary rocks incorporate microscopic amounts of volatiles. However, volatile distribution in NAMs and their effect on physical properties of rocks remain controversial. Thus, constraining trace volatile concentrations in NAMs is tantamount to our understanding of the evolution of rocky planets and planetesimals. Here, we present an approach of trace-element quantification using micro-scale Nuclear Magnetic Resonance (NMR) spectroscopy. This approach employs the principle of enhanced mass-sensitivity in NMR microcoils. We were able to demonstrate that this method is in excellent agreement with standard methods across their respective detection capabilities. We show that by simultaneous detection of internal reference nuclei, the quantification sensitivity can be substantially increased, leading to quantifiable trace volatile element amounts of about 50 ng/g measured in a micro-meter sized single anorthitic mineral grain, greatly enhancing detection capabilities of volatiles in geologically important systems.

Effect of crystal-water on the optical and dielectric characteristics of calcium sulfate in the THz band

The effect of crystal-water contents on the optical properties and dielectric characteristics of calcium sulfate in the THz band is investigated. The complex dielectric constant and conductivity are analyzed using the Drude-Smith model. The refractive index and absorption coefficient are linearly increased with the content of crystal-water, and the corresponding linear fitting lines of R2 over 0.97 are obtained. The dielectric properties of calcium sulfate are significantly affected by the crystal-water content. These results indicate that a new method to quantitative measurement of the crystal-water content in hydrous minerals is provided.

Scientific objectives and payload configuration of the Chang'E-7 mission

As the cornerstone mission of the fourth phase of the Chinese Lunar Exploration Program, Chang'E-7 (CE-7) was officially approved, and implementation started in 2022, including a main probe and a communication relay satellite. The main probe, consisting of an orbiter, a lander, a rover and a mini-flying probe, is scheduled to be launched in 2026. The lander will land on Shackleton crater's illuminated rim near the lunar south pole, along with the rover and mini-flying probe. The relay satellite (named Queqiao-2) will be launched in February 2024 as an independent mission to support relay communication during scientific exploration undertaken by Chang'E-4, the upcoming Chang'E-6 in 2024 and subsequent lunar missions. The CE-7 mission is mainly aimed at scientific and resource exploration of the lunar south pole. We present CE-7's scientific objectives, the scientific payloads configuration and the main functions for each scientific payload with its key technical specifications.