The image of a bone-dry surface in the Moon's non-polar regions impinged by the Apollo missions was changed by the detection of widespread absorption near 3 mu m in 2009, interpreted as a signature of hydration. However, debates persist on the relative contribution of molecular water (H2O) and other hydroxyl (OH) compounds to this hydration feature, as well as the cause of the potential temperature-dependence of the OH/H2O abundance. Resolving these debates will help to estimate the inventory of water on the Moon, a crucial resource for future space explorations. In this study, we measured the abundance and isotope composition of hydrogen within the outermost micron of Chang'e-5 soil grains, collected from the lunar surface and from a depth of 1 m. These measurements, combined with our laboratory simulation experiments, demonstrate that solar-wind-induced OH can be thermally retained in lunar regolith, with an abundance of approximately 48-95 ppm H2O equivalent. This abundance exhibits small latitude dependence and no diurnal variation. By integrating our results with published remote sensing data, we propose that a high amount of molecular water (similar to 360 +/- 200 ppm H2O) exists in the subsurface layer of the Moon's non-polar regions. The migration of this H2O accounts for the observed latitude and diurnal variations in 3 mu m band intensity. The inventory of OH and H2O proposed in this study reconciles the seemingly conflicting observations from various instruments, including infrared/ultraviolet spectroscopies and the Neutral Mass Spectrometer (NMS). Our interpretation of the distribution and dynamics of lunar hydration offers new insights for future lunar research and space missions.

In the scientific field of collisionless shocks, interplanetary space comprises a critical natural laboratory allowing the study of processes at spatial scales which are impossible to recreate in laboratories on Earth. Despite decades of research, key questions in the dynamics of collisionless shocks including energy transport and exchange remain unresolved due to instrumental limitations. With the return of humanity to the Moon and the upcoming construction of the Lunar Platform: Gateway (LOP-G) space station, the possibility arises to study the pristine solar wind in unprecedented detail, with the space station potentially enabling significant power capacity and data rates which would be challenging to achieve on smaller unmanned spacecraft. The space station's location in a lunar halo orbit allows the study of the solar wind away from the contaminating influence of the terrestrial bow shock. Here we propose to utilize nitrogen-vacancy (NV) diamond technology to combine magnetometer, temperature and plasma density measurements into a single instrument which can sample kHz-range magnetic field with sensitivities on the order of <1e-5 nT, while also sounding the local plasma density and temperature. These capabilities will generate datasets which will contribute significantly to shock science, helping answer key outstanding questions in the field. Simultaneously, these observations will improve understanding of space weather dynamics, contribute to cross-calibrating complementary missions, and probe the lunar exosphere. With the paucity of long-term, high-cadence, high-sensitivity pristine solar wind datasets, the Diamond Experiment In the MagnetOSphere (DEIMOS) will fill a key need for the solar wind and collisionless shocks community.

In the coming decades, exploration of the lunar surface is likely to increase as multiple nations execute ambitious lunar exploration programs. Among several environmental effects of such activities, increasing traffic near and on the lunar surface will result in the injection of anthropogenic neutral gases into the lunar exosphere. The subsequent ionization of such anthropogenic neutrals in the lunar environment may contribute to and ultimately exceed the generation of 'native' lunar pickup ions, thereby altering the fundamental space plasma interaction with the Moon. To better understand these possible effects, we conducted plasma simulations of the solar wind interaction with the Moon in the presence of increasing ion production rates from an anthropogenic lunar exosphere. At ionization levels between 0.1 and 10 times the native lunar exospheric ion production rate, little to no changes to the solar wind interaction to the Moon are present; however, ionization levels of 100 and 1000 times the native rate result in significant mass loading of the solar wind and disruption of the present-day structure of the Moon's plasma environment. Comparing to the planned Artemis landings, which are likely to contribute only an additional X10% of the native lunar exospheric ion production rate, we conclude that the Artemis program will have little effect on the Moon's plasma environment. However, more frequent landings and/or continual outgassing from human settlements on the Moon in the more distant future are likely to fundamentally alter the lunar plasma environment. (c) 2024 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Context. The solar wind protons implanted in silicate material and combined with oxygen are considered crucial for forming OH/H2O on the Moon and other airless bodies. This process may also have contributed to hydrogen delivery to planetary interiors through the accretion of micrometre-sized dust and planetesimals during early stages of the Solar System. Aims. This paper experimentally investigates the depth distribution of solar wind protons in silicate materials and explores the mechanisms that influence this profile. Methods. We simulated solar wind irradiation by implanting 3 keV D-2(+) ions in three typical silicates (olivine, pyroxene, and plagio-clase) at a fluence of similar to 1.4 x 10(17) ions/cm(2). Fourier transform infrared spectroscopy was used to analyse chemical bond changes, while transmission electron microscopy (TEM) characterised microstructural modifications. Nanoscale secondary ion mass spectrometry (NanoSIMS) was employed to measure the D/O-16 ratio and determine the depth distribution of implanted deuterium. Results. The newly produced OD band (at 2400-2800 cm(-1)) in the infrared spectrum reveals the formation of O-D bonds in the irradiated silicates. The TEM and NanoSIMS results suggest that over 73% of the implanted D accumulated in fully amorphous rims with a depth of 70 nm, while 25% extended inwards to similar to 190 nanometres, resulting in partial amorphisation. The distribution of these deuterium particles is governed by the collision processes of the implanted particles, which involve factors such as initial energy loss, cascade collisions, and channelling effects. Furthermore, up to 2% of the total implanted D penetrated the intact lattice via diffusion, reaching depths ranging from hundreds of nanometres to several micrometres. Conclusions. Our results suggest that implanted solar wind protons can be retained in silicate interiors, which may significantly affect the hydrogen isotopic composition in extraterrestrial samples and imply an important source of hydrogen during the formation of terrestrial planets.

Lunar soils record the history and spectral changes resulting from the space-weathering process. The solar wind and micrometeoroids are the main space-weathering agents leading to darkening (decreasing albedo) and reddening (increasing reflectance with longer wavelength) of visible and near-infrared spectra. Nevertheless, their relative contributions are not well constrained and understood. In this study, we examine the near-infrared spectral variation as a function of lunar latitude and chemical composition using remote spectroscopic analysis of mare basalts and swirl regions. The results indicate that the reflectance of lunar mature soils darkens and the spectral slope flattens (reddening effect saturation) in areas of enhanced solar wind flux. We propose a previously unrecognized stage of space weathering (the post-mature stage), in which solar wind implantation may contribute to the growth and coarsening of metallic iron particles into larger microphase iron. This space-weathering mechanism is dominated by the solar wind and has important implications for understanding the alteration processes of airless bodies across our solar system.

Space weathering is a primary factor in altering the composition and spectral characteristics of surface materials on airless planets. However, current research on space weathering focuses mainly on the Moon and certain types of asteroids. In particular, the impacts of meteoroids and micrometeoroids, radiation from solar wind/solar flares/cosmic rays, and thermal fatigue due to temperature variations are being studied. Space weathering produces various transformation products such as melted glass, amorphous layers, iron particles, vesicles, and solar wind water. These in turn lead to soil maturation, changes in visible and near-infrared reflectance spectra (weakening of characteristic absorption peaks, decreased reflectance, increased near-infrared slope), and alterations in magnetism (related to small iron particles), collectively termed the lunar model of space weathering transformation. Compared to the Moon and asteroids, Mercury has unique spatial environmental characteristics, including more intense meteoroid impacts and solar thermal radiation, as well as a weaker particle radiation environment due to the global distribution of its magnetic field. Therefore, the lunar model of space weathering may not apply to Mercury. Previous studies have extensively explored the effects of micrometeoroid impacts. Hence, this work focuses on the effects of solar-wind particle radiation in global magnetic-field distribution and on the weathering transformation of surface materials on Mercury under prolonged intense solar irradiation. Through the utilization of high-valence state, heavy ion implantation, and vacuum heating simulation experiments, this paper primarily investigates the weathering transformation characteristics of the major mineral components such as anorthite, pyroxene, and olivine on Mercury's surface and compares them to the weathering transformation model of the Moon. The experimental results indicate that ion implantation at room temperature is insufficient to generate np-Fe-0 directly but can facilitate its formation, while prolonged exposure to solar thermal radiation on Mercury's surface can lead directly to the formation of np-Fe-0. Therefore, intense solar thermal radiation is a crucial component of the unique space weathering transformation process on Mercury's surface.

The extent of volatile elements on the surface and interior of the Moon remains a highly debated topic. Previous studies conducted on bulk lunar soil samples and solar wind samples collected by the Genesis mission indicate a discernible isotope mass- or non-mass-dependent fractionation of krypton and xenon. However, a detailed investigation of these processes is missing, particularly in determining the possible incorporation of cometary volatiles in the lunar regolith. New lunar soil samples returned by the Chang'e-5 mission provide a chance to answer these key questions. In this study, noble gas isotopes of nine subsamples from a Chang'e-5 scooped sample were analysed through stepwise-heating and total fusion laser extraction. The results reveal that a simple binary mixture of solar wind and cosmogenic components did not explain alone the isotopic composition of these samples. The Xe data shows insignificant amounts of atmospheric Xe and presents clear evidence of cometary contributions to the lunar regolith, with a significant depletion of 134,136Xe compared to that in the solar wind. Additionally, a meteoritic component is identified. Compared to the Apollo results, our findings further validate the theory of Earth's atmospheric escape, substantiate the plausibility of these exogenous admixtures to elucidate the isotopic fractionation mechanisms of Kr and Xe within the lunar regolith, and provide novel insights into long-term constancy in the solar wind composition.

The ratio of 40 Ar/ 36 Ar trapped within lunar grains, commonly known as the lunar antiquity indicator, is an important semi -empirical method for dating the time at which lunar samples were exposed to the solar wind. The behavior of the antiquity indicator is governed by the relative implantation fluxes of solar wind -derived 36 Ar ions and indigenously sourced lunar exospheric 40 Ar ions. Previous explanations for the behavior of the antiquity indicator have assumed constancy in both the solar wind ion precipitation and exospheric ion recycling fluxes; however, the presence of a lunar paleomagnetosphere likely invalidates these assumptions. Furthermore, most astrophysical models of stellar evolution suggest that the solar wind flux should have been significantly higher in the past, which would also affect the behavior of the antiquity indicator. Here, we use numerical simulations to explore the behavior of solar wind 36 Ar ions and lunar exospheric 40 Ar ions in the presence of lunar paleomagnetic fields of varying strengths. We find that paleomagnetic fields suppress the solar wind 36 Ar flux by up to an order -of -magnitude while slightly enhancing the recycling flux of lunar exospheric 40 Ar ions. We also find that at an epoch of similar to 2 Gya, the suppression of solar wind 36 Ar access to the lunar surface by a lunar paleomagnetosphere is - somewhat fortuitously - nearly equally balanced by the expected increase in the upstream solar wind flux. These counterbalancing effects suggest that the lunar paleomagnetosphere played a critical role in preserving the correlation between the antiquity indicator and the radioactive decay profile of indigenous lunar 40 K. Thus, a key implication of these findings is that the accuracy of the 40 Ar/ 36 Ar indicator for any lunar sample may be strongly influenced by the poorly constrained history of the lunar magnetic field.

We review studies of physical processes associated with the impact of external factors in outer space flows of micrometeoroids and solar radiation on the lunar regolith. Under the influence of these factors, regolith microparticles can detach from the surface and levitate. Near-surface plasma and levitating dust particles form a plasma-dust exosphere of the Moon. Under anthropogenic effects on the lunar environment, charged levitating microparticles can have an extremely negative impact on the engineering systems of lunar landers and on the activity and health of astronauts on the Moon. Based on information gained by automated and manned lunar missions and in laboratory experiments, we discuss modern ideas about physical processes occurring near the Moon's surface. Unsolved problems associated with the plasma-dust exosphere of the Moon are considered, and the principal strategies for their solution are outlined.

Knowledge regarding the abundance and distribution of solar wind (SW)-sourced water (OH/H2O) on the Moon in the shallow subsurface remains limited. Here, we report the NanoSIMS measurements of H abundances and D/H ratios on soil grains from three deepest sections of the Chang'E-5 drill core sampled at depths of 0.45-0.8 m. High water contents of 0.13-1.3 wt.% are present on approximately half of the grain surfaces (topmost similar to 100 nm), comparable to the values of Chang'E-5 scooped soils. The extremely low delta D values (as low as -995 parts per thousand) and negative correlations between delta D and water contents indicate that SW implantation is an important source of water beneath the lunar surface. The results are indicative of homogeneous distribution of SW-derived water in the vertical direction, providing compelling evidence for the well-mixed nature of the lunar regolith. Moreover, the findings demonstrate that the shallow subsurface regolith of the Moon contains a considerable amount of water.