Previous lunar missions, such as Surveyor, Apollo, and the Lunar Atmosphere and Dust Environment Explorer (LADEE), have played a pivotal role in advancing our understanding of the lunar exosphere's dynamics and its relationship with solar wind flux. The insights gained from these missions have laid a strong foundation for our current knowledge. However, due to insufficient near-surface observations, the scientific community has faced challenges in interpreting the phenomena of lunar dust lofting and levitation. This paper introduces the concept of signals of opportunity (SoOP), which utilizes radio occultation (RO) to retrieve the near-surface dust density profile on the Moon. Gravity Recovery and Interior Laboratory (GRAIL) radio science beacon (RSB) signals are used to demonstrate this method. By mapping the concentration of lunar near-surface dust using RO, we aim to enhance our understanding of how charged lunar dust interacts with surrounding plasma, thereby contributing to future research in this field and supporting human exploration of the Moon. Additionally, the introduced SoOP will be able to provide observational constraints to physical model development related to lunar surface particle sputtering and the reactions of near-surface dust in the presence of solar wind and electrostatically charged dust grains.

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.

The circumlunar environment is a dusty plasma consisting of small particles of lunar regolith, photoelectrons, electrons, and solar wind ions. When moving around the Earth, part of the trajectory of the Moon passes through the Earth's magnetosphere. In addition, the magnetic field is characteristic for some areas on the Moon, the so-called lunar magnetic anomalies. The magnetic field values above these areas can exceed the magnetic field values of the Earth's magnetosphere in the region of the Moon's trajectory by one or two orders of magnitude. The magnetic field and photoelectron density gradients can lead to the development of drift turbulence. The relevant conditions are discussed in this work.

The lunar exosphere is an ensemble of multiple overlapping, noninteracting neutral distributions that reflect the primary physical processes acting on the lunar surface. While previous observations have detected and constrained the behavior of some species, many others have only circumstantial evidence or theoretical modeling suggesting their presence. Many species are so tenuous as to be unobservable by direct neutral sampling, yet in comparison, measurements in their ionized form provide a particularly sensitive method of detection. To better aid the interpretation of past measurements and planning of future observations, we present a model for the production of lunar pickup ions from the Moon consisting of two components: An analytic model for the distributions of 18 neutral species produced by various mechanisms and an analytic model for the ionization and subsequent acceleration of 20 exospheric and surface-sputtered pickup ion species. The dominant lunar pickup ions in the model are H2+ ${\mathrm{H}}_{2}{+}$, He+, CO+, Ar-40(+), Al+, Na+, K+, Si+, Ca+, and O+ with an asymmetric distribution favoring the positive interplanetary electric field hemisphere of the Moon. We compare the model predictions to statistically averaged pickup ion fluxes around the Moon as observed by the ARTEMIS spacecraft over the past decade. By filtering for interplanetary electric field-aligned, high-energy observations, we find that the pickup ion model lacks an additional source of heavy species. We suggest that a dense CO2 exosphere of 3 x 10(4) - 1 x 10(5) cm(-3) could account for the missing pickup ion flux as part of the recycling of solar wind carbon ions incident to the Moon.

The Moon is generally depleted in volatile elements and this depletion extends to the surface where the most abundant mineral, anorthite, features <6 ppm H2O. Presumably the other nominally anhydrous minerals that dominate the mineral composition of the global surface-olivine and pyroxene-are similarly depleted in water and other volatiles. Thus the Moon is tabula rasa for the study of volatiles introduced in the wake of its origin. Since the formation of the last major basin (Orientale), volatiles from the solar wind, from impactors of all sizes, and from volatiles expelled from the interior during volcanic eruptions have all interacted with the lunar surface, leaving a volatile record that can be used to understand the processes that enable processing, transport, sequestration, and loss of volatiles from the lunar system. Recent discoveries have shown the lunar system to be complex, featuring emerging recognition of chemistry unanticipated from the Apollo era, confounding issues regarding transport of volatiles to the lunar poles, the role of the lunar regolith as a sink for volatiles, and the potential for active volatile dynamics in the polar cold traps. While much has been learned since the overturn of the Moon is dry paradigm by innovative sample and spacecraft measurements, the data point to a more complex lunar volatile environment than is currently perceived.

The program of scientific research of the Luna-25 lunar lander includes the experiment Dust monitoring of the Moon (in Russian, Pylevoi monitoring Luny (PmL)), which provides for the study of the dynamics of lunar microparticles and parameters of the near-surface dusty plasma. Using the PmL instrument, it is planned to record for a long time individual microparticles above the lunar surface, to measure and evaluate their physical characteristics (momentum, velocity, charge, mass, and concentration), as well as to monitor the dynamics of the parameters of the near-surface dusty plasma environment (density, temperature, and potential). The instrument has passed successfully the entire range of ground tests.

We report the first observation of Argon-40 (Ar-40) in the mid latitude regions (-60 degrees to +60 degrees) of the lunar exosphere from CHandra's Atmospheric Composition Explorer-2 (CHACE-2) experiment aboard Chandrayaan-2 orbiter. The number density of Ar-40 shows pre-sunrise, sunrise and sunset peaks as well as nightside minima, typical of a condensable gas, which is similar to the features seen at the low latitudes in previous observations. The CHACE-2 observed number densities of Ar-40 and its diurnal variation at low latitudes (-30 degrees to +30 degrees) is consistent with LACE/Apollo observations. CHACE-2 observations show Ar-40 enhancements over certain longitude sectors. In addition to KREEP region, Ar-40 bulges are observed at other longitudes, including the South Pole Aitken (SPA) terrain. The global distribution of Ar-40 shows that the sunrise peak is observed at the same local time over highlands and mare regions. These observations call for a deeper understanding of the surface-exosphere interactions and source distribution. Plain Language Summary The Moon is known to possess a tenuous atmosphere, known as surface bound exosphere. Lunar exosphere exists as a result of a dynamic equilibrium between several sources and sink processes. Noble gases serves as important tracers to understand such processes. Though, Argon-40 (Ar-40) is known to exist in lunar exosphere, the knowledge on its distribution at higher latitudes is lacking. For the first time, CHandra's Atmospheric Composition Explorer-2 (CHACE-2) experiment aboard Chandrayaan-2 orbiter has continuously observed Ar-40 in latitude range of -60 degrees to +60 degrees. It is found that the Ar-40 density variation with local solar time shows the behavior of a condensable gas, which is similar to that observed earlier at low latitudes. The distribution of Ar-40 shows spatial heterogeneity with localized enhancements over KREEP and South Pole Aitken terrain. This suggests that there may be other regions with lower activation energy as the source of Ar-40. The observed global distribution indicates that the interaction of Ar-40 with the surface are similar in low and mid latitude regions. The CHACE-2 observations hint at requirement for improvement in our understanding of the surface-exosphere interactions and source distributions of Ar-40. Key Points First observation of Argon-40 in the mid latitude exosphere of the Moon Observed nightside minimum and sunrise and sunset peaks in Ar-40 abundance is similar to that at low latitudes Enhanced Ar-40 number density is observed at few longitudes, including South Pole Aitken terrain, in addition to KREEP

The ionization-type cosmic dust detector METEOR-L is being developed for the lunar orbiter Luna-26 and is designed to study the distribution of meteoric bodies in space by mass and velocity, and for long-term monitoring of the dynamic evolution of the dust component in the lunar exosphere. Recent studies of dust clouds around the Moon show a close relationship between the constant and dynamic evolution of the components of the lunar exosphere, the geological history of the formation of the lunar regolith, the processes of formation and accumulation of volatiles in the lunar regolith with the constant impact of such components of the interplanetary medium as interplanetary dust of predominantly cometary origin and meteoroids from the belt asteroids. The cosmic dust detector is capable of registering meteoric particles 0.1-3 mu m in size with a mass of 10(-14)-10(-9) g and speeds from 3 to 35 km s(-1). Tests and calibration at a particle accelerator have confirmed the declared functionality of the detector for detecting cosmic dust particles with parameters characteristic of the lunar exosphere.

This study demonstrates the visualization and recovery of the 3D dynamic trajectories of charged microparticles in electric field conditions. The main aim of this work is to simulate plasma-dust processes above the surfaces of the Moon and other Solar system bodies without atmospheres. The experimental setup includes two parts: a vacuum chamber, in which microparticles imitate lunar dust dynamics under electrostatic field conditions, and a stereo camera system for image registration combined with laser and optics for illuminating the investigation volume. Image processing techniques for estimating the 3D particle trajectory were developed. Examples of processing results and their prospective application are discussed.

The surface of the Moon, like that of any airless body in the Solar System, constantly experiences micrometeorite bombardment as well as the influence of solar radiation, solar wind, and other factors of outer space. As a result of the impacts of high-velocity micrometeorites over billions of years, the lunar surface silicate basis crumbles, turning into particles with a wide size distribution. Considering the explosive nature of their origin, these particles are characterized by an extremely irregular shape with sharp edges or conglomerates sintered at high temperatures or almost spherical droplets. On the illuminated side of the Moon, solar radiation, especially the ultraviolet part of its spectrum, and solar wind streams interact with the upper regolith layer, charging the regolith surface. The photoelectrons generated above the surface create, together with the charged regolith surface, a near-surface double layer. The electric field generated in this layer, as well as the particle charge fluctuations on the surface, create conditions under which electric forces may exceed the gravitational force and the van der Waals force of adhesion. As a result, micron- and submicron-sized regolith particles become capable of detaching from the surface and levitating above it. These dynamic processes cause the transport of dust particles above the lunar surface and the scattering of sunlight on these particles. Glows of this kind were observed over the lunar surface by television systems of American and Soviet landing vehicles in the early stages of lunar exploration. American astronauts who landed on the lunar surface during the Apollo program also discovered manifestations of lunar dust. It turns out that dust particles levitating over the regolith surface due to natural processes and those took off the surface due to anthropogenic factors cause many technological problems that compromise the performance of landing vehicles and their systems, hamper astronaut activity on the lunar surface, and are detrimental to their health. Based on the results of these missions, it is concluded that micron- and submicron-sized dust particles, levitating above the surface, pose a major, barely surmountable obstacle in further research and exploration of the Moon. Since then, studies of physical processes associated with the behavior of lunar dust, manifestations of its aggressive properties (toxicity), and ways to reduce the harmful effects of dust on engineering systems and on humans have become topical in theoretical and experimental research. In this review, the results of the past half century of studies on the behavior of dust particles serve as a basis to discuss the formation of the lunar regolith and the Moon's near-surface plasma-dust exosphere under the influence of outer space factors. The causes and conditions underling the behavior of dust particles are examined as well as implications of these processes, the influence of anthropogenic factors, and possible hazards to spacecraft and engineering systems during the implementation of the currently planned programs of lunar research and exploration. The main unsolved problems are listed in studying the behavior of the dust component of the lunar regolith; ways to address the problematic issues are discussed.