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This study reviews major sensing technologies for the Lunar environment and its resources, as they have been developed since the times of Apollo missions. Selected technologies of sensors and instruments for the chemical, isotopic, and structural analysis of Lunar rocks and regoliths, as well as of the Lunar exosphere environment, are presented in a critical review towards an optimised and information-rich framework. Special focus is given on the activated Lunar regolith, and especially the Lunar dust, describing the development of Lunar simulants as the only accessible materials for experimentation and testing of the above technologies. New technologies are also highlighted, such as the development of the OxR microfluidic and spectroscopy integrated device, which, in its small scale aims to detect reactive oxygen species in the Lunar regolith, while in its larger format it is used to release oxygen gas from the Lunar dust and regolith, enabling astronaut respiration and fuel production on the Moon. It is finally suggested that miniaturisation of instruments and sensors, together with the standardisation of output information and characterisation protocols through holistic informational frameworks, will enhance the dynamic expansion and further integration and interoperation of sensors and devices, aiming to an efficient, safer, and resilient utilisation on the Moon and the establishment of sustainable settlements in the near future. [ABSTRACT FROM AUTHOR]

The Moon has a tenuous atmosphere produced by space weathering. The short-lived nature of the atoms surrounding the Moon necessitates continuous replenishment from lunar regolith through mechanisms such as micrometeorite impacts, ion sputtering, and photon-stimulated desorption. Despite advances, previous remote sensing and space mission data have not conclusively disentangled the contributions of these processes. Using high-precision potassium (K) and rubidium (Rb) isotopic analyses of lunar soils from the Apollo missions, our study sheds light on the lunar surface-atmosphere evolution over billions of years. The observed correlation between K and Rb isotopic ratios (d 87Rb = 0.17 d 41K) indicates that, over long timescales, micrometeorite impact vaporization is the primary source of atoms in the lunar atmosphere. [ABSTRACT FROM AUTHOR]

This article explores the topic of cosmic dust and its significance in understanding the universe. Cosmic dust is found throughout our solar system and beyond, and it has posed challenges for astronomers in studying celestial objects. However, advancements in science and technology have allowed researchers to use cosmic dust as a valuable source of information about the composition and evolution of distant bodies in the universe. The article discusses the different types of cosmic dust, its role in phenomena such as interstellar reddening, and its potential to provide insights into the early stages of the universe and the origin of life on Earth. It also highlights recent space missions and laboratory simulations that have contributed to our understanding of cosmic dust. The collection of articles in this special issue of Philosophical Transactions of the Royal Society A focuses on specific aspects of cosmic dust research, including the detection and analysis of meteors and meteorites, in situ detection of dust particles in interplanetary space, and laboratory simulations of icy dust grains from subsurface ocean-bearing icy moons. [Extracted from the article]

The Moon is a unique natural laboratory for the study of the deep space plasma and energetic particles environment. During more than 3/4 of its orbit around the Earth it is exposed to the solar wind. Being an unmagnetized body and lacking a substantial atmosphere, solar wind and solar energetic particles bombard the Moon's surface, interacting with the lunar regolith and the tenuous lunar exosphere. Energetic particles arriving at the Moon's surface can be absorbed, or scattered, or can remove another particle from the lunar regolith by sputtering or desorption. A similar phenomenon occurs also with the galactic cosmic rays, which have fluxes and energy spectra representative of interplanetary space. During the remaining part of its orbit the Moon crosses the tail of the terrestrial magnetosphere. It then provides the opportunity to study in-situ the terrestrial magnetotail plasma environment as well as atmospheric escape from the Earth's ionosphere, in the form of heavy ions accelerated and streaming downtail. The lunar environment is thus a unique natural laboratory for analysing the interaction of the solar wind, the cosmic rays and the Earth's magnetosphere with the surface, the immediate subsurface, and the surface-bounded exosphere of an unmagnetized planetary body. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades (part 2)'. [ABSTRACT FROM AUTHOR]

The Moon was previously believed to be dry, but recent discoveries of indigenous water in lunar materials have changed our understanding of the Moon's water content. The origin of this water in the lunar interior is important for understanding the formation of the Moon. The water in the Moon may have come from the same source as the water on Earth, and it could have been partially retained in the protolunar disk during the Moon's formation or added to the Moon during its molten stage. Further research is needed to test these hypotheses and better understand the physical and chemical conditions during the Moon's formation. [Extracted from the article]

We analyze the emission of energetic neutral atom (ENA) flux from charge exchange between Jovian magnetospheric ions and the atmospheres of Callisto and Europa. For this purpose, we combine the draped electromagnetic fields from a hybrid plasma model with a particle tracing tool for the energetic ions. We determine the ENA flux through a concentric sphere located just outside of each moon's atmosphere, thereby capturing the complete physics imprinted in these emission patterns. In order to constrain the modifications to the ENA emissions that arise from the periodic change of the ambient plasma conditions, we calculate the emission morphology at multiple positions during a Jovian synodic rotation. To isolate the influence of field line draping, we compare to the emission patterns in uniform fields. Our major results are: (a) At Europa and Callisto, the majority of detectable ENA emissions are concentrated into a band normal to the Jovian magnetospheric field. (b) The fraction of observable ENA flux that contributes to this band depends on the number of complete gyrations that the parent ions can complete within the moon's atmosphere. (c) Field line draping partially deflects impinging parent ions around both moons, thereby attenuating the ENA flux and driving significant morphological changes to the emission patterns. (d) The band of elevated ENA flux is locally maximized on the opposite (antipodal) side of the moon where the flux is locally minimized. At Europa, detectable ENA emissions are maximized slightly west of the ramside apex. At Callisto, they maximize near the Jupiter‐facing apex. Key Points: We model the energetic neutral atom (ENA) flux generated by charge exchange of magnetospheric ions with Callisto's and Europa's atmospheresThe bulk of the ENA flux is detectable in a band normal to the magnetospheric field and created by ions with pitch angles near 90°Magnetic field line draping attenuates the intensity of observable ENA flux and qualitatively alters the emission morphology at both moons [ABSTRACT FROM AUTHOR]

We calculate the time‐varying spatial distribution of energetic magnetospheric electron influx onto Europa's surface by combining a hybrid model of the moon's draped electromagnetic environment with a relativistic particle tracer. We generate maps of the energetic electron influx patterns at four distinct locations of Europa relative to the center of the Jovian magnetospheric current sheet. For a full synodic rotation of Jupiter, these results are applied to constrain the averaged number and energy influx patterns as well as the O2 sputtering rates associated with energetic electron precipitation. We also determine the relative contributions of magnetospheric ions and electrons to surface erosion and exospheric genesis at Europa. Our major results are: (a) Except for a small region near Europa's downstream apex, the moon's entire surface is exposed to heavy irradiation by magnetospheric electrons. (b) The spatial distribution of energetic electron influx onto Europa's surface is only slightly modified by field line draping and the induced magnetic field from the moon's subsurface ocean. (c) The contributions of magnetospheric electron and ion impacts to energy deposition onto Europa's surface are of the same order of magnitude. (d) Within uncertainties, impinging magnetospheric electrons and ions make similar contributions to O2 sputtering from Europa's surface. (e) The spatial distribution of electron energy influx and the observed concentrations of sulfuric acid (H2SO4) are only weakly correlated, suggesting that energy deposition by magnetospheric electron impacts is not a necessary agent for H2SO4 production within Europa's surface. Key Points: Europa's plasma interaction and induced magnetic field cause only subtle changes to energetic electron influx patterns on the moon's surfaceIntegrated across Europa's entire surface, impinging magnetospheric electrons deposit a similar amount of energy as magnetospheric ionsMagnetospheric electron and ion impacts release comparable numbers of oxygen molecules from Europa's surface into the moon's exosphere [ABSTRACT FROM AUTHOR]

The inelastic scattering dynamics of the isobaric molecules, naphthalene (C10H8) and 2-octanone (C8H16O), on highly oriented pyrolytic graphite (HOPG) have been investigated as part of a broader effort to inform the inlet design of a mass spectrometer for the analysis of atmospheric gases during a flyby mission through the atmosphere of a planet or moon. Molecular beam–surface scattering experiments were conducted, and the scattered products were detected with the use of a rotatable mass spectrometer detector. Continuous, supersonic beams were prepared, with average incident translational energies, ⟨Ei⟩, of 247.3 kJ mol−1 and 538.2 kJ mol−1 for naphthalene and 268.6 kJ mol−1 and 433.8 kJ mol−1 for 2-octanone. These beams were directed toward an HOPG surface, held at 530 K, at incident angles, θi, of 30°, 45°, and 70°, and scattered products were detected as functions of their translational energies and scattering angles. The scattering dynamics of both molecules are very similar and mimic the scattering of atoms and small molecules on rough surfaces, where parallel momentum is not conserved, suggesting that the dynamics are dominated by a corrugated interaction potential between the incident molecule and the surface. The effective corrugation of the molecule–surface interaction is apparently caused by the structure of the incident molecule and the consequent myriad available energy transfer pathways between the molecule and the surface during a complex collision event. In addition, the HOPG surface contributes to the corrugation of the interaction potential because it can absorb significant energy from collisions with incident molecules that have high mass and incident energy. Small differences in the scattering dynamics of the two molecules are inferred to arise from the details of the molecule–surface interaction potential, with 2-octanone exhibiting dynamics that suggest a slightly stronger interaction with the surface than naphthalene. These results add to a growing body of work on the scattering dynamics of organic molecules on HOPG, from which insight into the hypervelocity sampling and analysis of such molecules may be obtained. [ABSTRACT FROM AUTHOR]

The lunar ionosphere is a ∼100 km thick layer of electrically charged plasma surrounding the moon. Despite knowledge of its existence for decades, the structure and dynamics of the lunar plasma remain a mystery due to lack of consistent observational capacity. An enhanced observational picture of the lunar ionosphere and improved understanding of its formation/loss mechanisms is critical for understanding the lunar environment as a whole and assessing potential safety and economic hazards associated with lunar exploration and habitation. To address the high priority need for observations of the electrically charged constituents nikear the lunar surface, we introduce a concept study for the Radio Instrument Package for Lunar Ionospheric Observation (RIPLIO). RIPLIO would consist of a multi‐CubeSat constellation (at least two satellites) in lunar orbit for the purpose of conducting "crosslink" radio occultation measurements of the lunar ionosphere, with at least one satellite carrying a very high frequency (VHF) transmitter broadcasting at multiple frequencies, and at least one satellite flying a broadband receiver to monitor transmitting satellites. Radio occultations intermittently occur when satellite‐to‐satellite signals cross through the lunar ionosphere, and the resulting phase perturbations of VikHF signals may be analyzed to infer the ionosphere electron content and high‐ resolution vertical electron density profiles. As demonstrated in this study, RIPLIO would provide a novel means for lunar observation, with the potential to provide long‐term, high‐resolution observations of the lunar ionosphere with unprecedented pan‐lunar detail. Plain Language Summary: The lunar ionosphere comprises electrically charged particles within the lunar atmosphere and is derived from a wide range of sources and formation mechanisms that are not fully resolved. Although extremely tenuous compared to that of Earth's, the lunar ionosphere plays an integral role in physical processes occurring within the lunar environment. The composition and dynamics of the lunar ionosphere are mostly unknown at this point and may be linked to the lunar surface and sub‐surface, solar wind, magnetosphere, and Earth's atmosphere. Observation of the lunar ionosphere is essential to develop a complete picture of its structure and dynamic behavior and how it is formed. This is a critical aspect of assessing its physical role within the lunar environment and potential safety hazards for future lunar exploration and habitation. This paper presents the concept of a radio‐based mission for lunar ionospheric observation called the Radio Instrument Package for Lunar Ionospheric Observation (RIPLIO). This mission would employ multiple CubeSats in lunar orbit, equipped with radio transmitters and receivers, to observe the lunar ionosphere with unprecedented detail. This paper presents preliminary simulations of radio measurements of the lunar ionosphere, and discusses requirements for a potential RIPLIO mission and relevance to international science objectives. Key Points: We propose a "crosslink" radio occultation method of observing electrically charged constituents of the lunar exosphereSimulations demonstrate that two CubeSats in lunar orbit result in a substantial increase in lunar ionosphere observational capacityWe demonstrate that a VHF transmitter‐receiver "crosslink" setup is ideal for making radio occultation observations of the lunar ionosphere [ABSTRACT FROM AUTHOR]

The origin, evolution, and cycling of volatiles on the Moon are established by processes such as the giant moon forming impact, degassing of the lunar magma ocean, degassing during surface eruptions, and lunar surface gardening events. These processes typically induce mass‐dependent stable isotope fractionations. Mass‐independent fractionation of stable isotopes has yet to be demonstrated during events that release large volumes of gas on the moon and establish transient lunar atmospheres. We present quadruple sulfur isotope compositions of orange and black glass beads from drive tube 74002/1. The sulfur isotope and concentration data collected on the orange and black glasses confirm a role for magmatic sulfur loss during eruption. The Δ33S value of the orange glasses is homogenous (Δ33S = −0.029‰ ± 0.004‰, 2SE) and different from the isotopic composition of lunar basalts (Δ33S = 0.002‰ ± 0.004‰, 2SE). We link the negative Δ33S composition of the orange glasses to an anomalous sulfur source in the lunar mantle. The nature of this anomalous sulfur source remains unknown and is either linked to (a) an impactor that delivered anomalous sulfur after late accretion, (b) sulfur that was photochemically processed early during lunar evolution and was transported to the lunar mantle, or (c) a primitive sulfur component that survived mantle mixing. The examined black glass preserves a mass‐dependent Δ33S composition (−0.008‰ ± 0.006‰, 2SE). The orange and black glasses are considered genetically related, but the discrepancy in Δ33S composition among the two samples calls their relationship into question. Plain Language Summary: Using isotopic compositions measured in volatile elements, we can identify the processes linked to isotopic fractionations and ultimately understand processes involved in a planets' evolution. We present sulfur isotope compositions of lunar glass beads from drive tube 74002/1 and demonstrate that an anomalous sulfur source was erupted from the lunar mantle with the orange glass beads. The observed isotopic anomaly has an unknown origin, but it requires a source of sulfur that was photochemically processed prior to its delivery to the lunar mantle and eruption at ∼3.6 Ga. Our results suggest that the lunar mantle is not well mixed with respect to sulfur sources and requires future multi‐disciplinary investigations to reconcile these important observations. Key Points: Orange glass 74002 preserves negative Δ33S valuesThe negative Δ33S associated with orange glass is linked to photochemically processed sulfur in the erupted sourceOrange and black glass preserve different S isotope compositions that calls into question their genetic relationship [ABSTRACT FROM AUTHOR]

Because of radiogenic processes, the lunar interior is a source of rare gases like helium ( ^4 He), argon ( ^40 Ar), and radon ( ^222 Rn) that might be released continuously, or impulsively during moonquakes. The detection of radon is therefore important in the sense that it can help trace the crustal dynamics on the Moon. In this study, we will introduce a Monte Carlo–based model designed to investigate the time-dependent transient dynamics of the lunar ^222 Rn exosphere. Our model accounts for the background emission and transient ejection of gas molecules from the lunar surface, encompassing loss processes such as radioactive decay, photoionization, and the cold trapping in permanently shadowed regions near the poles. Additionally, it incorporates the diurnal temperature fluctuations of the lunar surface, which significantly influence the condensation duration of the radon atoms and their subsequent release near the sunrise. This model also can support future observations in missions such as Chang’E 6 or other lunar explorations.

The kinetics of water formation on the lunar surface from impact-driven melts (IM) of meteoroids and recombinative desorption (RD) of solar-wind-implanted regolith grains is assessed. The ratio of water generated from RD:IM is ultimately controlled by the diffusion constant of the implanted defects. Higher diffusion activation energies of hydroxyls (-OH) result in more trapping of the implanted defects and, consequently, higher water production from IM versus RD. At diffusion activation energies >1 eV, water production from RD is negligible and IM is the dominant channel. Our results suggest that RD can be associated with the observed latitude and diurnal dependence but RD and/or micrometeorite IM are not major contributors to the water ice observed within the permanently shadowed regions (PSRs). This suggests that volcanic and/or delivery via large impactors are the more likely major sources of water on the Moon. However, our model generally agrees with the observed latitudinal dependence of the inferred OH/H _2 O and the overall diurnal trend from orbital observations in the infrared. In addition, our results also suggest that micrometeorites are responsible for the high content of molecular water in the glass of regolith grains.

The sunlight reflected from the Moon during a total lunar eclipse has been transmitted through the Earth's atmosphere on the way to the Moon. The combination of multiple scattering and inhomogeneous atmospheric characteristics during that transmission can potentially polarize that light. A similar (although much smaller) effect should also be observable from the atmosphere of a transiting exoplanet. We present the results of polarization observations during the first 15 min of totality of the lunar eclipse of 2022 May 16. We find degrees of polarization of 2.1 ± 0.4 per cent in B , 1.2 ± 0.3 per cent in V , 0.5 ± 0.2 per cent in R , and 0.2 ± 0.2 per cent in I. Our polarization values lie in the middle of the range of those reported for previous eclipses, providing further evidence that the induced polarization can change from event to event. We found no significant polarization difference (<0.02 per cent) between a region of dark Mare and nearby bright uplands or between the lunar limb and regions closer to the disc centre due to the different angle of incidence. This further strengthens the interpretation of the polarization's origin being due to scattering in the Earth's atmosphere rather than by the lunar regolith. [ABSTRACT FROM AUTHOR]

Today's moon is vastly different from what it was 3 billion years ago. At that time, it was home to a collisional atmosphere formed through massive amounts of volcanism, releasing enough subsurface gas to sustain surface pressures of up to 1 kPa. Observations of our solar system have taught us that all dense atmospheres are host to clouds and aerosols, and we expect the Moon's to be no different. Knowing when, where, and under what conditions cloud particles form is important for understanding the evolution of the lunar atmosphere, how it reacted to temperature gradients, and how it cycled volatiles. To study this, I investigated the immersion freezing properties of three aerosols: JSC- 1A lunar simulant, which is similar in composition and properties to lunar sample #14163 returned by the Apollo 14 Mission; Exolith LMS- 1D Lunar Mare simulant, which simulates volcanic deposits on the Moon's surface; and Arizona Test Dust (ATD), a standard for Earth atmospheric studies. A Peltier thermoelectric cooler and droplet freezing array were used to isolate Millipore water droplets with aerosols cooled to temperatures as low as - 18 ° C. Aerosol type, aerosol concentration, and droplet size was varied across these experiments. Both lunar simulants were found to nucleate ice less frequently than ATD, with JSC- 1A nucleating more droplets than LMS- 1D, which exhibited freezing properties similar to pure water. The results indicate that water ice nucleation is possible but highly variable on lunar regolith aerosols, and cloud formation on volcanic dust may have been possible in the ancient lunar atmosphere. [ABSTRACT FROM AUTHOR]

Stepwise crushing and combustion methods were applied to study the KREEP-rich lunar breccia Dhofar 1442, the clastic material of which is cemented by porous matrix. The stepwise crushing released significant amount of gases of extraterrestrial origin from gas voids. Argon, nitrogen, and carbon are simultaneously released by stepwise combustion at 1100°С. The simultaneous high-temperature degassing of these gases, as well as the coincidence of С/N ratio and nitrogen and carbon contents in high-temperature combustion steps with those of crushing indicate that the gas carriers are voids in high-temperature phases (in particular, minerals, glasses), which are decomposed/melted at these temperatures. Helium and neon are released from the same positions at lower temperatures. The isotopic composition of neon obtained by stepwise combustion and crushing corresponds to the composition of fractionated solar wind. The fraction of argon in the first crushing steps is higher than that of any other of studied gases. The 40Ar/36Ar in the trapped lunar argon is ~18, which is not consistent with empirical model implying that 40Аr is implanted from lunar atmosphere (McKay et al., 1986; Eugster et al., 2001; Joy et al., 2011). We believe that the entrapment of volatile elements in gas voids of the meteorite Dhofar 1442 was caused by the redistribution of gases from one structural sites into others during impact events that accompanied the cratering, in particular, leading to the formation of the impact melt breccia Dhofar 1442. The trapped gases of the meteorite Dhofar 1442 contain not only typical volatile components (solar, radiogenic, cosmogenic, re-implanted 40Ar) of lunar breccias, but also nitrogen and carbon formed through the oxidation of organic matter of metamorphosed chondrites, which are present in the breccia. With increasing number of strokes and, correspondingly, a degree of crushing, the elemental ratios change. A slight decrease of 4He/20Ne ratio during crushing is likely related to the different diffusion ability and permeability of helium relative to neon under temperature influence and/or to the heterogeneous distribution of these gases in voids of different size. The 4He/36Ar, 20Ne/36Ar, 14N/36Ar, and 12С/36Ar ratios increase by factors of 10–100 during crushing. This can be explained by the combination of dynamically different processes leading to the argon fractionation relative to other gases and uneven redistribution of gases from different positions in voids of different sizes during impact metamorphism. [ABSTRACT FROM AUTHOR]

The semidiurnal (12.42 h) and semimonthly (14.76 days) lunar tides have been well-known by fishermen for several centuries. The gravitational force of the relative positions between the Sun, the Moon, and the Earth results in two symmetrical tidal bulges (double bulges) appearing at equatorial latitudes directly under and opposite the Moon. We utilize ionospheric GNSS (Global Navigation Satellite System) radio occultation soundings to show the global three-dimensional structures and dynamics of the double bulges of ionospheric lunar tides for the first time. The double-bulge amplitude of ionospheric F2-peak height hmF2, lagging the sublunar or antipodal point by about 2–3 h, is about 3–5 km at the equator and 1.5–2.0 km at ± 35° magnetic latitude. The electron density further depicts global three-dimensional plasma flows in the ionosphere. [ABSTRACT FROM AUTHOR]

In the White Paper, submitted in response to the European Space Agency (ESA) Voyage 2050 Call, we present the importance of advancing our knowledge of plasma-neutral gas interactions, and of deepening our understanding of the partially ionized environments that are ubiquitous in the upper atmospheres of planets and moons, and elsewhere in space. In future space missions, the above task requires addressing the following fundamental questions: (A) How and by how much do plasma-neutral gas interactions influence the re-distribution of externally provided energy to the composing species? (B) How and by how much do plasma-neutral gas interactions contribute toward the growth of heavy complex molecules and biomolecules? Answering these questions is an absolute prerequisite for addressing the long-standing questions of atmospheric escape, the origin of biomolecules, and their role in the evolution of planets, moons, or comets, under the influence of energy sources in the form of electromagnetic and corpuscular radiation, because low-energy ion-neutral cross-sections in space cannot be reproduced quantitatively in laboratories for conditions of satisfying, particularly, (1) low-temperatures, (2) tenuous or strong gradients or layered media, and (3) in low-gravity plasma. Measurements with a minimum core instrument package (< 15 kg) can be used to perform such investigations in many different conditions and should be included in all deep-space missions. These investigations, if specific ranges of background parameters are considered, can also be pursued for Earth, Mars, and Venus. [ABSTRACT FROM AUTHOR]

In the original hypothesis of ice in lunar polar cold traps, it was presumed that meteoritic water acquired by the lunar surface would be concentrated in cold traps by exospheric lateral transport. That supposition is proven to be false by the absence of evidence of exospheric water in data obtained by the neutral mass spectrometer on the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft. The upper limit for exospheric water at the lunar surface, ∼3 molecules cm−3, is deficient by several orders of magnitude in accounting for transport of the present influx of meteoritic water to cold traps. The proffered process for removal of meteoritic water from the lunar regolith is solar wind sputter. This LADEE result does not rule out the possibly of past impulsive exospheric events like cometary impacts but does place a rigid constraint on the modern day water cycling. Plain Language Summary: Whether vast deposits of water ice have accumulated in lunar polar cold traps may hinge on an unproven hypothesis that water acquired from meteor impacts and possibly other sources is moved to polar cold traps by the dynamic transport process of the lunar exosphere (a rarefied, collisionless atmosphere). Movement of exospheric molecules over the lunar surface is a two‐dimensional random walk process in which the steps are random segments of ballistic trajectories that begin with thermal desorption from soil grains and end with adsorption at distances measured in hundreds of kilometers. Obviously, trajectories that end in cold traps must create ice deposits. However, the upper bound for exospheric water derived here from data collected in 2013–2014 by the neutral mass spectrometer on the Lunar Atmosphere and Dust Environment Explorer spacecraft, about three molecules/cc, pales in comparison to the concentration of ∼15,000 molecules/cc needed to sequester the meteoritic water influx. The only pragmatic conclusion is that the hypothesis for water ice accumulation at the poles due to exospheric transport is false. This conclusion forces the question of the fate of water that accretes on the lunar surface. Key Points: The upper limit for water in the lunar exosphere is ∼3 molecules/ccThe lunar exosphere does not transport meteoritic water to polar cold trapsLunar regolith is arid [ABSTRACT FROM AUTHOR]

Sometimes when we look up into the night sky we see a big glowing ball; other times when we look up into the night sky we might see a tiny sliver of the Moon. Making Moon Craters The Moon may be visible during the day and night, but it is most easily noticed in a night sky. Children can see the Moon with the naked eye and often are curious about the Moon and other objects in the sky, like the Sun and the stars. Children could also zoom in to the surface of the Moon using Google Moon, or they could use their new knowledge of the Moon and its surface to create their own Moon models. [Extracted from the article]

A realistic model of physico-chemical processes during collisions between meteoroids and the Moon considering condensation of refractory elements in the form of minerals and variable adiabatic index during expansion of impact-produced clouds was developed. Quenched chemical composition of impact-produced cloud is estimated. In accordance with this model relative fraction of atoms delivered to the lunar exosphere by impacts of meteoroids is significantly higher than that previously estimated with usage of the model with constant adiabatic index and without considering condensation as a factor affecting on pressure in impact-produced clouds. • Advanced model of adiabatically expanding impact-produced hot clouds is developed. • Variable adiabatic index and condensation of minerals are considered. • Quenching parameters of the composition of impact-produced clouds are estimated. • Main species delivered to the lunar exosphere by impacts of meteoroids are determined. • Hydrogen is delivered to the exosphere by impacts mainly in the form of H and OH. [ABSTRACT FROM AUTHOR]

The Earth/Moon system likely results from a giant impact between a Mars-size object and the proto-Earth. This high-energy impact leads to extreme conditions under which volatile elements would not normally be preserved in the protolunar disk. However, recent measurements of lunar samples highlight the presence of a non-negligible amount of water in the Moon's interior (from 1.2 to 74 ppm). The aim of the present work is to quantify the water contribution of the late accretion on the early Moon. Here, we use a 2D axisymmetric model with the hydrocode iSALE-Dellen to study the fate of a large impactor on a target body similar to the early Moon with a crust, a magma ocean, and a mantle. For this purpose, we compute different models to monitor the depth to which the impacted material is buried at the end of the impact event and the degree of devolatilisation of the impactor. Three parameters are explored: the crustal thickness (ranging from 10 to 80 km), the impactor radius (ranging from 25 to 200 km) and the impactor velocity (ranging from 1 to 4 times the target escape velocity). Our models show that impactors with a radius greater than 25 km impacting a partially molten lunar body with a crust thinner than 40 km could significantly contribute to the water content of the lunar mantle even for impact velocities close to the lunar escape velocity. For impact velocities greater than 3 times the target escape velocity, the impactor material is significantly molten and its water content is devolatilised within the lunar atmosphere. Depending on the water content of the impactor material and the ability of the lunar magma ocean to maintain chemical heterogeneities, the late lunar accretion following the Moon-forming giant impact could explain the differences in water content among the lunar samples. • We model the ability of a large impactor to penetrate within a lunar magma ocean. • We use iSALE Dellen 2D axi-symmetrical hydrocode models. • We show that impactors larger than 25 km can penetrate a 40 km thick lunar crust. • Low velocity impactors melt and dehydrate within the deep lunar magma ocean. • Late accretion can contribute to the lunar mantle water content by 1–10 ppm. [ABSTRACT FROM AUTHOR]

We combine the electromagnetic fields from a hybrid plasma model with a particle tracing tool to study the spatial distribution of energetic neutral atoms (ENAs) emitted from Titan's atmosphere when the moon is exposed to different magnetospheric upstream regimes. These ENAs are generated when energetic magnetospheric ions undergo charge exchange within Titan's atmosphere. The spatial distribution of the emitted ENA flux is largely determined by the parent ions' trajectories through the draped fields in Titan's interaction region. Since images from the ENA detector aboard Cassini captured only a fraction of the ENA population, we provide context for such observations by calculating maps of the ENA flux through a spherical detector concentric with Titan. We determine the global distribution of ENA emissions and constrain deviations between the locations of ENA production and detection. We find that the ENA flux is highest in a band that encircles Titan perpendicular to the ambient magnetospheric field, which was strictly perpendicular to the moon's orbital plane during only one Cassini flyby. The field line draping strongly attenuates the emitted ENA flux, but does not alter the overall morphology of the detectable flux pattern. The majority of detectable ENAs leave Titan's atmosphere far from where they are produced, that is, even a spacecraft located directly above the moon's atmosphere would detect ENAs generated beyond its immediate environment. Some energetic parent ions produce ENAs only after they are mirrored by the field perturbations in Titan's wake and return to the moon, demonstrating the complex histories of detectable ENAs. [ABSTRACT FROM AUTHOR]

The article discusses China's upcoming Chang'e-6 mission, which aims to retrieve samples from the Moon's South Pole–Aitken (SPA) Basin, the largest and oldest impact crater on the lunar far side. Topics include the mission's goal of dating the SPA impact event, potential geological insights from the retrieved samples, and the broader implications for understanding the Moon's formation and the "late heavy bombardment" hypothesis.

The atmosphere of Titan, Saturn's largest moon, exhibits interesting UV- and radiation-driven chemistry between nitrogen and methane, resulting in dipolar, nitrile-containing molecules. The assembly and subsequent solvation of such molecules in the alkane lakes and seas found on the moon's surface are of particular interest for investigating the possibility of prebiotic chemistry in Titan's hydrophobic seas. Here we characterize the solvation of acetonitrile, a product of Titan's atmospheric radiation chemistry tentatively detected on Titan's surface [H. B. Niemann et al., Nature 438, 779-784 (2005)], in an alkane mixture estimated to match a postulated composition of the smaller lakes during cycles of active drying and rewetting. Molecular dynamics simulations are employed to determine the potential of mean force of acetonitrile (CH3CN) clusters moving from the alkane vapor into the bulk liquid. We find that the clusters prefer the alkane liquid to the vapor and do not dissociate in the bulk liquid. This opens up the possibility that acetonitrile-based microscopic polar chemistry may be possible in the otherwise nonpolar Titan lakes. [ABSTRACT FROM AUTHOR]

Lunar volcanic volatiles are crucial for understanding eruption dynamics on the Moon as well as the potential formation, life span, and dissipation of a lunar secondary atmosphere. We review literature concerning volatile content, degassing extent, and speciation during the mare eruption period on the Moon from 4.0 to 1.2 Ga, providing a realistic summary of degassed compositions for the traditional volcanic elements C-O-H-S-F-Cl. The most reliable estimates of lunar volcanic volatiles come from high‑titanium (high-Ti) glass beads sampled during the Apollo 17 mission. Analysis of these samples demonstrates that hydrogen is the most abundant element by mole in erupted volcanic gases, so a hydrogen species should be the most abundant molecule in the lunar gas, rather than carbon monoxide. This hydrogen is expected to speciate mostly as H 2 , rather than H 2 O, at the predicted oxygen fugacity for lunar magma. This difference is important because H 2 more easily escapes from the Moon, whereas H 2 O could freeze out on the lunar surface, and potentially persist within permanently shadowed regions near the poles. We also find that sulfur, rather than carbon, is the third most abundant element in lunar volcanic gas, after hydrogen and oxygen. • This review evaluates elemental compositions for the volcanic gases released by lunar pyroclastic and mare eruptions. • Hydrogen was the most abundant element by mole in the gas, followed by oxygen, sulfur and then carbon. • The oxygen content of lunar magma will affect the most abundant hydrogen species. • Previous estimates of lunar volcanic gas show a larger compositional range than justified by samples. • Understanding volatile metals in lunar volcanic gas will be crucial for future research. [ABSTRACT FROM AUTHOR]

Aims. An asymmetric dust cloud was detected around the Moon by the Lunar Dust Experiment on board the Lunar Atmosphere and Dust Environment Explorer mission. We investigate the dynamics of the grains that escape the Moon and their configuration in the Earth-Moon system. Methods. We use a plausible initial ejecta distribution and mass production rate for the ejected dust. Various forces, including the solar radiation pressure and the gravity of the Moon, Earth, and Sun, are considered in the dynamical model, and direct numerical integrations of trajectories of dust particles are performed. The final states, the average life spans, and the fraction of retrograde grains as functions of particle size are computed. The number density distribution in the Earth-Moon system is obtained through long-term simulations. Results. The average life spans depend on the size of dust particles and show a rapid increase in the size range between 1 and 10 μm. About 3.6 × 10−3 kg s−1 (~2%) particles ejected from the lunar surface escape the gravity of the Moon, and they form an asymmetric torus between the Earth and the Moon in the range [10 RE, 50 RE], which is offset toward the direction of the Sun. A considerable number of retrograde particles occur in the Earth-Moon system. [ABSTRACT FROM AUTHOR]

Can uninterrupted photovoltaic power feasibly be realized without energy storage? Although on planet Earth the answer appears to be negative, we depict and evaluate how it can be achieved on the Moon with a strategy that exploits the combination of the absence of a lunar atmosphere and the near-zero tilt of the Moon's polar axis with respect to the ecliptic plane. This strategy may be of considerable value in the current revival of lunar colonization initiatives, where the envisioned level of uninterrupted electricity for the oxygen production plants that will constitute the principal energy consumer is of order ∼10 MW, with the flexibility of large distances between power production and power consumption. This approach is also shown to offer noticeably superior specific power (kW/kg) than the current proposed designs of either nuclear reactors or solar with battery storage. • Continuous PV electricity production without storage for lunar colonies • High-latitude deployment permits viable transmission to near-polar consumers • Specific power (kW/kg) is far superior to nuclear reactors or adding battery storage • No atmosphere, a near-zero axis tilt and small size enable a unique lunar solution [ABSTRACT FROM AUTHOR]

We investigate the comparative effect of impacts by trans-Neptunian Objects on the atmospheres of the moons Ganymede, Callisto, Europa, and Titan. We derive an analytic prescription for the 'stalling mass' (i.e. the atmosphere mass at which equilibrium between erosion and volatile delivery occurs), which is tested against a numerical model, demonstrating that the behaviour of the atmosphere matches the analytic prediction, albeit with stochastic events causing orders of magnitude variability. We find that bombardment, neglecting other effects, predicts atmosphere erosion on Ganymede, Callisto, and Europa leading to masses in quantitative agreement with the observed atmospheres. The predicted masses are relatively insensitive to the impactor size and velocity distributions, but sensitive to impactor density and volatile content. Crucially, we find that in this model the frequent arrival of 1–20 km-sized objects sets the quiescent atmosphere masses of the different moons, with atmospheres returning to these levels on ∼100 Myr time-scales at current bombardment levels, and larger impactors causing stochastic excursions to larger atmosphere masses. This quiescent level is higher on Titan than the Jovian moons due to the typically slower impact velocities, but to recreate Titan's massive current atmosphere an additional volatiles contribution is needed, which may be provided by impact-triggered outgassing. If so, the predicted mass is then dependent on the outgassing efficiency and the volatile mass contained in the crust, both of which are uncertain. This work highlights the role that impacts may have played in shaping the atmosphere evolution of outer Solar system moons, and the importance of stochastic effects. [ABSTRACT FROM AUTHOR]

Studying lunar dust is vital to the exploration of the Moon and other airless planetary bodies. The Ultraviolet and Visible Spectrometer on board the Lunar Atmosphere and Dust Environment Explorer spacecraft conducted a series of Almost Limb activities to look for dust near the dawn terminator region. During these activities the instrument stared at a fixed point in the zodiacal background off the Moon's limb while the spacecraft moved in retrograde orbit from the sunlit to the unlit side of the Moon. The spectra obtained from these activities probe altitudes within a few kilometers of the Moon's surface, a region whose dust populations were not well constrained by previous remote‐sensing observations from orbiting spacecraft. Filtering these spectra to remove a varying instrumental signal enables constraints to be placed on potential signals from a dust atmosphere. These filtered spectra are compared with those predicted for dust atmospheres with various exponential scale heights and particle size distributions to yield upper limits on the dust number density for these potential populations. For a differential size distribution proportional to s−3 (where s is the particle size) and a scale height of 1 km, we obtain an upper limit on the number density of dust particles at the Moon's surface of 142 m−3. Plain Language Summary: The Moon has a tenuous atmosphere of dust particles. It is important to study this dust environment in order to develop solutions for dust‐related problems with exploration of the lunar surface, as well as understand the effects of dust transport on other airless planetary bodies. Lunar Atmosphere and Dust Environment Explorer's Ultraviolet and Visible Spectrometer made a series of Almost Limb observations that enable us to probe the Moon's dust atmosphere at altitudes ranging from 1 and 10 km above the surface. Data from these observations are processed and compared to the predicted signals from a variety of different dust populations. These comparisons yield new upper limits on dust density within a few kilometers of the lunar surface, providing additional constraints on dust population at low altitudes. Key Points: Lunar Atmosphere and Dust Environment Explorer's Ultraviolet And Visible Spectrometer made a series of observations that enable us to probe the Moon's dust atmosphere at altitudes between 1 and 10 kmThese observations are filtered to isolate dust signals and are compared to predicted dust atmospheresFor a dust population with power law size distribution of index −3 and scale height 1 km, the upper limit on the dust density is 142 m−3 [ABSTRACT FROM AUTHOR]

The formation mechanism of longitudinal ridges in long runout landslides has been proposed to require ice and/or clay minerals, as low friction materials would allow the spreading of the deposit, causing the development of longitudinal ridges by tensile deformation of the slide. The necessity of ice in the formation of longitudinal ridges has been challenged by the finding that the wavelength of longitudinal ridges is 2–3 times the thickness of the deposit in both ice‐free laboratory experiments on rapid granular flows and in a martian and terrestrial long runout landslide, suggesting a scale‐ and environment‐independent mechanism. We conduct morphometric analysis of the longitudinal ridges in two landslides on the Moon, considered ice‐free throughout its geological history: the Tsiolkovskiy crater landslide, and the Light Mantle avalanche in Taurus‐Littrow Valley. We show that Tsiolkovskiy crater landslide exhibits a scaling relationship between the wavelength of its longitudinal ridges and the thickness of its deposit that is consistent with previous studies, supporting the idea that ice is not a necessary condition for the development of longitudinal ridges. As the Tsiolkovskiy crater landslide is laterally confined, it demonstrates that neither the development of longitudinal ridges nor the occurrence of the scaling relationship between the wavelength of the ridges and the thickness of the deposit depend on the lateral spreading of the deposit. Finally, we use the Light Mantle to test the use of the scaling relationship as a tool to estimate the thickness of the deposit when classical geomorphological methods are not applicable. Plain Language Summary: The origin of a pattern of ridges that extend in the direction of motion (called longitudinal ridges) seen in hypermobile landslides is debated. One hypothesis suggests that the pattern derives from landslides spreading over low friction surfaces, such as ice or clay minerals. However, other studies disagree on the necessity of ice and suggest an environment‐independent mechanism, showing that the distance between ridge crests scales with the thickness of the deposit in both ice‐free laboratory simulations, and martian and terrestrial slides. In this study, we measure the distance between the ridge crests and calculated the thickness of the Tsiolkovskiy crater landslide on the Moon, in a region where extensive ice cover is excluded through its history. We find a scaling relationship consistent with previous studies, which supports the hypothesis that ice is not necessary to form longitudinal ridges. As the Tsiolkovskiy crater landslide is laterally confined, we conclude that the lateral spreading is also not necessary to form longitudinal ridges but it does affect the thickness of landslides and the distance between the ridges. We use the Apollo 17 Light Mantle avalanche to test the application of the scaling relationship to infer landslide thickness by measuring the distance between ridges. Key Points: Wavelength of longitudinal ridges and thickness of lunar landslides scale in agreement with laboratory, martian, and terrestrial resultsThe formation of longitudinal ridges does not depend on the presence of ice nor on the lateral spreading of the slide during emplacementThe wavelength of longitudinal ridges can be used to estimate the thickness of landslides when other methods are not applicable [ABSTRACT FROM AUTHOR]

The long‐ and short‐term drivers and transport mechanisms of lunar rockfalls are currently not well understood, but could provide valuable information about the geologic processes that still shape the surface of the Moon today. Here, we compare the global distribution of rockfalls with relevant geophysical data, such as seismic, topographic, thermal, gravity anomaly, and tidal displacement data sets. Rockfalls appear to predominantly occur (a) on equator‐facing slopes and thus in regions with large thermal amplitudes, (b) on slope angles well above‐average (Δ ∼ 10°), and (c) in regions with above‐average rock abundance. We do not observe a qualitatively or statistically relevant relation between rockfall abundance, monitored Apollo‐era shallow seismic activity, and the distribution of visible tectogenetic features. Informed by our global analysis, we conduct a targeted, in‐depth study of 687 rockfall boulders and trajectories in 13 sites across the Moon, including 7 craters, 2 volcanic vents, 2 tectonic structures, and 2 unclassified geomorphic regions. We identify four different source region types, where the type appears to control the occurrence of rockfalls. The source region type in turn is controlled by surface age rather than geomorphic context. We find that rockfall trajectories are mainly controlled by the trigger energy and the geometry of the slope. Our results suggest that erratic small‐scale impacts (mainly in old, Imbrian‐Nectarian, shallow terranes), aided by solar‐induced thermal fatigue of fractured bedrock (mainly in young, Copernican‐Eratosthenian steep terranes), were the dominant, global‐scale long‐ and short‐term drivers of rockfalls in the Moon's recent geologic past. Plain Language Summary: The processes that drive rockfall occurrence are largely unknown, but could provide valuable information about the past and current evolution of the Moon's surface and interior. We compare the global distribution of rockfalls with a series of maps, such as seismic, topographic, thermal, and gravity anomaly maps and observe that rockfalls mainly occur (a) on equator‐facing slopes and thus in regions with large temperature differences, (b) on slope angles above‐average, and (c) in regions with rocky surfaces. We do not observe a relation between rockfall abundance, Apollo‐era seismic activity, and the distribution of visible tectonic features. Informed by our global‐scale analysis we study 687 rockfalls in 13 sites of interest in greater detail, including volcanic‐, tectonic‐, and impact‐related geomorphic regions. We observe that the source region type appears to control rockfall occurrence, which in turn is controlled by the surface age. We find that the lunar rockfall transport process appears to be mainly controlled by the driver energy and the steepness of the slope. Our results suggest that small‐scale impacts (mainly in old, shallow regions) and solar‐driven thermal breakdown of fractured bedrock (mainly in young, steep regions) were the main, global‐scale drivers of rockfalls in the Moon's recent geologic past. Key Points: We study the drivers and transport mechanisms of lunar rockfalls on a local and global scaleThe two dominant, global‐scale rockfall drivers appear to be: (a) impacts and (b) solar‐driven thermal fatigueThe rockfall driver depends on the source region age and type rather than the geomorphic context [ABSTRACT FROM AUTHOR]

We analyzed high accuracy time delays of laser signals sent from the Earth to the retroreflector arrays on the Moon in conjunction with several other sets of solar‐system astrometric data. Using especially the lunar laser ranging data obtained from the Apache Point Observatory telescope site in New Mexico and the Apollo 11 and Apollo 14 retroreflectors on the Moon, we have set a bound on their relative motion along the connecting great circle of 4 mm/yr over a 14‐year period. Plain Language Summary: Earth's surface is covered with plates, which move with respect to each other at rates from about 15 to 150 mm/year. Almost all scientists who study the Moon believe no such plate motion exists on the lunar surface. Thanks to three sets of retroreflectors left on the Moon by Apollo astronauts and two sets by Soviet spacecraft, we have the capability to accurately measure the round‐trip times of very short laser pulses sent from telescopes on Earth to these retroreflectors. The most precise of such measurements now have an equivalent one‐way distance uncertainty of under 2 mm. We began analysis of these round‐trip times to seek evidence for changes with time in the distances between the first two left there by Apollo astronauts. Their separation along the lunar surface is about 1,248 km. We detected no change in this distance, with an uncertainty of 4 mm/year, from the highest accuracy measurements, made from 2006 to 2020. In the future, with more and more accurate data from all sets of lunar retroreflectors, a similar analysis might, for example, allow determination of the size and other characteristics of a lunar core, as well as possibly permit detection of lunar plate motions. Key Point: Analysis of 14 years of lunar laser ranging data bounds to under 4 mm/year the distance rate between the retro arrays from the Apollo 11 and 14 missions [ABSTRACT FROM AUTHOR]

The Cassini-Huygens mission that explored the Saturn system during the period 2004–2017 revolutionized our understanding of Titan, the only known moon with a dense atmosphere and the only body, besides Earth, with stable surface liquids. Its predominantly nitrogen atmosphere also contains a few percent of methane that is photolyzed on short geological timescales to form ethane and more complex organic molecules. The presence of a significant amount of methane and 40Ar, the decay product of 40K, argues for exchange processes from the interior to the surface. Here we review the information that constrains Titan's interior structure. Gravity and orbital data suggest that Titan is an ocean world, which implies differentiation into a hydrosphere and a rocky core. The mass and gravity data complemented by equations of state constrain the ocean density and composition as well as the hydrosphere thickness. We present end-member models, review the dynamics of each layer, and discuss the global evolution consistent with the Cassini-Huygens data. Titan is the only moon with a dense atmosphere where organic molecules are synthesized and have sedimented at the surface. The Cassini-Huygens mission demonstrated that Titan is an ocean world with an internal water shell and liquid hydrocarbon seas at the poles. Interactions between water, rock, and organics may have occurred during most of Titan's evolution, which has strong astrobiological implications. Data collected by the Dragonfly mission and comparison with the JUpiter ICy moons Explorer (JUICE) data for Ganymede will further reveal Titan's astrobiology potential. [ABSTRACT FROM AUTHOR]

Hydroxylation by solar wind protons has been simulated in our laboratory on Apollo 17 lunar sample 78421, a very mature regolith sample that is rich with agglutinates (68%). The goal of this study was to determine the rate of hydroxyl formation and their thermal stability by monitoring changes in the SiOH (hydroxyl) stretching band near 3 μm using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). A 2 keV H2+ ion beam was used to simulate proton implantation on 78421 and on a crushed fused silica sample. We find that the OH band does not change unless the samples have been annealed in vacuum prior to irradiation. Qualitatively, the OH bands for the fused silica and 78421 are very different. The OH band for fused silica is centered at 2.74 μm and is relatively sharp ranging from 2.67 to 3.1 μm at full width at half maximum (FWHM), while the OH band for 78421 is centered at 3.0 μm and ranges from 2.74 to 3.37 μm at FWHM. The increase in wavelength and broadened nature of the OH band in 78421 may be associated with the OH's proximity to surface defects and/or lattice vacancies. The lack of the H2O bending mode at 6.1 μm indicates that any adsorbed terrestrial H2O is below our detection limit, and therefore the H2O stretching mode at 2.9 μm is not significantly contributing to the broad 3 μm OH band and implies that proton implantation by itself does not lead to water formation. To simulate the maximum dayside temperature on the lunar surface, the lunar sample was heated after proton irradiation. The proton induced OH concentration was reduced by as much as 25% after heating to 400 K (127°C). Plain Language Summary: We performed laboratory experiments to mimic solar wind protons implanting into lunar soils. We measured changes in the OH absorption band near 3 microns using infrared spectroscopy to determine the rate of hydroxyl formation and their thermal stability after proton irradiation. The lunar sample designated 78421, was collected during Apollo 17's manned mission to the Moon. The 78421 sample is composed mostly of clumps of small grains that were exposed to the harsh environment of space. For these experiments, we used a crushed fused silica powder as a control sample for the experiment. Our spectral data shows that the absorption band for OH is much broader for the Apollo sample than for the fused silica control. We did not observe a corresponding bending mode for H2O at 6.1 μm, which indicates that water is not produced during proton implantation and that the OH stretch near 3 μm is not from adsorbed water. After heating our proton irradiated Apollo soil to 400 K (127°C), the Moon's midday surface temperature, a reduction of up to 25% of the initial OH band area was observed indicating that hydroxyls (or hydrogen) can diffuse in or out of the lunar grains during the day. Key Points: Laboratory measurements show solar wind energy protons produce hydroxyls in Apollo 17 lunar sample 78421Diffuse reflectance infrared spectra of 78421 show the OH band near 3 μm increases in wavelength and broadens due to space weatheringNewly formed hydroxyls diffuse during heating to 400 K, and up to 25% are lost [ABSTRACT FROM AUTHOR]

We investigate the dynamics of a water pumping mechanism driven by temperature variations in the lunar subsurface. The thermal environment at three polar sites and three sites in the Clavius region was simulated, taking into account local terrain and scattered radiation. A separate heat and mass transfer model was used to simulate depth‐dependent, temperature‐dependent, and pressure‐dependent properties of the lunar subsurface. The results suggest that diurnally varying heat fluxes create suitable conditions for water migration at many sites across the lunar surface. Enabled by a constant supply to the lunar surface, water molecules typically migrate a few centimeters deep via the formation of distinct concentration peaks, and a downward flux driven by the repeated desorption and resorption. With a constant supply rate of 10−15 kg/(m2 s), the quantity of adsorbed water stored at Ga timescales reaches values on the order of 10−10 to 10−7 mol/m2 at the investigated sites. Based on our results, we present a new relation for the water migration depth that takes into account the ratios of surface temperatures. The results of a sensitivity analysis show that the desorption activation energy is a dominant factor for the quantity and depth of water migration. In addition to long‐term accumulation of subsurface adsorbate, the model shows that temporarily captured water at shallower depths can be released during the lunar day at quantities of up to several µg m−2. This, as well as exposure of shallow water disturbed by impacts, may be a relevant source for surface water in illuminated areas. Plain Language Summary: Water bound to the lunar soil is released by the daily temperature cycle on the Moon. A portion of it is subsequently lost to space, but some of it is transported to deeper layers in the lunar soil. How much water will be transported within the soil depends on the temperature distribution, timescales, and how strongly the water bonds with the soil. Using a simulation model for the heat exchange at the lunar surface and the heat and mass transfer within the lunar soil, we show how pronounced this phenomenon is at six selected sites in the lunar south polar region and the Clavius region. We find that the quantities of accumulated subsurface water are generally low, on the order of several micrograms per unit area, and tend to be higher at the polar sites. Subsurface water can be found at depths of only a few centimeters and the depth of the peak concentration can be determined using a newly established relation for surface temperature ratios. Such shallow accumulated water is also partly released during some lunar days and could in principle be observed during day at the surface, even at warmer mid‐latitudes, such as the Clavius region. Key Points: Our model combines 3D lunar surface temperatures and a detailed parametrization of heat and mass transfer properties of the subsurfaceWater typically accumulates at depths <10 cm with a distinct peak and migration depth can be estimated based on surface temperature ratiosWater can be temporarily trapped at shallow depth even at mid‐latitudes, where it is partially released to the exosphere during day [ABSTRACT FROM AUTHOR]

The lunar mascon basins are characterized by high gravity anomalies and thin crust. Study of the density structure beneath the mascon basins can help to understand the origin of these gravity anomalies and infer their formation and evolution. We propose an efficient forward gravity method based on the 3‐D Gauss‐Legendre quadrature (GLQ) and Fast Fourier Transforms combined with the adaptive discretization strategy to ensure high accuracy. The numerical example demonstrates that computational efficiency is increased by about three orders of magnitude compared to the traditional 3D GLQ method. We employ this forward method in a 3‐D inversion of the gravity data derived from the lunar gravity model GL1500E. The inverted results show prominent high‐density structures (namely, mascons) representing significant mantle uplift and thinned crust beneath most impact basins. Marked low‐density rings surround the mascons. Most of the corresponding low‐density anomalies extend from the near‐surface to the Moho, indicating a thick, low‐density crust. Our density model is consistent with the formation processes of mascons that an impact causes collapse of the transient crater and then the shocked mantle drives mantle flow. The low‐density rings surrounding the mascons may stem from the crust thickening following an impact and extensive fracturing of the crustal column. Plain Language Summary: Mascons (i.e., mass concentration) have been found beneath most of the lunar impact basins. Knowledge of their density distribution is vital for understanding of their structure and evolution. The mass excesses in some impact basins extend from the base of the lunar crust to about 60 km depth and correspond to a density anomaly of up to 400 kg/m3. These mass concentrations are usually surrounded by a ring of low‐density crust. These features are consistent with the hypothesis that the mascons were formed after an asteroid impact and the upwelling mantle material filling the impact crater. This high‐density material produces the mass excess under the impact basins, while the broken crustal material forms the thick low‐density crust around the mascons. Key Points: A highly efficient forward modeling method for gravity calculations is proposed and used in inversionProminent high‐density structures represent significant mantle uplift and thinned crust beneath most of the impact basinsNegative density anomalies around the mascons form outer rings which may be associated with crustal thickening [ABSTRACT FROM AUTHOR]

China's Chang'e-6 mission aims to land in the South Pole-Aitken Basin (SPA), the Moon's largest and oldest impact crater, to collect rocks and soil samples. Scientists hope that these samples will provide insights into the timing and nature of the SPA impact, which is still a topic of debate. The samples may also shed light on the differences between the Moon's near side and far side, as well as the formation of the Moon itself. Chang'e-6 is part of China's successful lunar exploration program and is expected to share samples internationally. [Extracted from the article]

Under lunar polar cold traps, volatile molecules within porous regolith may experience temperature and depth dependent slow mobility. Many degraded lunar craters exhibit thick regolith fill based on models of topographic diffusion and observations of fresh and degraded craters. Regolith has a low thermal conductivity relative to megaregolith and may act as a blanket for internal lunar heat flow, leading to increased temperatures at depth. We develop 2D thermal models of fresh and regolith-filled lunar craters over depths of meters to hundreds of meters below the surface. We find that the base of the stability and slow mobility zones migrate upward with regolith fill, which leads to temperatures that may increase the sublimation rate of volatiles at depth. For a notional cold trap crater 1.6 km in diameter and 3.6 billion years old, topographic diffusion fills it with approximately 90 m of regolith, and the regolith fill's blanketing effect causes the 110 K isotherm to shift about 180 m upward. This places it approximately 25 m below the current cold trap surface and well above the initial crater floor. The slow water ice mobility zone below the 110 K isotherms also shifts upward with regolith fill, potentially increasing volatile concentrations at shallower depths. These secondary volatile concentrations may be targets for sampling and testing hypotheses of volatile system processes. In addition, remobilized volatile concentrations may be a resource for future In-Situ Resource Utilization (ISRU) applications. The thick regolith fill in degraded craters and volatile remobilization potential in lunar subsurface cold traps have implications for future exploration instruments, sampling, and ISRU architectures. • Subsurface lunar polar cold traps impact volatile mobility. • Many lunar craters show enhanced regolith thickness. • Low thermal conductivity regolith can act as a thermal blanket. • Planar 2D thermal models reveal stability zone migration with regolith fill. • Remobilized subsurface volatile concentration potential and ISRU implications. [ABSTRACT FROM AUTHOR]

The lunar surface is constantly bombarded by the solar wind, photons, and meteoroids, which can liberate Na atoms from the regolith. These atoms are subsequently accelerated by solar photon pressure to form a long comet‐like tail opposite the sun. Near new moon, these atoms encounter the Earth's gravity and are "focused" into a beam of enhanced density. This beam appears as the ∼3° diameter Sodium Moon Spot (SMS). Data from the all sky imager at the El Leoncito Observatory have been analyzed for changes in the SMS shape and brightness. New geometry‐based relationships have been found that affect the SMS brightness. The SMS is brighter when the Moon is north of the ecliptic at new moon; the SMS is brighter when new moon occurs near perigee; and the SMS peaks in brightness ∼5 h after new moon. After removing these effects, the data were analyzed for long term and seasonal patterns that could be attributed to changes in source mechanisms. No correlation was found between the SMS brightness and the 11‐year solar‐cycle, the proton or the He++ flow pressure, the density, the speed or the plasma temperature of the solar wind, but an annual pattern was found. A ∼0.83 correlation (Pearson's "r") was found between the SMS brightness and a 4‐year average of sporadic meteor rates at Earth, suggesting a cause‐and‐effect. The new insights gained from this long‐term study put new constraints on the variability of the potential sources of the Na atoms escaping from the Moon. Plain Language Summary: Once a month, at the time of new moon a small, diffuse spot of light appears in the sky opposite the Sun. This spot is about five times the diameter of the full moon, and is 50 times fainter than can be seen with the unaided eye. The spot is reflected light from millions of sodium atoms that two days earlier were on the surface of the Moon. These atoms were liberated from the Moon's surface by meteoroid impacts, the solar wind and photons. Once free of the lunar surface, the atoms are pushed by light pressure into a long comet‐like tail. When this very diffuse cloud of sodium atoms encounters the Earth's gravity, it is "focused" into a region of enhanced density becoming visible to sensitive cameras equipped with filters tuned to the orange light emitted by sodium near 589.3 nm. All‐Sky‐Imager data were analyzed to see how the brightness of this spot varies over time, with a goal of finding a correlation with one (or more) of the above mentioned source processes. A correlation was found between the brightness of the sodium spot and the meteor rate observed at Earth using meteor radar data. Key Points: Brightness of the Sodium Moon Spot (SMS) is dominated by the Earth‐Moon‐Sun geometryThe SMS brightness appears to be correlated with the sporadic source of meteorsThe SMS brightness appears not to be correlated with the density, the speed, the pressure, or the temperature of the solar wind [ABSTRACT FROM AUTHOR]

The evolution and compositional structure of the lunar mantle has been extensively modeled but insufficiently constrained by observations. Here, we identify and characterize mantle materials exposed by the Moon's largest impact basin to better understand the composition, stratigraphy, and evolution of the upper mantle. The vast South Pole-Aitken Basin (SPA) exhibits a broad, crescent-shaped thorium and potassium distribution. These incompatible elements are predicted to be concentrated in the dregs of the lunar magma ocean during end-stage crystallization. Through consideration of basin formation models convolved with subsequent geologic evolution, we demonstrate that the distribution and implied stratigraphy of Th- and K-bearing materials across SPA are consistent with an upper mantle ejecta origin. The most pristine exposures of these materials are confined to northwest SPA and also exhibit elevated Ti and Fe (relative to the farside highlands) in association with a gabbronoritic mineralogy. This is consistent with latestage magma ocean assemblages predicted by petrologic models. In contrast, SPA impact melt derived from greater depths is associated with a low-Ca pyroxene-dominated assemblage. Together, these compositional patterns are evidence for a stratified ancient upper mantle. Importantly, the incompatible-element-enriched, ilmenite-bearing ferroan gabbronoritic cumulates evidently had not participated in gravitational overturn at the time of SPA formation. Contrary to recent hypotheses invoking nearside sequestration of incompatible elements to explain hemispherical differences in crustal building and volcanic resurfacing, it follows that incompatible elements were globally distributed in the magma ocean at the time of SPA formation. [ABSTRACT FROM AUTHOR]

Lunar horizon glows observed by the Apollo missions suggested a dense dust exosphere near the lunar terminator. But later missions failed to see such a high‐density dust exosphere. Why the Apollo missions could observe so large number of dust grains remains a mystery. For the first time, we report five dust enhancement events observed by the Lunar Dust Experiment on board Lunar Atmosphere and Dust Environment Explorer mission, which happen near a twilight crater with dust densities comparable to the Apollo measurements. Moreover, the dust densities are larger on the downstream side of the crater and favor a higher solar wind temperature, consistent with an electrostatic dust lofting from the negatively charged crater floor. We also check the Apollo observations and find similar twilight craters, suggesting that the so‐called dust exosphere is not a global phenomenon but just a local electrified dust fountain near twilight craters. Plain Language Summary: With in situ dust measurements, we find that a shadowed crater near the terminator can dramatically change the surface electrical environment and bring a dense dust cloud surrounding the crater, which should be carefully assessed by engineers for future lunar explorations. Moreover, our findings have the general implications in studying the dust environment near large topographic features (mountains and deep craters) of all kinds of airless bodies. Key Points: We find five dust enhancements events near twilight craters, with the in situ dust measurements of the LADEE missionThe dust enhancement events can be caused by an electrostatic dust lofting from the leeward wall of a twilight craterThe lunar horizon glow observed in the Apollo missions can be also related to a twilight crater [ABSTRACT FROM AUTHOR]

The article discusses that the study of the Apollo lunar samples reveal that the Moon generated its own global magnetosphere. Topics discussed include Solar storms strip a planet's atmosphere over time, and only a strong magnetosphere would be able to provide maximum protection; and present simplified magnetic dipole field modeling confined within a paraboloidal-shaped magnetopause to show how the expected Earth-Moon coupled magnetospheres provide a substantial buffer.

A transient lunar atmosphere formed during a peak period of volcanic outgassing and lasting up to about ~70 Ma was recently proposed. We utilize forward‐modeling of individual lunar basaltic eruptions and the observed geologic record to predict eruption frequency, magma volumes, and rates of volcanic volatile release. Typical lunar mare basalt eruptions have volumes of ~102–103 km3, last less than a year, and have a rapidly decreasing volatile release rate. The total volume of lunar mare basalts erupted is small, and the repose period between individual eruptions is predicted to range from 20,000 to 60,000 years. Only under very exceptional circumstances could sufficient volatiles be released in a single eruption to create a transient atmosphere with a pressure as large as ~0.5 Pa. The frequency of eruptions was likely too low to sustain any such atmosphere for more than a few thousand years. Transient, volcanically induced atmospheres were probably inefficient sources for volatile delivery to permanently shadowed lunar polar regions. Plain Language Summary: Could gas emitted from volcanic eruptions during the most intense and voluminous period of lunar mare volcanism produce a temporary lunar atmosphere? Could the presence of such an atmosphere enable volatiles to reach the cold traps in the permanently shadowed regions at the lunar poles? We use information from lunar geology and sample analyses to predict the number of eruptions with time, the volume of individual eruptions, the rates of volcanic gas release during each eruption, and the time between eruptions. We find that only under rare circumstances could a single eruption or two eruptions closely spaced in time release enough gas to create a transient atmosphere with a pressure as large as ~0.5 Pa. Furthermore, it is difficult to sustain such an atmosphere for more than a few thousand years. These results suggest that volcanically produced atmospheres are inefficient source mechanisms for delivery of volatiles to form deposits in permanently shadowed polar regions of the Moon; this favors volatile‐rich impactors as the major source of polar ice. Key Points: A transient lunar atmosphere from peak volcanic degassing lasting up to ~70 Ma was recently proposed as a source of lunar polar volatilesWe forward‐model individual eruption volume, degassing patterns, and duration of periods between eruptions (repose periods)Transient, volcanically induced atmospheres are inefficient sources for volatile delivery to permanently shadowed lunar polar regions [ABSTRACT FROM AUTHOR]

Global exosphere models of alkali gases surrounding Mercury and the Moon assume that the primary effect of the porous soil is to reduce the effective desorption rates. We demonstrate with a kinetic simulation that, following adsorption, the complicated structure of soils has two additional effects on the fate of previously released alkali atoms: (1) trapping of free atoms at lunar temperatures by microscopic shadows and inward diffusion, which becomes the primary sink mechanism, and (2) high‐energy barriers for thermal desorption compared to what would be retrieved from experiments on thin films or compacted pellets, especially when surface diffusion of adsorbates is considered. Lunar soils retain one fifth to two thirds of recycled adsorbates, depending on the assumed adsorbate mobility, photodesorption cross section, and soil thermal gradient. A transition from a retentive surface to full outgassing at T > 500 K will produce complex feedback mechanisms of alkali circulation at Mercury. Plain Language Summary: This paper seeks to understand physical processes that occur on mineral surfaces throughout the Solar System and which affect the atmospheres of Mercury and the Moon. When meteoroids and the solar wind impact the surface, they vaporize sodium and potassium atoms, some of which cannot escape the body's gravity and can populate the atmosphere with successive bounces until they are lost to space via ionization, react with the surface, or penetrate into the soil. We quantify the competition between evaporation and diffusion within the top 1 mm of the soil, which supports the atmosphere reservoir, by following test particle trajectories in soils simulated with a sphere packing code. The simulations provide empirically constrained insights about the longevity of these free atoms. These findings provide context for understanding observations from ground‐based telescopes, MESSENGER and LADEE observations, and laboratory experiments and pave the way for higher‐fidelity models of exospheres for these species. Key Points: We modeled processes occurring on very different timescales in the soil of Mercury and the MoonMicroscopic shadows trap up to half of the deposited sodium and potassium atoms at lunar temperaturesDesorption of previously trapped atoms at higher temperatures could induce additional feedback in Mercury sodium circulation models [ABSTRACT FROM AUTHOR]

Conditions on Saturn's moon Titan suggest that dust devils, which are convective, dust‐laden plumes, may be active. Although the exact nature of dust on Titan is unclear, previous observations confirm an active aeolian cycle, and dust devils may play an important role in Titan's aeolian cycle, possibly contributing to regional transport of dust and even production of sand grains. The Dragonfly mission to Titan will document dust devil and convective vortex activity and thereby provide a new window into these features, and our analysis shows that associated winds are likely to be modest and pose no hazard to the mission. Plain Language Summary: Saturn's moon Titan may host active dust devils, small dust‐laden plumes, which could significantly contribute to transport of dust in that moon's atmosphere. Although the exact nature of dust on Titan is unclear, previous observations confirm that there is actively blowing dust on that world. If dust devils are active on Titan's surface, NASA's upcoming Dragonfly mission is likely to encounter them, but dust devils on Titan are unlikely to pose a hazard to the mission. Key Points: As probed by Huygens, the meteorological conditions near the surface of Saturn's moon Titan appear conducive to dust devil formationDust devils may contribute significantly to Titan's aeolian cycleIf dust devils are active on Titan, NASA's upcoming Dragonfly mission is likely to encounter them [ABSTRACT FROM AUTHOR]

The Dual Frequency Radio Science experiment aboard Chandrayaan-2 uses the communication channel between orbiter and ground in radio occultation mode to study the temporal evolution of electron density in the lunar ionosphere. It consists of a highly stable 20 MHz evacuated miniaturized crystal oscillator source, having a stability of the order of 10-11, which generates two coherent signals at the X (8496 MHz) and S (2240 MHz) bands of radio frequencies. The coherent radio signals, transmitted simultaneously from the satellite and received at the ground-based deep station network receivers would be used to study temporal and spatial variations in the lunar ionosphere. The major science objectives of the experiments include: (i) to study variations in the ionosphere/atmosphere of the Moon; (ii) to explore if the ionosphere of the Moon is omnipresent or has episodic appearances, and (iii) to confirm the source of ions in the lunar ionosphere - whether dusty or molecular. [ABSTRACT FROM AUTHOR]

Designing long-duration lunar orbiter missions is challenging due to the Moon's highly nonlinear gravity field and the third-body perturbations induced by the Earth, Sun and other large bodies. The absence of a Lunar atmosphere has offered the possibility for mission designers to search for extremely low-altitude, quasi-stable lunar orbits. In addition to the reduced amount of propellant required for station-keeping maneuvers, these orbits present great opportunities for unique scientific studies such as high resolution imaging and characterization of the polar ice deposits in deep craters. Prior to the GRAIL mission, mission planning for Lunar orbiters had suffered from inaccuracies, mainly due to the lack of an accurate Lunar gravity model, which resulted in severe deviations with respect to the spacecraft's nominal orbit. We study station-keeping feasibility for spacecraft in near-polar and extremely low-altitude, quasi-frozen orbits around the Moon, that are perturbed by a high-fidelity lunar gravity model and third-body effects from the Earth and Sun. For several candidate orbits, we compare the trade-space between mission duration and Δ V budget, considering impulsive maneuvers applied once every ' N ∈ { 2,6,10,14,18 } ' orbits at periselene or aposelene. Additionally, we investigate the propulsive cost for different orbit insertion dates, the location of impulsive corrections for arresting argument of periselene (ω) drift, and controlling periselene altitude. • Analytical insights on ω variation drawn and specific trends for polar orbits reported. • Six extremely low-altitude (Periselene alt. ~ 20 km), quasi-frozen polar orbits are presented. • Investigation on optimal gravity of the Moon's fidelity model is conducted. • High-fidelity GRAIL model and third-body effects from Earth and Sun are considered. • Station-keeping analyses performed for different orbit insertion dates and maneuver points. [ABSTRACT FROM AUTHOR]

We consider the features of the mechanisms of the electric charging of dust particles, emergence of electric fields, and discharges in the atmospheres of planets and near the surface of the Moon. We find a significant difference in the nature of the influence of electric fields (discharges) on the vortex motions of two-phase (gas and dust) in the atmospheres of the planets and single-phase (dust) near the surface of the Moon. [ABSTRACT FROM AUTHOR]

A double pulse laser system that combines Raman spectroscopy and laser induced plasma spectroscopy (LIPS) in a single unit is demonstrated. The study attempts to improve the atomic signals of LIPS while simultaneously extracting the desired molecular signals from Raman. In low pressure conditions such as the lunar atmosphere, the detection of plasma emission is difficult due to the low electron density and short persistence time causing a rapid plasma expansion. Moreover, in the integration of the spectroscopic system aimed at space exploration, the system size and weight should be minimized. Simultaneous molecular and atomic detection that gave highly resolved spectra of both LIPS and Raman at pressure below 0.07 Torr is achieved. First, a low-energy laser pulse was used to produce a small plasma and to detect the molecular signals through the inelastic scattering effect. Then, the laser pulse at a higher energy is used to produce a larger plasma plume for detecting the atomic signals. Amongst eight rock samples tested, plasma stacking by generating two sequential plasmas produced from the double-pulse laser on Calcite for example enhanced the signal intensities of calcium and oxygen lines by twofold, compared to a conventional LIPS. Unlabelled Image • Double-pulse lasing with inter-delay time is applied to Raman-LIPS detection. • Previous attempts on simultaneous Raman-LIPS have never achieved signal enhancement. • Simultaneous molecular and atomic signals on eight rock samples were detected. • Improved sensitivity and signal enhancement were achieved. [ABSTRACT FROM AUTHOR]

We observed lunar exospheric potassium D1 (7,698.9646 Å) emissions using a high‐spectral resolution Fabry‐Perot spectrometer in 2014. We present the first potassium line profile measurements, which are representative of the potassium velocity distribution. Inferred temperatures are greater during the waxing gibbous phase, 1920±630 K and lower at waning gibbous phase, 980±200 K. Exosphere models suggest that the measured line widths are a combination of photon‐stimulated desorption and impact vaporization sources. The relative potassium emission intensity decreases by ∼2.5 between lunar phases 80° and 30° and is brightest off the northwest limb near the Aristarchus crater, which is a potassium‐rich surface region. Additionally, the emissions off the northern limb are brighter than the southern limb. The intensity decrease and the greater line width during the waxing gibbous versus the waning gibbous phase suggests a dawn‐dusk asymmetry. Plain Language Summary: Potassium is one of the constituents in the rarefied but measurable lunar atmosphere. Although not the most abundant element, it can be observed spectroscopically from Earth and can be used to understand processes that are responsible for sustaining the lunar atmosphere. We present the first atmospheric potassium data set of ground‐based observations to cover several months and the first potassium line profile measurements. We analyze potassium in the Moon's atmosphere in terms of temperature and intensity as it relates to the lunar phase. The potassium temperature during waxing phases is approximately 2 times hotter than the temperature during the waning phases, creating a noticeable asymmetric pattern. The potassium intensity gradually decreases as the Moon gets brighter until the emission signal is lost in scattered moonlight then increases again with time after full Moon. Data near surface regions known to be rich in potassium have higher intensities in the atmosphere than at other locations. Studying temperature and intensity patterns combined with future modelling gives insight to the processes regulating the Moon's atmosphere. Key Points: The average potassium effective temperature is 1920 +/‐ 630 K and 980 +/‐ 200 K for waxing and waning gibbous phases, respectivelyThe relative intensity curve suggests that the source rate decreases more rapidly with local time for waxing than waning phasesThe relative intensity is affected by location, being brightest above potassium‐rich KREEP soils [ABSTRACT FROM AUTHOR]