Andrew Poppe -- Space Sciences Lab., Univ. California, Berkeley

The Moon is a unique and dynamic place in the solar system in which to study the fundamental physics governing the interactions of solid-surface planetary bodies with their space environments. In this talk, I will review recent findings with regard to the lunar surface plasma environment and highlight exciting upcoming in-situ investigations both landed on and in-orbit around the Moon. Among recent results, I will touch on (i) complex surface electron emission and charging characteristics recently observed by the twin-probe ARTEMIS mission, (ii) simulations and observations of solar wind interactions with crustal magnetic anomalies, (iii) the unique aspects of the Moon’s plasma and energetic particle environment while crossing the terrestrial magnetotail, and (iv) the intriguing controversy over the presence and variability of a lunar “ionosphere”. Finally, I will review current and future in-situ plasma and field observations at the Moon, including the ongoing THEMIS-ARTEMIS mission, the HERMES particle and field suite onboard the Lunar Gateway, and the plethora of plasma and field measurements onboard various CLPS-hosted payloads to be landed on the lunar surface.

Rhyan Sawyer -- Dept. of Physics and Astronomy, University of Iowa

The near lunar surface environment provides a natural test bed for observing plasmas with a non-zero hall electric field, as well as a potential location for electron-only reconnection. Owing to the small scale sizes of lunar crustal magnetic fields relative to the ion gyroradius, the ions can become demagnetized, while the electrons remain magnetized, resulting in a non-zero Hall electric field. This Hall electric field has been suggested as a possible explanation for particle acceleration and deceleration near lunar crustal magnetic fields. Additionally, there remains an open question as to whether the solar wind IMF reconnects with lunar crustal magnetic fields. Given the small spatial scale of the lunar fields, it is expected that, if reconnection is occurring, it is likely to be electron-only reconnection. This study utilizes data from a THEMIS-ARTEMIS orbit that reached ~15 km altitude above the lunar surface on 04 Dec 2013. The observations show evidence of demagnetized ions and magnetized electrons, resulting in a non-zero Hall electric field. Thus, the observations presented here are consistent with previous studies which predict Hall electric fields near lunar crustal magnetic fields. In addition, the spacecraft traversed a closed magnetic field structure containing solar wind electrons, suggestive of magnetic reconnection having occurred at some point between the solar wind IMF and a lunar crustal magnetic field.

Paul Szabo -- Space Sciences Lab., Univ. California, Berkeley

Observations by several spacecraft have shown that about 10 – 20% of precipitating solar wind protons are backscattered from the lunar surface, mostly as energetic neutral atoms (ENAs). The scattering process is influenced by properties of both the impacting particles as well as the surface and thus, ENA studies represent an opportunity to probe both. To better understand this process, we apply a regolith grain stacking implementation in the ion-surface interaction code SDTrimSP-3D to model the scattering of solar wind protons from the lunar regolith. The model is capable of reproducing all major ENA characteristics observed at the Moon, such as the total backscattering probability, preferential scattering in the sunward direction, and a broad energy loss in the reflection process. Using our model, the reflection probability is shown to significantly depend on the regolith porosity at the surface, which we can constrain to about 85% ± 15%. This high value thus supports a global extremely loose grain stacking at the top of the lunar surface, likely connected to continuous grain lofting processes. We discuss further effects that could be investigated with ENA measurements at the Moon and other bodies, such as constraining surface precipitation in magnetic anomaly regions or complex plasma environments. Additionally, we examine further surface parameters that are likely to influence the scattering process and might be probed with ENA measurements.

Lucas Liuzzo -- Space Sciences Lab., Univ. California, Berkeley

This study presents observations of Solar Energetic Particle (SEP) protons that have penetrated Earth's magnetotail to reach the lunar environment. We apply data from Wind as an upstream monitor and compare to observations from THEMIS-ARTEMIS within the tail to show clear signatures of SEPs at the Moon during two events. We show that SEP protons at energies above ~25 keV gain access to the Moon's position deep within the magnetotail through field lines that are open on one end to the solar wind. These results contradict previous studies that have suggested that the magnetotail is effective in shielding the Moon from SEPs with energies up to 1 GeV. Instead, our findings highlight that Earth's magnetosphere cannot protect the Moon from any SEPs. To understand how these SEPs gain access to the magnetotail, we present test particle simulations which highlight that these particles enter the tail far downstream of the Moon and travel on open field lines to irradiate the lunar surface. Our results have important implications regarding the safety of astronauts during planned missions to the Moon.

Heidi Haviland [Charles Swenson] -- NASA MSFC [Utah State University]

SelenITA is a dual CubeSat mission that will provide the first multi-point dust, plasma, and magnetic field measurements in lunar orbit. This mission will advance the understanding of the electromagnetic space environment at the Moon in support of the Artemis program, exploration, and the geosciences. Here we present the science rationale motivating the mission. The candidate mission science objectives include: (1) constrain the origins of crustal magnetic fields; (2) determine the nature of plasma interactions with crustal magnetic fields; (3) characterize plasma waves and turbulence at the Moon; (4) characterize the lunar surface electric potential in varying plasma environments; (5) constrain the composition, thermal state, and structure of the lunar upper mantle and crust; (6) characterize the ionizing radiation in lunar orbit; and lastly, (7) determine the density of the dust exosphere as a function of latitude, longitude, and altitude, including the lunar polar space environment. The measurement requirements include simultaneous two-point observations of the 3-component vector magnetic field, plasma distribution (flux, energy, density, temperature), and single-point observations of energetic particles (protons, electrons, gamma rays), and dust. These measurements are important because it helps us understand how future astronauts, robots, and space hardware will live and work on the lunar surface.

Paul Hayne -- LASP, University of Colorado

Dust is pervasive on the lunar surface, a natural product of eons of impact bombardment. Meteoritic and cometary impacts also deliver water and other volatiles to the Moon, which may migrate through the exosphere and eventually become cold-trapped in permanently shadowed regions at the poles. The dusty surface layer is therefore an important interface with the space environment, recording processes occurring on a range of timescales. Observations by orbiting spacecraft and Earth-based telescopes have revealed the physical properties of this "epiregolith" layer and its volatile content. Here, I will highlight contributions of the NASA Lunar Reconnaissance Orbiter mission to understanding the Moon's dust and volatile environment. Infrared measurements from the Diviner instrument have played a key role in this understanding. In addition to Diviner measurements, ground-based observations of the Moon's cooling during lunar eclipses have provided unique insights into the widespread dust layer and its relationship to regolith formation. Finally, I will suggest some possible ways dust and volatile processes may be intertwined on the Moon and other planetary bodies.

Xu Wang -- LASP, University of Colorado

Electrostatic dust charging and transport on the lunar surface is a more than five-decade old problem, which was first indicated from several Apollo observations and has recently attracted increased attention as human exploration is returning to the surface of the Moon. It is important, in a timely manner, to monitor and understand such dust environment on the lunar surface and its impact on crew safety and operation of exploration systems. Recent findings from a series of laboratory studies have greatly advanced the fundamental understanding of the initial dust charging and lofting mechanisms, and provided insights into the properties of lofted dust, including the initial charge and velocity, the size distribution, and the lofting rate. These lab results provide critical parameters to the design of a dedicated dust instrument - Electrostatic Dust Analyzer (EDA) to measure electrostatically lofted dust particles on the lunar surface. The EDA development is funded by the NASA DALI program and recently achieved Technology Readiness Level 6. A dust campaign has been performed to characterize the performance of the instrument. Additionally, measurements enabled by the EDA on the lunar surface make important implications for the surface evolution of the Moon and other airless bodies in the solar system.

Angel Abbud-Madrid -- Colorado School of Mines

Throughout human history, resources have been the driving force for exploration and also the means to do so. However, as we continue our exploration of space, our efforts will eventually become limited by the materials that we can carry from Earth. In recent years, space agencies and the private sector have increasingly realized that further exploration and economic activity in space will require collection and extraction of materials, production of propellants, and power generation from extraterrestrial resources for more affordable and flexible transportation, facilities construction, energy production, and life support. Nowhere is this more evident than on the rapidly rising interest around the world for the search, extraction, and in-situ utilization of resources on the Moon. This growing interest may be about to radically influence not just new science missions, but also the expansion of economic activity beyond our planet. However, before the full potential of lunar resources can be realized, important fundamental information will be needed on the properties, composition, abundance, and accessibility of these resources under the unique environmental conditions present on the lunar surface. This presentation will address the key role that science can play to provide this information and how prospecting, collecting, extracting, and utilizing lunar resources can in turn enable future scientific investigations on our nearest celestial neighbor.

Cesare Grava -- Southwest Research Institute

The structure of the lunar exosphere is determined by the interactions between its constituents and the surface. This interaction is a crucial yet poorly understood process. Surface temperature, in particular, affects residence time (adsorption time) of molecules on surface grains, and is therefore important to understand cold trapping. It also affects the migration of volatiles in the exosphere (the warmer the surface, the longer the ballistic hop) and in the subsurface, which can cause sequestration of volatiles at depth. Topography also plays a role: while it has been shown that micro-scale topography, in particular shadows from nearby grains, plays a role in the adsorption and transport of water molecules, the effects of orography (crater walls, mountains, etc.) on the exosphere have not been investigated in detail. We present results from Monte Carlo simulations of the lunar exosphere that incorporate realistic relief and temperature maps from LOLA and Diviner, two instruments onboard the Lunar Reconnaissance Orbiter (LRO). We chose two exospheric species: argon, an endogenic species that adsorbs on the cold lunar surface, and neon, a gas of solar wind origin that does not condense on the lunar surface. We compare modeled densities with those measured by LACE and LADEE mass spectrometers. Our results shed light on the preferred location of sequestered volatiles on the Moon and support ongoing measurements of the lunar exosphere by the UV spectrograph LAMP onboard LRO.

JR Dennison -- Utah State University

Charging of lunar regolith has been recognized since the Apollo era as one of the most immediate and critical issues facing our return to the moon. Charging of bulk lunar regolith and dust through interactions with space environment fluxes are largely determined by electron yields (EY). Lack of accurate EY measurements of bulk highly-insulating granular materials due to many experimental complexities has led to a critical knowledge gap for both engineering strategies and basic science issues. Such knowledge is essential for myriad important lunar applications and simulations related to lunar dust and regolith electrostatic charging. Methods have been developed to prepare bulk dusty samples and to measure accurate EY curves which show minimal charging effects, in contrast to previous results for dust which showed highly suppressed yields due to severe charging effects. EY measurements are presented here for standard lunar simulants and for closely related very high-yield, highly-insulating granular materials including Al2O3 and SiO2. These studies investigated samples representative of diverse lunar regolith, including highly-angular, spherical, and cubic particle shapes with a range particle size from ~1 μm to ~100 μm from low coverages to multilayers with varying porosity and compactness.

Trinesh Sana -- Physical Research Laboratory, Ahmedabad, India

A space-charge region near the sunlit lunar surface, i.e., the photoelectron sheath (PES), is created because of a dynamic interaction between UV radiation, solar wind/ambient plasma and lunar regolith, where the charged dust particles can float due to Coulomb repulsion. Understanding the electric potential and plasma dynamics is essential for efficient instrument operation on lunar modules. We present an analytical formulation of complex potential structures around sunlit moon, taking into account various factors such as solar radiation flux and spectrum, solar wind plasma, surface temperature, surface material characteristics, and angle of solar inclination. Our results show that non-monotonic potential structures exist within the sheath, which is more stable towards the terminator region, while both monotonic and non-monotonic potential structures are equally probable near the equator region. A traditional Debye sheath forms in the region of marginal/zero photoemission (very close to the terminator). These potential structures give rise to complex dust charging and dynamics within the PES. Our study also suggests that a sufficiently strong negative charge develops in the terminator region while the Moon passes through exotic plasma conditions of the Earth's magnetosphere - it may harm long-term efficient instruments functioning over the Moon. This study could be valuable in developing test procedures for future lunar exploration missions.

Kristen John -- NASA STMD

Unknowns remain regarding several lunar dust characteristics, and the lunar dust mitigation community, in collaboration with the science community, is compiling a list of lunar dust characterization needs. It is expected, through the course of currently planned or future lunar surface mission instrumentation, lab experiments, or analysis, that some of these unknowns will be characterized. This list is derived from several sources including findings from the 2020 publication “The Impact of Lunar Dust on Human Exploration”, NASA-STD-1008, SLS-SPEC-159 DSNE, and known gaps identified within NASA programs and projects. The goal of this information collection process is to create a list of dust characterization needs based on scientific and engineering knowledge gaps that will aid in the design and survival of designed and future systems, and address the challenges related to defining the lunar environment and mitigating lunar dust effects on systems and operations. Examples of dust properties and characterization needs include detailed examination of the finest fraction of lunar regolith as it varies by surface location, understanding dust transfer within natural and induced environments, determination of the effects of the lunar plasma environment with regards to materials and hardware, understand the triboelectric charging effects for activities and hardware in contact with the regolith, including grain to grain electrostatic interactions, and material adhesive properties.

Cecily Sunday -- University of Maryland, College Park

Dust transport on the Moon has been directly observed by astronauts during the Apollo missions, and more recently, by cameras on the Chang’e landers. These missions have shown that significant dust migration can occur during powered descents to the Moon, and that high-speed dust sprays can obscure camera views, damage instruments, and alter the topography of landing sites. Several models have been proposed to predict dust erosion due to plume impingement. Near-field dust sprays, however, are difficult to characterize due to the complex nature of gas-surface interactions. Here, we use the direct simulation Monte Carlo (DSMC) method to simulate dust transport due to plume impingement on the surface of the Moon. We model high and low-thrust descent systems by generating source molecules at fixed heights above the Moon’s surface. As the exhaust plume expands, the gas molecules diffusely reflect off the surface and transport lofted dust particles away from the landing site. The dust is created using an empirical erosion model, which is based on experimental data and observations from the Apollo missions [1, 2], and the gas and dust particles interact via the approach described in [1, 3]. In this work, we examine the height, velocity, ejection angle, and displacement of dust that is generated by Apollo and Chang’e-like landing systems. [1] Morris et al. (2015). JSR, 52, 2. [2] Metzger et al. (2010). Earth and Space 2010, 191-207. [3] Burt and Boyd. (2004). AIAA, 2004-1351.

Benjamin Farr -- LASP, University of Colorado

As learned from the Apollo missions, lunar dust causes a series of issues on exploration systems. As NASA prepares to send humans back to the Moon and stay, dust mitigation must be resolved for future long-term, sustainable lunar surface exploration in a timely manner. Though various methods have been under development, there is a lack of technologies to efficiently mitigate lunar dust hazards. A novel Electron-beam Lunar Dust Mitigation (ELDM) technology has been recently developed and demonstrated in laboratory conditions. The ELDM technology is based on a novel dust charging theory and utilizes a hot filament to generate a low-energy (100-300 eV) electron beam to aim at dust-covered surfaces to be cleaned. The electron beam creates sufficient charges on dust particles, causing them to repel each other to be ejected from the protected surfaces. The laboratory demonstrations show high cleaning efficiency (up to ~92%) for a variety of surfaces, including spacesuits, optical surfaces, thermal blankets, and solar panels. The ELDM technology provides a potential solution to efficiently mitigate dust risks to upcoming human and robotic missions.

Ron Creel -- RACI

Mr. Creel introduced this subject in his DAP-2017 presentation titled "Coping with Dust for Extraterrestrial Exploration". Since then, he has been leading the "Isolation Technologies" Subgroup for the Lunar Surface Innovation Consortium Dust Mitigation Focus Group, and will present that team's important recommendations for keeping hazardous lunar dust out of the lungs of Artemis crews and their habitats on the Moon.

Pierre Henri -- Côte d'Azur Observatory, France

Cometary environments are multiphase media where neutral gas, plasma and dust interact together, from the comet nucleus surface, through the coma, to the plasma and dust cometary tails. I will review some of the main results obtained by the Rosetta ESA mission regarding the cometary plasma environments and their interaction with the solar wind. Focusing on the near-nucleus coma, I will summarize what has been understood regarding the interaction between the plasma environment of comets and cometary dust. After the Rosetta mission, the Comet Interceptor ESA mission is currently being developed to perform the first multi-spacecraft fly-by of a dynamically-new comet. I will discuss plans and expectations regarding its future cometary dusty plasma measurements.

Sean Hsu -- LASP, University of Colorado

The surface properties of asteroids have been the focus of exploration and scientific study since the beginning of planetary science. The particle size distribution is of particularly interest because it reflects the nature of surface shaping processes and has important implications in remote sensing observations and in situ studies. Here we present a numerical model simulating regolith size distribution evolution considering three fundamental processes: thermal fragmentation, impact-induced fragmentation and ejecta escape, and electrostatic dust removal. Fragmentation processes act as a conveyor belt gradually transforming boulders to fine-grained material. Impact ejecta escape and electrostatic dust transport serve as removal processes for fine-grained regolith. The combination of these processes results in a coupled evolution among different grain size populations. Our results show that, at 1 AU distance, km-sized or smaller bodies where electrostatic dust removal is active, the fine-grained regolith could be depleted in a million years, leading to a lag-deposit-like surface scenery on small Near Earth Asteroids as seen by recent asteroid missions. For small Main Belt asteroids, the depletion time is longer at ~ 4 Myr. These results are also relevant to understand the evolution of asteroids, including space weathering and orbital evolution, which will be discussed in the presentation.

Roy Christoffersen -- Jacobs, NASA Johnson Space Center

To obtain better understanding of how small scale impact effects contribute to space weathering as a function of impactor speed and size we produced artificial microcraters in San Carlos olivine using Fe metal dust particles 0.10 to 5 µm in diameter electrostatically accelerated to speeds between 0.35 to 25 km s-1. The crater morphologies, size distribution and microstructures were characterized by field-emission SEM (FE-SEM) and FIB supported field-emission scanning transmission electron microscopy (FE-STEM). These same techniques were also applied to study a natural 20 µm-diameter microcrater in a olivine grain on the surface of lunar rock 12075. Microcrater diameters in the experimental sample range between 0.20 to 5 µm with larger craters having more irregular outlines dominated by spallation fractures. FE-SEM and FE-STEM imaging document the formation of shock melt lining crater cavities in the size population of experimental craters below approximately 1 µm in diameter, corresponding to particle impact speeds in the 10-25 km s-1 range. The natural olivine crater exhibits similar shock melt features along the perimeter of its cavity, but the shock melt also contains nanophase Fe metal particles, something not observed in the experimental samples. FE-STEM imaging of the experimental craters reveals complex shock-generated dislocation and nanofracture microstructures in zones extending 1-2 µm into the olivine from the crater cavity.

Dani DellaGiustina -- University of Arizona

OSIRIS-REx is NASA's first spacecraft mission to sample an asteroid. The mission aims to provide insights into the formation of the Solar System, the origins of life, and potential asteroid impacts on Earth. Data and imagery from the mission unveiled a surprising characteristic of the target, asteroid Bennu: a remarkably low abundance of surface dust and fine regolith. This observation challenges prevailing theories regarding small body evolution and raises fundamental questions about surface processes on Bennu. However, when OSIRIS-REx's sampling mechanism contacted and agitated Bennu's surface, it generated a disturbance that mobilized fine particles and boulders alike. This unexpected event led to the spacecraft collecting a substantial amount of material, exceeding the mission's requirements. It also hinted that fine-grained material on Bennu may reside primarily in the subsurface. OSIRIS-REx will return samples of Bennu in September 2023. Analysis of the samples, including a detailed examination of the dust particles, will provide a deeper understanding of the physical and chemical properties of Bennu's regolith. These findings will also contribute to our knowledge of the potential role of asteroids in delivering organic compounds and volatiles to Earth.

Alex Doner -- University of Colorado

Polyvinylidene Fluoride (PVDF) dust detectors are simple and reliable instruments for measuring dust flux and size distribution in space. These detectors have made their mark across the solar system on a variety of missions starting on Vega 1 and 2 to comet Halley and, most notably, onboard the New Horizons Spacecraft’s Student Dust Counter (SDC). Upon impacting the film, hypervelocity particles form a crater whose volume corresponds to a charge pulse between the surfaces of the film. Charge sensitive electronics (CSEs) can measure the amplitude of this pulse, which is a function of the mass and velocity of an impacting particle. PVDF based instruments have been tested and calibrated at the dust accelerator facility at the University of Colorado, Boulder. However, due to the previous configuration of the dust accelerator and the CSEs, prior experiments were limited to dust grains with masses in the range of 10-13-10-6 g and speeds in the range of 1-20 km/s. This talk will report on a new set of experiments to explore the minimum detectable dust masses and velocities with PVDF detectors. A new configuration of CSEs were designed to increase the gain of the charge pulse, therefore expanding the detectable range of dust grains. Results from this experiment will find the low value edge of the PVDF calibration and identify the possible contributions of various PVDF charge generation mechanisms, including depolarization, piezo, and pyroelectric effects.

Elena Opp -- University of Colorado

Electrostatic dust transport has been suggested as plausible causes for spectral variation on airless bodies over time. In this work we carry out laboratory experiments to examine the relationship between fine-grained material – lunar mare and highland simulant and asteroid simulant crystalline olivine powder. By characterizing the size distribution of electrostatic lofted dust with different materials, our experiment will confirm previous studies and inform us our method to observe the spectra variation is accurate. These experiments allow us to characterize the electrostatic dust size-sorting effect and examine their relationship to spectral variation under controlled laboratory conditions. Previous experiments show that smaller grains are more likely to be transported and their lofting speeds are likely higher. On airless bodies, smaller regolith grains are thus more likely to be transported and/or removed, resulting in size-sorted regolith. Smaller particles also tend to have higher intensities than larger particles. This suggests that as small particles loft from an asteroid over long periods of time, they would impact the brightness and spectra on that body. We will present visible-to-near infrared reflectance spectra of dusty surfaces before and after electrostatic processing. Our measurements will provide quantitative information to examine the viability of studying electrostatic dust transport on airless bodies in relation to spectra using remote sensing techniques.

Fabrice Cipriani -- ESA

The Lunar Ejecta and Meteorites Experiment was part of the Apollo Lunar Surface Experiment Package deployed in the Taurus-Littrow area during the Apollo 17 mission, aiming at characterizing the cosmic dust environment at the lunar surface and the nature of lunar ejecta. The data returned by the LEAM have been extensively analyzed, Interestingly, most of the events were detected in the terminator region, suggesting an electrostatic dust levitation mechanism. In the present study, we perform a parametric study accounting for the environment variability encountered during a lunation (including Sun illumination angle), lunar regolith physical properties and LEAM surface materials properties. This allows determining the LEAM local electrostatic environment possibly leading to dust mobilization and collection by the sensors and instrument surfaces. The largest electrostatic potential difference between the LEAM surface and the lunar regolith tends to be observed at low SZA (sunset / sunrise conditions). In addition, due to the low conductivity of the LEAM surface materials, strong asymmetries occur between sunlit / upstream areas and shadowed / downstream areas of the experiment. The dust dynamic is very sensitive to such in-homogeneities in the near environment of the senor. Close to sunrise and sunset, larger dust fluxes are generally observed on the illuminated side of the sensor, which fits well with the dawn flux enhancements observed by the LEAM EAST sensor.

Sean Gopalakrishnan -- University of Colorado

Understanding surface charging of objects in space, including the Moon, asteroids, dust, and spacecraft, is important for determining plasma-surface interactions at airless planetary bodies, dust dynamics, and the performance of plasma and dust instruments onboard spacecraft. Secondary electron or photoelectron emission often plays an important role in determining the surface charging and potential of these objects. Studies show that secondary emission may vary with the surface temperature, depending on how secondary electrons interact with conduction band electrons and lattice vibrations. We perform laboratory experiments to investigate such effect. Surface materials are attached to a hot plate to reach a temperature range of 25 – 100 C and exposed to a 130-eV electron beam. A double Langmuir probe is used to characterize both the beam electrons and secondary electrons emitted from the surface. The surface potential is measured by an emissive probe. Preliminary results of a dielectric Kapton surface show that the secondary emission current increases as the surface temperature increases, which is consistent with the increasing surface potential results. Future work includes to investigate such effect with temperatures below room temperature using a cold plate, and with different surface materials.

Dan Hallatt -- University of Kent / Université de Lille

Materials recently sampled from asteroid Ryugu are providing the possibility for unique insights to be made into space weathering. This method of surface alteration is not yet well understood from the perspective of carbonaceous bodies, largely thanks to their composition being dominated by hydrated, delicate minerals (phyllosilicates) which have largely not been found from past returned sample missions. We characterize the morphology of craters from experimental micron-scale mechanical impacts on Ryugu-inspired phyllosilicates, made with a light-gas gun at the University of Kent (1-30 um PMMA and Al2O3 projectiles at 2-5 km/s). First, concerning our literature standard sample, we were able to reproduce both the dent and pit-plus-spall morphologies of lunar microcraters in San Carlos olivine. However, the morphology of microcraters in either olivine or our phyllosilicate targets do not follow a simple relationship with either projectile speed or peak shock pressure. It appears that more complex impact metrics should be considered in order to interpret our crater morphologies according to impact conditions (fluence and kinetics for example). We also find a large variance in the morphological details from each particular impact experiment, implying that finely resolving such cratering processes based on their morphology may necessitate tighter experimental control. Interestingly, we find an apparent influence of the polymorph of phyllosilicates on their microcrater morphology.

Jared Long-Fox -- University of Central Florida

Designing rovers and planning rover-based operations on the lunar surface requires knowledge of the surface, the systems interacting with the surface, and the effects of those interactions on the surface and shallow subsurface layers. Development of this knowledge relies on the ability to both test and predict forces, displacements, efficiency, and dust mitigation strategies. The Regolith Interactions for the Development of Extraterrestrial Rovers (RIDER) rover wheel testbed and Simulator for Planetary Interactions for Dust and Regolith (SPIDR) discrete element modeling algorithms are being developed in tandem to answer fundamental questions in lunar terramechanics. RIDER enables investigations of rover wheel performance as a function of both rover and regolith properties in a dust-contained 3.8 x 0.9 x 0.5 m deep simulant bin. The initial testing campaign of RIDER, Geotechnical Assessment of Trafficability on Regolith (GATOR, April 2023), includes a Lunar Roving Vehicle (LRV) replica wheel, a VIPER-like Resource Prospector prototype wheel, and an Astrobotic Polaris prototype wheel. SPIDR ingests CAD-based wheel geometries (currently testing LRV) to simulate wheel-regolith interactions in the lunar environment (reduced gravity, charged particles, electric fields) to inform safe rover operations. Material properties of the particles in SPIDR are undergoing calibration based on video data from column collapse experiments using returned Apollo regolith samples 15071 and 61141.

Libor Nouzak -- Charles University, Prague, Czech Republic

Interplanetary and interstellar dust populations within our solar system can be inferred from dust impacts on spacecraft equipped by electric field antennas. The recorded dust impact waveforms show diversity in their shape and duration according to the antenna operation mode (dipole vs. monopole), impact location with respect to the antennas, spacecraft potential or dust particles properties. In this study we present laboratory investigation of the space and velocity distribution of expanding ions induced by hypervelocity dust impacts. A unique experimental setup with delay line detector (DLD) is developed for characterization of the ion cloud expanding from the impact generated plasma. Spherical iron dust particles of micron and sub-micron size are accelerated to velocities higher than 1 km/s on tungsten target plate by dust accelerator operated at the University of Colorado. The produced ions are detected using the DLD that provides the position of their detection and time-of-flight since dust impact. The preliminary results indicate that the impact-generated ions expand in the form of cloud into all directions and the expanding cloud has slow and fast ion component. The content of slow and fast ion component varies with velocity of dust particles.

Jose Pagan Munoz -- University of Colorado

Dust particles on the surface of airless bodies, like the Moon and asteroids, become charged due to exposure to solar wind plasma and solar ultraviolet radiation. Understanding their charging, mobilization, and subsequent transport provides insight into their effects on the physical properties of the surface and helps to develop efficient dust hazard mitigation strategies for human exploration. Recent laboratory studies have made significant advancements in our understanding of the physics involved in the charging and mobilization of dust particles on regolith surfaces. This talk focuses on monolayered dust particles on dielectric surfaces, like lunar rocks or exploration system surfaces, exposed to plasmas in various conditions. Dust particles were exposed to an electron beam and helium plasma that was generated by ionizing the neutral background gas in our vacuum chamber. The dust mobility was recorded by a camera and measured by the shift of bright pixels in the recorded images. A double-sided Langmuir probe was used to characterize the beam profile and the background plasma, and an emissive probe measured the plasma potential near the surface. These measurements were repeated changing the neutral pressure and the electron beam energy to understand their effects on dust charging.

Abhay Vidwans -- Washington University, St. Louis

Measuring lunar dust particle charging is central to understanding its transport and developing appropriate mitigation strategies, but measurements of very fine dust particles (<25µm) in vacuum are lacking. In this work, fine dust particle charge was measured via electric field deflection in a vacuum chamber (~10^-8 Torr). In the upper portion, a container of fine dust simulant is irradiated with a high-power ns-pulsed laser to simulate micrometeoroid impacts. The laser generated plasma causes charging and subsequent ejection of dust particles. Particles falling towards the center of the chamber enter the lower chamber through a pinhole, then pass a linear electric field that deflects particles by their charge-to-mass ratio. In the first set of experiments, the electric field will be set to its lowest and highest strength, and a strip of carbon tape below the electric field region will capture grains to visualize under SEM and measure particle size and dispersion. Next, the carbon tape will be replaced with an optical particle counter that estimates particle size in real-time. We will apply various intermediate field strengths and use the output of the optical particle counter to resolve 1) the charge-to-mass frequency distribution and 2) the size-dependent charge distribution of dust particles. In future experiments, the setup can be extended to study other dust charging processes such as photoemission (UV source) and ion attachment (differential pumping of ions).

Kelyan Taylor -- University of Colorado

Dust issues have been recognized during the Apollo missions as lunar dust particles readily stick to all surfaces of exploration systems, causing damage to spacesuits, degradation of thermal radiators and solar panels, and interference with the hatch seals of Extravehicular Activity (EVA) systems, for example. The nature of these dust particles being charged due to exposure to the solar wind or solar UV radiation only worsens these situations. This work focuses on charging and mobilization of monolayered dust particles on conductive surfaces of exploration systems. Silica particles <45 microns are spread on an aluminum surface and charged by an electron beam or UV light. After the charging process, a high-voltage electrode grid is brought above the surface to lift up the charged dust particles, which size and charge magnitude and polarity are determined from recorded high-speed videos. Results presented from this work will help find dust mitigation strategies and methods for future lunar surface exploration.

Tianrun Wu --University of Colorado

This study investigates the dynamics of binary asteroid system formation under the framework of the rotational breakup theory. We demonstrate the reshaping effect of dust accretion on seeds outside of the fluid Roche limit. We found that the eccentricity of an attractor accreting materials from a dust ring decreases rapidly as the inverse of the total mass of the attractor, which is faster than the tidal locking mechanism observed in planet-moon binaries. We also established that for a typical secondary in a binary asteroid system with elongated loose granular aggregate structure, its rotation period must be less than around three to five times that of the orbital period for the binary system to remain stable. Furthermore, we explored and ruled out the possibility of a secondary forming a synchronous orbit from the accretion of slowly approaching seeds and concluded that a sparse dust ring environment during formation is necessary to align observations within the rotational fission framework. Finally, we discussed seed migration and the tidal-locking mechanism in dust-sparse environments.

Shaosui Xu -- University of California, Berkeley

Electrons emitted from the lunar surface include photo-electrons, cold secondary electrons, and backscattered electrons, all of which contribute to the surface-charging environment. Among these electron populations, secondary electrons have been well characterized by previous studies but not so much for the other two populations that make up the high-energy tail. Recently, we reported of oxygen Auger electron observations at the Moon by the ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun) spacecraft, which provides a unique feature to identify photoelectrons emitted from the lunar surface. This Auger feature allows for the creation of empirical templates for photoelectrons and backscattered electrons to disentangle these two populations and examine their characteristics separately. By utilizing the Auger electron feature, we identify cases that are separately dominated by either photoelectrons or pure backscattered electrons and then create energy spectral templates for each population, when the Moon is immersed in the solar wind. With such templates, we then fit the total measured electron spectrum from the lunar surface as observed by ARTEMIS from mid-2012 to the end of 2020 and determine the relative contributions of the two populations. We then characterize each population separately and examine their properties via statistical analysis.