David T. Blewett

IntroductionThe Lunar Vertex mission [1, 2] will study the Reiner Gamma magnetic anomaly and swirl at the surface of the Moon (Figure 1). The Reiner Gamma swirl is a curvilinear albedo feature that is co-located with a magnetic anomaly, both of unknown origin. The scientists is studying Reiner Gamma in the fields of plasma physics, magnetism, and geology, each having played a role at some point on the evolution of the Reiner Gamma formation dating back to ~2.9 Ga [3]. Figure 1. Reiner Gamma Swirl. Oblique view from west to east, captured by the NAC camera aboard LRO satellite. NAC image reference: M1127569280L,ROur research focuses on geology. The intriguing layout of two large craters in the vicinity of Reiner Gamma suggests they have potentially played a role in resurfacing the swirl via ballistic sedimentation of their ejecta. Hood et al. [3, 4] documented the presence of clusters of ellipsoid craters on the western part of Reiner Gamma in Lunar Orbiter IV images. These craters seem to be the extension of ejecta deposits, which extrapolated to the distance, pass through the center of the Cavalerius crater. The geologic map of the Reiner Gamma region at 1:5 M [5] also suggests the presence of lineaments (ejecta deposits) directionally leading to the Reiner and Cavalerius craters.Our main objective is to determine whether fresh material from surrounding craters could have been deposited on the Reiner Gamma magnetic anomaly after its formation. The specific objectives are to (1) identify the material ejected from Reiner and Cavalerius craters at a fine spatial scale, and (2) study the similarity between the material found on the Reiner Gamma magnetic anomaly and that of these craters.DatasetThe Narrow Angle Camera (NAC) aboard the American Lunar Reconnaissance Orbiter (LRO) spacecraft has been imaging the lunar surface of the Moon since 2009, at an altitude of ~50 km [6]. These cameras capture panchromatic images in the 400–760 nm wavelength range with ~50 cm spatial resolution.SLDEM2015 [7] is a digital elevation model (DEM) created for the lunar surface covering latitudes of ±60°. It has a vertical resolution of ~3 to ~4 m and a spatial resolution of 60 m. SLDEM2015 is a combination of LOLA (LRO) and Terrain Camera (Kaguya) products and was created to provide users with a more accurate DEM.The “Multiband Imager” (MI) camera aboard the Japanese satellite Kaguya was placed into lunar orbit in 2007 at an altitude of 100 km. The instrument has 9 bands, including 5 in the visible spectrum (415, 750, 900, 950, and 1,000 nm) at 20 m spatial resolution and 4 in the near-infrared spectrum (1,000, 1,050, 1,250, and 1,550 nm) at 62 m spatial resolution. Maps of the Optical Maturity (OMAT) index [8] can be derived from MI data. The physical evolution of the lunar surface due to exposure to the space environment is termed maturation, and maturity is the degree to which a particular lunar soil possesses quantitative characteristics consistent with that exposure.The Imaging Infrared Spectrometer (IIRS) camera aboard the Indian Chandrayaan-2 satellite was placed into lunar orbit in 2019 at an altitude of 100 km. The instrument has 256 continuous spectral bands at 80 m spatial resolution. The spectral resolution is approximately 20 nm. The spectral range is between 0.8 and 5 μm.MethodologyWe will first map the distribution of four ejecta facies in and around Reiner and Cavalerius as defined in Thesniya et al. [9]. Facies A represents the proximal ejecta extending from the crater rim to one crater radius. Facies B represents smooth deposits of low-albedo molten material generally present in topographic depressions. Facies C represents areas of smooth, low-albedo melt deposits interspersed with chaotically dispersed blocks of varying sizes, extending from the crater rim and exhibiting preferential flow toward topographically low areas. Facies D represents a cluster of ellipsoidal craters located near the rim crest extending to the distal part of the ejecta. Each Facies represents an ejecta unit with specific characteristics in terms of its surface texture, pattern, and the type and nature of deposition [9]. We will then identify small fresh craters in the continuous ejecta blankets of Reiner and Cavalerius craters near their rim crest (Facies A) and ellipsoidal craters arising from both Reiner and Cavalerius craters on the surface of the lunar swirl (Facies D) and study their respective spectra.Scope of the researchThe ejecta facies of the Reiner and Cavalerius will be mapped for the first time. Our research will allow us to determine the extent of spectral similarity between Reiner and Cavalerius and the Reiner Gamma swirl itself. This information will provide context for the Lunar Vertex mission and contribute to the understanding of lunar swirl formation. Our project will also open research avenues for conducting detailed mapping at other lunar swirls.References[1] Blewett et al. (2023). PRISM-1 Lunar Vertex: Five Instruments and a Rover. Annual Meeting of the Lunar Exploration Analysis Group (vol. 2887, p. 2892). https://ui.adsabs.harvard.edu/abs/2023LPICo2887.2892B[2] Blewett et al. (2024). The Lunar Vertex PRISM Payload: Ready to Launch. 55th Lunar and Planetary Science Conference (vol. 3040, p. 1553). https://ui.adsabs.harvard.edu/abs/2024LPICo3040.1553B[3] Hood et al. (1979b). The Moon: Sources of the Crustal Magnetic Anomalies. Science, Volume 204, Issue 4388, pp. 53-57. https://ui.adsabs.harvard.edu/link_gateway/1979Sci...204...53H/doi:10.1126/science.204.4388.53[4] Hood et al. (1979a). Lunar nearside magnetic anomalies. Lunar and Planetary Science Conference, 10th, Houston, Tex., March 19-23, 1979, Proceedings. Volume 3. (A80-23677 08-91) New York, Pergamon Press, Inc., 1979, p. 2235-2257. https://ui.adsabs.harvard.edu/abs/1979LPSC...10.2235H/abstract[5] Fortezzo et al. (2020). Unified Map of the Moon U.S. Geological Survey....

IntroductionLunar Vertex, NASA’s first Payloads and Research Investigations on the Surface of the Moon (PRISM) delivery, will explore the Reiner Gamma lunar swirl (Figure 1) (Blewett et al., 2025). Swirls consist of high and low albedo variations in the form of loops and ribbons sometimes associated with crustal magnetic “anomalies”. Different hypotheses have been proposed to explain the presence of swirls (summarized in Blewett et al., 2021), including magnetic shielding of the surface from the darkening effects of the solar wind, scouring by gas and dust during the collision of a comet's coma or a meteoroid swarm, and accumulation of fine-grained dust in response to magnetic or electric fields associated with the magnetic anomaly. Studies have investigated the photometric properties of the uppermost regolith at swirls without reaching a consensus regarding their origin but suggest that solar wind shielding and dust levitation/sorting may both play a role (e.g., Denevi et al., 2016; Chrbolková et al. 2019; Kinczyk et al., 2025). Geomorphological studies suggest that on-swirl regions are lower than the off-swirl region by ~4 m at Reiner Gamma (Weirich et al., 2023), supporting the dust migration hypothesis, or local topographic variations pre-dating the formation of the swirls.In this study, we investigate potential differences in regolith properties between on-swirl and off-swirl regions at Reiner Gamma to provide context for the Lunar Vertex mission. Our first objective is to quantify morphometric parameters from the bowl-shaped crater population to investigate potential dust migration mechanisms which may contribute to preferential crater infill on-swirl, or different regolith properties. Our second objective is to estimate regolith thickness using the non-bowl-shaped crater population to see if variations in local regolith thicknesses exist, and in turn, if dust migration mechanisms or differences in pre-impact topography could contribute to these variations.Datasets and methodsWe trained and used a YOLOv5-based model (e.g., Bickel et al., 2025) to detect craters across Reiner Gamma in hillshade images derived from Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) digital terrain models (DTMs) at spatial resolutions from 2 to 5 meters. We developed “MorphoPy”, a Python-based automated crater morphology characterization tool (Martinez et al., 2026), which calculates morphometric parameters (e.g., depth, diameter, wall slope, rim slope, circularity, eccentricity, freshness) on DTMs for craters that have 36 semi-profiles each containing 10 valid measurements. Morphometric parameters are calculated for craters with a diameter (D) equal to or larger than 20 times the spatial resolution of the input DTM, here D≥40 m. In parallel, we manually identified non-bowl-shaped craters (e.g., flat floored, concentric craters, mound) in LROC NAC images on Quickmap and estimated regolith thicknesses using the formula of Bart et al. (2011).Figure 1. Map of Reiner Gamma showing the location of NAC DTMs used to investigate crater morphology overlain by the intensity of the magnetic field (Ravat et al., 2020) (swirl outline from Denevi et al., 2016).Preliminary resultsThe YOLOv5 algorithm identified ~70 000 craters, and “MorphoPy” calculated morphometric parameters for ~25 000 of those. To investigate a subset of the freshest primary craters, we extracted values for craters having a circularity ≥ 0.9, opposite rim slope < 8˚ and a measurable rim for ≥ 50% of their half-profiles. Plots of depth versus diameter values (Figure 2) suggest that most of the freshest primary craters in the Reiner Gamma region have d/D values centered around ~0.1, especially for strength-dominated craters (D < 400 m). Depth versus diameter trends suggest that off-swirl craters are systematically deeper (hence have higher d/D values) than their on-swirl counterpart for a given crater diameter. Analyses will be conducted next to see if the trends are statistically different.Figure 2. Depth versus diameter values for the freshest on-swirl and off-swirl craters in DTMs of different spatial resolution (solid line d/D=0.2, dashed line d/D=0.1, dotted line d/D=0.05).We identified 918 non-bowl-shaped craters on Quickmap, and calculated regolith thickness for the 503 craters that exhibit a clear rim (apparent diameter, DA) and “inner feature” (measured at the base of the normal crater wall slope, DF). Bart et al. (2014) suggest that craters where DF/DA varies between 0.2 and 0.7 and where DA < 300 m are well suited to infer regolith thickness. In our case, 467 craters respect such values (296 off swirl, 171 on swirl) and yield a mean regolith thickness of 6.6 m off-swirl versus 6.1 on-swirl and median values of respectively 4.1 and 4.2 m. These values are consistent with those reported for mare surfaces (3.1–7.8 m; Cooper et al., 1974; Nakamura et al., 1975; Bart et al., 2011). The “regolith thickness” values calculated range between ~1 and 50 m. Impact craters that encounter a strength transition in the target have non-bowl-shaped morphologies. The strength transition can be a layer of regolith over bedrock but can also be a strength transition farther beneath the surface such as layering in the basalt (Bart et al, 2014). A hot spot analysis (Getis-Ord Gi) on the 467 regolith thickness measurements suggests that some high (hot spot) and low (cold spot) regolith thickness values cluster spatially and are statistically significant. Hot spots mostly occur on-swirl and towards the southern portion of Reiner Gamma, while cold spots mostly occur off-swirl and towards the northern portion of Reiner Gamma. The region at ~7.5˚N, 59.5˚W notably exhibits cold spots (regolith thickness values on the order of 1-3 m) in proximity to hot spots (“regolith thickness” or strength contrast at 5-50 m).Figure 3....

The Planetary Surface Texture Laboratory at the Johns Hopkins University Applied Physics Laboratory is a facility for the study of the photometric and polarization behavior of regolith analogs using an ∼1.5‐m‐radius arc goniometer system. This system characterizes the photometric and polarization response of granular materials (planetary regolith analogs) at various illumination and viewing angles in the principal plane, enabling both forward and backward scattering observations at phase angles as low as 20 ± 5°. A polarimetric camera with linear polarizers at 0°, 45°, 90°, and 135° captures visible‐wavelength images of samples illuminated by semi‐collimated, unpolarized light. Imaging polarimetry and photometric studies are important for their ability to reveal sub‐pixel information about the nature of planetary surfaces, in particular, texture‐related properties such as porosity and roughness. We develop a calibration pipeline for the system and illustrate how the system can be utilized to understand the polarization and photometric response of planetary surface analog materials relevant to a range of airless Solar System bodies. We present an initial case study using a lunar regolith simulant, JSC‐1A, illuminated with broadband white light and observed between phase angles of 20 ± 5° and 120 ± 5°. We find that the radiance reflected from JSC‐1A decreases with increasing phase angle, while the degree of linear polarization increases, consistent with previous studies. This work illustrates the system's potential to enhance the interpretation of data sets such as those from the PolCam instrument on the Danuri lunar orbiter, and astronomical observations of asteroids.

Photometry measures the intensity of light from a source, most commonly used in optics and remote sensing, in order to analyze planetary surfaces and measure brightness, also known as reflectance. Reflectance is particularly important in lunar surface analysis because it offers valuable insights into surface composition and properties. The Planetary Surface Texture Laboratory (PSTL) is a facility at Johns Hopkins Applied Physics Laboratory that houses a goniometer system designed to improve the understanding of the polarization and photometric characterizations of planetary surface analog materials. This large arc system, (~1.5 meter radius), includes a sample stage and 2 caddies; one holds the polarimetric camera while the other holds the semi-collimated, unpolarized light. The phase angles range between 20° (at i = 40°) to 120° (at i = -60°) for this study; the camera (viewing angle) remains constant as the light source moves throughout the data collection. The reflectance of a material varies with the photometric conditions and is a function of properties such as particle size, porosity, roughness, and internal particle scattering behavior. The overall albedo and color of a surface may vary with the phase geometry (angles between the light source and the detecting optics). This is of particular importance because of the extreme viewing geometries encountered at the lunar south pole.Lunar Simulant Evaluation The availability and use of lunar regolith simulants is crucial for future lunar missions and understanding how to support a sustainable presence on the surface. When using lunar simulants, we have to keep in mind that the simulants are approximations and do not possess all the same characteristics of lunar regolith. However, understanding how lunar simulants differ spectrally from lunar regolith by observing the optical properties is important for providing crucial information about the composition, application, and formation history of the Moon. We assessed 12 different lunar regolith simulants from 5 different simulant provider companies; Colorado School of Mines (CSM), Off Planet Research, Space Resource Technologies (previously Exolith), NASA/United States Geological Survey (USGS) and Deltion, (4 based in the United States, 1 based in Canada, respectively). These simulants included representation for dust, mare, nearside and farside highland regolith. Our preliminary analysis shows that the composition of these simulants has an effect on the reflectance behavior. All of the highland simulants have a higher overall reflectance than the mare simulants. This is because the majority of minerals that make up the lunar highland simulants is largely plagioclase, which absorb little light, causing a higher reflectance. While the majority of minerals that make up the lunar mare simulants is largely olivine and pyroxene, which absorbs more light, causing a lower reflectance. Any variation in reflectance as a function of phase angle can be attributed to several factors such as albedo, composition, and physical properties including the scattering behavior of the individual particles, and porosity. We also collected measurements of samples that were prepped differently in order to show similarities to actual lunar terrains (as viewed from an Earth-based telescope or from orbit). Typically, to understand the full reflectance range of the material, our samples are prepped with a smooth surface. We also prepared a textured sample that was randomly chopped until it had the same depth as the sample holder. As expected, the contrasting degree of shadowing between a smooth and a rough surface can be seen. The textured sample has a rougher surface, therefore, has more micro-shadowing, causing the textured surface to be darker than the smooth surface. The effect is most pronounced in forward scattering conditions (i.e., large phase angles, >90°). Overall, our initial findings produced expected results, although a more detailed study is underway. In general, these simulants can provide a means for developing in-situ resource utilization technologies, lunar soil testing, extraction, construction, and astronaut trainings. We can also use this data to improve remote sensing techniques and calibrate upcoming mission instruments to refine photometric simulations. Being able to provide a framework for improved interpretations of phase and polarimetric observations of planetary surfaces would ultimately be beneficial for future planetary studies.

Hollows are geologically young depressions on Mercury, most likely associated with the loss of volatile species. The distribution and morphometric properties of hollows provide information about the overall volatile budget of Mercury's (shallow) subsurface, with significant implications for our understanding of the evolution of Mercury and airless planetary bodies in general. Here, we use a convolutional neural network to map the global geographic distribution and morphometric properties of hollows in MESSENGER orbital images and assess their geostatistical relationships with the thermophysical environment. We identify up to 19,110 hollows in the MESSENGER MDIS Narrow‐Angle Camera data set and discover previously unidentified hollows in more than twenty large‐scale geographic regions. Globally, the detected hollows are predominantly located in the northern hemisphere, where MESSENGER image coverage and spatial resolution are highest. Hollows are preferentially detected in impact craters, at low elevations, on low slope angles, and cluster toward the maxima of ejecta mass production by micrometeoroid bombardment. We observe that hollows tend to be located on equator‐facing slopes and increase in size toward the equator and hot‐pole longitudes. Our observations provide new, global‐scale evidence that micrometeoroid bombardment and insolation are the primary drivers of hollow formation and evolution. Our hollow catalogs are openly available and are anticipated to inform systematic, global‐scale studies of hollow formation as well as future orbital imaging efforts by the ESA/JAXA BepiColombo mission.

Hollows are small, shallow, irregularly shaped landforms, widespread across Mercury, interpreted to have formed via loss of volatiles. Here, we present the first global analysis of hollow degradation states using a new machine learning‐derived global catalog. We define three classes, grading from younger/potentially active “Stage 1” (sharp morphology, high visible reflectance) to older/potentially expired “Stage 3” (softened morphology, reflectance similar to that of surroundings). Most analyzed hollows are Stage 1 (N = 1,545 individual hollows), which are more common than Stage 2 (N = 1,111) or Stage 3 (N = 10) hollows near the equator, consistent with the idea that insolation is a primary driver for hollow initiation/growth. Areas where Stage 2 hollows are more common than Stage 1 hollows may indicate regions of relative volatile depletion. Stage 3 hollows are rare, suggesting they are systematically missed during image review, or that hollows on Mercury are mostly young, have been recently reactivated, or are quickly erased once they become inactive. Temperature may limit hollow growth, given that only small hollows are identified in the coldest terrains. There is no meaningful difference in the distribution of hollow sizes between stages, suggesting that their morphological and reflectance properties are not substantially muted until they are fully grown. Stage 1 hollows are more commonly found on steeper slopes than nearby Stage 2 hollows, suggesting that slopes may be an important control on how long hollows remain active. Our hollow classifications are openly available and can help to inform global‐scale studies of hollow evolution, and upcoming targeting efforts by the ESA/JAXA BepiColombo mission.

Lunar Vertex, selected as NASA’s first Payloads and Research Investigations on the Surface of the Moon (PRISM) delivery, will explore a portion of Reiner Gamma (7.585° N, 58.725° W) with instruments mounted on a lander and small rover. Reiner Gamma (RG) is home to a magnetic anomaly, a region of magnetized crustal rocks. The RG magnetic anomaly is co-located with the type example of a class of irregular high-reflectance markings known as lunar swirls. The Lunar Vertex payload was designed to address three science goals: (1) test hypotheses for the origin of the RG magnetic anomaly, (2) test hypotheses for the origin of the RG swirl, and (3) determine the structure of the RG mini-magnetosphere. The payload suite consists of three instruments on the lander, and two instruments on a small commercial rover.The Lunar Vertex payload will be carried to the lunar surface on a commercial lander as part of NASA's Commercial Lunar Payload Services (CLPS) program. The lander and payload are designed for operation during one lunar daylight period (i.e., no night operations or survival). NASA selected Intuitive Machines as the CLPS provider for the Reiner Gamma delivery. At the time of this writing, the launch will be no earlier than June of 2024.Lander Instruments: The three Lunar Vertex lander instruments were delivered to Intuitive Machines in June 2023. The Magnetic Anomaly Plasma Spectrometer (MAPS), built by the Southwest Research Institute, is capable of measuring the ion and electron velocity distribution over a 292.5° x 90° FOV from 8 eV/e to 17.5 keV/e. The Vector Magnetometer–Lander (VML) suite, built by APL, is comprised of a tetrahedral array of four commercial fluxgate magnetometers mounted on the bottom of a 0.5-meter mast, with a science-grade dual-ring core fluxgate magnetometer at the top of the mast. Together, MAPS and VML will characterize the magnetic field and surface plasma environment within RG. The Vertex Camera Array (VCA) suite, built by Redwire, is a set of three clusters of three RGB cameras. VCA images will be used to characterize the landing site geology and to understand the physical properties of the lunar regolith around the lander.Rover and Rover Instruments: The rover vehicle is from vendor Lunar Outpost. The rover instruments were integrated with the vehicle at APL, and environmental testing was carried out on the integrated system. The Vector Magnetometer–Rover (VMR), built by APL, is also comprised of a tetrahedral array of commercial fluxgate sensors, mounted on a 0.2-meter mast. With VML, VMR will characterize local spatial structuring of the magnetic field at RG. The Rover Multispectral Microscope (RMM), mounted inside the rover body, is a close-up imager that can provide information on soil texture, as well as active LED illumination at a set of UV to NIR wavelengths chosen for their utility in determining the composition and maturity state of the regolith. The rover will be delivered to Intuitive Machines in early January 2024.

Whitepaper #149 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: space weather applications; basic research. Additional topics: planetary magnetospheres; inner heliosphere.

Lunar Vertex is a mission at the intersection of multiple science communities, from planetary geology to space plasma physics. As the first Payloads and Research Investigations on the Surface of the Moon (PRISM1) investigation, scheduled for delivery to the Reiner Gamma (RG) magnetic anomaly in 2024 aboard a commercial lunar lander, Lunar Vertex will unravel the nature of the RG anomaly, the connection to and origin of the associated lunar swirl surface feature, and the structure and impact of the “mini-magnetosphere” in this region. Lunar Vertex includes a suite of magnetometers (Vector Magnetometer – Lander; VML), a fixed-mounted set of cameras (Vertex Camera Array; VCA), and a low-energy ion and electron plasma analyzer (Magnetic Anomaly Plasma Spectrometer; MAPS) on the lander. In addition, a second suite of commercial fluxgate magnetometers (Vector Magnetometer – Rover; VMR) and a multispectral imager (Rover Multispectral Microscope; RMM) are mounted on a dedicated rover that will traverse a distance of at least 500 m from the lander, providing additional multi-point measurements. The combination of magnetic field measurements taken during cruise and descent by VML and during surface operations by both VML and VMR will characterize the surface magnetic field within a strong lunar magnetic anomaly. The combined magnetic field and plasma measurements from VML and MAPS will provide direct observations of plasma populations reaching the lunar surface and the associated local magnetic field configuration. Furthermore, the lunar regolith within the RG magnetic anomaly and over different regions of the associated lunar swirl will be characterized by RMM and VCA to reveal the surface texture, composition, and particle distribution around both the lander and rover locations and the correspondence to potential surface weathering processes.