Composition Of Regolith Research Articles

Surface Properties of the Kalliope–Linus System from ALMA and VLA Data

The abundance and distribution of metal in asteroid surfaces can be constrained from thermal emission measurements at radio wavelengths, informing our understanding of planetesimal differentiation processes. We observed the M-type asteroid (22) Kalliope and its moon Linus in thermal emission at 1.3, 9, and 20 mm with the Atacama Large Millimeter/submillimeter Array and the Karl G. Jansky Very Large Array over most of Kalliope's rotation period. The 1.3 mm data provide ∼30 km resolution on the surface of Kalliope, while both the 1.3 and 9 mm data resolve Linus from Kalliope. We find a thermal inertia for Kalliope of 116−91+326 J m−2 s−0.5 K−1 and emissivities of 0.65 ± 0.02 at 1.3 mm, 0.56 ± 0.03 at 9 mm, and 0.77 ± 0.02 at 20 mm. Kalliope's millimeter wavelength emission is suppressed compared to its centimeter wavelength emission, and is also depolarized. We measure emissivities for Linus of 0.73 ± 0.04 and 0.85 ± 0.17 at 1.3 and 9 mm, respectively, indicating a less metal-rich surface composition for Linus. Spatial variability in Kalliope’s emissivity reveals a region in the northern hemisphere with a high dielectric constant, suggestive of enhanced metal content. These results are together consistent with a scenario in which Linus formed from reaggregated ejecta from an impact onto a differentiated Kalliope, leaving Kalliope with a higher surface metal content than Linus, which is distributed heterogeneously across its surface. The low emissivity and lack of polarization suggest a reduced regolith composition where iron is in the form of metallic grains and constitutes ∼25% of the surface composition.

Rapid heating rates define the volatile emission and regolith composition of (3200) Phaethon

Asteroid (3200) Phaethon experiences extreme solar radiant heating ( ~ 750 °C) during perihelion (0.14 au), leading to comet-like activity. The regolith composition and mechanism of volatile emission are unknown but key to understanding JAXA’s DESTINY+ mission data (fly-by in 2029) and the fate of near-Sun asteroids more generally. By subjecting CM chondrite fragments to fast, open system, cyclic heating (2-20 °C/min), simulating conditions on Phaethon we demonstrate that rapid heating rates combine with the low permeability, resulting in reactions between volatile gases and decomposing minerals. The retention of S-bearing gas limits the thermal decomposition of Fe-sulphides, allowing these minerals to survive repeated heating cycles. Slow escape of S-bearing gases provides a mechanism for repeated gas release from a thermally processed surface and, therefore the comet-like activity without requiring surface renewal to expose fresh material each perihelion cycle. We predict Phaethon regolith is composed of olivine, Fe-sulphides, Ca-sulphates and hematite.

Chandrayaan-3 APXS elemental abundance measurements at lunar high latitude.

The elemental composition of the lunar surface provides insights into mechanisms of the formation and evolution of the Moon1,2. The chemical composition of lunar regolith have so far been precisely measured using the samples collected by the Apollo, Luna and Chang'e 5 missions, which are from equatorial to mid-latitude regions3,4; lunar meteorites, whose location of origin on the Moon is unknown5,6; and the in situ measurement from the Chang'e 3 and Chang'e 4 missions7-9, which are from the mid-latitude regions of the Moon. Here we report the first in situ measurements of the elemental abundances in the lunar southern high-latitude regions by the Alpha Particle X-ray Spectrometer (APXS) experiment10 aboard the Pragyan rover of India's Chandrayaan-3 mission. The 23 measurements in the vicinity of the Chandrayaan-3 landing site show that the local lunar terrain in this region is fairly uniform and primarily composed of ferroan anorthosite (FAN), a product of the lunar magma ocean (LMO) crystallization. However, observation of relatively higher magnesium abundance with respect to calcium in APXS measurements suggests the mixing of further mafic material. The compositional uniformity over a few tens of metres around the Chandrayaan-3 landing site provides an excellent ground truth for remote-sensing observations.

Oxygen production by solar vapor-phase pyrolysis of lunar regolith simulant

The oxide-rich lunar surface regolith can be used to extract the oxygen needed for the future of lunar exploration efforts as a consumable for life-support systems and spacecraft propulsion. Various techniques for the extraction of oxygen have been developed already, with solar vapor-phase pyrolysis shown to be a promising yet understudied approach. In contrast to other techniques, it requires only locally available resources, such as unbeneficiated regolith, sunlight, and vacuum in order to liberate oxygen and oxygen-bearing molecules. This study presents experimental work conducted in a purpose-built solar-vacuum furnace showing the evaporation of sodium and iron from a regolith simulant sample and their deposition on the crucible surface. This is matched by the thermochemical equilibrium modeling done in FactSage, which analyzes the process at varying pressures down to ultra-high vacuum. It highlights the need for precise temperature and pressure control, as well as the impact of regolith composition on oxygen dissociation for an efficient extraction of molecular oxygen.

Additive manufacturing development of construction materials for a lunar base via spark plasma sintering of volcanic rocks using in-situ resource utilization concept

This work presents an innovative approach for creating ceramic materials based on andesite-basalts for construction on the Moon. Employing the concept of in-situ resource utilization (ISRU), the authors simulated the composition of lunar regolith using volcanic rocks from Kamchatka and Primorsky Krai (Russia, Far East). These rocks were ground into submicron powders and sintered via spark plasma sintering (SPS) at temperatures of 800, 900, and 1000 °C. The resulting ceramic samples demonstrate exceptional physicomechanical properties comparable to lunar regolith – compressive strength up to 566 MPa and Vickers hardness up to 650 HV. Optimal characteristics were achieved at a sintering temperature of 1000 °C with a heating rate of 300 °C/min. It was determined that the heating rate during sintering has a decisive influence on the density of the resulting ceramics.This research vividly demonstrates the potential of SPS technology and the ISRU concept for creating high-strength construction materials on the Moon using local lunar raw materials, paving the way for large-scale construction of lunar bases utilizing the Moon's own mineral resources.

Applying machine learning to a nonlinear spectral mixing model for mapping lunar soils composition using CHANDRAYAAN-1 M3 data

We present a newly developed method which combines the nonlinear spectral mixing model of Shkuratov et al. (1999) with a machine learning algorithm to map the lunar regolith composition using spectral data. The new method performs orders of magnitude faster than the traditionally used numerical optimization approaches, allowing the mapping of regolith properties (including mineralogical composition, average grain size and optical maturity) over large areas of the lunar surface. A new set of basic mineral spectra of the lunar soil for using with spectral mixing models is proposed. Used together with the nonlinear mixing model (Shkuratov et al., 1999), the set is able to describes Chandrayaan-1 M3 instrument spectra collected from test areas which includes the Shapley crater with its surroundings containing mare and highland terrains well. The new set includes a virtual “gray component” with a “flat” (constant) spectrum, accounting for the factors that change general surface albedo, such as spectrally neutral components (e.g., agglutinate glasses), errors in the photometric reduction, uncertainties in estimations of lunar regolith porosity q and the mean grain size S of the basic minerals. The proposed new method takes into account the influence of space weathering and nonlinear correlation between the compositional and spectral parameters of the lunar soils delivering values for the optical properties and mineralogical abundance determination of the lunar regolith which are compatible with the results found from lunar samples measurements in the laboratory. The proposed approach can be used for analyzing spectral observations not only of the lunar surface but also for other surfaces with are covered by regolith.

Mineralogy of Surface Materials at the Chang'E‐5 Landing Site and Possible Exotic Sources From In Situ Spectral Observations

AbstractChina's Chang'E‐5 (CE‐5) mission landed at 43.06°N and 51.92°W on 1 December 2020, within the Northern Oceanus Procellarum region of the Moon. The CE‐5 landing site is situated within a young lunar basalt unit estimated to be around 2.0 Ga. A comprehensive understanding of the lunar regolith composition within the CE‐5 region is pivotal as it furnishes additional scientific evidence concerning its origin. This, in turn, would further improve our understanding of lunar geology and evolution. In our studies, we employed a variety of spectral data and derived products including the CE‐5 Lunar Mineralogical Spectrometer data, the ferrous mineral abundance derived from Kaguya Multiband Imager, and the Chandrayaan‐1 Moon Mineralogical Mapper data. These data enabled us to determine and analyze the compositions of the diverse materials present in the CE‐5 region and to pinpoint the origins of exotic materials found therein. Our results indicated that the exotic material within the CE‐5 region is principally composed of clinopyroxene and plagioclase (Pl). Further analysis unveils that the CE‐5 regolith embodies a blend of two distinct varieties of clinopyroxene, designated as Type A and Type B, along with feldspar. This discovery markedly diverges from the conclusions drawn by preceding studies, which relied solely on remote sensing data. Moreover, the exotic materials are predominantly constituted by the ejecta of Harpalus and Aristarchus craters. This finding furnishes a substantial geological background for the analysis of exotic materials in the samples returned by the CE‐5 mission in forthcoming studies.

WNMS: A New Basaltic Simulant of Mars Regolith

The use of planetary regolith can be explored via the utilization of simulants. The existing Martian simulants have differences due to varying source materials and design parameters. Additional simulants are needed because the few available simulants do not replicate the compositional diversity of Martian regolith. This study discusses the development of a low-cost construction simulant of Mars. The area of Winder Nai in Pakistan was selected for field sampling of basalt because of local availability and easy access. The dust was produced from rock samples through mechanical crushing and grinding. The physical properties, composition, mineralogy, and surface morphology were evaluated via geotechnical tests, Energy Dispersive X-ray (EDX) spectroscopy, X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM), respectively. The designed simulant has a well-graded particle size distribution with a particle density and bulk density of 2.58 g/cm3 and 1.16 g/cm3, respectively. The elemental composition of Winder Nai Mars Simulant (WNMS) is within ±5 wt% of the Rocknest and the average Martian regolith composition except for SO3. For SiO2, Al2O3, and Fe2O3, WNMS has a good match with the Martian regolith. The content of CaO and TiO2 in WNMS is higher than, and content of MgO is lower than, the average Martian values. The rock can be classified as basalt based on the Total Alkali Silica (TAS) diagram. XRD spectrum indicates the occurrence of plagioclase and pyroxene as the main signature minerals of basalt. The particle morphology of WNMS is angular to subangular, and the simulant indicates the presence of 3.8 wt% highly paramagnetic particles. The volatile loss is 0.25 wt% at 100 °C, 1.73 wt% at 500 °C, and 3.05 wt% at 950 °C. The composition of WNMS, basaltic mineralogy, morphology, magnetic properties, and volatile content are comparable with MMS-2 and a few other simulants.

Electrochemical Oxygen Evolution from Metal Oxides Using Perovskite Anodes Towards Lunar Resource Utilization

In-situ resource utilization (ISRU) has been proposed for realizing sustainable lunar development. One of the representative resources on the Moon is lunar regolith, which covers the lunar surface. The chemical composition of lunar regolith resembles the constituents of the Earth: silica (SiO2) is the most abundant oxides in the lunar regolith. Silicon, which can be produced by silica reduction, will be the material for solar cells, and oxygen is essential for manned space exploration. Enormous amounts of silicon and oxygen will be obtainable on the Moon without transportation from the Earth by establishing silicon reduction methods without consumables. However, the conventional silica reduction method consumes vast amounts of carbon, which cannot be mined on the Moon.For realizing carbon free silica reduction method consistent with the concept of ISRU, molten salt electrolysis processes using perovskite anodes has been researched. In this method, the silica dissolved in molten salts is electrolyzed using voltage with passage of direct current through electrodes, which generate oxygen gas and silicon by the electrochemical process. The perovskite oxides have high electrical conductivity and oxidation resistance. Therefore, the perovskite anodes have been expected as oxygen generation inert anodes.In this study, we report the characteristics of perovskite-type anodes for oxygen generation measured in the electrolysis experiments. In molten fluoride containing silica at a temperature over 500℃, the measured cyclic voltammograms with a perovskite-type anode show drastically increases of current density at 2.6 V vs K+/K, which was approximately same to the oxygen generation potential in the previous molten salt electrolysis result without the perovskite anodes. The characteristics of perovskite-type anodes for oxygen generation will be discussed from the results of electrochemical measurements and chemical analysis using XRD, SEM, EDX, and ICP-AES analysis.

On the influence of the trace element composition of regoliths on the labor safety of astronauts on the Moon

Introduction. The problem of using near-Earth space to meet various human needs, including the development of minerals, especially on the Moon, is becoming relevant, which increases the importance of research on occupational safety in these conditions. The study aims to research the trace element composition of regoliths in comparison with terrestrial rocks and its significance for the safety of astronauts on the lunar surface. Materials and methods. The researchers evaluated the trace element composition of the regolith by calculating the concentration coefficients and the quality drop coefficient. When identifying homogeneous classes of regoliths by concentrations of 38 chemical elements, we used computer technology to classify multidimensional observations under conditions of self-organization. Results. We know that the concentrations of many trace elements in regoliths significantly exceed their concentrations in terrestrial soils. Calculated for the Luna-16 and Luna-24 marine regoliths, as well as for Apollo-11 and Apollo-12, the quality reduction coefficient varies from 27 to 100, which corresponds to the "crisis" category. This indicates that the content of trace elements in the regolith ranges from weekly critical (27 for the Luna-16 regolith) to highly critical (100 for the Apollo-12 regolith). The researchers identified trace elements whose concentrations in lunar regoliths significantly exceed their concentrations in terrestrial soils: Cr, Be, Co, Sc, Ho, Se, Ni, Au, Ag, Er, Tm, Y, Sm, Gd, Tb, Dy Yb, Lu, Cd, Zr, Sr, Ce, Pr, Nd, Eu. Trace trace elements are included in the group of substances with allergenic, fibrogenic and carcinogenic effects and can have a negative impact on the health of future lunar colonists. Limitations. The authors have conducted the study for the composition of regolith on the surface of the Moon and did not cover aspects of human protection from lunar dust by space stations, structures, spacesuits and special equipment. Conclusion. When assessing the impact of environmental factors on the safety of astronauts during the colonization of the Moon, attention should be paid to the toxicological aspects of working conditions, in particular the trace element composition of regoliths and lunar dust.

Thermophysical property evolution during molten regolith electrolysis

The electrolysis of lunar regolith for oxygen generation has been under investigation since before the Apollo missions. One critical and overlooked aspect in work to date has been how the composition and physical properties of the molten regolith change during electrolysis process as oxides are reduced. The regolith composition also varies across the surface of the moon, and thus the molten properties will also vary. In this work we aggregate previous empirical models for physical properties of mixtures of molten oxides spanning the possible composition ranges of the electrolyte. The physical properties most important to reactor operation are liquidus temperature, electrical conductivity, and viscosity. In this work we show that these properties vary dramatically for compositions present on the lunar surface and during electrolysis. From this model review we illustrate that the liquidus temperature and heat capacity of the melt rises during electrolysis while viscosity, electrical resistivity, and thermal conductivity increase with the removal of iron oxide and decrease with the removal of silicon oxide. This new framework provides Molten Regolith Electrolysis (MRE) system designers a more accurate method for evaluating system performance during operation. In addition to lunar applications, the models reviewed herein are applicable to those seeking to develop Molten Oxide Electrolysis (MOE) for terrestrial, carbon-free metal production. The code developed during this project has been released on github file exchange; a link is provided as supplementary material.

The concept of gamma-ray remote sensing of Martian surface composition onboard a Mars Rover

A novel concept of γ-ray remote sensing experiment onboard a Mars Rover is considered for studies of Martian shallow subsurface composition with a high spatial resolution. Only those photons produced in reactions of neutron inelastic scattering on nuclei of surface constituting elements are recorded by the proposed gamma-ray spectrometer, which use time tags of particles of Galactic Cosmic Rays (GCR), producing these reactions. It is shown that the composition of the Martian regolith may be determined by this gamma-ray spectrometer with a spatial resolution of meters along the traverse of a Mars Rover.

Mineralization of ion-adsorption type rare earth deposits in Western Yunnan, China

With the widespread application of heavy rare earth elements (HREEs) in high-tech fields, ion-adsorption type rare earth element (iREE) deposits have attracted much attention as the main output deposit type of HREE metals. In recent years in western Yunnan, southwest China, iREE deposits have made some large discoveries and received a high degree of attention. In this article, we summarize the metallogenic background, distribution, and metallogenic characteristics of iREE deposits in the Tengchong and the Lincang Granite Belt in western Yunnan, and analyzes the roles of ore-forming parent rock, regional metamorphism and alteration, epigenesis, and granite regolith composition in the metallogenesis of the iREE deposit in western Yunnan. It is believed that the high REE content granite parent rocks, metamorphic or magmatic-hydrothermal alteration, hot and humid climate, gentle topography, large and thick granite regolith are all favorable factors for iREE deposit formation. The long-term and multi-stage magmatic evolution formed high REE content granite parent rocks. Strong magmatic-hydrothermal activity and strong metamorphism associated with regional slip movement have contributed to the enrichment of REE elements and the formation of easily dissociated REE-bearing minerals, laying the material foundation for iREE deposits. The humid, hot and rainy climate and the vegetation-rich surface environment are conducive to weathering, which contributes to the formation of granite regolith and clay minerals, and the dissociation of REE-bearing minerals. Favorable topographical areas help to retain large-scale and thicker granite regolith, in which the clay minerals continue to adsorb the REE ions which have been infiltrated and migrated by the aqueous solution downward, leading to the gradual enrichment of REE elements and the formation of iREE deposits.

Ground truth constraints and remote sensing of lunar highland crust composition

AbstractWe review constraints on the magnitude and possible causes of discrepancies, or at least major disparities, among global and near‐global data sets for lunar highland surface composition. When compared with data from other sources, reported mafic mineral abundance results from the Kaguya Spectral Profiler (Kaguya SP) spectral reflectance method for four Apollo 16 soils appear systematically low by a factor of 0.6, or an even more extreme factor (~1/3) if viewed in relation to the soils’ nonglass or CIPW mineralogy. Also, whether evaluated on a global median basis or on the basis of site‐by‐site comparison (for Apollo 16, Luna 20, and Apollo 17), the compositions found by the Kaguya SP technique show discrepancy, or at least disparity, versus other mafic abundance observations by that same factor of ~1/3. Spectral reflectance does not supply a simple bulk analysis of the target soil. The reflectance mineralogical signal is preponderantly determined by the nonglass fraction, and especially the masswise subordinate 10–20 µm grain size fraction. Literature data show that in anorthositic lunar soil, chemical composition is fractionated, more extremely anorthositic, for the nonglass component compared to the glass component. Also, the grain size fraction (10–20 μm) that most closely matches bulk reflectance has a significantly higher abundance of impact/agglutinitic glass than does the coarser material that dominates the soil mass. The Kaguya SP mafic abundance calibration needs adjustment by a factor of nearly 3 if results are to be interpreted as indicative of the mineralogy of the underlying crust. A claimed detection of several hundred lunar 500 m scale purest anorthosite (PAN; ≥98 vol% plagioclase) locales among millions of spectral reflectance observations is dubious, in part because with large data sets, compositional extremes are inevitably exaggerated as a byproduct of analytical uncertainty. Preponderance of PAN composition is rare among terrestrial layered intrusive anorthosites and is neither required nor expected for the flotation crust of a global magma ocean. Buoyant flotation and compaction would not suffice to yield pure plagioclase unless adcumulus growth was negligible, and trace element contents of ferroan anorthosites show that their mafic silicate components are for the most part of adcumulus, not “trapped melt,” derivation. A PAN‐dominated crust would imply a curiously fractionated (low) thorium/aluminum ratio for the crust, an implausibly high mantle/crust Th concentration ratio, and an oddly low Th/Al for the bulk Moon. Remote sensing techniques for planetary regolith composition are not easy to calibrate, particularly near the extremes of composition‐space and sensitivity.

Mineral Content Estimation of Lunar Soil of Lunar Highland and Lunar Mare Based on Diagnostic Spectral Characteristic and Partial Least Squares Method

Extraction of mineral and rock information of lunar regolith is of far-reaching significance to the study of material composition, geological structure and historical evolution of lunar regolith. Visible and near-infrared spectra can reflect mineral composition information, and can be used to extract mineral composition and distribution characteristics of lunar regolith. In this paper, the LSCC (Lunar Soil Characterization Consortium) data of lunar regolith is taken as the research object. The partial least squares (PLS) regression model is used to estimate the spectra of lunar regolith measured in RELAB laboratory of Brown University. The mineral contents of plagioclase, pyroxene, olivine, ilmenite, agglutinate and volcanic glass in lunar regolith have been optimized and retrieved. The LSCC spectra of lunar regolith have been pre-processed by multivariate scattering correction (MSC), which highlight the spectral features of lunar regolith. The optimal number of principal components has been selected by cross-validation test. The PLS regression have been established for samples from lunar highland and lunar mare respectively. Two-thirds of samples have been randomly selected as experimental group to establish the prediction relationship between the spectra of lunar regolith and mineral content. The remaining one-third of samples have been used as verification group to further validate the prediction relationship. The results show that the partial least squares regression model has high accuracy and good stability. It is of theoretical and practical significance to optimize the inversion of mineral content in lunar regolith using spectral data of lunar regolith.

Archean-Proterozoic unconformity on the Fennoscandian Shield: Geochemistry and Sr, C and O isotope composition of Paleoproterozoic carbonate-rich regolith from Segozero Lake (Russian Karelia)

Precambrian paleoweathering profiles provide insight into environmental changes and mark stratigraphic boundaries. However, the well-preserved and exposed stratigraphic boundaries, not affected by tectonics, are rare for the Precambrian. We report sedimentological, geochemical and Sr, C and O isotopic data for the Paleoproterozoic weathering profile in Chapanshary Island on Lake Segozero, Central Karelia, the eastern part of the Fennoscandian Shield. The Chapanshary Island weathering crust contains a unique carbonate caliche, rarely developed on the Archean granite-gneiss basement. The crust laterally grades into carbonate-cemented boulder conglomerate, which is overlain by sedimentary carbonate. The chemical index of alteration (CIA; 60–67) and plagioclase index of alteration (PIA; 53–82) values for the weathering crust correspond to weathered felsic/mafic substrate and to illite and K-rich composition of the regolith. The δ18O values of carbonate cement and sedimentary carbonate are highly negative (−22.3 to −17.6‰ V-PDB). The 87Sr/86Sr values of Fe- and Mn-rich carbonate of the regolith, boulder conglomerate cement and sedimentary carbonate are 0.7133 to 0.7242 and are exceptionally high for marine Paleoproterozoic carbonate. The high δ13C values (+3.9 to + 5.2‰ V-PDB) of carbonate cement and sedimentary carbonate indicate deposition during the ca. 2.22–2.06 Ga Lomagundi-Jatuli carbon isotope excursion of the early Paleoproterozoic. The Chapanshary Island weathering profile developed in a terrestrial setting with arid to semi-arid climate ca. 2.2–2.1 Ga ago under atmosphere with high CO2 content. The overlying sedimentary carbonates were deposited in a shallow-water setting (ephemeral ponds and lakes) evolved in the inner part of Fennoscandia.

Igneous rock powder identification using colour cameras: A powerful method for space exploration

Powdered rocks are commonly present at the surface of extraterrestrial bodies and are widely analysed by in situ space probes. Moreover, a number of rovers exploring the surface of Mars are equipped with drills enabling them to access unaltered material and collect samples. During drilling operations, a cone of powder made of the drilled materials forms at the surface. These powders will be particularly large during the ESA/Roscosmos ExoMars 2022 mission since the rover Rosalind Franklin will drill to 2 m depth below the Martian surface. These fines are generally observed by the rovers' cameras after the drilling process and analysed by a limited range of instruments. In order to maximise the scientific return of planetary missions to Mars and other bodies in the solar system, we propose to use the images taken by rover cameras to identify the composition of the powdered materials. This could be particularly useful during the ExoMars 2022 mission where the CLUPI camera will take pictures during drilling and could thus document changes in the regolith composition (Josset et al., 2017). In the absence of a controlled light source, we used an image processing method called CaliPhoto that we previously developed for generic purposes. To test the ability of the method to identify volcanic rocks, more than twenty Mars-analogue samples were crushed at various grain sizes and photographed. The images were then processed via the CaliPhoto method and used to construct a database of reference images. New images were then taken under different lighting conditions, processed using the same method, and compared to the database. We show that it is possible to estimate igneous rock powder lithology with greater than 90% accuracy considering the uncertainties. Furthermore, when using images of polished and powdered samples, identification reaches 100%. We also show that the method permits precise lithological identification of samples that are not in the initial database. Finally, we demonstrate that the proposed method is extremely efficient, while at the same time very easy to implement on any in situ space probe. It could thus be used to help in identifying powdered igneous rocks during future missions to Mars or other rocky body in the solar system.

Observations of Phobos and Deimos with SpeX at NASA infrared telescope facility

We measured near-infrared (NIR) reflectance spectra of Phobos and Deimos, using the prism (0.7–2.52 μm) and long-wavelength cross dispersed (LXD: 1.9–4.2 μm) modes of NASA Infrared Telescope Facility (IRTF)’s SpeX instrument. The goal of this study is to investigate the surface composition of Phobos and Deimos and search for any mineralogical absorption signatures that may be present on their surfaces, especially in the LXD spectral range. Prism spectra of Phobos showed significant slope variation at shorter wavelengths (λ < 1.3 μm), which indicates surface heterogeneity possibly due to regolith's composition and grain size, and/or space weathering. Deimos' prism spectra were found to be consistent with the more red-sloped prism spectra of Phobos. The measured LXD spectra of Deimos revealed evidence of hydration with 3-μm band depths at 2.90 μm of 4–5%. The 3-μm band in Deimos could be attributed to exogenic sources such as solar wind implantation or OH-bearing impactors, or to an endogenic source and the presence of carbonaceous material on its surface. Phobos' and Deimos' prism and LXD spectra, however, show no indications for absorption signatures of mafic silicates (i.e., pyroxene, olivine), organics nor carbonates.

Composition variations of major lunar elements: Possible impacts on lunar albedo spectra

Understanding the elemental composition of the lunar regolith is important for expanding our knowledge of the history and geology of the Moon. Several methods have already been used to achieve this purpose, including direct analysis of lunar samples and satellite spectroscopy. Since computer modeling is important for processing the collected data, and for the preparation of future missions, this work uses Monte Carlo simulations to study the radiation emitted by the lunar surface, via nuclear interactions between the incident radiation environment and lunar regolith, to characterize the elemental composition of the Moon. When high energy primary galactic cosmic rays and solar energetic particles strike the lunar surface, they either scatter to free space or produce secondaries through cascades of interactions, some of which escape the lunar surface. Both the scattered primaries and escaping secondaries constitute the lunar “albedo” particles studied in this paper. The purpose of this work is to determine whether enhancing the abundances of any of the major lunar elements (O, Na, Mg, Al, Si, Ca, Ti, Mn, and Fe) causes an observable difference in the spectra of albedo particles emitted by the regolith. The model-based results herein show that charged albedo particles do not display any significant differences for any element. They also confirm that low-energy neutrons and gamma rays produce observable variations with different lunar compositions. This provides evidence that albedo neutrons and/or gamma rays, and not protons, are the source of the variations observed in a recent map of the lunar albedo, generated by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument.

Asteroid 16 Psyche: Shape, Features, and Global Map

Abstract We develop a shape model of asteroid 16 Psyche using observations acquired in a wide range of wavelengths: Arecibo S-band delay-Doppler imaging, Atacama Large Millimeter Array (ALMA) plane-of-sky imaging, adaptive optics (AO) images from Keck and the Very Large Telescope (VLT), and a recent stellar occultation. Our shape model has dimensions 278 (−4/+8 km) × 238(−4/+6 km) × 171 km (−1/+5 km), an effective spherical diameter D eff = 222-1/+4 km, and a spin axis (ecliptic lon, lat) of (36°, −8°) ± 2°. We survey all the features previously reported to exist, tentatively identify several new features, and produce a global map of Psyche. Using 30 calibrated radar echoes, we find Psyche’s overall radar albedo to be 0.34 ± 0.08 suggesting that the upper meter of regolith has a significant metal (i.e., Fe–Ni) content. We find four regions of enhanced or complex radar albedo, one of which correlates well with a previously identified feature on Psyche, and all of which appear to correlate with patches of relatively high optical albedo. Based on these findings, we cannot rule out a model of Psyche as a remnant core, but our preferred interpretation is that Psyche is a differentiated world with a regolith composition analogous to enstatite or CH/CB chondrites and peppered with localized regions of high metal concentrations. The most credible formation mechanism for these regions is ferrovolcanism as proposed by Johnson et al. (2020).