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The porosity of the upper centimeter or so of the lunar regolith strongly affects several properties that are commonly studied remotely. Hence, it is important to determine its value. We have reanalyzed the data of Ohtake et al. (Ohtake et al. [2010]. Space Sci. Rev., 154, 57-77), who used spacecraft and laboratory reflectance measurements of the M...
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... a soil with a porosity this low is relatively incompressible, whereas even a cursory glance at a photograph of an astronaut footprint ( Fig. 1 ) shows that the upper regolith is compressible, which implies a high porosity. ...
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... to see if this might be an inflight calibration problem LRO/WAC images were used to measure the spectral reflectance of the sample site. The values at the LRO/WAC filter wavelengths were interpolated to λ = 415 and extrapolated to 750 nm, and the resulting I / F value adjusted to be equal to the Kaguya I / F at 750 nm. The results are shown in Fig. 10 . A model K was fitted to the LRO/WAC 415 nm I / F using the same values for the other parameters as for the rest of the filters. The fitted value of K is 1.13 which, although not physically excluded, is well outside the estimated error for the average of the other points. Thus, the 415 nm discrepancy probably cannot be explained ...
Citations
... Past research on lunar space weathering has focused on the formation and evolution of lunar surface regolith and understanding space weathering conditions using a combination of remote sensing observations and analyses of returned samples (Hapke & Sato, 2016;Jozwiak et al., 2015;Kuznetsov et al., 2017;Thompson et al., 2017). However, despite significant knowledge gained through these approaches, gaps remain in our understanding of the links between large-scale compositional observations and local particulate microstructure. ...
The microstructural characterization of lunar agglutinate samples serves many essential purposes in lunar science and cosmochemistry, from understanding the formation process of lunar regolith to preparing for human activity on the Moon. In this study, an advanced correlative characterization methodology was employed to examine the microstructure of a lunar agglutinate particle retrieved from the Apollo 11 mission. The multimodal characterization efforts were centered around 3-D x-ray computed tomography (XCT) and were complemented by 2-D techniques, including scanning electron microscopy and energy-dispersive x-ray spectroscopy. The nondestructive nature of the XCT allowed us to preserve the lunar dust particles, while its 3-D nature allowed us to extract meaningful microstructural information inaccessible via traditional 2-D characterization techniques. The multimodal correlative analysis further allowed us to identify the compositional and microstructural features of the agglutinate. These observations were linked to the formation process of the agglutinate to inform a hypothesis on the dynamic formation sequence of lunar regolith.
... One potential boulder field formation mechanism may be regolith draining (e.g., Miyamoto et al. 2007). Any deformation of the mare basalts-or regolith in the case of small, decameterscale wrinkle ridges-is likely to result in the creation of void space along the associated fault zone given the high porosity and pulverized nature of the lunar regolith (e.g., Hapke & Sato 2016;Wyrick & Buczkowski 2022). As the upper mare basalts and regolith buckle under compressional stresses to form wrinkle ridges, it is expected to result in layer parallel extension due to flexural bending (Watters 1988;Watters & Johnson 2010). ...
Wrinkle ridges are the predominant tectonic structure on the nearside lunar maria. Although lunar wrinkle ridge formation began as early as ∼3.9–4.0 Ga, recent investigations have identified wrinkle ridges in the lunar maria that were tectonically active as recently as the Copernican period of lunar geologic history. Some of those geologically young wrinkle ridges were identified by the presence of dense fields of meter-scale boulders on their scarps and topographic crests. Other investigations have identified recently active lunar wrinkle ridges that lack the ubiquitous presence of boulder fields, thereby rendering the presence of boulder fields ambiguous in the search for ongoing tectonic activity on the Moon. Here we assess boulder populations associated with 1116 wrinkle ridge segments on the lunar maria that are inferred to be recently active (<1.5 Ga) based on their crisp morphologies and crosscutting relationships with small impact craters. We utilize data from the Lunar Reconnaissance Orbiter Mini-RF and Diviner Lunar Radiometer Experiment instruments to assess surface rock populations across these recently active structures. Our results indicate that, where present, meter-scale boulder fields are likely indicators of fault-slip-induced ground acceleration given the short lifespan of lunar surface boulders. However, elevated boulder populations are not observed on all recently active ridges analyzed here. This latter observation supports the notion that wrinkle ridge boulder fields are a nonunique indicator of recent tectonic activity. Furthermore, the spatial distribution of those boulder fields indicates that variable mare protolith properties may play a role in boulder field formation.
... A value for the compressibility of volcanic ash of 0.3 MPa -1 is used (Palmer & Wick, 2003) (Table S2). Lunar regolith is used to approximate silicate or rock dust with values of ϕo = 0.7 and ρp = 3.0 gm/cm 3 with a derived ρb is 0.9 gm/cm 3 well approximate the measured value of 1.0 gm/cm 3 (Mitchell, et al., 1972;Hapke & Sato, 2016). A value for the compressibility of 1.0 MPa -1 lunar regolith. ...
... 5. Kawabata E. et al. (2015) 6. Mitchell et al. (1972). 7. Hapke & Sato (2016). Watters et al. (2007) MARSIS MFF has low permittivity and is composed of large amounts of ice or is an anomalously low-density material. ...
... In fact, the porosity of the lunar regolith can be as high as 0.8-0.9 (Hapke & van Horn 1963;Hapke & Sato 2016). Szabo et al. (2022bSzabo et al. ( , 2023 found that lunar regolith porosity has an effect on the reflection coefficient and energy of ENA with numerical simulations. ...
Solar wind can directly interact with the lunar surface and bring a space weathering effect. Some solar wind protons can be scattered as energetic neutral atoms (ENAs), which include rich information of the solar wind-surface interaction. However, people still know little about the ENA truth on the lunar ground due to the lack of in situ measurements. Different from the previous in-orbit measurements, here we present the first ground-based ENA measurements by the Chang'E-4 rover and find a good correlation between the mean ENA energy and the solar wind energy. Moreover, the loss rate of ENA energy can strongly depend on both the solar wind energy and the solar zenith angle (SZA), in which the energy loss rate can be enhanced by 73% when the solar wind energy increases from 400 to 1400 eV and can be reduced by 32% when the SZA increases from 57°to 71°. Combined with numerical simulations by SDTrimSP code, we propose that the solar wind protons can penetrate deeper into the lunar surface with a longer path length when the solar wind energy is higher or the SZA is lower, which results in a larger energy loss rate for the scattered ENAs. Our results provide an important constraint for the solar wind-surface research and have general implications in studying the surficial space weathering of the Moon and other airless bodies. Unified Astronomy Thesaurus concepts: Solar wind (1534); Lunar surface (974); The Moon (1692)
... Ultimately, the lunar regolith porosity at the surface could be constrained to 0.85 +0.15 −0.14 . This agreed with the value from Hapke and Sato (2016), which was derived for the Apollo 16 site to be 0.83 ± 0.03. However, our result is valid on a global scale and did not require analysis of returned samples, demonstrating one example for the capability of surface studies with ENAs. ...
The reflection of solar wind protons as energetic neutral atoms (ENAs) from the lunar surface has regularly been used to study the plasma‐surface interaction at the Moon. However, there still exists a fundamental lack of knowledge of the scattering process. ENA emission from the surface is expected to similarly occur at Mercury and will be studied by BepiColombo. Understanding this solar wind backscattering will allow studies of both Mercury's plasma environment as well as properties of the hermean surface itself. Here, we expand on previous simulation studies of the solar‐wind‐regolith interaction with 3D grains in SDTrimSP‐3D to compare the predicted scattering energies and angles to ENA measurements from the Moon by the Chandrayaan‐1 and IBEX missions. The simulations reproduce a backward emission toward the Sun, which can be connected to the geometry of the regolith grain stacking. In contrast, the ENA energy distribution and its Maxwellian shape is mostly connected to the solar wind velocity. Our simulations also correctly describe a lunar ENA albedo between 10% and 20% and support its decrease with solar wind velocity. We further expand our studies to illustrate how BepiColombo will be able to observe ENAs at Mercury using hybrid simulations of Mercury's magnetosphere as an input for the complex surface precipitation patterns. We demonstrate that the variable ion precipitation will directly influence ENA emission from the surface. The orbits of BepiColombo's Mercury Planetary Orbiter and Mercury Magnetospheric Orbiter/Mio spacecraft are shown to be suitable to observe ENA emission patterns both on a local and a global scale.
... An additional process, impact gardening, results in high regolith porosities, as is the case for high porosity (80%) in the lunar regolith (e.g., Arnold 1975;Hapke & Sato 2016;Pieters & Noble 2016). Interestingly, the MIR spectra of the Moon and Trojans are significantly different from each other (e.g., Shirley & Glotch 2019), which suggests a surface scattering-dominated spectral regime on the Moon. ...
Jovian Trojan asteroids make up a large group of primitive bodies that populate Jupiter's L4 and L5 Lagrange points. The Trojans’ dynamics and composition carry insight into the formation mechanisms that shaped our solar system. Mid-infrared (MIR; 5–35 μ m) spectra of Trojans exhibit puzzling silicate emission features, like spectra of optically thin comet comae, which may be interpreted as “fluffy” regoliths. By understanding the physical properties of the regolith (e.g., particle size and regolith porosity), more accurate compositional interpretations can be made. Here we show 14 Spitzer Space Telescope MIR spectra of Trojans and their compositional makeup. Through parameterization of spectral features and comparison to laboratory and remote-sensing spectra, the results show that the Trojans have highly porous regoliths of fine-particulate crystalline (forsterite, enstatite, and possibly a small amount of fayalite and diopside) and amorphous silicates. These results are consistent with a primordial Kuiper Belt origin.
... However, even the smallest constituents of thin sections analyzed with an IR microscope will not show a TF, due to the presence as a closed surface without porosity. In addition, compacting a powder sample leads to a decreased TF (Hapke & Sato, 2016;Salisbury & Eastes, 1985;Weber et al., 2020). This shows, that the porosity of the sample, which can be correlated with the grain size but more strongly with the sample preparation, is an important underlying factor that affects the spectral behavior, most importantly the TF (Salisbury & Eastes, 1985;Weber et al., 2020). ...
Plain Language Summary
ESA's and Japan Aerospace Exploration Agency’s spacecraft BepiColombo is equipped, beside other instruments, with a thermal infrared (IR) radiometer and spectrometer called MErcury Radiometer and Thermal Infrared Spectrometer (MERTIS). For the accurate interpretation of the data from the MERTIS instrument, laboratory analog material is necessary. This analog material must fulfill different characteristics, such as different chemical and mineralogical compositions. Another not yet studied property is the availability of oxygen during the formation of the minerals. Depending on how much oxygen is available, different minerals form. However, this is an important feature, because Mercury is thought to have evolved under highly reducing conditions, as opposed to Earth where nearly all material formed significant more oxidizing conditions. One phase that is strongly associated with reducing magma formation conditions is metallic iron. There are only few natural outcrops on Earth, were stronger reducing conditions were present so that metallic iron could be formed. One of these outcrops is the Bühl quarry in northern Hesse, Germany. From there we used different samples to analyze the effect of oxygen availability on mid‐IR spectra of plagioclase feldspars.
... Previous research on space weathering has focused on returned samples in the laboratory and orbital remote sensing datasets while lacking in situ spectral measurements on the lunar surface. The particle size, porosity and bulk density are critical physical factors affecting VNIR reflectance spectra of lunar soils 9,10 . These parameters obtained in the laboratory are not representative of soils on the lunar surface because the primary state of the lunar soils has been disturbed during the sampling procedure 11 . ...
... The abundances of Fe 0 particles were derived via comparing the observed spectra (CH1-M 3 , SEL-MI, CE5-LMS and SDU-ASD) and the modelled spectral library (a total of 20,301 spectra), which was established based on the modified Hapke radiative transfer model using equations (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) (Methods) with measured mineral modes from the returned CE-5 soils 15 . The space-weathering effect is simulated through adding npFe (4-33 nm) content of 0.00-1.00 ...
... Here filling factor ϕ was set to 0.41 for lunar samples analysed in the laboratory 49 and 0.17 for the upper lunar regolith measured in situ on the lunar surface 10 . ...
Space weathering on airless bodies produces metallic iron (Fe0) particles in the rims of mineral grains, which affect visible and near-infrared spectra and complicate the identification of surface materials. The Chang’e-5 mission provides an opportunity to couple information gained from its returned samples with in situ observations and orbital monitoring to gain insight on the details of space weathering on extremely Fe-rich basalts. By putting together all these data, we could extract a soil maturity index (Is/FeO) at the Chang’e-5 landing site of ~66 ± 3.2, indicative of a formation age for the Xu Guangqi crater, whose ejecta dominate the site, of 240–300 Myr ago. In addition, abundant large Fe0 particles were found in the sample, indicating that both the inherited Fe0 particles from late-stage mare basalts and the dense clustering of oversaturated Fe0 in extremely FeO-rich (>17 wt%) basalts contribute to observed Fe0 abundances. We suggest that space weathering of Fe-richer basalt generates Fe0 particles with a larger grain size and faster production rate. A multi-observational study including laboratory analysis of the Chang’e-5 mission samples, in situ measurements and orbital datasets determined the high level of maturity and iron content of the Chang’e-5 landing site regolith. Heavily processed by space weathering, it mostly comes from the nearby Xu Guangqi crater, formed 240–300 Myr ago.
... Our calculated porosity of the lunar surface of = 0.85 +0.15 −0.14 is in line with the value of 0.83 ± 0.03 found from infrared reflectance measurements (Hapke & Sato, 2016). However, the result of Hapke and Sato (2016) isstrictly speaking -only valid for the Apollo 16 landing site, while the ENA measurements allow the determination of the porosity of the upper lunar regolith on a global scale. ...
... Our calculated porosity of the lunar surface of = 0.85 +0.15 −0.14 is in line with the value of 0.83 ± 0.03 found from infrared reflectance measurements (Hapke & Sato, 2016). However, the result of Hapke and Sato (2016) isstrictly speaking -only valid for the Apollo 16 landing site, while the ENA measurements allow the determination of the porosity of the upper lunar regolith on a global scale. Figure 2b shows the depth that solar wind protons can access in the regolith. ...
... This supports significant adhesion between lunar regolith grains and could also indicate that electrostatic dust transport of single grains plays an important role in forming the uppermost regolith layers (Hood et al., 2022;Schwan et al., 2017;Wang et al., 2016;Yeo et al., 2021). These results are in agreement with previous infrared measurements of the Apollo 16 landing site (Hapke & Sato, 2016). Compared to such infrared studies, ENA reflection coefficients are less sensitive to other surface parameters and thus less dependent on laboratory calibration. ...
The porosity of the upper layers of regolith is key to the interaction of an airless planetary body with precipitating radiation, but it remains difficult to characterize. One of the effects that is governed by regolith properties is Energetic Neutral Atom (ENA) emission in the form of reflected and neutralized solar wind protons. We simulate this process for the surface of the Moon by implementing a regolith grain stacking in the ion-solid-interaction software SDTrimSP-3D, finding that proton reflection significantly depends on the regolith porosity. Via comparison with ENA measurements by Chandrayaan-1, we derive a globally averaged porosity of the uppermost regolith layers of 0.85 [+0.15, -0.14]. These results indicate a highly porous, fairy-castle-like nature of the upper lunar regolith, as well as its importance for the interaction with impacting ions. Our simulations further outline the possibility of future regolith studies with ENA measurements, for example by the BepiColombo mission to Mercury.
... Regolith particles are fragments of lunar rocks, minerals, glasses, lithified breccia, and meteorite fragments. The top layer of regolith (several mm) is an extremely porous (>80%) structure (Hapke and Sato, 2016). The density of regolith increases with depth, and infrared measurements show that the characteristics of the upper $10 cm of regolith are approximately the same over the entire surface of the Moon, with the exception of newly formed impact craters (Hayne et al., 2017). ...
The article is a review of the state of research on physical processes occurring near the surface of airless bodies, in particular, the Moon, asteroids, comets, which lead to their erosion, that is, to the modification of superficial and sometimes even deeper layers. External influences on the bodies are considered—micrometeor streams, solar wind and geomagnetic tail plasma flows, solar electromagnetic radiation, and cosmic rays, which are the main causes of erosion. The main features of airless bodies belonging to different classes are given. The main physical mechanisms that can lead to the release and removal of dust particles from the surface of regolith are analyzed, in particular, the energy aspects of high-speed micrometeor impacts, electrostatic processes of particle release from the surface, and thermodynamic processes occurring in the near-surface layers of cometary nuclei. The conditions for the removal of dust particles from the surface of a rotating body and the conditions under which the body can collapse are considered. Depending on the characteristics of these bodies, the processes of erosion, as well as the causes of its occurrence, can vary significantly. The main unresolved problems associated with the processes of erosion of bodies, which require further research, are considered.
