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1.
It is essential that accurate modal (i.e., volume) percentages of the various mineral and glass phases in lunar soils be used for addressing and resolving the effects of space weathering upon reflectance spectra, as well as for their calibration such data are also required for evaluating the resource potential of lunar minerals for use at a lunar base. However, these data are largely lacking. Particle-counting information for lunar soils, originally obtained to study formational processes, does not provide these necessary data, including the percentages of minerals locked in multi-phase lithic fragments and fused-soil particles, such as agglutinates. We have developed a technique for modal analyses, sensu stricto, of lunar soils, using digital imaging of X-ray maps obtained with an energy-dispersive spectrometer mounted on an electron microprobe. A suite of nine soils (90 to 150 micrometers size fraction) from the Apollo 11, 12, 15, and 17 mare sites was used for this study. This is the first collection of such modal data on soils from all Apollo mare sites. The abundances of free-mineral fragments in the mare soils are greater for immature and submature soils than for mature soils, largely because of the formation of agglutinitic glass as maturity progresses. In considerations of resource utilization at a lunar base, the best lunar soils to use for mineral beneficiation (i.e., most free-mineral fragments) have maturities near the immature/submature boundary (Is/FeO approximately or = 30), not the mature soils with their complications due to extensive agglutination. The particle data obtained from the nine mare soils confirm the generalizations for lunar soils predicted by L.A. Taylor and D.S. McKay (1992, Lunar Planet Sci. Conf. 23rd, pp. 1411-1412 [Abstract]).  相似文献   

2.
Z.C. Ling  Alian Wang 《Icarus》2011,211(1):101-113
Laser Raman spectroscopy is used to investigate four lunar soils, focusing on mineralogy of grains of <45 μm size. Apollo samples 14163, 15271, 67511, and 71501 were selected as endmembers to study, based on their soil chemistry, maturity, and sample locations. Typical Raman spectral features for major and minor lunar minerals are discussed on the basis of major vibrational modes. We used the Raman peak shift to calculate Mg/(Mg + Fe + Ca) and Ca/(Mg + Fe + Ca) for pyroxene and Mg/(Mg + Fe) for olivine, and thus obtained the compositional distributions of these two minerals in each of the four lunar soils. Classification of feldspar grains was made based on recognition of their Raman patterns. A Raman point-counting procedure was applied to derive mineral modes of the soils, and these are found to be consistent with published modal analysis of these soils. The compositional distributions of pyroxene and olivine grains in each soil sample, as well as the mineral modes, reflect characteristics of the main source materials for these soils. Raman patterns and peak positions also reflect shock effects on plagioclase and quartz, found in 14163.  相似文献   

3.
Abstract— We studied patinas on lunar rocks 75075 and 76015 from the Apollo collection using a multi-disciplinary approach, including scanning electron microscopy (SEM), energy dispersive x-ray spectrometry (EDS), transmission electron microscopy (TEM), wavelength-dispersive x-ray (WDS) mapping, Mössbauer spectroscopy, spectral reflectance, and microspectrophotometry. Based on SEM petrography, we have defined three textural types of patina: glazed, fragmental, and classic (cratered). The presence of classic patina is diagnostic of lunar samples that have been exposed directly to the space weathering environment. It is characterized by the presence of microcraters and glass pancakes and is the patina type studied by earlier workers. Classic patina is found on 76015 but not on 75075. Glazed patina is found on both 76015 and 75075, whereas fragmental patina is found only on 75075. The glazed and fragmental patinas on 75075 were probably formed as a result of relatively large nearby impacts; and although these two types of patina are not strictly the result of direct exposure to the space weathering environment, they are important because they affect the optical properties of the rocks. Field emission gun SEM (FE-SEM) of classic patina on 76015 shows evidence of possible solar wind sputtering erosion. Transmission electron microscope studies of 76015 reveal the presence of impact-generated deposits and solar flare particle tracks which, like microcraters and pancakes, are diagnostic of direct exposure to space weathering processes. The outermost surface of the 76015 patina consists of an amorphous rim very much like the rims found on individual lunar soil grains; this amorphous patina rim probably formed by similar processes of impact-generated vapor condensation and possible sputter deposition. Wavelength-dispersive x-ray element maps of polished thin sections of 75075 and 76015 indicate that patina compositions are poor indicators of the compositions and mineralogies of the rocks underlying them. On average, the reflectance spectra of patinas on both samples are slightly darker than those of their unweathered equivalents. Microreflectance measurements show that a thick patina can dramatically alter the optical properties of the rock on which it forms. The backscatter Mössbauer (BaMS) spectrum of a patina-covered surface of 76015 is very similar to that of an unweathered surface, indicating that the Mössbauer signal is generated from beneath the patina. Because BaMS “sees” through surface space-weathering effects to the underlying rock, this technique has great potential for use in robotic missions to other planetary bodies.  相似文献   

4.
《Icarus》1987,72(3):492-506
The effects of particle size and mineral proportions on the spectral characteristics of plagioclase and pyroxene mixtures are investigated. Size separates (<25 μm, 25–45 μm, 45–75 μm, 75–125 μm, 125–250 μm, and 250–500 μm) have been prepared for the following labradorite/enstatite compositional mixtures: 100/0%, 95/5%, 85/15%, 50/50%, and 0/100%. Spectrally, the labradorite and enstatite samples are representative of the plagioclase feldspars and the orthopyroxenes: the labradorite exhibits a weak, broadband centered near 1.25 μm and the enstatite exhibits two well-defined bands centered near 0.9 and 1.9 μm. From analysis of the plagioclase bands of the mixtures, it is found that (1) the amount of plagioclase necessary for the plagioclase band to be observed as a discrete absorption band is dependent on particle size and (2) plagioclase can be detected by flattening of the pyroxene reflectance “peak” between the 0.9- and 1.9-μm absorption bands if significant amounts of plagioclase are present. Analogs for immature and mature lunar highland soils have been created to examine the combined effects of particle size and mineral proportions on spectra of plagioclase and pyroxene mixtures. bidirectional reflectance spectra of these soil analogs are used to examine the detectability of plagioclase in soil-like particle size distributions. Plagioclase in significant amounts is detected by the flattening of the pyroxene reflectance “peak” between the 0.9- and 1.9-μm absorption bands, and the plagioclase absorption band itself is observed with 85% plagioclase present. The soil analogs reveal that particle size accounts for only a minor spectral difference between immature and mature lunar highland soils. From comparisons with spectra of returned lunar samples, agglutinates are found to dominate the spectral variations associated with soil maturity. Spectra of the immature soil analogs can be used to estimate the minimum pyroxene abundance for immature regions observed remotely.  相似文献   

5.
Abstract— The lunar soil characterization consortium, a group of lunar‐sample and remote‐sensing scientists, has undertaken the extensive task of characterization of the finest fractions of lunar soils, with respect to their mineralogical and chemical makeup. These compositional data form the basis for integration and modeling with the reflectance spectra of these same soil fractions. This endeavor is aimed at deciphering the effects of space weathering of soils on airless bodies with quantification of the links between remotely sensed reflectance spectra and composition. A beneficial byproduct is an understanding of the complexities involved in the formation of lunar soil. Several significant findings have been documented in the study of the <45 μm size fractions of selected Apollo 17 mare soils. As grain size decreases, the abundance of agglutinitic glass increases, as does the plagioclase, whereas the other minerals decrease. The composition of the agglutinitic glass is relatively constant for all size fractions, being more feldspathic than any of the bulk compositions; notably, TiO2 is substantially depleted in the agglutinitic glass. However, as grain size decreases, the bulk composition of each size fraction continuously changes, becoming more Al‐rich and Fe‐poor, and approaches the composition of the agglutinitic glasses. Between the smallest grain sizes (10–20 and < 10 μm), the IS/FeO values (amount of total iron present as nanophase Fe0) increase by greater than 100% (>2x), whereas the abundance of agglutinitic glass increases by only 10–15%. This is evidence for a large contribution from surface‐correlated nanophase Fe0 to the IS/FeO values, particularly in the <10 μm size fraction. The surface nanophase Fe0 is present largely as vapor‐deposited patinas on the surfaces of almost every particle of the mature soils, and to a lesser degree for the immature soils (Keller et al., 1999a). It is reasoned that the vapor‐deposited patinas may have far greater effects upon reflectance spectra of mare soils than the agglutinitic Fe0.  相似文献   

6.
The spectral reflectance (0.32–1.06 μm) of Mercury was measured during two elongations, September–October 1974 and March 1975. The spectra are much improved over the previously available measurements. The reflectance increases almost linearly with wavelength and no electronic transition absorption bands are evident to the precision of the data. The new spectra agree very well with the reflectance of mature lunar mare and upland soils and are dissimilar to those of any other observed solar system object. This suggests that the surface materials and the weathering processes controlling their optical properties are similar for both the Moon and Mercury. Differences between the spectra for the two observation periods may indicate differences in the average composition for the different regions of Mercury observed.  相似文献   

7.
We find the lunar darkening process could be due neither to simple addition of impact-melted glass nor to addition of devitrified glass to crushed lunar rock. There is evidence that lunar soil grains have thin, very light-absorbing coatings that mask absorption bands, seen in the reflection spectra of freshly crushed lunar rock, in the same manner as they are masked in the spectra of lunar soils. We believe the processes that produce these coatings are (1) deposition of atoms sputtered from lunar soil grains by solar wind particles and (2) deposition of vapor species vaporized from lunar soil grains by micrometeorite impacts. Coatings produced in laboratory simulations of these processes owe their strong light-absorbing properties in large part to the presence of abundant metallic Fe grains smaller than 100 Å in diameter. Another process, which depends on implantation of solar wind protons in lunar soil grains and their later mobilization during micrometeorite impacts to produce metallic Fe in the impact glass, also seems reasonable but has not yet been demonstrated experimentally. As a result of impact vaporization the Moon would preferentially lose minor amounts of light elements, principally monatomic oxygen, and this would result in oxygen depletion in the vapor condensate. This type of fraction would be more extreme on airless bodies with lower escape velocities. Sputtering occurs at higher effective temperatures and this would cause loss of all common rock-forming elements in approximately equal amounts. There would be some bias in this process toward retention of very heavy trace elements— a characteristic that has been observed in the lunar soil. This bias would be less important for smaller airless bodies. We describe an apparent new type of fractionation that occurs during deposition of sputtered atoms. This fractionation favors retention of higher mass atoms over lower mass atoms, and appears to be a linear function of mass. This may explain observed isotopic fractionations in lunar soil, in which the heavier isotope always appears to be enriched relative to the lighter one. This “first bounce fractionation” process should operate on all airless bodies. Na and K apparently do not conform to this fractionation process and have a much greater tendency to escape. This may help explain the presence of high Na concentrations around Io.  相似文献   

8.
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9.
Abstract— Evidence in favor of the model fusion of the finest fraction (F3) for the origin of lunar agglutinitic glass has been accruing. They include (1) theoretical expectations that shock pulses should engulf and melt smaller grains more efficiently than larger grains, (2) experimental results of impact shock, albeit at lower than presumed hypervelocity impacts of micrometeorites on the lunar regolith, and (3) new analyses confirming previous results that average compositions of agglutinitic glass are biased towards that of the finest fraction of lunar soils from which they had formed. We add another reason in support of the F3 model. Finer grains of lunar soils are also much more abundant. Hence, electrostatic forces associated with the rotating terminator region bring the finest grains that are obviously much lighter than courser grains to the surface of the Moon. This further contributes to the preferential melting of the finest fraction upon micrometeoritic impacts. New backscattered electron imaging shows that agglutinitic glass is inhomogeneous at submicron scale. Composition ranges of agglutinitic glass are extreme and deviate from that of the finest fraction, even by more than an order of magnitude for some components. Additionally, we show how an ilmenite grain upon impact would produce TiO2‐rich agglutinitic glass in complete disregard to the requirements of fusion of the finest fraction. We propose an addition to the F3 model to accommodate these observations (i.e., that micrometeorite impacts indiscriminately melt the immediate target regardless of grain size or grain composition). We, therefore, suggest that (1) agglutinitic glass is the sum of (a) the melt produced by the fusion of the finest fraction of lunar soils and (b) the microvolume of the indiscriminate target, which melts at high‐shock pressures from micrometeoritic impacts, and that (2) because of the small volume of the melt and incorporating cold soil grains, the melt quenched so rapidly that it did not mix and homogenize to represent any preferential composition, for example, that of the finest fraction.  相似文献   

10.
The mineralogy of a planetary surface is a diagnostic product of its formation and geologic evolution. Global assessment of lunar mineralogy at high spatial resolution has been a long standing goal of lunar exploration. Currently, the only global data available for such study is multispectral imagery from the Clementine mission. We use the detailed compositional, petrographic, and spectroscopic data of lunar soils produced by the Lunar Soil Characterization Consortium to explore the use of multispectral imaging as a diagnostic tool. We compare several statistically optimized formulations of links between spectral and mineral parameters and apply them to Clementine UV-VIS data. The most reliable results are for estimations of pyroxene abundance and maturity parameters (agglutinate abundance, Is/FeO). Estimations of different pyroxene composition (low-Ca versus high-Ca) appear good in a relative sense, but absolute values are limited by residual wavelength dependent Clementine photometric calibrations. Since the signal-to-noise of Clementine multispectral data is good at the 1-km scale, almost any combination of parameters that capture inherent spectral variance can provide spatially coherent maps, although the parameters may not actually be directly related to composition. Clementine estimates are useful for identifying scientific or exploration targets for imaging spectrometer sensors of the next generation that are specifically designed to characterize mineralogy.  相似文献   

11.
Abstract— The fine fraction of lunar soils (<45 μm) dominates the optical properties of the bulk soil. Definite trends can be seen in optical properties of size separates with decreasing particle size: diminished spectral contrast and a steeper continuum slope. These trends are related to space weathering processes and their affects on different size fractions. The finest fraction (defined here as the <10 μm fraction) appears to be enriched in weathering products relative to the larger size fractions, as would be expected for surface correlated processes. This <10 μm fraction tends to exhibit very little spectral contrast, often with no distinguishable ferrous iron absorption bands. Additionally, the finest fractions of highland soils are observed to have very different spectral properties than the equivalent fraction of mare soils when compared with larger size fractions. The spectra of the finest fraction of feldspathic soils flatten at longer wavelengths, whereas those of the finest fraction of basaltic soils continue to increase in a steep, almost linear fashion. This compositional distinction is due to differences in the total amount of nanophase iron that accumulates in space weathering products. Such ground‐truth information derived from the <10 μm fraction of lunar soils provides valuable insight into optical properties to be expected in other space weathering environments such as the asteroids and Mercury.  相似文献   

12.
The near-IR spectral properties of minerals, meteorites, and lunar soil vary with temperature. The manner in which these materials vary is diagnostic of aspects of their composition. We quantify the spectral dependence on temperature by reporting the change in relative reflectance with temperature as a function of wavelength. We call this quantity, ΔR/ΔT (in units of K−1), as a function of temperature the “thermo-reflectance spectrum.” The thermo-reflectance spectra of olivine and pyroxene are distinct, and most of the observable structure in thermo-reflectance spectra of the ordinary and carbonaceous chondrites can be understood in terms of a mixture of the thermo-reflectance spectra of olivine and pyroxene. The magnitude of thermo-reflectance spectra of meteorites and lunar soils is much less than that of pure minerals. Lunar soils are particularly subdued. While conventional analysis of remotely obtained spectra of the Moon can neglect temperature effects, spatially resolved measurements of the surface of the asteroid Vesta will likely have a strong temperature-dependent component based on measurements of a eucrite and a howardite.  相似文献   

13.
Reflectance Spectral Characteristics of Lunar Surface Materials   总被引：2，自引：0，他引：2  
Based on a comprehensive analysis of the mineral composition of major lunar rocks (highland anorthosite, lunar mare basalt and KREEP rock), we investigate the reflectance spectral characteristics of the lunar rock-forming minerals, including feldspar, pyroxene and olivine. The affecting factors, the variation of the intensity of solar radiation with wavelength and the reflectance spectra of the lunar rocks are studied. We also calculate the reflectivity of lunar mare basalt and highland anorthosite at 300 nm, 415 nm, 750 nm, 900 nm, 950 nm and 1000 nm. It is considered that the difference in composition between lunar mare basalt and highland anorthosite is so large that separate analyses are needed in the study of the reflectivity of lunar surface materials in the two regions covered by mare basalt and highland anorthosite, and especially in the region with high Th contents, which may be the KREEP-distributed region.  相似文献   

14.
Abstract— Soils of the 62-cm deep Apollo 16 double drive tube 60013/14 are mature at the top and submature at the bottom. Modal analyses of 5529 grains from the 90–150 μm and the 500–1000 μm. fractions from 12 levels of the core show that, in general, agglutinate abundance increases somewhat monotonically to the top and mimics the Is/FeO profile. There is a general decrease in the modal abundance of monomineralic fragments towards the top, suggesting that agglutinates were formed in part at the expense of monomineralic grains, especially feldspars, which are by far the most abundant mineral in these soils. In detail, the top 27 cm of the core differs from the bottom 21 cm, and the middle 14 cm is intermediate in its properties. In the upper segment, variations in the abundances of feldspars correspond with those of feldspathic fragmental breccias and cataclastic anorthosites; in the bottom segment, a similar but weak correspondence between feldspars and crystalline matrix breccias is observed. Mixing of the comminuted products of these three rock types likely produced the bulk of the core material. Many single feldspars in all size fractions are remarkably fresh, show no damage from shock, and are similar in appearance to the large feldspars in anorthosites and feldspathic fragmental breccias, which we consider to be the primary sources of single feldspars in this core. Major (Na, Al, Si, K, Ca) and minor (Fe, Ba) element analyses of 198 single feldspar grains indicate the presence of only one population of feldspars, which is consistent with our interpretation of feldspar provenance. Classification of 890 monomineralic feldspar, olivine, pyroxene, and glass spherules on the basis of the presence or absence of thin brownish coating—related to reworking at the surface—shows that coated grains are much more abundant in the top segment than in the bottom segment. A comparison with the mixing and maturation model (McKay et al., 1977) of soils in the core 60009/10, some 60 m away from 60013/14, shows that mixtures of an immature, nearly pure plagioclase soil (dominant in 60009/10) and another immature, crystalline breccia-rich soil (dominant in 60013/14) may have matured through in situ reworking to produce the soils under investigation. We conclude that the soils in this core are products of mixing along soil evolution Path 2 of McKay et al. (1974). Superimposed on that soil column is the reworking of the upper part, which has evolved more recently along Path 1. This core thus represents a consanguineous column of the lunar regolith with an upper reworked segment.  相似文献   

15.
J. Warell  B.J.R. Davidsson 《Icarus》2010,209(1):164-178
An implementation of Hapke’s radiative transfer-based photometric model for light scattering in semi-transparent porous media is presented with special emphasis on the analysis of reflectance spectra of Mercury. The model allows intimate mixing of an arbitrary number of regolith components with varying modal abundances, modal chemistries and grain sizes, matured by microphase iron. Reflectance spectra of suites of silicates of varying grain sizes and chemistries are used to calculate the imaginary coefficient of the complex index of refraction as a function of chemistry, thus limiting the modeling effects of chemically atypical laboratory samples, and allowing controlled modeling of minerals with varying chemical compositions. The performance of the model in the visual to near-infrared wavelength range is evaluated for a range of chemically characterized silicate mixtures of terrestrial powders, meteorite powders, matured lunar return samples, and remotely sensed lunar spectra.  相似文献   

16.
Lunar mare basalts, highland anorthosites and KREEP are the three major lunar rock types reported from the lunar surface. In the present study, we interpret the reflectance spectral behavior of lunar analog basalts including massive basalt, vesicular basalt and amygdaloidal basalt collected from the Deccan basaltic region, which are considered as equivalent of lunar mare basalts. Reflectance spectra of analog basalts were measured at three different environments: in the field, under controlled field conditions and in the lab. In field conditions the reflectance spectra were measured under 350-1050 nm spectral range. During controlled field and lab condition, reflectance spectra were measured under 350-2500 nm range covering the UV, visible, NIR, and SWIR regions. The spectral characteristics of basalts measured under different environments and their merits and demerits were discussed. However, lab spectra have given clear, reliable diagnostic spectral information for our present objective. The major oxides and minerals of analog basalts were compared with lunar mare basalts. The presence of Ca-pyroxene, ferrous and ferric iron and their diagnostic spectral features in basalts are discussed for study of lunar mare region.  相似文献   

17.
We suggest a technique to determine the chemical and mineral composition of the lunar surface using artificial neural networks (ANNs). We demonstrate this powerful non-linear approach for prognosis of TiO2 abundance using Clementine UV-VIS mosaics and Lunar Soil Characterization Consortium data. The ANN technique allows one to study correlations between spectral characteristics of lunar soils and composition parameters without any restrictions on the character of these correlations. The advantage of this method in comparison with the traditional linear regression method and the Lucey et al. approaches is shown. The results obtained could be useful for the strategy of analyzing lunar data that will be acquired in incoming lunar missions especially in case of the Chandrayaan-1 and Lunar Reconnaissance Orbiter missions.  相似文献   

18.
Abstract— Impact-induced comminution of planetary surfaces is pervasive throughout the solar system and occurs on submillimeter to global scales, resulting in comminution products that range from fine-grained surface soils, to massive, polymict ejecta deposits, to collisionally fragmented objects. Within this wide range of comminution products, we define regoliths in a narrow sense as materials that were processed by repetitive impacts to dimensional scales comparable to or smaller than that of component minerals of the progenitor rock(s). In this paper, we summarize a wide variety of impact experiments and other observations that were primarily intended to understand the evolution of regoliths on lunar basalt flows, and we discuss some of their implications for asteroidal surfaces. Cratering experiments in both rock and noncohesive materials, combined with photogeologic observations of the lunar surface, demonstrate that craters <500 m in diameter contribute most to the excavation of local bedrock for subsequent processing by micrometeorites. The overall excavation rate and, thus, growth rate of the debris layer decreases with time, because the increasingly thicker fragmental layer will prevent progressively larger projectiles from reaching bedrock. Typical growth rates for a 5 m thick lunar soil layer are initially (～≥3 Ga ago) a few mm/Ma and slowed to <1 mm/Ma at present. The coarse-grained crater ejecta are efficiently comminuted by collisional fragmentation processes, and the mean residence time of a 1 kg rock is typically 10 Ma. The actual comminution of either lithic or monomineralic detritus is highly mineral specific, with feldspar and mesostasis comminuting preferentially over pyroxene and olivine, thus resulting in mechanically fractionated fines, especially at grain sizes <20 μm. Such fractionated fines also participate preferentially in the shock melting of lunar soils, thus giving rise to “agglutinate” melts. As a consequence, agglutinate melts are systematically enriched in feldspar components relative to the bulk composition of their respective host soil(s). Compositionally homogeneous, impact derived glass beads in lunar soils seem to result from micrometeorite impacts on rock surfaces, reflecting lithic regolith components and associated mineral mixtures. Cumulatively, experimental and observational evidence from lunar mare soils suggests that regoliths derive substantially from the comminution of local bedrock; the addition of foreign, exotic components is not necessary to explain the modal and chemical compositions of diverse grain size fractions from typical lunar soils. Regoliths on asteroids are qualitatively different from those of the Moon. The modest impact velocities in the asteroid belt, some 5 km s?1, are barely sufficient to produce impact melts. Also, substantially more crater mass is being displaced on low-gravity asteroids compared to the Moon; collisional processing of surface boulders should therefore be more prominent in producing comminuted asteroid surfaces. These processes combine into asteroidal surface deposits that have suffered modest levels of shock metamorphism compared to the Moon. Impact melting does not seem to be a significant process under these conditions. However, the role of cometary particles encountering asteroid surfaces at presumably higher velocities has not been addressed in the past. Unfortunately, the asteroidal surface processes that seemingly modify the spectral properties of ordinary chondrites to match telescopically obtained spectra of S-type asteroids remain poorly understood at present, despite the extensive experimental and theoretical insights summarized in this report and our fairly mature understanding of lunar surface processes and regolith evolution.  相似文献   

19.
J. Warell  D.T. Blewett 《Icarus》2004,168(2):257-276
We present new optical (0.4-0.65 μm) spectra of Mercury and lunar pure anorthosite locations, obtained quasi-simultaneously with the Nordic Optical Telescope (NOT) in 2002. A comparative study is performed with the model of Lucey et al. (2000, J. Geophys. Res. 105, 20297-20305, and references therein) between iron-poor, mature, pure anorthosite (>90% plagioclase feldspar) Clementine spectra from the lunar farside and a combined 0.4-1.0 μm mercurian spectrum, obtained with the NOT, calculated for standard photometric geometry. Mercury is located at more extreme locations in the Lucey ratio-reflectance diagrams than any known lunar soil, specifically with respect to the extremely iron-poor mature anorthosites. Though quantitative prediction of FeO and TiO2 abundances cannot be made without a more generally applicable model, we find qualitatively that the abundances of both these oxides must be near zero for Mercury. We utilize the theory of Hapke (2002, Icarus 157, 523-534, and references therein), with realistic photometric parameters, to model laboratory spectra of matured mineral powders and lunar soils, and remotely sensed spectra of lunar anorthosites and Mercury. An important difference between fabricated and natural powders is the high value for the internal scattering parameter necessary to interpret the spectra for the former, and the requirement of rough and non-isotropically scattering surfaces in the modelling of the latter. The mature lunar anorthosite spectra were well modelled with binary mixtures of calcic feldspars and olivines, grain sizes of 25-30 μm and a concentration of submicroscopic metallic iron (SMFe) of 0.12-0.15% in grain coatings. The mercurian spectrum is not possible to interpret from terrestrial mineral powder spectra without introducing an average particle scattering function for the bulk soil that increases in backscattering efficiency with wavelength. The observed spectrum is somewhat better predicted with binary mixture models of feldspars and pyroxenes, than with single-component regoliths consisting of either albite or diopside. Correct spectral reflectance values were predicted with a concentration of 0.1 wt% SMFe in coatings of 15-30 μm sized grains. Since reasonable cosmogonical formation scenarios for Mercury, or meteoritic infall, predict iron concentrations at least this high, we draw the conclusion that the average grain size of Mercury is about a factor of two smaller than for average returned lunar soil samples. The 0.6-2.5 μm spectrum of McCord and Clark (1979, J. Geophys. Res. 178, 745-747) is used to further limit the possible range of mineralogical composition of Mercury. It is found that an intimately mixed and matured 3:1 labradorite-to-enstatite regolith composition best matches both the optical and near-infrared spectra, yielding an abundance of ∼1.2 wt% FeO and ∼0 wt% TiO2.  相似文献   

20.
The goal of this study is to develop an efficient and accurate model for using visible–near infrared reflectance spectra to estimate the abundance of minerals on the lunar surface. Previous studies using partial least squares (PLS) and genetic algorithm–partial least squares (GA–PLS) models for this purpose revealed several drawbacks. PLS has two limitations: (1) redundant spectral bands cannot be removed effectively and (2) nonlinear spectral mixing (i.e., intimate mixtures) cannot be accommodated. Incorporating GA into the model is an effective way for selecting a set of spectral bands that are the most sensitive to variations in the presence/abundance of lunar minerals and to some extent overcomes the first limitation. Given the fact that GA–PLS is still subject to the effect of nonlinearity, here we develop and test a hybrid partial least squares–back propagation neural network (PLS–BPNN) model to determine the effectiveness of BPNN for overcoming the two limitations simultaneously. BPNN takes nonlinearity into account with sigmoid functions, and the weights of redundant spectral bands are significantly decreased through the back propagation learning process. PLS, GA–PLS and PLS–BPNN are tested with the Lunar Soil Characterization Consortium dataset (LSCC), which includes VIS–NIR reflectance spectra and mineralogy for various soil size fractions and the accuracy of the models are assessed based on R2 and root mean square error values. The PLS–BPNN model is further tested with 12 additional Apollo soil samples. The results indicate that: (1) PLS–BPNN exhibits the best performance compared with PLS and GA–PLS for retrieving abundances of minerals that are dominant on the lunar surface; (2) PLS–BPNN can overcome the two limitations of PLS; (3) PLS–BPNN has the capability to accommodate spectral effects resulting from variations in particle size. By analyzing PLS beta coefficients, spectral bands selected by GA, and the loading curve of the latent variable with the largest weight in PLS–BPNN, we conclude that spectral information incorporated into the three models is directly derived from the diagnostic absorption bands associated with the individual minerals. It is concluded that the PLS–BPNN model should be applicable to both Clementine UV–VIS–NIRs and Moon Mineralogy Mapper (M3) data.  相似文献   

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