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The lunar surface evolves over time due to space weathering, and the visible–near‐infrared spectra of more mature (i.e., heavily weathered) soils are lower in reflectance and steeper in spectral slope (i.e., darker and redder) than their immature counterparts. These spectral changes have traditionally been attributed to the space‐weathered rims of soil grains (and particularly nanophase iron therein). However, understudied thus far is the spectral role of agglutinates—the agglomerates of mineral and lithic fragments, nanophase iron, and glass that are formed by micrometeoroid impacts and are ubiquitous in mature lunar soils. We separated agglutinates and non‐agglutinates from six lunar soils of varying maturity and composition, primarily from the 125–250 μm size fraction, and measured their visible–near‐infrared reflectance spectra. For each soil, the agglutinate spectra are darker, redder, and have weaker absorption bands than the corresponding non‐agglutinate and unsorted soil spectra. Moreover, greater soil maturity corresponds to darker agglutinate spectra with weaker absorption bands. These findings suggest that agglutinates (rather than solely the space‐weathered rims) play an important role in both the darkening and reddening of mature soils—at least for the size fractions examined here. Comparisons with analog soils suggest that high nanophase iron abundance in agglutinates is likely responsible for their low reflectance and spectrally red slope. Additional studies of agglutinates are needed both to more comprehensively characterize their spectral properties (across size fractions and in mixing with non‐agglutinates) and to assess the relative roles of agglutinates and rims in weathering‐associated spectral changes. In the scientific study of the Moon, one key focus is surface processes: how do the physical and chemical properties of the Moon's surface change over time due to weathering (e.g., bombardment by micrometeoroids and by particles from the Sun)? Such investigations provide valuable insights into the Moon's history (such as the ages of impact craters) that are often deduced from measurements of reflected light; as a soil is weathered, it reflects light differently, which manifests visually as a progressive darkening of the soil. This phenomenon had primarily been attributed to weathering‐associated development of rims on individual soil grains, but in this work we explored an alternative cause: soil particles known as agglutinates (misshapen, vesicular agglomerates of mineral fragments, iron, and glass that form due to weathering processes). We isolated agglutinates of six soil samples from the Moon and measured how they reflect light. We find that they reflect light in patterns reminiscent of how the Moon's surface behaves when weathered. These findings suggest that agglutinates play a more important role than previously thought in determining the light‐reflecting properties of the Moon's surface, thus warranting a greater and more nuanced consideration in future studies of how the Moon's surface changes over time. We measured the reflectance spectra of agglutinates and non‐agglutinates separated from six lunar soils of varying composition and maturitySpectral comparisons suggest that spectral reddening of mature soils is expressed mainly via agglutinates (for the size fractions measured)These findings reframe our understanding of the relative spectral roles of agglutinates and soil grain rims in weathered lunar soils We measured the reflectance spectra of agglutinates and non‐agglutinates separated from six lunar soils of varying composition and maturity Spectral comparisons suggest that spectral reddening of mature soils is expressed mainly via agglutinates (for the size fractions measured) These findings reframe our understanding of the relative spectral roles of agglutinates and soil grain rims in weathered lunar soils

Laboratory spectrophotometric measurements of minerals common on the lunar surface (olivine, pyroxene, plagioclase, and ilmenite) are measured over a wavelength range of 0.4 to 2.5 μm to better understand the effects of the particle phase function (PF; P[g]) on the application of Hapke's radiative transfer model to reflectance spectra of lunar materials. One objective of this work is to determine if accounting for wavelength‐dependent photometric effects can improve spectral estimates of mineral abundance in lunar materials, particularly that of ilmenite. We also discuss a two‐step calibration method to correct for the non‐Lambertian behavior and wavelength dependence of the common reference standard Spectralon. Both a two‐term Legendre polynomial representation of the PF and the Henyey‐Greenstein PF are examined. We use our results to apply the Hapke radiative transfer model to reflectance spectra of lab mixtures and test the effects of different PF characteristics and assumptions. Laboratory spectra indicate that ilmenite exhibits more backward scattering behavior compared with silicate minerals, which are more forward scattering. We find that the variations in PF can affect derived single‐scattering albedo values and thus spectral unmixing results. Because single‐scattering contribution dominates the reflectance properties of dark minerals such as ilmenite, large uncertainties in derived single‐scattering albedo values can be introduced by small changes in PFs. However, it is observed that the use of a wavelength‐dependent PF does not produce significant differences in spectral unmixing results for binary and ternary silicate mixtures. Olivine, pyroxene, plagioclase, and ilmenite are common minerals on the lunar surface, and knowledge on their spatial and temporal distributions can help to understand the geological evolutions of our Moon. Remote sensing reflectance spectroscopy is an important technique that can be used to identify those minerals, because their reflectance spectra have different diagnostic absorption features. Since reflectance spectra could vary with the change of illumination and viewing angles, the accurate estimation of mineral concentrations using reflectance spectra would rely on light scattering models that quantitatively describe how light is scattered from the target surface. The purpose of this study is to understand the accuracy of retrieving mineral concentrations in ilmenite‐bearing mixtures using the Hapke model widely used in quantitative analysis of reflectance spectra. We measured the reflectance spectra of the more transparent olivine, pyroxene, and plagioclase and the more opaque ilmenite at different viewing angles. Using these data, we quantified the scattering properties of these four minerals. We found that ilmenite is more backscattering while the other three minerals are more forward scattering. The mixing of these dark and bright materials makes the accurate interpretation of reflectance spectra data difficult. Our results suggest that well constrained scattering properties of the component minerals and their mixtures can help improve the accuracy of mineral abundance estimations. Spectrophotometric measurements on lunar‐relevant minerals including ilmenite were conducted over a wide range of phase anglesSpectral modeling using a two‐term Legendre polynomial and the Henyey‐Greenstein forms of phase function shows no significant differencesThe effects of changes in phase function on derived single‐scattering albedo are inversely proportional to sample's reflectance

We conducted ground-based performance evaluation tests of the Near-Infrared Spectrometer (NIRS3) onboard Hayabusa2 spacecraft in November 2013 and from April to May 2014 and established a method for evaluating its measured reflectance spectra. Reflectance spectra of nine powdered carbonaceous chondrite samples were measured by both NIRS3 and a Fourier transform infrared (FT-IR) spectrometer. We have established two methods for correcting the NIRS3 data by comparing them with the corresponding FT-IR data because raw data obtained by NIRS3 underwent spectral distortion caused by systematic offsets in sensitivity of individual pixels. The corrected NIRS3 spectra of carbonaceous chondrite samples are comparable with their FT-IR spectra. The depth of each band component Dλis defined for each wavelength λ(μm) to characterize the absorption bands in NIRS3 spectra. It is suggested that the relationship between the D2.72/D2.79ratio and the D2.76/D2.90ratio would be useful for estimating the degree of heating of the asteroid surface, if contributions of terrestrial adsorbed water on D2.79and D2.90are properly corrected. The degrees of heating and space weathering are also comprehensively evaluated by the relationship between D2.90and the D2.76/D2.90ratio. Reflectance spectra of asteroid Ryugu, the target asteroid of Hayabusa2, to be recorded by the NIRS3 instrument are expected to reveal the characteristics of the surface materials by using the evaluation technique proposed in this paper. Such information will be used for choosing the touchdown points for sampling and also for investigating the distribution of the materials similar to the returned samples on Ryugu.Graphical abstract.

Sulfate minerals are important indicators for aqueous geochemical environments. The geology and mineralogy of Mars have been studied through the use of various remote-sensing techniques, including thermal (mid-infrared) emission and visible/near-infrared reflectance spectroscopies. Spectral analyses of spacecraft data (from orbital and landed missions) using these techniques have indicated the presence of sulfate minerals on Mars, including Fe-rich sulfates on the iron-rich planet. Each individual Fe-sulfate mineral can be used to constrain bulk chemistry and lends more information about the specific formational environment [e.g., Fe2+sulfates are typically more water soluble than Fe3+sulfates and their presence would imply a water-limited (and lower Eh) environment; Fe3+sulfates form over a range of hydration levels and indicate further oxidation (biological or abiological) and increased acidification]. To enable better interpretation of past and future terrestrial or planetary data sets, with respect to the Fe-sulfates, we present a comprehensive collection of mid-infrared thermal emission (2000 to 220 cm-1; 5-45 μm) and visible/near-infrared (0.35-5 μm) spectra of 21 different ferrous- and ferric-iron sulfate minerals. Mid-infrared vibrational modes (for SO4, OH, H2O) are assigned to each thermal emissivity spectrum, and the electronic excitation and transfer bands and vibrational OH, H2O, and SO4overtone and combination bands are assigned to the visible/near-infrared reflectance spectra. Presentation and characterization of these Fe-sulfate thermal emission and visible/near-infrared reflectance spectra will enable the specific chemical environments to be determined when individual Fe-sulfate minerals are identified.

Olivine exhibits highly diagnostic absorption features across visible to near-infrared (VNIR) wavelengths due to electronic transitions of Fe2+in its crystal structure. The properties of these absorptions vary with composition, enabling compositional analysis of olivine through VNIR spectroscopy, both in the laboratory and through remote sensing. Previous analyses of these trends have relied on natural olivine samples, which are influenced by the presence of minor cations that can affect the diagnostic absorptions. We conduct a systematic analysis of a suite of synthetic (pure Mg/Fe) olivine samples with VNIR (300-2600 nm) reflectance spectroscopy and quantitative spectral deconvolutions. From the full suite of samples described and characterized by Dyar et al. (2009), we identify a small suite of well-characterized and chemically pure olivine samples that demonstrates consistent and reliable spectral reflectance properties across visible to near-infrared wavelengths. This suite covers the stoichiometric olivine solid solution from x = Mg/(Mg+Fe) = 0 to x = 70 (Fo0to Fo70). Because of their tight compositional control, these synthetic samples improve on previous analyses of natural samples. The results of this study provide a new standard for spectral reflectance properties of olivine across visible to near-infrared wavelengths for the compositions present in the suite. We present updated data on the trends in olivine band position as a function of olivine composition, which are the basis for remote compositional evaluation of olivine with visible to near-infrared reflectance spectroscopy. For these reasons, these improved olivine band position trends are of major importance to remote compositional analyses of terrestrial planets.

AbstractOlivine exhibits highly diagnostic absorption features across visible to near-infrared (VNIR) wavelengths due to electronic transitions of Fe2+in its crystal structure. The properties of these absorptions vary with composition, enabling compositional analysis of olivine through VNIR spectroscopy, both in the laboratory and through remote sensing. Previous analyses of these trends have relied on natural olivine samples, which are influenced by the presence of minor cations that can affect the diagnostic absorptions. We conduct a systematic analysis of a suite of synthetic (pure Mg/Fe) olivine samples with VNIR (300-2600 nm) reflectance spectroscopy and quantitative spectral deconvolutions. From the full suite of samples described and characterized by Dyar et al. (2009), we identify a small suite of well-characterized and chemically pure olivine samples that demonstrates consistent and reliable spectral reflectance properties across visible to near-infrared wavelengths. This suite covers the stoichiometric olivine solid solution from x = Mg/(Mg+Fe) = 0 to x = 70 (Fo0to Fo70). Because of their tight compositional control, these synthetic samples improve on previous analyses of natural samples. The results of this study provide a new standard for spectral reflectance properties of olivine across visible to near-infrared wavelengths for the compositions present in the suite. We present updated data on the trends in olivine band position as a function of olivine composition, which are the basis for remote compositional evaluation of olivine with visible to near-infrared reflectance spectroscopy. For these reasons, these improved olivine band position trends are of major importance to remote compositional analyses of terrestrial planets.

Beidellites may exist on Mars and represent intermediate alteration products; their presence would indicate different alteration environments than previously identified because montmorillonite is a low-grade alteration mineral whereas beidellite is a higher-temperature alteration mineral, and often represents a step toward illite formation. The reflectance spectra of beidellites are under study to support their orbital detection on Mars, where spectral signatures of other Al-rich phyllosilicates have been observed. Reflectance spectra of ten Al-rich smectites are presented here which include pure beidellites and Al smectites having compositions between those of beidellite and montmorillonite, and emphasis is placed here on the OH combination bands near 4545 cm−1(2.2 μm) as these vibrational features are commonly used in the identification of phyllosilicates on Mars. Shifts were observed in the Al2OH band centers, which occur near 4590 cm−1(2.18 μm) in reflectance spectra of beidellite and near 4525 cm−1(2.21 μm) in reflectance spectra of montmorillonite. These are compared with the Al2OH bending vibrations observed near 941–948 cm−1(10.5–10.6 μm) for beidellite and near 918–926 cm−1(10.8–10.9 μm) for montmorillonite. Although the octahedral site cation composition provides the greatest influence on the vibrational energies of the M2OH groups, the tetrahedral site cation composition also influences these vibrations. Shifts were observed in the Si-O-Al bending vibrations from 552 and 480 cm−1(18.1 and 20.8 μm) in beidellite spectra to 544 and 475 cm−1(18.4 and 21.0 μm) in montmorillonite spectra. Gaussian modeling of the 4545 cm−1(2.2 μm) bands led to the discrimination of four overlapping bands in each of the ten Al smectite spectra examined in this study. Shifts in the band center and area of the primary spectral band are coordinated with substitution of Al for Si in the tetrahedral sheet. This is consistent with beidellites having a greater tetrahedral layer charge than montmorillonites. The observed spectral differences were sufficiently large that these Al-rich smectites can be differentiated in orbital data of Mars. A pure beidellite-type spectrum is observed in an isolated Al phyllosilicate-bearing outcrop in Libya Montes, a region where Fe-rich smectite is common but Al-rich smectite is rare. Beidellite-type reflectance spectra were also observed in one area of the Nili Fossae region. In contrast, a variety of Al phyllosilicates were found in the ancient rocks at Mawrth Vallis, including some smaller clay-bearing regions exhibiting spectral signatures more consistent with beidellite-like than montmorillonite-like chemistry.

In the remote detection of mineral compositions of planetary surface materials on airless bodies, space weathering is an obstacle which makes reflectance spectra redder and darker and weakens spectral features. This study attempts to model an effect of space weathering due to vapor coating by accounting for the change in surface reflectivity of regolith particles wherein nanophase-reduced iron (npFe0) particles are concentrated on their surfaces. When applied to a suite of reflectance spectra of lunar soils having different degrees of space weathering, this model can estimate the degrees of space weathering in terms of the thicknesses of the coating layer and provide an absorption coefficient spectrum of the host material.

Abstract—We obtained color images of near‐Earth asteroid 25143 Itokawa by the Hayabusa multiband imaging camera to characterize the regional color properties. Images were obtained for the whole disk from the gate position (GP) and home position (HP) at a spatial resolution of 0.8–3.7 m/pixel. Whole‐disk spectra are adjusted to the telescopic data obtained by the University of Hawai'i's 88‐inch telescope using the Eight Color Asteroid Survey (ECAS) system. The disk‐resolved measurements show large variations in the three visible channels. We present a map of an index related to the degree of space weathering, which has been newly developed based on laboratory measurements. We find large variations in the degree of space weathering on Itokawa. Fresh materials are observed in regions of steep slopes and craters, whereas mature materials are ubiquitously distributed. This result suggests that pristine ordinary chondrite‐like materials have been exposed through weathered layers by excavation. By also examining close‐up images obtained during touchdown rehearsal, we find that most rocks in Itokawa's rough terrains are weathered. Instead of a regolith blanket, the surface of this small asteroid is covered with weathered rocks and gravels.

Abstract—Based on recent progress in simulating space weathering on asteroids using pulse‐laser irradiation onto olivine and orthopyroxene samples, detailed analyses of two of the A and R type asteroid reflectance spectra have been performed using reflectance spectra of laser‐treated samples. The visible‐near‐infrared spectrum of olivine is more altered than that of pyroxene at the same pulse‐laser energy, suggesting that olivine weathers more rapidly than orthopyroxene in space. The same trend can be detected from reflectance spectra of the asteroids, where the more olivine an asteroid has, the redder its 1 μm band continuum can become. Comparison of the 1 μm band continuum slope and the 2/1 μm band area ratio between the asteroids and olivine and pyroxene samples (including the laser‐treated ones) suggests that asteroids may be limited in the degree of space weathering they can exhibit, possibly due to the short life of their surface regolith. Their pyroxenes may also have a limited chemical composition range. Fitting the visible continuum shape and other parts of the spectra (especially the 2μm part) has been impossible with any combination of common rock‐forming minerals such as silicates and metallic irons. However, this study shows, for the first time, excellent fits of reflectance spectra of an A asteroid (Aeternitas) and an R asteroid (Dembowska), including their visible spectral curves, band depths and shapes, and overall continuum shapes. Our results provide estimates that Aeternitas consists of 2% fresh olivine, 93% space‐weathered olivine, 1% space‐weathered orthopyroxene, and 4% chromite, and that Dembowska consists of 1% fresh olivine, 55% space‐weathered olivine, and 44% space‐weathered orthopyroxene. These results suggest that space weathering effects maybe important to the interpretation of asteroid reflectance spectra, even those with deep silicate absorption bands. Modified Gaussian model deconvolutions of the laser‐irradiated olivine samples show that their identity as olivine remained. The most recent submicroscopic mineralogical analyses have revealed that the laser‐irradiated olivine samples contain nanophase iron particles similar to those in space‐weathered lunar samples.

Although asteroid 4 Vesta and Vestoids have been believed to be the source of a group of basaltic meteorites called HEDs, there have been detailed spectral analyses on the spectral redness and the 506.5 nm absorption band, suggesting controversy on their space weathering processes and origins. In order to evaluate a possibility that such an apparent inconsistency may be explained by the space weathering, the 506.5 nm spectral feature and reddening trend are examined for Vesta and Vestoids, HED meteorites, lunar soils, and laser irradiated pyroxene samples in this paper. Our results indicate that all fresh HED meteorites have the 506.5 nm band at different wavelengths according to their classes, lunar soils seem to lose the 506.5 nm band as they mature, and pulse laser irradiation on the pyroxene sample seems to reduce the 506.5 nm band. Therefore, absence of the 506.5 nm band on some Vestoids can be due to space weathering although the relationship between the visible redness and presence/absence of the 506.5 nm band of Vesta and Vestoids is inconsistent with the assumed HED-lunar space weathering trend based on the above laboratory results. Other possible explanations are that some Vestoids experienced shock heavy enough to erase the 506.5 nm band and that pyroxenes on some Vestoids are not similar to those in HED meteorites. Even if the latter case is true and some Vestoids are not made of HED materials, HED meteorites could still come from Vesta unless we assume all Vestoids have to be fragments of Vesta.

For the purpose of simulating the surface alteration process called “space weathering”, experiments of pulse laser irradiation, proton implantation, and laser irradiation to proton implanted samples were performed and reflectance spectra of altered materials were measured. To simulate the impact heating by micrometeorite bombardments, we made a new apparatus using a pulse laser whose pulse duration is 6–8 nanoseconds, comparable with a timescale of micrometeorite impacts. We find that the degree of space weathering, i.e., change of reflectance spectrum should depend on mineral composition. Laser irradiation onto olivine produces the largest reduction of albedo and the highest reddening of reflectance spectrum. In general, variation of olivine spectra is much larger than that of pyroxenes. Depths of absorption bands do not change in the scaled spectra. The olivine spectrum after the laser irradiation can match spectra of some olivine asteroids within a subtype of S-type asteroids. Comparison of Vesta spectrum with altered pyroxene spectra suggests that Vesta surface would be relatively older than olivine asteroids. We also investigate the influence of solar wind proton and pyroxene FeO content. The proton implantation causes small changes in olivine and enstatite spectra. Implanted protons do not influence spectral change by the laser irradiation: the laser irradiation and the proton implantation do not produce multiplicative but additive changes on the reflectance spectra. FeO content of pyroxenes does not relate to the degree of reflectance change.

The stony iron model for the S asteroids has been tested using observed reflectance spectra of the S asteroids and modeled spectra of meteoritic components. Observed reflectance spectra of 40 S asteroids were fit with linear combinations of laboratory reflectance spectra of 6 representative primitive achondrites and an iron meteorite. Specular and diffuse reflection components were taken into account for metallic-iron reflectance. Even with this limited set of meteorite spectra, 16 of those 40 S asteroids were fit fairly well in terms of absorption-band features and spectral profiles. The number of well-fit S asteroids may be greater if the number and variety of metallic and stony domains are expanded. This initial result suggests that many of the S-asteroidal surfaces may be various kinds of regional mixtures of primitive achondrites and metallic iron. If true, the S asteroids could have been originally formed of chondrite-like source materials because mineral assemblages of primitive achondrites seem to have recrystallized from chondrites by segregation of metallic components and loss of partial melts. Copyright 1993, 1999 Academic Press

Two minor absorption bands in the visible range of the S-class asteroid reflectance spectra have been discovered. The CCD reflectance spectra of 10 S asteroids were deconvolved using the modified Gaussian model, and 9 of them are shown to have two minor absorption bands centered around 0.60 and 0.67 μm in wavelength. Among the tested common geologic minerals, the obtained absorption-band centers and widths of the S asteroids were most consistent with those of oxidized Fe–Ni metal and spinel-group minerals. These results are consistent with the idea that the S asteroids are made of stony-iron-like material and the recent identification of two spinel-bearing S asteroids based on the comparison of the 1- and 2-μm band strengths. Because both oxidized iron compounds and spinel-group minerals have spectral features very different from the S-asteroid ones in a wider wavelength region, they must be at most minor constituents in the S-asteroid surface regoliths.

Visible and near-infrared reflectance spectra (0.4-1.0 µm) of 21 Vesta-like asteroids and 12 HED meteorite powders (<25 µm in grain size) have been compared. Each reflectance spectrum was deconvolved into modified Gaussians and a constant background to allow comparisons of the 1-µm absorption band position and shape. The 1-µm band centers and widths of Vesta-like asteroids and HED meteorites generally overlap, but asteroids have a slightly wider range of band centers and widths indicating a wider range of Fe, Mg, and Ca content of their pyroxenes. Many of the Vesta-like asteroids, however, have shallower 1-µm absorption bands than HED meteorites. The weaker 1-µm band suggests that the surface regoliths of those asteroids may contain a larger amount of either fine grains or plagioclase than the laboratory-prepared HED meteorite powders. The most serious spectral difference between Vesta-like asteroids and HED meteorites is their visible absorption strength (reflectance drop-off shortward of ~0.7 µm) relative to the 1-µm band strength. Vesta-like asteroids tend to have stronger visible absorption than HED meteorites. The difference in the visible absorption strength may be due to some minor transition elements (Ti, Cr, etc.) in pyroxene, other unidentified mineral components, or space weathering processes. Copyright 1995, 1999 Academic Press

Abstract—Spectroscopic measurement and analysis of Martian meteorites provide important information about the mineralogy of Mars, as well as necessary ground‐truths for deconvolving remote sensing spectra of the Martian surface rocks. The spectroscopic properties of particulate ALH 84001 from 0.3 to 25 μm correctly identify low‐Ca pyroxene as the dominant mineralogy. Absorption bands due to electronic transitions of ferrous iron are observed at 0.94 and 1.97 μm that are typical for low‐Ca pyroxene. A strong, broad water band is observed near 3 μm that is characteristic of the water band typically associated with pyroxenes. Weaker features near 4.8, 5.2 and 6.2 μm are characteristic of particulate low‐Ca pyroxene and can be distinguished readily from the features due to high‐Ca pyroxene and other silicate minerals. The reflectance minimum occurs near 8.6 μm for the ALH 84001 powder, which is more consistent with high‐Ca pyroxene and augite than low‐Ca pyroxene. The dominant mid‐infrared (IR) spectral features for the ALH 84001 powder are observed near 9 and 19.5 μm; however, there are multiple features in this region. These mid‐IR features are generally characteristic of low‐Ca pyroxene but cannot be explained by low‐Ca pyroxene alone.

Abstract—Reflectance spectra of splits 92 and 271 from the Martian meteorite Allan Hills (ALH) 84001 are presented and analyzed in this paper. Although the visible and infrared spectra of both chips show that the dominant mineralogy is low‐Ca pyroxene, the focus here is on identification of the minor constituents. Infrared spectra measured at multiple spots along the surface of chips 92 and 271 show subtle spectroscopic variations due to changes in the low‐Ca pyroxene texture and composition and to the presence of secondary minerals. Absorption bands observed near 0.93 and 1.95 μm are characteristic of low‐Ca pyroxene. Strong mid‐infrared reststrahlen bands are observed near 9 and 19.5 μm in all surface spectra, and additional bands near 7, 10.5, 11.4, 17.8, 20.5 and 23 μm are variable depending on the low‐Ca pyroxene texture and the presence of secondary minerals. Selected spectra exhibit carbonate features near 4, 6.4–7.1 and 11.3 μm. Detailed analysis of these carbonate features indicates the presence of Mg‐Fe carbonate, which is consistent with petrographic studies. Many of these spectra with strong carbonate features exhibit a magnetite feature near 17.9 μm and a shoulder near 20.5 μm that cannot be uniquely ascribed to one mineral. Spectroscopic identification of the minor carbonate and magnetite minerals in this probable piece of Mars indicates that detection of small amounts of these minerals of possible biological significance will be possible using infrared hyperspectral analyses of the Martian surface. Also of importance for remote sensing on Mars is the result that Mg, Fe and Mg‐Fe carbonates in a low‐Ca pyroxene matrix should be distinguishable from one another in the spectral region measured by the thermal emmitance spectrometer (TES).

Crystal-field theory was applied to Fe2+ ions in three types of silicates in an attempt to assign all the major absorption bands with only one parameter to adjust. Coulomb potential energy field were calculated by Fourier method based on all the actual atomic coordinates refined by X-ray diffraction studies. Perturbed d-electron splitting energies of the central Fe2+ ion were calculated by introducing Configuration Interaction (CI) method for the lowest energy spectral states. All the major absorption bands observed in powdered bronzite, augite, and olivine, were assigned to the transitions between those calculated energy levels by optimizing only one parameter that expresses expansion or contraction of d-electron cloud. The result of the calculations gives almost the same assignments as the other previous works for bronzites, different assignments for augites, and a possibility of the existence of the fourth band hidden in the composite 1-µm band of olivines.

The isotropic Hfunctions defined in radiative transfer theory by Chandrasekhar (Radiative Transfer, Dover, New York, 1960) have been numerically recalculated for a larger number of single scattering albedo (w) values. The obtained Hfunctions should be accurate to five decimal places at least. The Hfunction values become highly nonlinear as wapproaches 1, where calculations were performed with many more points than in Chandrasekhar (1960). A simple linear interpolation of Chandrasekhar's Hfunction table could result in as much as 8% error in the Hfunction values and 16% in the H2values that appear in multiple scattering terms such as in Hapke (J. Geophys. Res.86, 3039-3054, 1981). On the other hand, Hapke's approximations (J. Geophys. Res.86, 3039-3054, 1981; Theory of Reflectance and Emittance Spectroscopy, Cambridge Univ. Press, New York, 1993) give Hvalues within 4.1% and 0.8% error, respectively.

Itokawa particles, which are samples recovered from the S-complex asteroid 25143 Itokawa by the Hayabusa spacecraft, demonstrate that S-complex asteroids are parent bodies of ordinary chondrite meteorites. Furthermore, they clarify that the space-weathering age of the Itokawa surface is of the order of several thousand years. Traditionally, Q-type asteroids have been considered fresh-surfaced. However, as the space-weathering timescale is approximately three orders of magnitude lesser than the conventionally considered age, the previously proposed formation mechanisms of Q-type asteroids cannot sufficiently explain the surface refreshening. In this study, we propose a new hypothesis on the surface state of Q-type asteroids: Q-type asteroids have a non-fresh weathered surface with a paucity of fine particles. For verifying this hypothesis, laboratory experiments on the space weathering of ordinary chondrites are performed. Based on the results of these experiments, we found that large (more than $100\, \mu \mathrm{m}$) ordinary chondritic particles with space weathering exhibit spectra consistent with Q-type asteroids.