Abstract— Using new techniques to examine the products of space weathering of lunar soils, we demonstrate that nanophase reduced iron (npFe0) is produced on the surface of grains by a combination of vapor deposition and irradiation effects. The optical properties of soils (both measured and modeled) are shown to be highly dependent on the cumulative amount of npFe0, which varies with different starting materials and the energetics of different parts of the solar system. The measured properties of intermediate albedo asteroids, the abundant S‐type asteroids in particular, are shown to directly mimic the effects predicted for small amounts of npFe0 on grains of an ordinary chondrite regolith. This measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids.

The search for water on the surface of the anhydrous Moon had remained an unfulfilled quest for 40 years. However, the Moon Mineralogy Mapper (M3) on Chandrayaan-1 has recently detected absorption features near 2.8 to 3.0 micrometers on the surface of the Moon. For silicate bodies, such features are typically attributed to hydroxyl- and/or water-bearing materials. On the Moon, the feature is seen as a widely distributed absorption that appears strongest at cooler high latitudes and at several fresh feldspathic craters. The general lack of correlation of this feature in sunlit M3 data with neutron spectrometer hydrogen abundance data suggests that the formation and retention of hydroxyl and water are ongoing surficial processes. Hydroxyl/water production processes may feed polar cold traps and make the lunar regolith a candidate source of volatiles for human exploration.

Abstract-Understanding the fundamental crystal chemical controls on visible and near-infrared reflectance spectra of pyroxenes is critical to quantitatively assessing the mineral chemistry of pyroxenes viewed by remote sensing. This study focuses on the analysis of spectroscopic measurements of a comprehensive set of synthetic Mg-Fe pyroxenes from the visible through the near-infrared (0.3-2.6 µm) to address the constraints of crystal structure and Fe 2+ content on spinforbidden and spin-allowed crystal field absorptions in Ca-free orthopyroxenes. The chemistry and oxidation state of the synthetic pyroxenes are characterized. Coordinated Mössbauer spectroscopy is used to determine site occupancy of Fe 2+ in the M1 and M2 crystallographic sites. Properties of visible and near-infrared absorption bands of the synthetic pyroxenes are quantified using the modified Gaussian model. The 1 and 2 µm spin-allowed crystal field absorption bands move regularly with increasing iron content, defining a much tighter trend than observed previously. A spin-allowed crystal field absorption band at 1.2 µm is explicitly verified, even at low total iron contents, indicating that some portion of Fe 2+ resides in the M1 site. The 1.2 µm band intensifies and shifts to longer wavelengths with increasing iron content. At visible wavelengths, spin-forbidden crystal field absorptions are observed in all iron-bearing samples. The most prominent absorption near 506 nm, attributed to iron in the M2 site, shifts to slightly longer wavelengths with iron content. The purity and extent of this pyroxene series allows visible wavelength absorption bands to be directly assigned to specific transitions of Fe 2+ in the M1 and M2 sites.

Studies of the dwarf planet (1) Ceres using ground-based and orbiting telescopes have concluded that its closest meteoritic analogues are the volatile-rich CI and CM carbonaceous chondrites. Water in clay minerals, ammoniated phyllosilicates, or a mixture of Mg(OH)2 (brucite), Mg2CO3 and iron-rich serpentine have all been proposed to exist on the surface. In particular, brucite has been suggested from analysis of the mid-infrared spectrum of Ceres. But the lack of spectral data across telluric absorption bands in the wavelength region 2.5 to 2.9 micrometres--where the OH stretching vibration and the H2O bending overtone are found--has precluded definitive identifications. In addition, water vapour around Ceres has recently been reported, possibly originating from localized sources. Here we report spectra of Ceres from 0.4 to 5 micrometres acquired at distances from ~82,000 to 4,300 kilometres from the surface. Our measurements indicate widespread ammoniated phyllosilicates across the surface, but no detectable water ice. Ammonia, accreted either as organic matter or as ice, may have reacted with phyllosilicates on Ceres during differentiation. This suggests that material from the outer Solar System was incorporated into Ceres, either during its formation at great heliocentric distance or by incorporation of material transported into the main asteroid belt.

Abstract-The central peaks of 109 impact craters across the Moon are examined with Clementine ultraviolet-visible (UVVIS) camera multispectral data. The craters range in diameter from 40 to 180 km and are believed to have exhumed material from 5-30 km beneath the surface to form the peaks, including both upper and lower crustal rocks depending on whether craters have impacted into highlands or basins. Representative five-color spectra from spectrally and spatially distinct areas within the peaks are classified using spectral parameters, including "key ratio" (which is related to mafic mineral abundance) and "spectral curvature" (linked to absorption band shape, which distinguishes between low-and high-Ca pyroxene and olivine). The spectral parameters are correlated to mineralogical abundances, related in turn to highland plutonic rock compositions. The derived rock compositions for the various central peaks are presented in a global map. From these results, it is evident that the lunar crust is compositionally diverse, both globally and at local 100 m scales found within individual sets of central peaks. Although the central peaks compositions imply a crust that is generally consistent with previous models of crustal structure, they also indicate a more anorthositic crust than generally assumed, with a bulk plagioclase content of -8 1%, evolving from "pure" anorthosite near the surface towards more mafic, low-Ca pyroxene-rich compositions with depth (comparable to anorthositic norite). Evidence for mafic plutons occurs in both highlands and basins and represent all mafic highland rock types. However, the lower crust is more compositionally diverse than the highlands, with both a greater range of rock types and more diversity within individual sets of central peaks.

Vesta's surface is characterized by abundant impact craters, some with preserved ejecta blankets, large troughs extending around the equatorial region, enigmatic dark material, and widespread mass wasting, but as yet an absence of volcanic features. Abundant steep slopes indicate that impact-generated surface regolith is underlain by bedrock. Dawn observations confirm the large impact basin (Rheasilvia) at Vesta's south pole and reveal evidence for an earlier, underlying large basin (Veneneia). Vesta's geology displays morphological features characteristic of the Moon and terrestrial planets as well as those of other asteroids, underscoring Vesta's unique role as a transitional solar system body.

Although visible and near‐infrared reflectance spectra contain absorption bands that are characteristic of the composition and structure of the absorbing species, deconvolving a complex spectrum is nontrivial. An improved approach to spectral deconvolution is presented here that accurately represents absorption bands as discrete mathematical distributions and resolves composite absorption features into individual absorptions bands. The frequently used Gaussian model of absorption bands is first evaluated and shown to be inappropriate for the Fe2+ electronic transition absorptions in pyroxene spectra. Subsequently, a modified Gaussian model is derived using a power law relationship of energy to average bond length. This modified Gaussian model successfully depicts the characteristic 0.9‐um absorption feature in orthopyroxene spectra using a single distribution. The modified Gaussian model is also shown to provide an objective and consistent tool for deconvolving individual absorption bands in the more complex orthopyroxene, clinopyroxene, pyroxene mixtures, and olivine spectra. The ability of this new modified Gaussian model to describe the Fe2+ electronic transition absorption bands in both pyroxene and olivine spectra strongly suggests that it be the method of choice for analyzing all electronic transition bands.

Abstract. Reflectance spectra of olivines spanning the forsterite-fayalite solid-solution series have been analyzed with the modified Gaussian model (MGM). The compositional variability of the three primary absorption bands that constitute the diagnostic 1.0-gm olivine feature has been quantified by examining the centers, widths, and relative strengths in 18 spectra ranging in composition from Mg-rich forsterite to Fe-rich fayalite. These analyses have also revealed several interrelationships among the three absorption bands that prpvide new insights into their crystallographic origins. The primary olivine absorptions near 1.0-gin are well behaved and provide a means to remotely identify and estimate the composition of olivine from reflectance spectra. However, the spectral resolution and signal-to-noise of current remotely acquired data, combined with the significant overlap in the 1.0-gm region, provide enough uncertainty to allow models based on simple least squares minimization to reach solutions that are mathematically satisfying yet physically unrealistic. More sophisticated models using inverse theory that incorporate constraints among the absorption bands as determined from these laboratory MGM analysis are shown to yield meaningful results which can be confidently used to estimate composition in remote data. The MGM and inverse theory are used to analyze the spectrum of the olivine-rich asteroid 246 Asporina and to quantitatively show that the olivine component on Asporina is magnesium-rich (i.e., forsteritic). In contrast to the systematic behavior of the three primary olivine absorptions, absorption features short of 0.7 gm are found to exhibit no obvious relationship to composition and as such are not recommended for use in remote applications.