On 25 October 2000, the Near Earth Asteroid Rendevous (NEAR)-Shoemaker spacecraft executed a low-altitude flyover of asteroid 433 Eros, making it possible to image the surface at a resolution of about 1 meter per pixel. The images reveal an evolved surface distinguished by an abundance of ejecta blocks, a dearth of small craters, and smooth material infilling some topographic lows. The subdued appearance of craters of different diameters and the variety of blocks and different degrees of their burial suggest that ejecta from several impact events blanketed the region imaged at closest approach and led to the building up of a substantial and complex regolith consisting of fine materials and abundant meter-sized blocks.

A positive identification of the minerals olivine, plagioclase, and several types of pyroxenes were made at several locations on the lunar surface by using remote measurements. For example, the crater Aristarchus is found to have an average pyroxene composition of augite, and plagioclase is obviously present. A dark mantle deposit in the crater J. Herschel is at least partly composed of a mixture of 70% olivine and 30% pyroxene. These determinations were possible because the reflectance spectra for 10–20 km diameter lunar areas have been measured for the first time in the IR spectral region (0.65–2.5 μm) with sufficient spectral resolution and photometric precision to define mineral electronic absorption bands. The reflectance for all lunar regions observed (over 100 to present) continues to increase toward longer wavelengths to at least 2.5 μm, and several mineral absorption bands appear. The telescopic spectra are of similar quality and contain features similar to laboratory spectra of lunar samples. The absorption features in several spectra have been quantitatively analyzed using newly developed computer processing techniques, including thermal flux removal and absorption band fitting, to produce these mineral identifications. Detection and quantitative analysis of these absorptions provide a much improved basis for remotely determining and mapping surface mineralogy quantitatively from the ground or using airborne or spacecraft platforms.

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Abstract-The near-Earth asteroid rendezvous (NEAR) mission carried x-ray/gamma-ray spectrometers and multi-spectral imagerhear-infrared spectrometer instrument packages which gave complementary information on the chemistry and mineralogy, respectively, of the target asteroid 433 Eros. Synthesis of these two data sets provides information not available from either alone, including the abundance of non-mafic silicates, metal and sulfide minerals. We have utilized four techniques to synthesize these data sets. Venn diagrams, which examine overlapping features in two data sets, suggest that the best match for 433 Eros is an ordinary chondrite, altered at the surface of the asteroid, or perhaps a primitive achondrite derived from material mineralogically similar to these chondrites. Normalized element distributions preclude FeO-rich pyroxenes and suggest that the x-ray and gammaray data can be reconciled with a common silicate mineralogy by inclusion of varying amounts of metal. Normative mineralogy cannot be applied to these data sets owing to uncertainties in oxygen abundance and lack of any constraints on the abundance of sodium. Matrix inversion for simultaneous solution of mineral abundances yields reasonable results for the x-ray-derived bulk composition, but seems to confirm the inconsistency between mineral compositions and orthopyroxene/clinopyroxene ratios. A unique solution does not seem possible in synthesizing these multiple data sets. Future missions including a lander to fully characterize regolith distribution and sample return would resolve the types of problems faced in synthesizing the NEAR data. INTRODUCTIONThe near-Earth asteroid rendezvous (NEAR)-Shoemaker mission spent almost a year in orbit around the asteroid 433 Eros, studying its mineralogy, surface chemistry, surface geology, surface topography, and gravitational and magnetic fields. This is the first time that such a diverse suite of data has been collected simultaneously from an asteroid by a spacecraft. 433 Eros is a particularly worthy target for this study, since ground-based spectral studies (Murchie and Pieters, 1996) indicate that it is a member of the S( IV) spectral class of Gaffey et al. (1993). Debate has raged for nearly 20 years about the relationship between S asteroids and ordinary chondrites (Wetherill and Chapman, 1988), the most abundant types of asteroids in the inner belt and meteorites observed to fall to Earth, respectively, and NEAR may allow solution of this conundrum, if only in this one specific case. While each data set can be interpreted individually, as evidenced by the series ofpapers Prelude prcprint MS#4616