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L.A. McFadden, D.D. Wellnitz (U. Maryland), J.F. Bell III, P. Martin, B.E. Clark, A. Harch, M. Bell, P. Thomas, J. Veverka (Cornell U.), N. Izenberg, J. Warren, S. Murchie (JHU/APL), C.R. Chapman (SWRI), P.G. Lucey (U. Hawaii)
The Near Earth Asteroid Rendezvous (NEAR) mission has a complement of six instruments designed to investigate the chemical and physical properties of 433 Eros. These instruments will conduct synergistic experiments designed to meet the mission's scientific objectives to further our understanding of the role of asteroids in the formation of the solar system. The Near Infrared Spectrometer (NIS) measures the reflected sunlight from Eros between 800 and 2500 nm where the minerals olivine, pyroxene, spinel and hydrated silicates have diagnostic absorption features. Ground-based spectra of Eros indicate the presence of olivine and pyroxene in different proportions on different hemispheres of the asteroid. With NEAR NIS spectra, we anticipate having the ability to discern this compositional heterogeneity and to map it on the surface. We will report on efforts to characterize the absorption bands and continuum using pre-flight measurements of laboratory samples acquired with this instrument. We will discuss constraints on mineral composition as well as the results of an interpretation contest held at the 1999 ACM meeting in July. To date, we have performed in-flight calibrations during cruise to characterize the instrument's sensitivity and responsivity. We will enter the orbital phase of the mission with a good understanding of the instrument's performance and capabilities. On February 14, 2000, NEAR will conduct a close approach flyby of Eros at 175 km at which time NIS will perform a low phase angle global mapping of the asteroid's northern hemisphere at 1-2 km resolution. NIS observations will continue to be made at each stage of the mission as the orbital radius is lowered to as low as 35 km. Operations will involve close collaboration with the MSI and XGRS investigations in order to generate combined mission data sets of high spatial resolution morphology, moderate spatial resolution mineralogy, and low spatial resolution elemental chemistry maps.
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