Near MSI and NIS: High-Resolution Orbital Imaging and Spectroscopy of the Asteroid 433 Eros

The Near Earth Asteroid Rendezvous (NEAR) spacecraft is scheduled for launch towards the asteroid 433 Eros (13x15x36 km) on February 14, 1996. This spacecraft will be equipped with 5 science instruments; Magnetometer (MAG), Multi-Spectral Imager (MSI), Near-Infrared Spectrograph (NIS), NEAR Laser Ranging (NLR), and X-Ray Gamma Ray Spectrometer (XGRS). This robust complement of instruments will allow for the first ever orbital investigation of an asteroid. Eros is a member of the most populous spectral type of asteroid, the S-Type. The S-Type asteroid class has been proposed to be the parent body for the ordinary chondrite meteorites (OCs) simply on the basis of sampling statistics; the S-Types are the most numerous asteroids, thus the most numerous meteorite class, the OCs, should represent the S-Type parent body. However, finding a spectral match between the two has proven to be difficult at best. Thus, the link between meteorites and asteroids has received a tremendous amount of research with little definitive connection between the largest class of meteorites and asteroids. The NEAR mission to Eros should provide the data necessary to determine if any link truly exists between OCs and S-Type asteroids. This poster will describe the MSI and NIS instruments and their scientific goals at Eros. The MSI consists of a 5 element refracting telescope with a Si CCD array sensitive from 400 1100 nm. The NIS is a scanning imaging spectrometer covering the wavelength range 800-2600 nm with two detectors, Ge and InGaAs each with 32 elements. During the initial encounter with Eros the MSI and NIS will view the asteroid with phase angles ranging from 60 degrees to 90 degrees. The ensuing close approach flyby will allow NIS and MSI measurements at or near 0 degrees phase, with a spatial resolution of about 5 km for NIS and 75 m for MSI. After initial encounter and a series of phasing maneuvers, NEAR will be placed in a mapping orbit about Eros from which global high resolution data will be acquired (MIS about 5 m/pixel and NIS about 350 m/pixel). These data will be used to address fundamental questions concerning the geology of Eros, some examples; 1) measure the size, shape, and volume (and hence density), 2) observe surface morphology down to a scale of about 5 m/pixel, 3) high resolution global color (400 nm to 1050 nm) and moderate resolution spectral (800 nm to 2600 nm) mapping to investigate the distribution of rock types on the surface, 5) the collisional and fragmentation history of small asteroids, and 6) the nature of space weathering on asteroidal surfaces. Combining the topography (MSI), high resolution color (MSI) and intermediate resolution spectra (NIS) along with data from the other instruments, the geologic history of Eros will be investigated in unprecedented detail allowing for a greater understanding of the processes that have shaped the evolution of small S-Type asteroids.