COMPOSITIONAL MAPPING WITH THE NEAR X-RAY GAMMA-RAY SPECTROMETER

The X ray/gamma ray spectrometer (XGRS) instrument on board the Near E arth Asteroid Rendezvous (NEAR) spacecraft will map asteroid 433 Eros in the 0.7 keV to 10 MeV energy region, Measurements of the discrete l ine X ray and gamma ray emissions in this energy domain dan be used to obtain both qualitative and quantitative elemental compositions with sufficient accuracy enable comparison to the major meteorite types. It is believed that Eros is an S-type asteroid, the most common of the n ear-Earth asteroids, The determination of whether Eros consists of eit her differentiated or undifferentiated materials is an important objec tive of this mission. Observations bf Eros during the NEAR mission wil l contribute significantly to our understanding of the Structure and c omposition of this asteroid. The NEAR spacecraft was successfully. lau nched on February 17, 1996. The NEAR XGRS was turned on during the wee k of April 7, 1996, and all detector systems operated nominally. Backg round spectra have been obtained.