Compositional mapping with the NEAR X ray/gamma ray spectrometer

Abstract

The X ray/gamma ray spectrometer (XGRS) instrument on board the Near Earth Asteroid Rendezvous (NEAR) spacecraft will map asteroid 433 Eros in the 0.7 keV to 10 MeV energy region. Measurements of the discrete line X ray and gamma ray emissions in this energy domain can be used to obtain both qualitative and quantitative elemental compositions with sufficient accuracy to enable comparison to the major meteorite typies. It is believed that Eros is an S‐type asteroid, the most common of the near‐Earth asteroids. The determination of whether Eros consists of either differentiated or undifferentiated materials is an important objective of this mission. Observations of Eros during the NEAR mission will contribute significantly to our understanding of the structure and composition of this asteroid. The NEAR spacecraft was successfully launched on February 17, 1996. The NEAR XGRS was turned on during the week of April 7, 1996, and all detector systems operated nominally. Background spectra have been obtained.