Elemental compositional from gamma-ray spectroscopy of the NEAR-shoemaker landing site on 433 Eros

Abstract

Elemental composition and composition ratios derived from gamma-ray measurements collected by the NEAR-Shoemaker spacecraft while on the surface of 433 Eros are reported. Performance of the gamma-ray spectrometer (GRS) during cruise and orbit is reviewed. The best gamma-ray data were collected on the surface of Eros after the spacecraft's controlled descent on 2001 February 12. Methods used in spectral analysis, to convert peak areas to incident photons, and photons to elemental composition are described in some detail. The elemental abundance of K and the Mg/Si, Fe/Si, Si/O and Fe/O abundance ratios were determined. The Mg/Si and Si/O ratios and the K abundance are roughly chondritic, but the Fe/Si and Fe/O ratios are low compared to expected chondritic values. Three possible explanations for the apparent Fe depletion are considered.