Peplowski, Patrick - Abundances of H and major-elements on asteroid 433 Eros: Revisiting the in-situ measurements of the NEAR Gamma-Ray Spectrometer

Abstract: 
We have reanalyzed gamma-ray measurements taken on the surface of asteroid 433 Eros by the Near-Earth Asteroid Rendezvous (NEAR) spacecraft. This dataset represents the first in-situ measurements acquired from the surface of an asteroid, and it provides important insights into the composition of near-earth asteroids. Our reanalysis, which utilizes improved knowledge of the detector response and gamma-ray production physics, has allowed us to link the composition of Eros to the LL-chondrites. Additionally, comparisons of Fe gamma rays from neutron inelastic scatter and neutron capture reactions provide constrains on the hydrogen content of the regolith. Our H abundance value of 0 to 300 ppm represents the first in-situ measurement of the hydrogen content of an asteroid. This value is lower than the average H content for LL-chondrite meteorites, both finds and observed falls, and suggests that hydrogen may be depleted in near-surface materials on Eros. This is consistent with observations of the depletion of the moderately volatile element S by the NEAR X-Ray Spectrometer. Depletion of volatile elements on asteroids has implications for human exploration and resource utilization of near-earth asteroids.