Planetary Neutron Spectroscopy for Metal-rich Compositions: Development
of Analysis Framework for Measurements at the Asteroid (16) Psyche
Abstract
Neutron spectroscopy has become a standard technique for remotely
measuring planetary surface compositions from orbital spacecraft around
various planets. Measurements have successfully been carried out at the
Moon, Mars, Mercury, and the asteroids Vesta and Ceres. The NASA Psyche
mission is planning to make neutron measurements to characterize the
composition of the M-class asteroid (16) Psyche. Earth-based remote
sensing measurements allow for a wide range of Fe concentrations,
ranging from ~25 wt.% to 90 wt.%, and geochemically
plausible Ni concentrations range from 0 wt.% to 10 wt.% or higher. To
prepare for the analysis of Psyche neutron data, we have developed a new
principal component analysis framework using four neutron energy ranges
of thermal, low-energy epithermal, high-energy epithermal, and fast
neutrons. With this analysis framework, we have demonstrated that the
neutron measurements can uniquely distinguish variations of
metal-to-silicate fraction, Ni, and hydrogen compositions. The strongest
principal component is that of metal-to-silicate; the second strongest
is Ni variations; the third is hydrogen variations. The validity of this
framework can be first tested during a Mars gravity assist prior to
arrival at Psyche.