Visible to Near-Infrared Reflectance Spectroscopy of Asteroid (16) Psyche: Implications for the Psyche Mission's Science Investigations

The NASA Psyche mission will explore the structure, composition, and other properties of asteroid (16) Psyche to test hypotheses about its formation. Variations in radar reflectivity, density, thermal inertia, and visible to near-infrared (VNIR) reflectance spectra of Psyche suggest a highly metallic composition with mafic silicate minerals (e.g., pyroxene) heterogeneously distributed on the surface in low abundance (<10 vol.%). The Psyche spacecraft's Multispectral Imager is designed to map >= 80% of the surface at high spatial resolution (<= 20 m/pixel) through a panchromatic filter and provide compositional information for about >= 80% of the surface using seven narrowband filters at VNIR wavelengths (similar to 400-1,100 nm) and at spatial scales of <= 500 m/pixel. We analyzed 359 reflectance spectra from samples consistent with current uncertainties in Psyche's composition and compared them to published reflectance spectra of the asteroid using a chi-square test for goodness of fit. The best matches for Psyche include iron meteorite powder, powders from the sulfide minerals troilite and pentlandite, and powder from the CH/CBb chondrite Isheyevo. Comparison of absorption features support the interpretation that Psyche's surface is a metal-silicate mixture, although the exact abundance and chemistry of the silicate component remains poorly constrained. We convolve our spectra to the Imager's spectral throughput to demonstrate preliminary strategies for mapping the surface composition of the asteroid using filter ratios and reconstructed band parameters. Our results provide predictions of the kinds of surface compositional information that the Psyche mission could reveal on the solar system's largest M-type asteroid. Plain Language Summary Current observations of the asteroid (16) Psyche suggest it to be metal-rich, but not entirely made of metal. We compared reflected light from a wide variety of Psyche-relevant materials to measurements of reflected light from the asteroid. This analysis confirms that Psyche's composition could be less metal-rich than previously thought. Other materials with reflectance properties similar to Psyche are metal-rich carbonaceous chondrites and sulfide minerals. We show how an instrument on the Psyche spacecraft, which will study the asteroid in detail, can resolve some uncertainties about the surface composition of the asteroid.