Constraining the Regolith Composition of Asteroid (16) Psyche via Laboratory Near-infrared Spectroscopy

TL;DR

This study uses laboratory near-infrared spectroscopy to analyze asteroid Psyche's surface composition, revealing it is less metallic and contains significant exogenic carbonaceous material, informing its formation and surface properties.

Contribution

First laboratory spectral analysis constrains Psyche's surface composition, indicating lower metallicity and presence of exogenic material, refining previous estimates.

Findings

Psyche's surface is approximately 82.5% metal, 7% low-Fe pyroxene, and 10.5% carbonaceous chondrite.

The asteroid's metallic content is less than previously thought (~94%).

Estimated surface porosity is around 35% based on spectral and density data.

Abstract

(16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Discovery-class Psyche mission. Despite gaining considerable interest in the scientific community, Psyche's composition and formation remain unconstrained. Originally, Psyche was considered to be almost entirely composed of metal due to its high radar albedo and spectral similarities to iron meteorites. More recent telescopic observations suggest the additional presence of low-Fe pyroxene and exogenic carbonaceous chondrites on the asteroid's surface. To better understand the abundances of these additional materials, we investigated visible near-infrared (0.35 - 2.5 micron) spectral properties of three-component laboratory mixtures of metal, low-Fe pyroxene, and carbonaceous chondrite. We compared the band depths and spectral slopes of these mixtures to the telescopic spectrum of (16) Psyche to constrain material abundances. We find that the best matching mixture to Psyche consists of 82.5% metal, 7% low-Fe pyroxene, and 10.5% carbonaceous by weight, suggesting that the asteroid is less metallic than originally estimated (~94%). The relatively high abundance of carbonaceous chondrite material estimated from our laboratory experiments implies the delivery of this exogenic material through low velocity collisions to Psyche's surface. Assuming that Psyche's surface is representative of its bulk material content, our results suggest a porosity of 35% to match recent density estimates.