The Heterogeneous Surface of Asteroid (16) Psyche

Abstract

Main‐belt asteroid (16) Psyche is the largest M‐type asteroid, a class of object classically thought to be the metal cores of differentiated planetesimals and the parent bodies of the iron meteorites. de Kleer, Cambioni, and Shepard (2021, https://doi.org/10.3847/psj/ac01ec) presented new data from the Atacama Large Millimeter Array (ALMA), from which they derived a global best‐fit thermal inertia and dielectric constant for Psyche, proxies for regolith particle size, porosity, and/or metal content, and observed thermal anomalies that could not be explained by surface albedo variations only. Motivated by this, here we fit a model to the same ALMA data set that allows dielectric constant and thermal inertia to vary across the surface. We find that Psyche has a heterogeneous surface in both dielectric constant and thermal inertia but, intriguingly, we do not observe a direct correlation between these two properties over the surface. We explain the heterogeneity in dielectric constant as being due to variations in the relative abundance of metal and silicates. Furthermore, we observe that the lowlands of a large depression in Psyche's shape have distinctly lower thermal inertia than the surrounding highlands. We propose that the latter could be explained by a thin mantle of fine regolith, fractured bedrock, and/or implanted silicate‐rich materials covering an otherwise metal‐rich surface. All these scenarios are indicative of a collisionally evolved world.

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

“…Since NASA's selection of the Psyche mission in early 2017, there has been renewed interest in visible to near‐infrared (VNIR) spectroscopic study and interpretation of the asteroid's surface mineralogy (e.g., Becker et al., 2020 ; Cantillo et al., 2021 ; Dibb et al., 2022 ; Sanchez et al., 2017 ; Takir et al., 2017 ). In addition to spectroscopic observations, density estimates and measurements of both radar reflectivity and thermal inertia of Psyche are consistent with the presence of core‐like materials, such as iron meteorites and sulfide minerals like troilite (FeS) (Cambioni et al., 2022 ; de Kleer et al., 2021 ; Elkins‐Tanton et al., 2020 ; Landsman et al., 2018 ; Matter et al., 2013 ; Shepard et al., 2021 ; Siltala & Granvik, 2021 ).…”

“…( 2017 ), our chi‐square results suggest that there could be significant compositional variation on the surface of the asteroid. This is further supported by variations in radar reflectivity and millimeter emissivity (e.g., Cambioni et al., 2022 ; de Kleer et al., 2021 ; Shepard et al., 2021 ) that are correlated with changes in optical albedo, consistent with potential variation in the metal‐silicate ratio across the surface of the asteroid.…”

Cold Compaction and Macro‐Porosity Removal in Rubble‐Pile Asteroids: 2. Applications

“…Therefore, our model does not support the hypothesis that Psyche is a homogeneous body of CB chondrite‐like material. That the entire asteroid is composed of a single type of material (such as CB chondrite) is also inconsistent with the finding of regional variations in metal content on the surface of Psyche (Cambioni et al., 2022; Shepard et al., 2021).…”

The Geologic Impact of 16 Psyche’s Surface Temperatures

“…All of these studies used a combination of telescopic observations (either infrared or radio) and thermal modeling. With their 1σ uncertainties, their preferred estimates are 123 ± 50 (Matter et al 2013), 15 ± 10 (Landsman et al 2018, and 280 ± 100 tiu (de Cambioni et al 2022). Of these preferred estimates, only Matter et al (2013) and de slightly overlap at 1σ, although Landsman et al (2018) also presented some retrievals that yield estimates of ∼100-200 tiu.…”