Comparative Mid-Infrared Spectroscopy of Dark, Primitive Asteroids: Does Shared Taxonomic Class Indicate Shared Silicate Composition?

TL;DR

This study compares mid-infrared spectra of primitive asteroids in the Main Belt and Jupiter Trojans to assess if their visible and near-infrared similarities reflect true compositional likeness, revealing both commonalities and diversity in silicate compositions.

Contribution

It provides the first mid-infrared spectral comparison of Main Belt and Trojan primitive asteroids, highlighting compositional differences and similarities.

Findings

Many Main Belt asteroids resemble Trojans with olivine-rich silicates.

(368) Haidea shows a distinct lack of olivine in MIR spectrum.

Diversity in silicate compositions suggests varied origins.

Abstract

Primitive asteroids with low albedos and red slopes in the visible and near infrared (VNIR) are found in both the Main Belt and the Jupiter Trojan clouds. In order to determine whether the VNIR spectral similarities of primitive Main Belt asteroids and Jupiter Trojans are reflective of a true compositional similarity, we compare the mid-infrared silicate emission features of Main Belt and Jupiter Trojan asteroids. Using archival data from the Spitzer Space Telescope's IRS spectrograph and observations from the Stratospheric Observatory for Infrared Astronomy's (SOFIA) FORCAST instrument, we analyze the 5-40 micron spectra of thirteen primitive Main Belt asteroids and compare them to those of Jupiter Trojans in the literature. We find that while many primitive asteroids in the Main Belt resemble their Trojan counterparts with strong spectral signatures of olivine-rich high-porosity silicate regoliths, we identify (368) Haidea as a spectrally distinctive asteroid that lacks strong evidence of olivine in its MIR spectrum. Differences in silicate compositions among D-type asteroids imply a diversity of origins for primitive asteroids.