A Near-Infrared Search for Silicates in Jovian Trojan Asteroids

TL;DR

This study used near-infrared spectroscopy to investigate silicate features in Jovian Trojan asteroids, finding mostly featureless spectra and suggesting compositions that include iron-poor silicates and possible aqueous alteration.

Contribution

It provides new near-infrared spectral data for Jovian Trojans, revealing the absence of silicate absorption features and proposing compositional insights.

Findings

All seven Trojans studied are featureless in near-infrared spectra.

The absence of the 1 micron silicate feature suggests iron-poor silicates.

Eurybates spectrum resembles CM2 carbonaceous chondrite, indicating aqueous alteration.

Abstract

We obtained near-infrared (0.8 - 2.5 micron) spectra of seven Jovian Trojan asteroids that have been formerly reported to show silicate-like absorption features near 1 micron. Our sample includes the Trojan (1172) Aneas, which is one of three Trojans known to possess a comet-like 10 micron emission feature, indicative of fine-grained silicates. Our observations show that all seven Trojans appear featureless in high signal-to-noise ratio spectra. The simultaneous absence of the 1 micron band and presence of the 10 micron emission can be understood if the silicates on (1172) Aneas are iron-poor. In addition, we present near infrared observations of five optically grey Trojans, including three objects from the collisionally produced Eurybates family. The five grey Trojans appear featureless in the near infrared with no diagnostic absorption features. The near infrared spectrum of Eurybates can be best fitted with the spectrum of a CM2 carbonaceous chondrite, which hints that the C-type Eurybates family members may have experienced aqueous alteration.