Ultraviolet Spectroscopy of Lucy Mission Targets with the Hubble Space Telescope

TL;DR

This study uses Hubble Space Telescope ultraviolet spectroscopy to analyze Lucy mission targets, revealing a spectral feature likely caused by fine-grained opaques on Trojan asteroid surfaces, advancing understanding of their composition.

Contribution

First near-ultraviolet spectra of Lucy mission targets analyzed, identifying spectral features explained by submicroscopic grains, and developing a Hapke model for surface composition insights.

Findings

Detected a UV reflectance minimum at 0.4 μm in Patroclus and Orus.

Spectral features explained by scattering from fine-grained opaques (20-80 nm).

Developed a Hapke optical model to interpret surface composition.

Abstract

The recently launched Lucy mission aims to understand the dynamical history of the Solar System by examining the Jupiter Trojans, a population of primitive asteroids co-orbital with Jupiter. Using the G280 grism on the Hubble Space Telescope's Wide Field Camera 3 we obtained near ultraviolet spectra of four of the five Lucy mission targets -- (617) Patroclus-Menoetius, (11351) Leucus, (3548) Eurybates, and (21900) Orus -- to search for novel spectral features. We observe a local reflectance minimum at 0.4 $\mu$m accompanied by an increase in reflectance from 0.35-0.3 $\mu$m in the spectra of Patroclus and Orus. We use the principles of Rayleigh scattering and geometric optics to develop a Hapke optical model to investigate whether this feature can be explained by the presence of submicroscopic grains on Trojan surfaces. The near ultraviolet "bump" feature can be explained by scattering due to fine-grained opaques (iron, amorphous carbon, or graphite) with grain sizes ranging from 20 - 80 nm.