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Observations of Lucy’s Trojan Targets with JWST MIRI

Presentation #107.04 in the session Asteroids: Future Mission Targets (Oral Presentation)

Published onOct 23, 2023
Observations of Lucy’s Trojan Targets with JWST MIRI

Jupiter Trojan asteroids (hereafter, Trojans) are a key small body population found in Jupiter’s L4 and L5 Lagrange points and are dynamically stable over the lifetime of the Solar System. These primitive asteroids link together formation theories and dynamical models that explain how our Solar System formed. Trojans share important characteristics with the dynamically excited Kuiper Belt populations and Neptunian Trojans. As such, Trojans may be one of the most accessible examples of the planetesimals that populated the outer protoplanetary disk. Mid-Infrared (MIR; 5-35 µm) spectral analysis of fourteen Trojans indicates their regoliths are dominated by fine-particulate amorphous and crystalline silicates, and is consistent with outer solar system formation theories. However, the low albedos and generally featureless global near infrared (NIR; 0.7 – 2.5 µm) spectra leave these objects mysterious still. Furthermore, the number of Trojans observed in the MIR remains extremely low compared to NIR observations. The Lucy mission, which launched in October of 2022, will be the first to explore the Trojan asteroids. Over the next ten years, Lucy will perform flybys of (3548) Eurybates, (15094) Polymele, (11351) Leucus, (21900) Orus, and (617) Patroclus and its binary Menoetius. MIR observations of the Lucy targets in concert with the Lucy mission will illuminate the Trojan’s dynamic history and current mineralogy. Leucus, Orus, Eurybates, Polymele, and Patroclus were observed by the James Webb Space Telescope (JWST) with Mid-Infrared Instrument (MIRI) in Medium Resolution spectroscopy (MRS) mode as part of the Cycle 1 GO program 2574 (PI M. Brown) on Nov. 15th, 2022 (10:31 – 11:52 UT), Feb. 23rd, 2023 (8:50-10:32 UT), March 21st, 2023 (17:26 – 18:43 UT), March 30th, 2023 (17:01 – 22:28 UT), and July 1st, 2023 (8:49-10:54 UT) respectively. MIRI MRS observations cover the ~5 – 27.9 spectral range, which will not be acquired by instruments on the Lucy spacecraft. We will present MIR spectra of Eurybates, Polymele, Leucus, Orus, and Patroclus and the results of our Near-Earth Asteroid Thermal Model (NEATM). Additionally, we compare JWST spectra of Eurybates and Patroclus to previously observed MIR spectra taken with the Spitzer Space Telescope. We will derive silicate mineralogy and compare their compositions to other dynamically linked small body populations (e.g., Neptune Trojans).

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