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Arxiv: JWST near-infrared spectroscopy of the Lucy Jupiter Trojan flyby targets: Evidence for OH absorption, aliphatic organics, and CO_{2} Published: 11/20/2023 6:30:12 AM Updated: 11/20/2023 6:30:12 AM

Paper abstract: We present JWST/NIRSpec observations of the five Jupiter Trojans that will bevisited by the Lucy spacecraft -- the Patroclus--Menoetius binary, Eurybates,Orus, Leucus, and Polymele. The measured 1.7-5.3 \mum reflectance spectragreatly supersede previous ground-based spectroscopy in spectral resolution,signal-to-noise ratio, and wavelength coverage and reveal several distinctabsorption features. We robustly detect a broad OH band centered at 3 \mumthat is most prominent on the less-red objects Eurybates, Patroclus-Menoetius,and Polymele. An additional absorption at 3.3-3.6 \mum, indicative ofaliphatic organics, is systematically deeper on the red objects Orus andLeucus. The collisional fragment Eurybates is unique in displaying anabsorption band at 4.25 \mum that we attribute to bound or trapped CO_2(e.g., clathrates). Comparisons with other solar system small bodies revealbroad similarities in the 2.7-3.6 \mum bands on the Trojans with analogousfeatures on Centaurs, Kuiper belt objects, and the active asteroid 238P. In thecontext of recent solar system evolution models, which posit that the Trojansinitially formed in the outer Solar System, the significant attenuation of the2.7-3.6 \mum absorptions on Trojans relative to Kuiper belt objects may bethe result of secondary thermal processing of the Trojans' surfaces at thehigher temperatures of the Jupiter region. The CO_2 band manifested on theyounger surface of Eurybates suggests that CO_2 may be a major constituent inthe bulk composition of Trojans, but resides in the subsurface or deeperinterior and is largely obscured by refractory material that formed from thethermophysical processes that were activated during their inward migration.