$0.7-2.5\mu$m spectra of Hilda asteroids

Abstract

The Hilda asteroids are primitive bodies in resonance with Jupiter whose origin and physical properties are not well understood. Current models posit that these asteroids formed in the outer Solar System and were scattered along with the Jupiter Trojans into their present-day positions during a chaotic episode of dynamical restructuring. In order to explore the surface composition of these enigmatic objects in comparison with an analogous study of Trojans (Emery et al. 2011), we present new near-infrared spectra (0.7-2.5 $\mu$m) of 25 Hilda asteroids. No discernible absorption features are apparent in the data. Synthesizing the bimodalities in optical color and infrared reflectivity reported in previous studies, we classify 26 of the 28 Hildas in our spectral sample into the so-called less-red and red sub-populations and find that the two sub-populations have distinct average spectral shapes. Combining our results with visible spectra, we find that Trojans and Hildas possess similar overall spectral shapes, suggesting that the two minor body populations share a common progenitor population. A more detailed examination reveals that while the red Trojans and Hildas have nearly identical spectra, less-red Hildas are systematically bluer in the visible and redder in the near-infrared than less-red Trojans, indicating a putative broad, shallow absorption feature between 0.5 and 1.0 $\mu$m. We argue that the less-red and red objects found in both Hildas and Trojans represent two distinct surface chemistries and attribute the small discrepancy between less-red Hildas and Trojans to the difference in surface temperatures between the two regions.

8 pages, 4 figures, accepted for publication in AJ

References in corpus (6)

• A hypothesis for the color bimodality of Jupiter Trojans
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Cited by in corpus (5)

• Asteroid Taxonomy from Cluster Analysis of Spectrometry and Albedo
• Discovery of two TNO-like bodies in the asteroid belt
• A thermophysical and dynamical study of the Hildas (1162) Larissa and (1911) Schubart
• Primitive asteroids in the main belt, Cybele, and Hilda populations from Gaia DR3
• On the forced orbital plane of the Hilda asteroids