# # Program information file # PROGRAM_ID 2021B124 PROGRAM_TITLE Constraining the composition and origin of Hilda asteroids: Exploring the 3-micron feature PROGRAM_INV1 Ian Wong PROGRAM_INV2 Michael Brown PROGRAM_INV3 Joshua Emery PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT solar system PROGRAM_ABSTRACT_BEG We propose a two-night program to observe four Hilda asteroids using the SpeX instrument on IRTF. With the LXD_short mode, we will obtain reflectance spectra at medium resolution spanning 2.2-3.8 microns. The objective is to probe the 3-3.5 micron region in search of a diagnostic absorption feature that has been seen in previous Hilda spectra. The spectral band is indicative of either water frost or ammoniated clays and will be crucial for constraining the formation and evolution of these enigmatic objects. The latter possibility immediately points toward an outer solar system origin for Hildas and would serve as a definitive confirmation of recent models of solar system evolution. Of particular importance is a careful comparison with extant near-infrared spectra of Jupiter Trojan asteroids that cover the same wavelength range; these spectra also show a discernible absorption feature at around 3.1 microns, with the depth correlating with visible color. By compiling a significant body of Hilda reflectance spectra spanning the 3-3.5 micron region, we will be able to increase the signal-to-noise of the observed absorption feature by averaging the spectra together, thereby enabling detailed modeling of the surface composition. We will also be able to probe for trends between the measured absorption depth and visible color, as was done for Jupiter Trojans. PROGRAM_ABSTRACT_END