Near-Infrared Spectroscopy of Low-Albedo Surfaces of the Solar System: Search for the Spectral Signature of Dark Material

Abstract

We obtained I–J–H–K band spectroscopy of 18 low-albedo objects of the Solar System using the University of Hawaii 88-in. telescope equipped with the near-infrared spectrograph KSPEC. Most of our targets were selected from among the population of the Cybele, Hilda, and Trojan groups of asteroids, based on their low albedos and the relatively steep slopes of their reflection spectra at visible wavelengths. The outer jovian satellite Himalia and the Apollo object 3200 Phaethon were also observed. None of the spectra show absorptions similar to those found in the spectrum of 5145 Pholus, which remains the only asteroid-like object whose H–K band reflection spectrum contains a few broad absorptions due to organics. The near-infrared slope and the (1.0- to 2.2-μm) infrared color-index have been derived for each surface. This sample of primitive objects of the Solar System can be interpreted in terms of cometary-like objects that have undergone different degrees of aging.