Albedos of Centaurs, Jovian Trojans, and Hildas

Abstract

Abstract We present optical V band albedo distributions for middle solar system minor bodies including Centaurs, Jovian Trojans, and Hildas. Diameters come mostly from the NEOWISE catalog. Optical photometry (H values) for about two-thirds of the ∼2700 objects studied are from Pan-STARRS, supplemented by H values from JPL Horizons (corrected to the Pan-STARRS photometric system). Optical data for Centaurs are from our previously published work. The albedos presented here should be superior to previous work because of the use of the Pan-STARRS optical data, which is a homogeneous data set that has been transformed to standard V magnitudes. We compare the albedo distributions of pairs of samples using the nonparametric Wilcoxon test. We strengthen our previous findings that gray Centaurs have lower albedos than red Centaurs. The gray Centaurs have albedos that are not significantly different from those of the Trojans, suggesting a common origin for Trojans and gray Centaurs. The Trojan L4 and L5 clouds have median albedos that differ by ∼10% at a very high level of statistical significance, but the modes of their albedo distributions differ by only ∼1%. We suggest the presence of a common “true background” in the two clouds, with an additional more reflective component in the L4 cloud. We find, in agreement with Grav et al. that the Hildas are darker than the Trojans by 15%–25%. Perhaps the Hildas are darker because of their passage near perihelion through zone III of the main asteroid belt, which might result in significant darkening by gardening.