Size Distribution of Small Hilda Asteroids

We present the size distribution for the Hilda asteroid group using optical survey data obtained by the 8.2 m Subaru Telescope with the Hyper Suprime-Cam. Our unbiased sample consists of 91 Hilda asteroids (Hildas) down to 1 km in diameter. We found that the Hildas’ size distribution can be approximated by a single-slope power law in the ∼1-10 km diameter range with the best-fit power-law slope of α = 0.38 ± 0.02 in the differential absolute magnitude distribution. Directly comparing the size distribution of Hildas with that of the Jupiter Trojans measured from the same data set indicates that the two size distributions are similar to each other within a diameter of ∼10 km, while these shapes are distinguishable from that of main-belt asteroids. The results suggest that Hildas and Jupiter Trojans share a common origin and have a different formation environment from main-belt asteroids. The total number of the Hilda population larger than 2 km in diameter is estimated to be ∼1 × 10⁴ based on the size distribution, which is less than that of the Jupiter Trojan population by a factor of about five.

Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.