FOSSIL. II. The Rotation Periods of Small-sized Hilda Asteroids
Chan-Kao Chang, Ying-Tung Chen, Wesley C. Fraser, M. J. Lehner, Shiang‐Yu Wang, Mike Alexandersen, Young‐Jun Choi, A. Paula Granados Contreras, Takashi Itô, Youngmin JeongAhn, Jianghui Ji, J. J. Kavelaars, Myung-Jin Kim, Samantha Lawler, Jian Li, Zhong-Yi Lin, Patryk Sofia Lykawka, Hong-Kyu Moon, Surhud More, Marco A. Muñoz-Gutiérrez, Keiji Ohtsuki, Rosemary E. Pike, Tsuyoshi Terai, Seitaro Urakawa, Fumi Yoshida, Hui Zhang, Haibin Zhao, Ji‐Lin Zhou
Abstract
Abstract Using the high-cadence lightcurves collected from the FOSSIL survey, rotation periods of 17 small (diameter 1 km < D < 3 km) Hilda asteroids (hereinafter Hildas) were obtained. Combined with the previously measured rotation periods of Hildas, a spin-rate limit appears at around 3 hr. Assuming rubble-pile structures for the Hildas, a bulk density of ∼1.5 g cm −3 is required to withstand this spin-rate limit. This value is similar to that of the C-type asteroids (1.33 g cm −3 ) and higher than the ∼1 g cm −3 bulk density of the Jupiter Trojans. This suggests that the Hildas population may contain more C-type asteroids than expected, and the limit at 3 hr simply reflects the spin-rate limit for C-type asteroids. In addition, a Hilda superfast rotator was found, which has a rotation period of 1.633 hr and an estimated diameter of 0.7 km. This object is unlikely to be explained by a rubble-pile or monolithic structure.