Size Frequency Distributions of Jupiter Trojans, Hildas, and Main Belt Asteroids

摘要

We have earried out survey observations for main belt asteroid (MBAs), Hildas, and Jupiter Trojans (JTs) since 2002 by the 8.2-m Subaru telescope equipped with the wide-field CCD cameras: Suprime-Cam (SC) or Hyper Suprime-Cam (HSC). A large aperture of the Subaru telescope and a large field of view of SC or HSC allow us to detect moving objects efficiently down to sub-km for MBAs and about 1km for Hildas and JTs. Our observations are the deepest survey for MBAs, Hildas and JTs so far. The detected objects from those survey were used for determining the faint end of the size frequency distribution of those object groups. In order to compare the SFDs between MBA, Hilda and JT groups, we combined our survey results with those obtained from the other surveys and established the SFD of each group of MBA, Hilda and JT at the size range from sub-km to 1000 km. When we plot the SFD of each group with R-plot and compare all SFDs, we noticed that the SFDs of JTs and Hildas are basically flat in the R-plot and the SFDs of MBAs has wavy structure on the R-plot. We also found that gradual change of the shape of SFDs from inner MBAs to outer MBAs, the SFDs are getting flatter to approach the shape of SFDs of JTs and Hildas. Since the SFDs of craters on Pluto and Charon obtained from preliminary analysis of New Horizons data are flat shape, the flat SFDs of JTs and Hildas which we found may indicate that Trans-Neptunian objects were captured into JT and Hilda groups during planet migration period as planet migration models suggest. The gradual change of SFDs from inner MBAs to JTs may indicate that the outer objects were implanted into not only JT and Hilda regions but also outer main belt region.