[P-PS03] Solar System Small Bodies: A New Frontier Arising Hayabusa 2, OSIRIS-REx and Other Projects

[PPS03-29] A kilometre-sized Kuiper belt object revealed by OASES stellar occultation observations

*Ko Arimatsu^1,2, Kohji Tsumura³, Fumihiko Usui⁴, Shinnaka Yoshiharu⁵, Kohei Ichikawa^3,6,7, Takafumi Ootsubo⁸, Takayuki Kotani^2,9, Takehiko Wada⁸, Koichi Nagase⁸, Jun-ichi Watanabe² (1.Astronomical Observatory, Graduate School of Science, Kyoto University, 2.National Astronomical Observatory of Japan, 3.Frontier Research Institute for Interdisciplinary Science, Tohoku University, 4.Center for Planetary Science, Graduate School of Science, Kobe University, 5.Laboratory of Infrared High-resolution Spectroscopy, Koyama Astronomical Observatory, Kyoto Sangyo University, 6.Department of Astronomy, Columbia University, 7.Department of Physics and Astronomy, University of Texas at San Antonio, 8.Department of Space Astronomy and Astrophysics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 9.Astrobiology Center, National Institutes of Natural Sciences)

Keywords:trans-Neptunian objects, Kuiper belt , ground based observations by optical telescopes

We will report the first detection of a single stellar occultation event candidate by a kilometer-sized (radius= 1-10 km) Kuiper belt object (KBO). Since the kilometer-sized KBOs are too faint to be detected directly, the monitoring of stellar occultation events is one possible way to discover them. With the aim of detecting the stellar occultation events, we launched an optical observation project named Organized Autotelescopes for Serendipitous Event Survey (OASES). We installed two low-cost OASES observation systems in different positions on the rooftop of the Miyako open-air school on Miyako Island, Miyakojima-shi, Okinawa Prefecture, Japan, and monitored up to 2000 stars simultaneously with a sampling cadence of 15.4Hz. In the 60-hour dataset obtained with the two-year OASES observations, we discovered one occultation candidate event by a KBO with a radius of approximately 1.3 km. Our present detection yields a surface number density of KBOs with radii exceeding 1.2 km is approximately 6 × 10⁵ deg⁻². This surface number density favors a theoretical size distribution model with an excess signature at a radius of 1–2 km. The present results suggest that planetesimals before their runaway growth phase grew into kilometer-sized objects in the primordial outer Solar System and remain as one of the major populations in the present-day Kuiper belt.