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

[PPS03-P24] Disk-Resolved Photometry Analysis of the Asteroid Ryugu Images Obtained by Hayabusa2 Visible Camera ONC

*横田 康弘^1,2、本田 理恵¹、巽 瑛理³、Domingue Deborah⁴、Schroeder Stefanus⁵、松岡 萌²、杉田 精司³、諸田 智克⁶、亀田 真吾⁷、神山 徹⁸、鈴木 秀彦⁹、山田 学¹⁰、坂谷 尚哉²、本田 親寿¹¹、早川 雅彦²、吉岡 和夫³、長 勇一郎³、澤田 弘崇² (1.高知大学、2.宇宙航空研究開発機構 宇宙科学研究所、3.東京大学、4.Planetary Science Institute、5.DLR、6.名古屋大学、7.立教大学、8.産総研、9.明治大学、10.千葉工業大学、11.会津大学)

キーワード：小惑星、測光、リュウグウ、はやぶさ2

Since June 2018, the Optical Navigation Camera (ONC) onboard Hayabusa2, has observed the C-type asteroid 162173 Ryugu at a distance below 20 km. ONC-T and ONC-W1 are used for surface imaging operations, and their images allow us to investigate the disk-resolved photometric properties of the surface. A narrow-angle camera ONC-T has 7 broad-band filters ranging in wavelength from 0.39–0.95 μm. ONC-W1 is a wide-angle (> 65°) pan-chromatic camera mainly used for optical navigation during cruise and low-altitude (< 20km) operations. We are proceeding the analysis of both dataset, ONC-T and ONC-W1.

Since Hayabusa2’s position is nominally fixed on the line connecting Ryugu and the Earth, the available solar phase angle range by ONC-T changes seasonally with the orbits of Earth and Ryugu around the sun. Therefore, we are collecting a large number of ONC-T images over a long period of time to cover a wide phase angle range.

ONC-W1 data has a strong point that it covers a wide phase angle range within a single frame during the descent operations, because of its wide field of view. One of our current challenges is deriving a precise viewing geometries (incidence angle, emission angle, and phase angle) at each pixel. Additionally, comparison of the absolute brightness value (radiance factor) with ONC-T is an ongoing issue.