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

[PPS03-P16] Global distribution and spectral characteristics of bright spots on asteroid Ryugu

*末満 雅徳¹、諸田 智克¹、本田 理恵²、亀田　 真吾¹⁵、巽 瑛理³、山田 学⁴、坂谷 尚哉⁵、神山 徹⁶、横田 康弘⁷、長 勇一郎⁸、鈴木 秀彦⁹、早川 雅彦¹⁰、松岡 萌¹⁰、本田 親寿¹¹、道上 逹広¹²、吉岡 和夫¹³、小川 和律¹⁴、澤田 弘崇⁵、杉田 精司³ (1.名古屋大学大学院環境学研究科、2.高知大学自然科学系理工学部門、3.東京大学大学院地球惑星科学専攻、4.千葉工業大学惑星探査研究センター、5.宇宙航空研究開発機構宇宙科学研究所、6.産業技術総合研究所、7.高知大学、8.東京大学理学系研究科地球惑星科学専攻、9.明治大学理工学部物理学科、10.国立研究開発法人宇宙航空研究開発機構宇宙科学研究所太陽系科学研究系、11.会津大学、12.近畿大学工学部、13.東京大学大学院新領域創成科学研究科、14.神戸大学、15.立教大学)

キーワード：小惑星、リュウグウ、ブライトスポット、スペクトル、ボルダ

On June 27, 2018, the asteroid explorer Hayabusa2 arrived at the target C-type asteroid 162173 Ryugu. The telescopic optical navigation camera (ONC-T) on-board Hayabusa2 has acquired the multiband image data for the entire surface of Ryugu with spatial resolutions better than 2 m/pixel. These data show that the Ryugu surface has the very low surface reflectance, flat spectra, and its spatial homogeneity [Sugita et al. 2019]. However, more detailed observations on Ryugu have revealed that many boulders exhibit different spectral properties and that a number of spots with distinctively brighter than the surroundings [Sugita et al. 2019]. Although larger boulders have been analyzed to show that they form two distinctive spectral trends, no substantial spectral analyses on bright spots have been conducted. Determining whether or not these bright spots are one of the materials that originate from the parent body of Ryugu is important to understand the differentiation and geologic processes on the parent body. In this study, in order to understand origins of the bright spots, we investigated spectral characteristics of the bright spots and compared those of the boulders on Ryugu. We used the ONC-T multiband images obtained in Box-A (20 km altitude) and mid-altitude (5 km altitude) operations.

We found seven meter-sized bright spots that have radiance factor 1.3 to 2.0 times higher than that of the surrounding area. The spectra of these bright spots were classified into two types, one being a flat spectrum type and another being a convex spectrum type. The former type has spectrum similar to but flatter and brighter than the mean spectra of the whole Ryugu and boulders, suggesting that the bright spots originate from parent body of Ryugu. The latter type has spectrum similar to those of S-type asteroids, suggesting their exogenous origin.