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

[PPS03-11] Geomorphological characteristics of asteroid Ryugu: implications to its evolutional history

*宮本 英昭¹、逸見 良道¹、菊地 紘¹、小松 吾郎²、本田 親寿³、道上 達広⁴、諸田 智克⁵、長 勇一郎¹、バーノイン オリビエ⁶、佐々木 晶⁷、平田 成³、平田 直之⁸、本田 理恵¹⁰、亀田 真吾¹¹、巽 瑛理¹、横田 康弘¹²、神山 徹¹³、鈴木 秀彦¹⁴、山田 学¹⁵、坂谷 尚哉¹²、早川 雅彦¹²、吉岡 和夫¹、松岡 萌¹²、平林 正稔⁹、澤田 弘崇¹²、杉田 精司¹ (1.東京大学、2.ダヌンツィオ大学、3.会津大学、4.近畿大学、5.名古屋大学、6.ジョンズホプキンス大学、7.大阪大学、8.神戸大学、9.オーバーン大学、10.高知大学、11.立教大学、12.宇宙科学研究所、13.産業総合研究所、14.明治大学、15.千葉工業大学)

キーワード：小惑星、はやぶさ２、リュウグウ

Observations by Hayabusa 2 spacecraft indicate that Ryugu is a highly porous C-type asteroid. Ryugu’s surface is covered by numerous boulders. These are consistent with the idea that Ryugu is a rubble-pile asteroid. Interestingly, Itokawa, the only other similarly-sized rubble-pile asteroid closely observed by spacecraft, is different from Ryugu in many aspects. For example, while the shape of Ryugu is a top-shape, that of Itokawa is somehow elongated cigar-like. Though Ryugu is generally homogeneous in terms of roughness, Itokawa has two distinctive areas such as smooth and rough terrains. Ryugu has an almost continuous equatorial ridge, though Itokawa does not have such a large-scale topographic feature.

These differences may come from the difference in evolutional processes; a top-shape of rubble pile asteroid is believed to result of rotationally induced deformation or from re-accumulation. Another possibility is that the differences may come from variations in mechanical properties of asteroid forming materials. We are investigating geological characteristics of Ryugu, which may hold clues for these aspects. In this talk, we report initial results of geological investigations mostly using visible images obtained by the Optical Navigation Camera (ONC) onboard the Hayabusa2 spacecraft, and discuss about their implications to evolutional history of Ryugu..