JpGU-AGU Joint Meeting 2020

Presentation information

[E] Oral

P (Space and Planetary Sciences ) » P-PS Planetary Sciences

[P-PS07] Solar System Small Bodies: Explorations of Ryugu, Bennu, and the Solar System at Large

convener:Taishi Nakamoto(Tokyo Institute of Technology), Tatsuaki Okada(Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency), Dante S Lauretta(University of Arizona), Masateru Ishiguro(Department of Physics and Astronomy, Seoul National University)

[PPS07-02] Surface evolution of carbonaceous asteroid Ryugu revealed from touchdown operation of Hayabusa2

★Invited Papers

*Tomokatsu Morota1, Seiji Sugita1, Yuichiro Cho1, Masanori Kanamaru2, ERI TATSUMI3, Naoya Sakatani4, Rie Honda5, Naoyuki Hirata6, Hiroshi Kikuchi4, Manabu Yamada7, yokota yasuhiro4, Shingo Kameda8, Moe Matsuoka4, Hirotaka Sawada4, Chikatoshi Honda9, Toru Kouyama10, Kazunori Ogawa4, Hidehiko Suzuki11, Kazuo Yoshioka1, Masahiko Hayakawa4, Naru Hirata9, Masatoshi Hirabayashi12, Hideaki Miyamoto1, Tatsuhiro Michikami13, Takahiro Hiroi14, Carolyn M. Ernst15, Olivier S. Barnouin15, Sei-ichiro WATANABE16 (1.The University of Tokyo, 2.Osaka University, 3.Universidad de La Laguna, 4.JAXA, 5.Kochi University, 6.Kobe University, 7.Chiba Institute of Technology, 8.Rikkyo University, 9.The University of Aizu, 10.AIST, 11.Meiji University, 12.Auburn University, 13.Kindai University, 14.Brown University, 15.APL/JHU, 16.Nagoya University)

Keywords:Hayabusa2, Ryugu, touchdown

The Hayabusa2 spacecraft touched down on the carbonaceous near-Earth asteroid 162173 Ryugu for the first time on 21 February 2019. In the process of the touchdown operation, Hayabusa2 the optical navigation camera (ONC) had taken extremely high-resolution images of Ryugu’s surface and observed its response to the physical disturbances by the sampling projectile collision and thruster gas jets. Based on the touchdown and global observations, we report the nature of the stratigraphy of the surface materials as expressed in the color observations on Ryugu.
The ONC data show that Ryugu’s surface has almost homogeneous reflectance and color at the macro scale, but there is the regional variation in the spectral slope (b-x slope). The bluer materials are distributed at the equatorial ridge and in the polar regions, while the redder materials are widely spread over the mid-latitude regions (Sugita et al. 2019). The latitudinal variation of spectral slope suggests that exposure of Ryugu’s materials to space has led to their reddening by solar heating and/or space weathering. The ONC images obtained during the touchdown showed that a large amount of debris was produced by the impact of the projectile shot from the sampler system and the reaction control system (RCS) thrust immediately after the touchdown, and the entire field-of-view of ONC-W1 was darkened uniformly. Color changes of boulders observed during the touchdown suggest that the dark fine grains originate from the redder materials that covered the boulder surface. The stratigraphic relationship between the identified craters and the redder materials suggests that surface reddening occurred over a short period of time. These results suggest that Ryugu underwent an orbital excursion near the Sun.