Japan Geoscience Union Meeting 2019

Presentation information

[E] Oral

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

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

Tue. May 28, 2019 10:45 AM - 12:15 PM A01 (TOKYO BAY MAKUHARI HALL)

convener:Masateru Ishiguro(Department of Physics and Astronomy, Seoul National University), Taishi Nakamoto(Tokyo Institute of Technology), Masanao Abe(Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency), Olivier S Barnouin(Johns Hopkins University Applied Physics Laboratory), Chairperson:Masateru Ishiguro(Seoul National University)

11:15 AM - 11:30 AM

[PPS03-03] Impact experiment on asteroid Ryugu by Small-Carry on impactor of Hayabusa-2 and observation of the impact ejecta by a Deployable CAMera-3

★Invited Papers

*Masahiko Arakawa1, Takanao Saiki2, Toshihiko Kadono3, Yasuhiko Takagi4, Koji Wada5, Yu-ichi Iijima2, Hiroshi Imamura2, Chisato Okamoto1, Yuri Shimaki2, Kei Shirai2, Satoru Nakazawa2, Masahiko Hayakawa2, Naru Hirata6, Hajime Yano2, Hirotaka Sawada2, Kazunori Ogawa1, Ko Ishibashi5, Hiroshi Kimura5, Masanori Kobayashi5, Naoya Sakatani2, Hajime Hayakawa2, Rie Honda7, Seiji Sugita8, Tomokatsu Morota9, Shingo Kameda10, ERI TATSUMI8, Chikatoshi Honda6, yokota yasuhiro2, Toru Kouyama11, Manabu Yamada5, Hidehiko Suzuki12, Kazuo Yoshioka13, Yuichiro Cho8, Moe Matsuoka2 (1.Graduate School of Science, Kobe University, 2.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3.University of Occupational and Environmental Health, 4.Aichi Toho University, 5.Planetary Exploration Research Center, Chiba Institute of Technology, 6.Dep. of Computer Science and Engineering, Univ. of Aizu, 7.Department of Science and Technology, System of Natual Science, Kochi University, 8.Department of Earth and Planetary Science, Graduate School of Science Sciece, The University of Tokyo, 9.Graduate School of Environmental Studies, Nagoya University, 10.School of Science, Rikkyo University, 11.National Institute of Advanced Industrial Science and Technology, 12.Department of physics, Meiji university, 13.Graduate School of frontier Science, The University of Tokyo)

Keywords:Asteroid Ryugu, Impact Experiment, Small carry-on impactor, Deployable camera3, Rubble pile body

A small carry-on impactor (SCI) equipped on Hayabusa2 is scheduled to be propelled toward to the surface of asteroid Ryugu this spring. Cratering process on Ryugu made by the impactor will simultaneously observed by a deployable camera 3 (DCAM3) detached from Hayabusa2. The mission objective of the impactor is to excavate the asteroid to expose a subsurface material as ejecta deposits around the crater. Thus, not only it enables us to give a good opportunity for obtaining a fresh or subsurface material by a sampler system, remote sensing instruments such as ONC, TIR, NIRS3 onboard Hayabusa2 will also have a good chance to observe the exposed subsurface material. Furthermore, this impact experiment on Ryugu is also a rare opportunity to verify the crater scaling law in the microgravity environment on the real asteroid materials, and is expected to enable us to improve the conventional scaling law, especially for the crater size and the ejecta velocity distribution.

After arrival at Ryugu, the surface morphology observation through remote sensing has turned out that a plenty of boulders cover throughout the surface, and many of the boulders are larger than 10 m. These boulders are distributed almost uniformly and the size frequency distribution of the boulders is a power law distribution with the power law index around -1, indicating relatively large boulders are dominant on the surface. Therefore, taking into account that the precision of an actual impact point toward an aiming point expands several 10 m, the impactor possibly collides with a large boulder, otherwise with small boulders having the power law size distribution, wherever the impactor would aim at on the surface of Ryugu. If the impactor collides with a large boulder, a crater should be formed in the strength regime, and if the impactor collides into a finer-boulder area, a crater will be formed in the gravity regime. The DCAM3 was designed for the observation of not only the impact cratering in the strength regime but also that in the gravity regime.

We believe that we will success to observe impact ejecta induced by the impactor when the SCI and DCAM3 operations are conducted as scheduled. We are planning to present a first report of the DCAM3 observation in this talk, and discuss how to search the impact point on the Ryugu surface using the DCAM3 images, beforehand the onboard imaging instruments. Moreover, the morphology of the ejecta curtain imaged by DCAM3 will bring us a lot of information about the crater formation process. We report the surface condition around the impact point, such as a large block or a small-boulders area, and an excavated area corresponding to the crater size. The DCAM3 will also observe individual dusts in the ejecta curtain to obtain information of the ejecta velocity distribution, so that we may have a chance to introduce these images. However, please note that this presentation strongly depends on the success of the SCI/DCAM3 operation.