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 1:45 PM - 3:15 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:Olivier Barnouin(Johns Hopkins University Applied Physics Laboratory)

1:45 PM - 2:00 PM

[PPS03-07] Asteroid Ryugu's parent body and its properties inferred from Haybusa2 multi-band imaging observations

★Invited Papers

*Seiji Sugita1,6, Rie Honda2, Tomokatsu Morota3, Shingo Kameda4, ERI TATSUMI1, Chikatoshi Honda7, yokota yasuhiro2,5, Toru Kouyama8, Naoya Sakatani5, Manabu Yamada6, Hidehiko Suzuki10, Kazuo Yoshioka1, Yuichiro Cho1, Moe Matsuoka5, Kazunori Ogawa9, Deborah Domingue11, Hideaki Miyamoto1, Olivier Barnouin12, Patrick Michel13, Carolyn Ernst12, Sei-ichiro WATANABE3, Yuichi Tsuda5 (1.University of Tokyo, 2.Kochi University, 3.Nagoya University, 4.Rikkyo University, 5.JAXA/ISAS, 6.Chiba Institute of Technology, PERC, 7.University of Aizu, 8.National Institute of Advanced Industrial Science and Technology, 9.Kobe University, 10.Meiji University, 11.Planetary Science Institute, 12.Johns Hopkins University/Applied Physics Laboratory, 13.Observatoire de la Coˆte d’Azur)

Keywords:Hayabusa2, Ryugu, The evolution of the solar system

JAXA’s Hayabusa2 has conducted global observations of Ryugu and revealed many important properties of Ryugu, such as Cb-type average spectrum, the lack of a strong 0.7-um absorption, very low 0.55-um geometric albedo (4.5+/-0.2) %, and very young (< a few Myr) crater retention age for small craters (>10m).

The Cb-type spectrum of Ryugu is consistent with Eulalia and Polana families in the inner main belt, which are dynamically most probable source families. This agreement between the prediction from dynamic calculations and spectral observations suggests that one of the two asteroids is likely Ryuguʼs parent body. These families are among the most widely dispersed C-complex families in the inner main belt, allowing to deliver family members at very high flux rate to the resonance zones (nue6 and 3:1) at both inner and outer boundaries of the inner main belt, which are the dominant source of near-Earth objects (NEOs).

Furthermore, high abundance of boulders are found on Ryugu. Evidence for mass wasting indicates mechanically unconsolidated surfaces, allowing surface boulders to move easily. The morphologies of impact craters on Ryugu are consistent with gravity-regime formation, in which impact events produce large ejecta masses. These suggest that large mass of boulders and pebbles can be ejected from Ryugu to space over time.

Consequently, a large mass of Ryugu-like macroscopic objects would enter Earthʼs atmosphere, suggesting the presence of counterparts in our meteorite collection. Among such candidates is moderately dehydrated carbonaceous chondrites, which have both very low albedo and flat spectra. They are also found with high abundance in Antarctica, which may represent the long-term average flux of infalling meteorites on Earth. Another is interplanetary dust particles (IDPs), which also have low albedos and account for large influx of extraterrestrial materials to Earth. Although a decisive conclusion may not be obtained before the analysis of Ryugu samples returned to Earth, currently available observational evidence, such as high boulder abundance on Ryugu, favors that its composition may be similar to moderately dehydrated carbonaceous chondrites. This would further suggest that Ryuguʼs relatively low abundance of hydrated minerals may be due to partial dehydration on Ryuguʼs parent body.