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Geologic History and Crater Morphology of Asteroid (162173) Ryugu
  • +29
  • Yuichiro Cho,
  • Tomokatsu Morota,
  • Masanori Kanamaru,
  • Naofumi Takaki,
  • Koki Yumoto,
  • Carolyn M. Ernst,
  • Masatoshi Hirabayashi,
  • Olivier S. Barnouin,
  • Eri Tatsumi,
  • Katharina A. Otto,
  • Nicole Schmitz,
  • Roland J Wagner,
  • Ralf Jaumann,
  • Hideaki Miyamoto,
  • Hiroshi Kikuchi,
  • Ryodo Hemmi,
  • Rie Honda,
  • Shingo Kameda,
  • Yasuhiro Yokota,
  • Toru Kouyama,
  • Hidehiko Suzuki,
  • Manabu Yamada,
  • Naoya Sakatani,
  • Chikatoshi Honda,
  • Masahiko Hayakawa,
  • Kazuo Yoshioka,
  • Moe Matsuoka,
  • Tatsuhiro Michikami,
  • Naru Hirata,
  • Hirotaka Sawada,
  • Kazunori Ogawa,
  • Seiji Sugita
Yuichiro Cho
The University of Tokyo, The University of Tokyo

Corresponding Author:[email protected]

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Tomokatsu Morota
The University of Tokyo, The University of Tokyo
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Masanori Kanamaru
Osaka University, Osaka University
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Naofumi Takaki
The University of Tokyo, The University of Tokyo
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Koki Yumoto
The University of Tokyo, The University of Tokyo
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Carolyn M. Ernst
The Johns Hopkins University Applied Physics Laboratory, The Johns Hopkins University Applied Physics Laboratory
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Masatoshi Hirabayashi
Auburn University, Auburn University
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Olivier S. Barnouin
The Johns Hopkins University Applied Physics Laboratory, The Johns Hopkins University Applied Physics Laboratory
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Eri Tatsumi
The University of Tokyo, The University of Tokyo
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Katharina A. Otto
German Aerospace Center (DLR), German Aerospace Center (DLR)
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Nicole Schmitz
German Aerospace Center (DLR), German Aerospace Center (DLR)
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Roland J Wagner
German Aerospace Center (DLR), German Aerospace Center (DLR)
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Ralf Jaumann
Free University Berlin, Free University Berlin
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Hideaki Miyamoto
The University of Tokyo, The University of Tokyo
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Hiroshi Kikuchi
The University of Tokyo, The University of Tokyo
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Ryodo Hemmi
The University of Tokyo, The University of Tokyo
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Rie Honda
Kochi University, Kochi University
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Shingo Kameda
Rikkyo University, Rikkyo University
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Yasuhiro Yokota
JAXA, JAXA
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Toru Kouyama
AIST, AIST
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Hidehiko Suzuki
Meiji University, Meiji University
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Manabu Yamada
Chiba Institute of Technology, Chiba Institute of Technology
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Naoya Sakatani
Rikkyo University, Rikkyo University
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Chikatoshi Honda
University of Aizu, University of Aizu
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Masahiko Hayakawa
JAXA, JAXA
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Kazuo Yoshioka
The University of Tokyo, The University of Tokyo
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Moe Matsuoka
JAXA, JAXA
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Tatsuhiro Michikami
Kindai University, Kindai University
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Naru Hirata
University of Aizu, University of Aizu
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Hirotaka Sawada
JAXA, JAXA
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Kazunori Ogawa
JAXA, JAXA
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Seiji Sugita
The University of Tokyo, The University of Tokyo
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Abstract

Crater morphology and surface age of asteroid (162173) Ryugu are characterized using the high-resolution images obtained by the Hayabusa2 spacecraft. Our observations reveal that the abundant boulders on and under the surface of the rubble-pile asteroid affect crater morphology. Most of the craters on Ryugu exhibit well-defined circular depressions, unlike those observed on asteroid Itokawa. The craters are typically outlined by boulders remaining on the rim. Large craters (diameter >100 m) host abundant and sometimes unproportionally large boulders on their floors. Small craters (<20 m) are characterized by smooth circular floors distinguishable from the boulder-rich exterior. Such small craters tend to have dark centers of unclear origin. The correlation between crater size and boulder number density suggests that some processes sort the size of boulders in the shallow (<30 m) subsurface. Furthermore, the crater size-frequency distributions (CSFDs) of different regions on Ryugu record multiple geologic events, revealing the diverse geologic history on this 1-km asteroid. Our crater counting analyses indicate that the equatorial ridge is the oldest structure of Ryugu and was formed 23-29 Myr ago. Then, Ryugu was partially resurfaced, possibly by the impact that formed the Urashima crater 5-12 Myr ago. Subsequently, a large-scale resurfacing event formed the western bulge and the fossae 2-9 Myr ago. Following this process, the spin of Ryugu slowed down plausibly due to the YORP effect. The transition of isochrons in a CSFD suggests that Ryugu was decoupled from the main belt and transferred to a near-Earth orbit 0.2-7 Myr ago.
Aug 2021Published in Journal of Geophysical Research: Planets volume 126 issue 8. 10.1029/2020JE006572