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Three-axial shape distributions of pebbles, cobbles and boulders smaller than a few meters on asteroid Ryugu

Over a broad size range, the shapes of impact fragments from catastrophic disruptions are distributed around the mean axial ratio 2: √2: 1, irrespective of experimental conditions and target materials. Although most blocks on asteroids are likely to be impact fragments, there is not enough quantitat...

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Published in:Icarus (New York, N.Y. 1962) N.Y. 1962), 2022-07, Vol.381, p.115007, Article 115007
Main Authors: Michikami, Tatsuhiro, Hagermann, Axel, Morota, Tomokatsu, Yokota, Yasuhiro, Urakawa, Seitaro, Okamura, Hiroyuki, Tanabe, Naoya, Yumoto, Koki, Ebihara, Tatsuki, Cho, Yuichiro, Ernst, Carolyn M., Hayakawa, Masahiko, Hirabayashi, Masatoshi, Hirata, Naru, Honda, Chikatoshi, Honda, Rie, Kameda, Shingo, Kanamaru, Masanori, Kikuchi, Hiroshi, Kikuchi, Shota, Kouyama, Toru, Matsuoka, Moe, Miyamoto, Hideaki, Noguchi, Takaaki, Noguchi, Rina, Ogawa, Kazunori, Okada, Tatsuaki, Sakatani, Naoya, Sasaki, Sho, Sawada, Hirotaka, Sugimoto, Chiho, Suzuki, Hidehiko, Tanaka, Satoshi, Tatsumi, Eri, Tsuchiyama, Akira, Tsuda, Yuichi, Watanabe, Sei-ichiro, Yamada, Manabu, Yoshikawa, Makoto, Yoshioka, Kazuo, Sugita, Seiji
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container_title Icarus (New York, N.Y. 1962)
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creator Michikami, Tatsuhiro
Hagermann, Axel
Morota, Tomokatsu
Yokota, Yasuhiro
Urakawa, Seitaro
Okamura, Hiroyuki
Tanabe, Naoya
Yumoto, Koki
Ebihara, Tatsuki
Cho, Yuichiro
Ernst, Carolyn M.
Hayakawa, Masahiko
Hirabayashi, Masatoshi
Hirata, Naru
Honda, Chikatoshi
Honda, Rie
Kameda, Shingo
Kanamaru, Masanori
Kikuchi, Hiroshi
Kikuchi, Shota
Kouyama, Toru
Matsuoka, Moe
Miyamoto, Hideaki
Noguchi, Takaaki
Noguchi, Rina
Ogawa, Kazunori
Okada, Tatsuaki
Sakatani, Naoya
Sasaki, Sho
Sawada, Hirotaka
Sugimoto, Chiho
Suzuki, Hidehiko
Tanaka, Satoshi
Tatsumi, Eri
Tsuchiyama, Akira
Tsuda, Yuichi
Watanabe, Sei-ichiro
Yamada, Manabu
Yoshikawa, Makoto
Yoshioka, Kazuo
Sugita, Seiji
description Over a broad size range, the shapes of impact fragments from catastrophic disruptions are distributed around the mean axial ratio 2: √2: 1, irrespective of experimental conditions and target materials. Although most blocks on asteroids are likely to be impact fragments, there is not enough quantitative data for reliable statistics on their three-axial lengths and/or ratios because it is difficult to precisely estimate the heights of the blocks. In this study, we evaluate the heights of blocks on asteroid Ryugu by measuring their shadows. The three-axial ratios of ~4100 small blocks with diameters from 5.0 cm to 7.6 m in Ryugu's equatorial region are investigated using eight close-up images of narrower localities taken at altitudes below 500 m, i.e. at
doi_str_mv 10.1016/j.icarus.2022.115007
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Although most blocks on asteroids are likely to be impact fragments, there is not enough quantitative data for reliable statistics on their three-axial lengths and/or ratios because it is difficult to precisely estimate the heights of the blocks. In this study, we evaluate the heights of blocks on asteroid Ryugu by measuring their shadows. The three-axial ratios of ~4100 small blocks with diameters from 5.0 cm to 7.6 m in Ryugu's equatorial region are investigated using eight close-up images of narrower localities taken at altitudes below 500 m, i.e. at &lt;5.4 cm/pixel resolution, obtained immediately before the second touch-down of the Hayabusa2 spacecraft. The purpose of this study is to investigate the block shape distribution, which is important for understanding the geological history of asteroid Ryugu. Specifically, the shape distribution is compared to laboratory impact fragments. Our observations indicate that the shape distributions of blocks smaller than 1 m on Ryugu are consistent with laboratory impact fragment shape distributions, implying that the dominant shape-determining process for blocks on Ryugu was impact fragmentation. Blocks several meters in size in the equatorial region seem to be slightly flatter than the rest, suggesting that some blocks are partly buried in a bed of regolith. 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cobbles and boulders smaller than a few meters on asteroid Ryugu</atitle><jtitle>Icarus (New York, N.Y. 1962)</jtitle><date>2022-07-15</date><risdate>2022</risdate><volume>381</volume><spage>115007</spage><pages>115007-</pages><artnum>115007</artnum><issn>0019-1035</issn><issn>1090-2643</issn><eissn>1090-2643</eissn><abstract>Over a broad size range, the shapes of impact fragments from catastrophic disruptions are distributed around the mean axial ratio 2: √2: 1, irrespective of experimental conditions and target materials. Although most blocks on asteroids are likely to be impact fragments, there is not enough quantitative data for reliable statistics on their three-axial lengths and/or ratios because it is difficult to precisely estimate the heights of the blocks. In this study, we evaluate the heights of blocks on asteroid Ryugu by measuring their shadows. The three-axial ratios of ~4100 small blocks with diameters from 5.0 cm to 7.6 m in Ryugu's equatorial region are investigated using eight close-up images of narrower localities taken at altitudes below 500 m, i.e. at &lt;5.4 cm/pixel resolution, obtained immediately before the second touch-down of the Hayabusa2 spacecraft. The purpose of this study is to investigate the block shape distribution, which is important for understanding the geological history of asteroid Ryugu. Specifically, the shape distribution is compared to laboratory impact fragments. Our observations indicate that the shape distributions of blocks smaller than 1 m on Ryugu are consistent with laboratory impact fragment shape distributions, implying that the dominant shape-determining process for blocks on Ryugu was impact fragmentation. Blocks several meters in size in the equatorial region seem to be slightly flatter than the rest, suggesting that some blocks are partly buried in a bed of regolith. In conclusion, the shape distributions of blocks from several-cm to several-m in the equatorial region of asteroid Ryugu suggest that these are mainly fragments originating from the catastrophic disruption of their parent body and/or from a later impact. •Blocks &lt;1 m on Ryugu have similar three-axial shape distributions to laboratory impact fragments.•Blocks several meters in size appear to be slightly flatter.•Some blocks several meters in size are partly buried in a bed of regolith.•The dominant shape-determining process for blocks may be impact fragmentation.</abstract><pub>Elsevier Inc</pub><doi>10.1016/j.icarus.2022.115007</doi><orcidid>https://orcid.org/0000-0001-9084-2858</orcidid><orcidid>https://orcid.org/0000-0002-1821-5689</orcidid><orcidid>https://orcid.org/0000-0001-5451-9367</orcidid><orcidid>https://orcid.org/0000-0001-6076-3614</orcidid><oa>free_for_read</oa></addata></record>
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identifier ISSN: 0019-1035
ispartof Icarus (New York, N.Y. 1962), 2022-07, Vol.381, p.115007, Article 115007
issn 0019-1035
1090-2643
1090-2643
language eng
recordid cdi_swepub_primary_oai_DiVA_org_ltu_90045
source Elsevier:Jisc Collections:Elsevier Read and Publish Agreement 2022-2024:Freedom Collection (Reading list)
subjects Asteroid Ryugu
Asteroids
Atmosfärsvetenskap
Atmospheric science
Impact process
Regolith
Sciences of the Universe
Surfaces
title Three-axial shape distributions of pebbles, cobbles and boulders smaller than a few meters on asteroid Ryugu
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