Boulder size and shape distributions on asteroid Ryugu

Tatsuhiro Michikami, Chikatoshi Honda, Hideaki Miyamoto, Masatoshi Hirabayashi, Axel Hagermann, Terunori Irie, Keita Nomura, Carolyn M. Ernst, Masaki Kawamura, Kiichi Sugimoto, Eri Tatsumi, Tomokatsu Morota, Naru Hirata, Takaaki Noguchi, Yuichiro Cho, Shingo Kameda, Toru Kouyama, Yasuhiro Yokota, Rina Noguchi, Masahiko HayakawaNaoyuki Hirata, Rie Honda, Moe Matsuoka, Naoya Sakatani, Hidehiko Suzuki, Manabu Yamada, Kazuo Yoshioka, Hirotaka Sawada, Ryodo Hemmi, Hiroshi Kikuchi, Kazunori Ogawa, Sei ichiro Watanabe, Satoshi Tanaka, Makoto Yoshikawa, Yuichi Tsuda, Seiji Sugita

研究成果: ジャーナルへの寄稿記事

抄録

In 2018, the Japanese spacecraft Hayabusa2, arrived at the small asteroid Ryugu. The surface of this C-type asteroid is covered with numerous boulders whose size and shape distributions are investigated in this study. Using a few hundred Optical Navigation Camera (ONC) images with a pixel scale of approximately 0.65 m, we focus on boulders greater than 5 m in diameter. Smaller boulders are also considered using five arbitrarily chosen ONC close-up images with pixel scales ranging from 0.7 to 6 cm. Across the entire surface area (~2.7 km2) of Ryugu, nearly 4400 boulders larger than 5 m were identified. Boulders appear to be uniformly distributed across the entire surface, with some slight differences in latitude and longitude. At ~50 km−2, the number density of boulders larger than 20 m is twice as large as on asteroid Itokawa (or Bennu). The apparent shapes of Ryugu's boulders resemble laboratory impact fragments, with larger boulders being more elongated. The ratio of the total volume of boulders larger than 5 m to the total excavated volume of craters larger than 20 m on Ryugu can be estimated to be ~94%, which is comparatively high. These observations strongly support the hypothesis that most boulders found on Ryugu resulted from the catastrophic disruption of Ryugu's larger parent body, as described in previous papers (Watanabe et al., 2019; Sugita et al., 2019). The cumulative size distribution of boulders larger than 5 m has a power-index of −2.65 ± 0.05, which is comparatively shallow compared with other asteroids visited by spacecraft. For boulders smaller than 4 m, the power-index is even shallower and ranges from −1.65 ± 0.05 to −2.01 ± 0.06. This particularly shallow power-index implies that some boulders are buried in Ryugu's regolith. Based on our observations, we suggest that boulders near the equator might have been buried by the migration of finer material and, as a result, the number density of boulders larger than 5 m in the equatorial region is lower than at higher latitudes.

元の言語英語
ページ(範囲)179-191
ページ数13
ジャーナルIcarus
331
DOI
出版物ステータス出版済み - 10 1 2019

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boulder
asteroids
asteroid
navigation
Japanese spacecraft
pixel
spacecraft
pixels
cameras
equatorial regions
regolith
parent body
equators
longitude
craters
polar regions
crater
surface area
fragments
distribution

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

これを引用

Michikami, T., Honda, C., Miyamoto, H., Hirabayashi, M., Hagermann, A., Irie, T., ... Sugita, S. (2019). Boulder size and shape distributions on asteroid Ryugu. Icarus, 331, 179-191. https://doi.org/10.1016/j.icarus.2019.05.019

Boulder size and shape distributions on asteroid Ryugu. / Michikami, Tatsuhiro; Honda, Chikatoshi; Miyamoto, Hideaki; Hirabayashi, Masatoshi; Hagermann, Axel; Irie, Terunori; Nomura, Keita; Ernst, Carolyn M.; Kawamura, Masaki; Sugimoto, Kiichi; Tatsumi, Eri; Morota, Tomokatsu; Hirata, Naru; Noguchi, Takaaki; Cho, Yuichiro; Kameda, Shingo; Kouyama, Toru; Yokota, Yasuhiro; Noguchi, Rina; Hayakawa, Masahiko; Hirata, Naoyuki; Honda, Rie; Matsuoka, Moe; Sakatani, Naoya; Suzuki, Hidehiko; Yamada, Manabu; Yoshioka, Kazuo; Sawada, Hirotaka; Hemmi, Ryodo; Kikuchi, Hiroshi; Ogawa, Kazunori; Watanabe, Sei ichiro; Tanaka, Satoshi; Yoshikawa, Makoto; Tsuda, Yuichi; Sugita, Seiji.

:: Icarus, 巻 331, 01.10.2019, p. 179-191.

研究成果: ジャーナルへの寄稿記事

Michikami, T, Honda, C, Miyamoto, H, Hirabayashi, M, Hagermann, A, Irie, T, Nomura, K, Ernst, CM, Kawamura, M, Sugimoto, K, Tatsumi, E, Morota, T, Hirata, N, Noguchi, T, Cho, Y, Kameda, S, Kouyama, T, Yokota, Y, Noguchi, R, Hayakawa, M, Hirata, N, Honda, R, Matsuoka, M, Sakatani, N, Suzuki, H, Yamada, M, Yoshioka, K, Sawada, H, Hemmi, R, Kikuchi, H, Ogawa, K, Watanabe, SI, Tanaka, S, Yoshikawa, M, Tsuda, Y & Sugita, S 2019, 'Boulder size and shape distributions on asteroid Ryugu', Icarus, 巻. 331, pp. 179-191. https://doi.org/10.1016/j.icarus.2019.05.019
Michikami T, Honda C, Miyamoto H, Hirabayashi M, Hagermann A, Irie T その他. Boulder size and shape distributions on asteroid Ryugu. Icarus. 2019 10 1;331:179-191. https://doi.org/10.1016/j.icarus.2019.05.019
Michikami, Tatsuhiro ; Honda, Chikatoshi ; Miyamoto, Hideaki ; Hirabayashi, Masatoshi ; Hagermann, Axel ; Irie, Terunori ; Nomura, Keita ; Ernst, Carolyn M. ; Kawamura, Masaki ; Sugimoto, Kiichi ; Tatsumi, Eri ; Morota, Tomokatsu ; Hirata, Naru ; Noguchi, Takaaki ; Cho, Yuichiro ; Kameda, Shingo ; Kouyama, Toru ; Yokota, Yasuhiro ; Noguchi, Rina ; Hayakawa, Masahiko ; Hirata, Naoyuki ; Honda, Rie ; Matsuoka, Moe ; Sakatani, Naoya ; Suzuki, Hidehiko ; Yamada, Manabu ; Yoshioka, Kazuo ; Sawada, Hirotaka ; Hemmi, Ryodo ; Kikuchi, Hiroshi ; Ogawa, Kazunori ; Watanabe, Sei ichiro ; Tanaka, Satoshi ; Yoshikawa, Makoto ; Tsuda, Yuichi ; Sugita, Seiji. / Boulder size and shape distributions on asteroid Ryugu. :: Icarus. 2019 ; 巻 331. pp. 179-191.
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title = "Boulder size and shape distributions on asteroid Ryugu",
abstract = "In 2018, the Japanese spacecraft Hayabusa2, arrived at the small asteroid Ryugu. The surface of this C-type asteroid is covered with numerous boulders whose size and shape distributions are investigated in this study. Using a few hundred Optical Navigation Camera (ONC) images with a pixel scale of approximately 0.65 m, we focus on boulders greater than 5 m in diameter. Smaller boulders are also considered using five arbitrarily chosen ONC close-up images with pixel scales ranging from 0.7 to 6 cm. Across the entire surface area (~2.7 km2) of Ryugu, nearly 4400 boulders larger than 5 m were identified. Boulders appear to be uniformly distributed across the entire surface, with some slight differences in latitude and longitude. At ~50 km−2, the number density of boulders larger than 20 m is twice as large as on asteroid Itokawa (or Bennu). The apparent shapes of Ryugu's boulders resemble laboratory impact fragments, with larger boulders being more elongated. The ratio of the total volume of boulders larger than 5 m to the total excavated volume of craters larger than 20 m on Ryugu can be estimated to be ~94{\%}, which is comparatively high. These observations strongly support the hypothesis that most boulders found on Ryugu resulted from the catastrophic disruption of Ryugu's larger parent body, as described in previous papers (Watanabe et al., 2019; Sugita et al., 2019). The cumulative size distribution of boulders larger than 5 m has a power-index of −2.65 ± 0.05, which is comparatively shallow compared with other asteroids visited by spacecraft. For boulders smaller than 4 m, the power-index is even shallower and ranges from −1.65 ± 0.05 to −2.01 ± 0.06. This particularly shallow power-index implies that some boulders are buried in Ryugu's regolith. Based on our observations, we suggest that boulders near the equator might have been buried by the migration of finer material and, as a result, the number density of boulders larger than 5 m in the equatorial region is lower than at higher latitudes.",
author = "Tatsuhiro Michikami and Chikatoshi Honda and Hideaki Miyamoto and Masatoshi Hirabayashi and Axel Hagermann and Terunori Irie and Keita Nomura and Ernst, {Carolyn M.} and Masaki Kawamura and Kiichi Sugimoto and Eri Tatsumi and Tomokatsu Morota and Naru Hirata and Takaaki Noguchi and Yuichiro Cho and Shingo Kameda and Toru Kouyama and Yasuhiro Yokota and Rina Noguchi and Masahiko Hayakawa and Naoyuki Hirata and Rie Honda and Moe Matsuoka and Naoya Sakatani and Hidehiko Suzuki and Manabu Yamada and Kazuo Yoshioka and Hirotaka Sawada and Ryodo Hemmi and Hiroshi Kikuchi and Kazunori Ogawa and Watanabe, {Sei ichiro} and Satoshi Tanaka and Makoto Yoshikawa and Yuichi Tsuda and Seiji Sugita",
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T1 - Boulder size and shape distributions on asteroid Ryugu

AU - Michikami, Tatsuhiro

AU - Honda, Chikatoshi

AU - Miyamoto, Hideaki

AU - Hirabayashi, Masatoshi

AU - Hagermann, Axel

AU - Irie, Terunori

AU - Nomura, Keita

AU - Ernst, Carolyn M.

AU - Kawamura, Masaki

AU - Sugimoto, Kiichi

AU - Tatsumi, Eri

AU - Morota, Tomokatsu

AU - Hirata, Naru

AU - Noguchi, Takaaki

AU - Cho, Yuichiro

AU - Kameda, Shingo

AU - Kouyama, Toru

AU - Yokota, Yasuhiro

AU - Noguchi, Rina

AU - Hayakawa, Masahiko

AU - Hirata, Naoyuki

AU - Honda, Rie

AU - Matsuoka, Moe

AU - Sakatani, Naoya

AU - Suzuki, Hidehiko

AU - Yamada, Manabu

AU - Yoshioka, Kazuo

AU - Sawada, Hirotaka

AU - Hemmi, Ryodo

AU - Kikuchi, Hiroshi

AU - Ogawa, Kazunori

AU - Watanabe, Sei ichiro

AU - Tanaka, Satoshi

AU - Yoshikawa, Makoto

AU - Tsuda, Yuichi

AU - Sugita, Seiji

PY - 2019/10/1

Y1 - 2019/10/1

N2 - In 2018, the Japanese spacecraft Hayabusa2, arrived at the small asteroid Ryugu. The surface of this C-type asteroid is covered with numerous boulders whose size and shape distributions are investigated in this study. Using a few hundred Optical Navigation Camera (ONC) images with a pixel scale of approximately 0.65 m, we focus on boulders greater than 5 m in diameter. Smaller boulders are also considered using five arbitrarily chosen ONC close-up images with pixel scales ranging from 0.7 to 6 cm. Across the entire surface area (~2.7 km2) of Ryugu, nearly 4400 boulders larger than 5 m were identified. Boulders appear to be uniformly distributed across the entire surface, with some slight differences in latitude and longitude. At ~50 km−2, the number density of boulders larger than 20 m is twice as large as on asteroid Itokawa (or Bennu). The apparent shapes of Ryugu's boulders resemble laboratory impact fragments, with larger boulders being more elongated. The ratio of the total volume of boulders larger than 5 m to the total excavated volume of craters larger than 20 m on Ryugu can be estimated to be ~94%, which is comparatively high. These observations strongly support the hypothesis that most boulders found on Ryugu resulted from the catastrophic disruption of Ryugu's larger parent body, as described in previous papers (Watanabe et al., 2019; Sugita et al., 2019). The cumulative size distribution of boulders larger than 5 m has a power-index of −2.65 ± 0.05, which is comparatively shallow compared with other asteroids visited by spacecraft. For boulders smaller than 4 m, the power-index is even shallower and ranges from −1.65 ± 0.05 to −2.01 ± 0.06. This particularly shallow power-index implies that some boulders are buried in Ryugu's regolith. Based on our observations, we suggest that boulders near the equator might have been buried by the migration of finer material and, as a result, the number density of boulders larger than 5 m in the equatorial region is lower than at higher latitudes.

AB - In 2018, the Japanese spacecraft Hayabusa2, arrived at the small asteroid Ryugu. The surface of this C-type asteroid is covered with numerous boulders whose size and shape distributions are investigated in this study. Using a few hundred Optical Navigation Camera (ONC) images with a pixel scale of approximately 0.65 m, we focus on boulders greater than 5 m in diameter. Smaller boulders are also considered using five arbitrarily chosen ONC close-up images with pixel scales ranging from 0.7 to 6 cm. Across the entire surface area (~2.7 km2) of Ryugu, nearly 4400 boulders larger than 5 m were identified. Boulders appear to be uniformly distributed across the entire surface, with some slight differences in latitude and longitude. At ~50 km−2, the number density of boulders larger than 20 m is twice as large as on asteroid Itokawa (or Bennu). The apparent shapes of Ryugu's boulders resemble laboratory impact fragments, with larger boulders being more elongated. The ratio of the total volume of boulders larger than 5 m to the total excavated volume of craters larger than 20 m on Ryugu can be estimated to be ~94%, which is comparatively high. These observations strongly support the hypothesis that most boulders found on Ryugu resulted from the catastrophic disruption of Ryugu's larger parent body, as described in previous papers (Watanabe et al., 2019; Sugita et al., 2019). The cumulative size distribution of boulders larger than 5 m has a power-index of −2.65 ± 0.05, which is comparatively shallow compared with other asteroids visited by spacecraft. For boulders smaller than 4 m, the power-index is even shallower and ranges from −1.65 ± 0.05 to −2.01 ± 0.06. This particularly shallow power-index implies that some boulders are buried in Ryugu's regolith. Based on our observations, we suggest that boulders near the equator might have been buried by the migration of finer material and, as a result, the number density of boulders larger than 5 m in the equatorial region is lower than at higher latitudes.

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