KINDAI UNIVERSITY


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MICHIKAMI Tatsuhiro

Profile

FacultyDepartment of Mechanical Engineering / General Education Division
PositionProfessor
Degree
Commentator Guidehttps://www.kindai.ac.jp/meikan/274-michikami-tatsuhiro.html
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Last Updated :2020/07/08

Education and Career

Education

  •  - 2001 , The University of Tokyo, Graduate School, Division of Science
  •  - 1997 , Hokkaido University, Faculty of Science

Academic & Professional Experience

  •   2019 04 ,  - 現在, Faculty of Engineering, Faculty of Engineering, Kindai University
  •   2003 , - ASSistant Professor, Fukushima National college of Technology

Research Activities

Research Interests

  • Regolith, Asteroid, Planetary Science

Published Papers

  • Three-dimensional imaging of crack growth in L chondrites after high-velocity impact experiments., Tatsuhiro Michikami, Axel Hagermann, Akira Tsuchiyama, Hirotaka Yamaguchi, Terunori Irie, Keita Nomura, Osamu Sasaki, Michihiko Nakamura, Satoshi Okumura, Sunao Hasegawa, Planetary and Space Science, Planetary and Space Science, 177(104690 (14pp.)), Nov. 2019 , Refereed
  • 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 Morot, Naru Hirata, Takaaki Noguchi, Yuichiro Cho, Shingo Kameda, Toru Kouyama, Yasuhiro Yokota, Rina Noguchi, Masahiko Hayakawa, Naoyuki 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, Icarus, Icarus, 331, 179 - 191, Oct. 2019 , Refereed
  • Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu-A spinning top-shaped rubble pile., S Watanabe, M Hirabayashi, N Hirata, Na Hirata, R Noguchi, Y Shimaki, H Ikeda, E Tatsumi, M Yoshikawa, S Kikuchi, H Yabuta, T Nakamura, S Tachibana, Y Ishihara, T Morota, K Kitazato, N Sakatani, K Matsumoto, K Wada, H Senshu, C Honda, T Michikami, H Takeuchi, T Kouyama, R Honda, S Kameda, T Fuse, H Miyamoto, G Komatsu, S Sugita, T Okada, N Namiki, M Arakawa, M Ishiguro, M Abe, R Gaskell, E Palmer, O S Barnouin, P Michel, A S French, J W McMahon, D J Scheeres, P A Abell, Y Yamamoto, S Tanaka, K Shirai, M Matsuoka, M Yamada, Y Yokota, H Suzuki, K Yoshioka, Y Cho, S Tanaka, N Nishikawa, T Sugiyama, H Kikuchi, R Hemmi, T Yamaguchi, N Ogawa, G Ono, Y Mimasu, K Yoshikawa, T Takahashi, Y Takei, A Fujii, C Hirose, T Iwata, M Hayakawa, S Hosoda, O Mori, H Sawada, T Shimada, S Soldini, H Yano, R Tsukizaki, M Ozaki, Y Iijima, K Ogawa, M Fujimoto, T-M Ho, A Moussi, R Jaumann, J-P Bibring, C Krause, F Terui, T Saiki, S Nakazawa, Y Tsuda, Science (New York, N.Y.), Science (New York, N.Y.), 364(6437), 268 - 272, Apr. 19 2019 , Refereed
    Summary:The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018. We present Hayabusa2 observations of Ryugu's shape, mass, and geomorphology. Ryugu has an oblate "spinning top" shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu's shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge.
  • Shape and Rotational Motion Models for Tumbling and Monolithic Asteroid 2012 TC4: High Time Resolution Light Curve with the Tomo-e Gozen Camera, Seitaro Urakawa, Ryou Ohsawa, Shigeyuki Sako, Shin-ichiro Okumura, Yuri Sakurai, Jun Takahashi, Kazuyoshi Imamura, Hiroyuki Naito, Fumitake Watanabe, Ryoma Nagayoshi, Yasuhiko Murakami, Ryo Okazaki, Tomohiko Sekiguchi, Masateru Ishiguro, Tatsuhiro Michikami, Makoto Yoshikawa, The Astronomical Journal, The Astronomical Journal, 157(155), Apr. 2019 , Refereed
  • The geomorphology, color, and thermal properties of Ryugu: Implications for parent-body processes, S. Sugita, R. Honda, T. Morota, S. Kameda, H. Sawada, E. Tatsumi, M. Yamada, C. Honda, Y. Yokota, T. Kouyama, N. Sakatani, K. Ogawa, H. Suzuki, T. Okada, N. Namiki, S. Tanaka, Y. Iijima, K. Yoshioka, M. Hayakawa, Y. Cho, M. Matsuoka, N. Hirata, N. Hirata, H. Miyamoto, D. Domingue, M. Hirabayashi, T. Nakamura, T. Hiroi, T. Michikami, P. Michel, R.-L. Ballouz, O. S. Barnouin, C. M. Ernst, S. E. Schröder, H. Kikuchi, R. Hemmi, G. Komatsu, T. Fukuhara, M. Taguchi, T. Arai, H. Senshu, H. Demura, Y. Ogawa, Y. Shimaki, T. Sekiguchi, T. G. Müller, A. Hagermann, T. Mizuno, H. Noda, K. Matsumoto, R. Yamada, Y. Ishihara, H. Ikeda, H. Araki, K. Yamamoto, S. Abe, F. Yoshida, A. Higuchi, S. Sasaki, S. Oshigami, S. Tsuruta, K. Asari, S. Tazawa, M. Shizugami, J. Kimura, T. Otsubo, H. Yabuta, S. Hasegawa, M. Ishiguro, S. Tachibana, E. Palmer, R. Gaskell, L. Le Corre, R. Jaumann, K. Otto, N. Schmitz, P. A. Abell, M. A. Barucci, M. E. Zolensky, F. Vilas, F. Thuillet, C. Sugimoto, N. Takaki, Y. Suzuki, H. Kamiyoshihara, M. Okada, K. Nagata, M. Fujimoto, M. Yoshikawa, Y. Yamamoto, K. Shirai, R. Noguchi, N. Ogawa, F. Terui, S. Kikuchi, T. Yamaguchi, Y. Oki, Y. Takao, H. Takeuchi, G. Ono, Y. Mimasu, K. Yoshikawa, T. Takahashi, Y. Takei, A. Fujii, C. Hirose, S. Nakazawa, S. Hosoda, O. Mori, T. Shimada, S. Soldini, T. Iwata, M. Abe, H. Yano, R. Tsukizaki, M. Ozaki, K. Nishiyama, T. Saiki, S. Watanabe, Y. Tsuda, Science, Science, 364, Apr. 2019 , Refereed
  • The western bulge of 162173 Ryugu formed as a result of a rotationally driven deformation process, Masatoshi Hirabayashi, Eri Tatsumi, Hideaki Miyamoto, Goro Komatsu, Seiji Sugita, Sei-ichiro Watanabe, Daniel J. Scheeres, Olivier S. Barnouin, Patrick Michel, Chikatoshi Honda, Tatsuhiro Michikami, Yuichiro Cho, Tomokatsu Morota, Naru Hirata, Naoyuki Hirata, Naoya Sakatani, Stephen R. Schwartz, Rie Honda, Yasuhiro Yokota, Shingo Kameda, Hidehiko Suzuki, Toru Kouyama, Masahiko Hayakawa, Moe Matsuoka, Kazuo Yoshioka, Kazunori Ogawa, Hirotaka Sawada, Makoto Yoshikawa, Yuichi Tsuda, The Astronomical Journal Letters, The Astronomical Journal Letters, 874(1), Mar. 2019 , Refereed
  • Asteroid Ryugu before the Hayabusa2 encounter, Koji Wada, Matthias Grott, Patrick Michel, Kevin J. Walsh, Antonella M. Barucci, Jens Biele, Jürgen Blum, Carolyn M. Ernst, Jan Thimo Grundmann, Bastian Gundlach, Axel Hagermann, Maximilian Hamm, Martin Jutzi, Myung-Jin Kim, Ekkehard Kührt, Lucille Le Corre, Guy Libourel, Roy Lichtenheldt, Alessandro Maturilli, Scott R. Messenger, Tatsuhiro Michikami, Hideaki Miyamoto, Stefano Mottola, Thomas Müller, Akiko M. Nakamura, Larry R. Nittler, Kazunori Ogawa, Tatsuaki Okada, Ernesto Palomba, Naoya Sakatani, Stefan E. Schröder, Hiroki Senshu, Driss Takir, Michael E. Zolensky, International Regolith, Science Group, IRSG) in Hayabusa, project, Progress in Earth and Planetary Science, Progress in Earth and Planetary Science, 5(82), Nov. 2018 , Refereed
  • Influence of petrographic textures on the shapes of impact experiment fine fragments measuring several tens of microns: Comparison with Itokawa regolith particles., T. Michikami, T.Kadokawa, A.Tsuchiyama, A.Hagermann, T. Nakano, K. Uesugi, S.Hasegawa, Icarus, Icarus, 302, 109 - 125, Mar. 2018 , Refereed
  • Anisotropic Ejection from Active Asteroid P/2010 A2: An Implication of Impact Shattering on an Asteroid., Y. Kim, M. Ishiguro, T.Michikami, A. M. Nakamura, The Astronomical Journal, The Astronomical Journal, 153, 228 - 238, Apr. 2017 , Refereed
  • Detection of Intact Lava Tubes at Marius Hills on the Moon by SELENE (Kaguya) Lunar Radar Sounder, T. Kaku, J. Haruyama, W. Miyake, A. Kumamoto, K. Ishiyama, T. Nishibori, K. Yamamoto, Sarah T. Crites, T. Michikami, Y. Yokota, R. Sood, H. J. Melosh, L. Chappaz, K. C. Howell, GEOPHYSICAL RESEARCH LETTERS, GEOPHYSICAL RESEARCH LETTERS, 44(20), 10155 - 10161, Oct. 2017 , Refereed
    Summary:Intact lunar lava tubes offer a pristine environment to conduct scientific examination of the Moon's composition and potentially serve as secure shelters for humans and instruments. We investigated the SELENE Lunar Radar Sounder (LRS) data at locations close to the Marius Hills Hole (MHH), a skylight potentially leading to an intact lava tube, and found a distinctive echo pattern exhibiting a precipitous decrease in echo power, subsequently followed by a large second echo peak that may be evidence for the existence of a lava tube. The search area was further expanded to 13.00-15.00 degrees N, 301.85-304.01 degrees E around the MHH, and similar LRS echo patterns were observed at several locations. Most of the locations are in regions of underground mass deficit suggested by GRAIL gravity data analysis. Some of the observed echo patterns are along rille A, where the MHH was discovered, or on the southwest underground extension of the rille.
  • Oblique impact cratering experiments in brittle targets: Implications for elliptical craters on the Moon, Tatsuhiro Michikami, Axel Hagermann, Tomokatsu Morota, Junichi Haruyama, Sunao Hasegawa, PLANETARY AND SPACE SCIENCE, PLANETARY AND SPACE SCIENCE, 135, 27 - 36, Jan. 2017 , Refereed
    Summary:Most impact craters observed on planetary bodies are the results of oblique impacts of meteoroids. To date, however, there have only been very few laboratory oblique impact experiments for analogue targets relevant to the surfaces of extraterrestrial bodies. In particular, there is a lack of laboratory oblique impact experiments into brittle targets with a material strength on the order of 1 MPa, with the exception of ice. A strength on the order of 1 MPa is considered to be the corresponding material strength for the formation of craters in the 100 m size range on the Moon. Impact craters are elliptical if the meteoroid's trajectory is below a certain threshold angle of incidence, and it is known that the threshold angle depends largely on the material strength. Therefore, we examined the threshold angle required to produce elliptical craters in laboratory impact experiments into brittle targets. This work aims to constrain current interpretations of lunar elliptical craters and pit craters with sizes below a hundred meters. We produced mortar targets with compressive strength of 3.2 MPa. A spherical nylon projectile (diameter 7.14 mm) was shot into the target surface at a nominal velocity of 2.3 km/s, with an impact angle of 5 degrees-90 degrees from horizontal. The threshold angle of this experiment ranges from 15 degrees to 20 degrees. We confirmed that our experimental data agree with previous empirical equations in terms of the cratering efficiency and the threshold impact angle. In addition, in order to simulate the relatively large lunar pit craters related to underground cavities, we conducted a second series of experiments under similar impact conditions using targets with an underground rectangular cavity. Size and outline of craters that created a hole are similar to those of craters without a hole. Moreover, when observed from an oblique angle, a crater with a hole has a topography that resembles the lunar pit craters. The relation between the impact velocity of meteoroids on the Moon and the probability of elliptical crater formation was investigated based on our experimental results and an existing empirical equation. The results suggest a distinct possibility that most craters in the 100 m size range on the Moon, given their elliptical shape, originated as secondary craters.
  • Fragment shapes in impact experiments ranging from cratering to catastrophic disruption, Tatsuhiro Michikami, Axel Hagermann, Tokiyuki Kadokawa, Akifumi Yoshida, Akira Shimada, Sunao Hasegawa, Akira Tsuchiyama, ICARUS, ICARUS, 264, 316 - 330, Jan. 2016 , Refereed
    Summary:Laboratory impact experiments have found that impact fragments tend to be elongated. Their shapes, as defined by axes a, b and c, these being the maximum dimensions of the fragment in three mutually orthogonal planes (a >= b >= c), are distributed around mean values of the axial ratios b/a similar to 0.7 and c/a similar to 0.5. This corresponds to a:b:c in the simple proportion 2:root 2:1. The shape distributions of some boulders on Asteroid Eros, the small- and fast-rotating asteroids (diameter <200 m and rotation period <1 h), and asteroids in young families, are similar to those of laboratory fragments created in catastrophic disruptions. Catastrophic disruption is, however, a process that is different from impact cratering. In order to systematically investigate the shapes of fragments in the range from impact cratering to catastrophic disruption, impact experiments for basalt targets 5-15 cm in size were performed. A total of 28 impact experiments were carried out by firing a spherical nylon projectile (diameter 7.14 mm) perpendicularly into the target surface at velocities of 1.60-7.13 km/s. More than 12,700 fragments with b a 4 mm generated in the impact experiments were measured. We found that the mean value of c/a in each impact decreases with decreasing impact energy per unit target mass. For instance, the mean value of c/a in an impact cratering event is nearly 0.2, which is considerably smaller than c/a in a catastrophic disruption (similar to 0.5). The data presented here can provide important evidence to interpret the shapes of asteroids and boulders on asteroid surfaces, and can constrain current interpretations of asteroid formation. As an example, by applying our experimental results to the boulder shapes on Asteroid Itokawa's surface, we can infer that Itokawa's parent body must have experienced a catastrophic disruption. (C) 2015 The Authors. Published by Elsevier Inc.
  • Impact cratering experiments in brittle targets with variable thickness: Implications for deep pit craters on Mars, T. Michikami, A. Hagermann, H. Miyamoto, S. Miura, J. Haruyama, P. S. Lykawka, PLANETARY AND SPACE SCIENCE, PLANETARY AND SPACE SCIENCE, 96, 71 - 80, Jun. 2014 , Refereed
    Summary:High-resolution images reveal that numerous pit craters exist on the surface of Mars. For some pit craters, the depth-to-diameter ratios are much greater than for ordinary craters. Such deep pit craters are generally considered to be the results of material drainage into a subsurface void space, which might be formed by a lava tube, dike injection, extensional fracturing, and dilational normal faulting. Morphological studies indicate that the formation of a pit crater might be triggered by the impact event, and followed by collapse of the ceiling. To test this hypothesis, we carried out laboratory experiments of impact cratering into brittle targets with variable roof thickness. In particular, the effect of the target thickness on the crater formation is studied to understand the penetration process by an impact. For this purpose, we produced mortar targets with roof thickness of 1-6 cm, and a bulk density of 1550 kg/m(3) by using a mixture of cement, water and sand (0.2 mm) in the ratio of 1:1:10, by weight. The compressive strength of the resulting targets is 3.2 +/- 0.9 MPa. A spherical nylon projectile (diameter 7 mm) is shot perpendicularly into the target surface at the nominal velocity of 1.2 km/s, using a two-stage light-gas gun. Craters are formed on the opposite side of the impact even when no target penetration occurs. Penetration of the target is achieved when craters on the opposite sides of the target connect with each other. In this case, the cross section of crater somehow attains a flat hourglass-like shape. We also find that the crater diameter on the opposite side is larger than that on the impact side, and more fragments are ejected from the crater on the opposite side than from the crater on the impact side. This result gives a qualitative explanation for the observation that the Martian deep pit craters lack a raised rim and have the ejecta deposit on their floor instead. (C) 2014 Published by Elsevier Ltd.
  • Three-dimensional structure of Hayabusa samples: origin and evolution of Itokawa regolith., Akira Tsuchiyama, Masayuki Uesugi, Takashi Matsushima, Tatsuhiro Michikami, Toshihiko Kadono, Tomoki Nakamura, Kentaro Uesugi, Tsukasa Nakano, Scott A Sandford, Ryo Noguchi, Toru Matsumoto, Junya Matsuno, Takashi Nagano, Yuta Imai, Akihisa Takeuchi, Yoshio Suzuki, Toshihiro Ogami, Jun Katagiri, Mitsuru Ebihara, Trevor R Ireland, Fumio Kitajima, Keisuke Nagao, Hiroshi Naraoka, Takaaki Noguchi, Ryuji Okazaki, Hisayoshi Yurimoto, Michael E Zolensky, Toshifumi Mukai, Masanao Abe, Toru Yada, Akio Fujimura, Makoto Yoshikawa, Junichiro Kawaguchi, Science (New York, N.Y.), Science (New York, N.Y.), 333(6046), 1125 - 8, Aug. 26 2011 , Refereed
    Summary:Regolith particles on the asteroid Itokawa were recovered by the Hayabusa mission. Their three-dimensional (3D) structure and other properties, revealed by x-ray microtomography, provide information on regolith formation. Modal abundances of minerals, bulk density (3.4 grams per cubic centimeter), and the 3D textures indicate that the particles represent a mixture of equilibrated and less-equilibrated LL chondrite materials. Evidence for melting was not seen on any of the particles. Some particles have rounded edges. Overall, the particles' size and shape are different from those seen in particles from the lunar regolith. These features suggest that meteoroid impacts on the asteroid surface primarily form much of the regolith particle, and that seismic-induced grain motion in the smooth terrain abrades them over time.
  • The shape distribution of boulders on Asteroid 25143 Itokawa: Comparison with fragments from impact experiments, Tatsuhiro Michikami, Akiko M. Nakamura, Naru Hirata, ICARUS, ICARUS, 207(1), 277 - 284, May 2010 , Refereed
    Summary:Laboratory impact experiments have found that the shape of fragments over a broad size range is distributed around the mean value of the axial ratio 2:root 2:1, which is independent of a wide range of experimental conditions. We report the shape statistics of boulders with size of 0.1-30 m on the surface of Asteroid 25143 Itokawa based on high-resolution images obtained by the Hayabusa spacecraft in order to investigate whether their shape distribution is similar to the distribution obtained for fragments (smaller than 0.1 m) in laboratory impact experiments. We also investigated the shapes of boulders with size of 0.1-150 m on Asteroid 433 Eros using a few arbitrary selected images by the NEAR spacecraft, in order to compare those with the shapes on Asteroid ltokawa. In addition, the shapes of small- and fast-rotating asteroids (diameter <200 m and rotation period <1 h), which are natural fragments from past impact events among asteroids, were inferred from archived light curve data taken by ground-based telescopes. The results show that the shape distributions of laboratory fragments are similar to those of the boulders on Eros and of the small- and fast-rotating asteroids, but are different from those on ltokawa. However, we propose that the apparent difference between the boulders of Itokawa and the laboratory fragments is due to the migration of boulders. Therefore, we suggest that the shape distributions of the boulders ranging from 0.1 to 150 m in size and the small- and fast-rotating asteroids are similar to those obtained for the fragments generated in laboratory impact experiments. (C) 2009 Elsevier Inc. All rights reserved.
  • A survey of possible impact structures on 25143 Itokawa, Naru Hirata, Olivier S. Barnouin-Jha, Chikatoshi Honda, Ryosuke Nakamura, Hideaki Miyamoto, Sho Sasaki, Hirohide Demura, Akiko M. Nakamura, Tatsuhiro Michikami, Robert W. Gaskell, Jun Saito, ICARUS, ICARUS, 200(2), 486 - 502, Apr. 2009 , Refereed
    Summary:We determined the morphologies and dimensions of possible impact craters on the surface of Asteroid 25143 Itokawa from images taken by the Hayabusa spacecraft. Circular depressions, circular features with flat floors or convex floors, and circular features with smooth surfaces were identified as possible craters. The survey identified 38 candidates with widely varying morphologies including rough, smooth and saddle-shaped floors, a lack of raised rims and fresh material exposures. The average depth/diameter ratio was 0.08 +/- 0.03: these craters are very shallow relative to craters observed on other asteroids. These shallow craters are a result of (1) target curvature influencing the cratering process, (2) raised rim not being generated by this process, and (3) fines infilling the craters. As many of the crater candidates have an unusual appearance, we used a classification scheme that reflects the likelihood of an observed candidate's formation by a hypervelocity impact. We considered a variety of alternative interpretations while developing this scheme, including inherited features from a proto-Itokawa, spall scars created by the disruption of the proto-Itokawa, spall scars following the formation of a large crater on Itokawa itself, and apparent depressions due to random arrangements of boulders. The size-frequency distribution of the crater candidates was close to the empirical saturation line at the largest diameter, and then decline with decreasing diameter. (C) 2009 Elsevier Inc. All rights reserved.
  • Size-frequency statistics of boulders on global surface of asteroid 25143 Itokawa, Tatsuhiro Michikami, Akiko M. Nakamura, Naru Hirata, Robert W. Gaskell, Ryosuke Nakamura, Takayuki Honda, Chikatoshi Honda, Kensuke Hiraoka, Jun Saito, Hirohide Demura, Masateru Ishiguro, Hideaki Miyamoto, EARTH PLANETS AND SPACE, EARTH PLANETS AND SPACE, 60(1), 13 - 20, 2008 , Refereed
    Summary:The surface of asteroid 25143 Itokawa is covered with numerous boulders although gravity is very small compared with that of other asteroids previously observed from spacecraft. Here we report the size-frequency statistics of boulders on the entire surface of Itokawa based on high-resolution images (1 pixel similar to 0.4 m) obtained by the Hayabusa spacecraft. There are 373 boulders larger than 5 m in mean horizontal dimension on the entire surface-0.393 km(2)-and the number density is nearly 10(3)/km(2). The cumulative boulder size distribution on the entire surface has a power-index of -3.1 +/- 0.1. For the east and west sides and the head and body portions of Itokawa, the power-index of the size distributions and the number densities of boulders of these areas are thought to be similar from the statistical point of view. A global mapping of boulders shows that there is no apparent correlation in the locations of boulders and craters. The ratio of the total volume of the boulders to the total excavated volume of the craters on Itokawa is similar to 25% when only craters larger than 50 m in mean diameter are considered, and this ratio is extremely larger than that on Eros and the Moon, respectively. The origin of boulders on the surface of Itokawa was examined quantitatively by calculating the number of boulders and the size of the largest boulder using a model based on impact cratering experiments. The result indicated that the boulders on the surface of Itokawa cannot solely be the product of craters. Our results suggest that the boulders originated from the disruption of the larger parent body of Itokawa, as has been described in previous papers (Fujiwata et al., Science, 312, 1330-1334, 2006; Saito et al., Science, 312, 1341-1344, 2006).
  • Impact process of boulders on the surface of asteroid 25143 Itokawa - fragments from collisional disruption, A. M. Nakamura, T. Michikami, N. Hirata, A. Fujiwara, R. Nakamura, M. Ishiguro, H. Miyamoto, H. Demura, K. Hiraoka, T. Honda, C. Honda, J. Saito, T. Hashimoto, T. Kubota, EARTH PLANETS AND SPACE, EARTH PLANETS AND SPACE, 60(1), 7 - 12, 2008 , Refereed
    Summary:The subkilometer-size asteroid 25143 Itokawa is considered to have a gravitationally bounded rubble-pile structure. Boulders appearing in high-resolution images retrieved by the Hayabusa mission revealed the genuine outcome of the collisional event involving the asteroid's parent body. Here we report that the boulders' shapes and structures are strikingly similar to laboratory rock impact fragments despite differences of orders of magnitude in scale and complexities of the physical processes. These similarities suggest the universal character of the process throughout the range of these scales, and the brittle and structurally continuous nature regarding the parent body of the boulders. The similarity was likely preserved because of relatively lesser comminuting processes acting on individual boulders; the close assemblages of similar appearing boulders (a boulder family) represent the impact destruction of boulders on the surface.
  • Regolith migration and sorting on asteroid Itokawa, Hideaki Miyamoto, Hajime Yano, Daniel J. Scheeres, Shinsuke Abe, Olivier Barnouin-Jha, Andrew F. Cheng, Hirohide Demura, Robert W. Gaskell, Naru Hirata, Masateru Ishiguro, Tatsuhiro Michikami, Akiko M. Nakamura, Ryosuke Nakamura, Jun Saito, Sho Sasaki, SCIENCE, SCIENCE, 316(5827), 1011 - 1014, May 2007 , Refereed
    Summary:High-resolution images of the surface of asteroid Itokawa from the Hayabusa mission reveal it to be covered with unconsolidated millimeter-sized and larger gravels. Locations and morphologic characteristics of this gravel indicate that Itokawa has experienced considerable vibrations, which have triggered global-scale granular processes in its dry, vacuum, microgravity environment. These processes likely include granular convection, landslide-like granular migrations, and particle sorting, resulting in the segregation of the fine gravels into areas of potential lows. Granular processes become major resurfacing processes because of Itokawa's small size, implying that they can occur on other small asteroids should those have regolith.
  • Ejecta velocity distribution for impact cratering experiments on porous and low strength targets, Tatsuhiro Michikami, Kouichi Moriguchi, Sunao Hasegawa, Akira Fujiwara, PLANETARY AND SPACE SCIENCE, PLANETARY AND SPACE SCIENCE, 55(1-2), 70 - 88, Jan. 2007 , Refereed
    Summary:Impact cratering experiments on porous targets with various compressive strength ranging from similar to 0.5 to similar to 250 MPa were carried out in order to investigate the relationship between the ejecta velocity, and material strength or porosity of the target. A spherical alumina projectile (diameter similar to 1 mm) was shot perpendicularly into the target surface with velocity ranging from 1.2 to 4.5 km/s (nominal 4 km/s), using a two-stage light-gas gun. The ejecta velocity was estimated from the fall point distance of ejecta. The results show that there are in fact a large fraction of ejecta with very low velocities when the material strength of the target is small and the porosity is high. As an example, in the case of one specific target (compressive strength similar to 0.5 MPa and porosity 43%), the amount of ejecta with velocities lower than 1 m/s is about 40% of the total mass. The average velocity of the ejecta decreases with decreasing material strength or increasing the porosity of the target. Moreover, in our experiments, the ejecta velocity distributions normalized to total ejecta, mass seem to be mainly dependent on the material strength of the target, and not so greatly on the porosity. We also compare our experimental results with those of Gault et al. [1963. Spray ejected from the lunar surface by meteoroid impact. NASA Technical Note D-1767] and Housen [1992. Crater ejecta velocities for impacts on rocky bodies. LPSC XXIII, 555-556] for the ejecta velocity distribution using Housen's nondimensional scaling parameter. The ejecta velocity distributions of our experiments are lower than those of Gault et al. [1963. Spray ejected from the lunar surface by meteoroid impact. NASA Technical Note D-1767] and Housen [1992. Crater ejecta velocities for impacts on rocky bodies. LPSC XIII, 555-556]. (c) 2006 Elsevier Ltd. All rights reserved.
  • Detailed images of asteroid 25143 Itokawa from Hayabusa, J Saito, H Miyamoto, R Nakamura, M Ishiguro, T Michikami, AM Nakamura, H Demura, S Sasaki, N Hirata, C Honda, A Yamamoto, Y Yokota, T Fuse, F Yoshida, DJ Tholen, RW Gaskell, T Hashimoto, T Kubota, Y Higuchi, T Nakamura, P Smith, K Hiraoka, T Honda, S Kobayashi, M Furuya, N Matsumoto, E Nemoto, A Yukishita, K Kitazato, B Dermawan, A Sogame, J Terazono, C Shinohara, H Akiyama, SCIENCE, SCIENCE, 312(5778), 1341 - 1344, Jun. 2006 , Refereed
    Summary:Rendezvous of the Japanese spacecraft Hayabusa with the near-Earth asteroid 25143 Itokawa took place during the interval September through November 2005. The onboard camera imaged the solid surface of this tiny asteroid ( 535 meters by 294 meters by 209 meters) with a spatial resolution of 70 centimeters per pixel, revealing diverse surface morphologies. Unlike previously explored asteroids, the surface of Itokawa reveals both rough and smooth terrains. Craters generally show unclear morphologies. Numerous boulders on Itokawa's surface suggest a rubble-pile structure.
  • Ejecta size-velocity relation derived from the distribution of the secondary craters of kilometer-sized craters on Mars, Y Hirase, AM Nakamura, T Michikami, PLANETARY AND SPACE SCIENCE, PLANETARY AND SPACE SCIENCE, 52(12), 1103 - 1108, Oct. 2004 , Refereed
    Summary:The relation between the size and velocity of impact crater ejecta has been studied by both laboratory experiments and numerical modeling. An alternative method, used here, is to analyze the record of past impact events, such as the distribution of secondary craters on planetary surfaces, as described by Vickery (Icarus 67 (1986) 224; Geophys. Res. Lett. 14 (1987) 726). We first applied the method to lunar images taken by the CLEMENTINE mission, which revealed that the size-velocity relations of ejecta from craters 32 and 40 km in diameter were similar to those derived by Vickery for a crater 39 km in diameter. Next, we studied the distribution of small craters in the vicinity of kilometer-sized craters on three images from the Mars Orbiter Camera (MOC) on board the Mars Global Surveyor (MGS). If these small craters are assumed to be secondaries ejected from the kilometer-sized crater in each image, the ejection velocities are of hundreds of meters per second. These data fill a gap between the previous results of Vickery and those of laboratory studies. (C) 2004 Elsevier Ltd. All rights reserved.

Research Grants & Projects

  • The Other Research Programs, Formation and Evolution of Asteroid