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Träfflista för sökning "WFRF:(Kikuchi Shota) "

Search: WFRF:(Kikuchi Shota)

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1.
  • Michikami, Tatsuhiro, et al. (author)
  • Three-axial shape distributions of pebbles, cobbles and boulders smaller than a few meters on asteroid Ryugu
  • 2022
  • In: Icarus. - : Elsevier. - 0019-1035 .- 1090-2643. ; 381
  • Journal article (peer-reviewed)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 <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.
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2.
  • Yabuta, Hikaru, et al. (author)
  • Macromolecular organic matter in samples of the asteroid (162173) Ryugu
  • 2023
  • In: Science. - : American Association for the Advancement of Science. - 0036-8075 .- 1095-9203. ; 379:6634
  • Journal article (peer-reviewed)abstract
    • Samples of the carbonaceous asteroid (162173) Ryugu were collected and brought to Earth by the Hayabusa2 spacecraft. We investigated the macromolecular organic matter in Ryugu samples and found that it contains aromatic and aliphatic carbon, ketone, and carboxyl functional groups. The spectroscopic features of the organic matter are consistent with those in chemically primitive carbonaceous chondrite meteorites that experienced parent-body aqueous alteration (reactions with liquid water). The morphology of the organic carbon includes nanoglobules and diffuse carbon associated with phyllosilicate and carbonate minerals. Deuterium and/or nitrogen-15 enrichments indicate that the organic matter formed in a cold molecular cloud or the presolar nebula. The diversity of the organic matter indicates variable levels of aqueous alteration on Ryugus parent body.
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