ORCID Profile
0000-0001-6076-3614
Current Organisation
University of Tokyo
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Publisher: Springer Science and Business Media LLC
Date: 20-12-2021
DOI: 10.1038/S41550-021-01550-6
Abstract: C-type asteroids 1 are considered to be primitive small Solar System bodies enriched in water and organics, providing clues to the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing 2–7 and on-asteroid measurements 8,9 with Hayabusa2 (ref. 10 ). However, the ground truth provided by laboratory analysis of returned s les is invaluable to determine the fine properties of asteroids and other planetary bodies. We report preliminary results of analyses on returned s les from Ryugu of the particle size distribution, density and porosity, spectral properties and textural properties, and the results of a search for Ca–Al-rich inclusions (CAIs) and chondrules. The bulk s le mainly consists of rugged and smooth particles of millimetre to submillimetre size, confirming that the physical and chemical properties were not altered during the return from the asteroid. The power index of its size distribution is shallower than that of the surface boulder observed on Ryugu 11 , indicating differences in the returned Ryugu s les. The average of the estimated bulk densities of Ryugu s le particles is 1,282 ± 231 kg m −3 , which is lower than that of meteorites 12 , suggesting a high microporosity down to the millimetre scale, extending centimetre-scale estimates from thermal measurements 5,9 . The extremely dark optical to near-infrared reflectance and spectral profile with weak absorptions at 2.7 and 3.4 μm imply a carbonaceous composition with indigenous aqueous alteration, matching the global average of Ryugu 3,4 and confirming that the s le is representative of the asteroid. Together with the absence of submillimetre CAIs and chondrules, these features indicate that Ryugu is most similar to CI chondrites but has lower albedo, higher porosity and more fragile characteristics.
Publisher: Springer Science and Business Media LLC
Date: 19-03-2019
Publisher: Springer Science and Business Media LLC
Date: 07-08-1900
DOI: 10.1038/S41550-022-01841-6
Abstract: Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of s les from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe 3+ to Fe 2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (–OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss.
Publisher: Research Square Platform LLC
Date: 21-06-2021
DOI: 10.21203/RS.3.RS-608561/V1
Abstract: C-type asteroids are considered to be primitive small Solar-System bodies enriched in water and organics, providing clues for understanding the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing and on-asteroid measurements with Hayabusa2, but further studies are expected by direct analyses of returned s les. Here we describe the bulk s le mainly consisting of rugged and smooth particles of millimeter to submillimeter size, preserving physical and chemical properties as they were on the asteroid. The particle size distribution is found steeper than that of surface boulders11. Estimated grain densities of the s les have a peak around 1350 kg m-3, which is lower than that of meteorites suggests a high micro-porosity down to millimeter-scale, as estimated at centimeter-scale by thermal measurements. The extremely dark optical to near-infrared reflectance and the spectral profile with weak absorptions at 2.7 and 3.4 microns implying carbonaceous composition with indigenous aqueous alteration, respectively, match the global average of Ryugu, confirming the s le’s representativeness. Together with the absence of chondrule and Ca-Al-rich inclusion of larger than sub-mm, these features indicate Ryugu is most similar to CI chondrites but with darker, more porous and fragile characteristics.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 04-03-2022
Abstract: The Hayabusa2 spacecraft investigated the C-type (carbonaceous) asteroid (162173) Ryugu. The mission performed two landing operations to collect s les of surface and subsurface material, the latter exposed by an artificial impact. We present images of the second touchdown site, finding that ejecta from the impact crater was present at the s le location. Surface pebbles at both landing sites show morphological variations ranging from rugged to smooth, similar to Ryugu’s boulders, and shapes from quasi-spherical to flattened. The s les were returned to Earth on 6 December 2020. We describe the morphology of grams of returned pebbles and sand. Their erse color, shape, and structure are consistent with the observed materials of Ryugu we conclude that they are a representative s le of the asteroid.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-11-2022
Abstract: The Hayabusa2 spacecraft returned to Earth from the asteroid 162173 Ryugu on 6 December 2020. One day after the recovery, the gas species retained in the s le container were extracted and measured on-site and stored in gas collection bottles. The container gas consists of helium and neon with an extraterrestrial
Location: United States of America
No related grants have been discovered for Seiji Sugita.