Macroporosity and Grain Density of Rubble Pile Asteroid (162173) Ryugu

Grott, M.; Biele, Jens; Michel, Patrick; Sugita, Seiji; Schröder, Stefan; Sakatani, Naoya; Neumann, Wladimir; Kameda, Shingo; Michikami, Tatsuhiro; Honda, Chikatoshi

doi:10.1002/essoar.10503201.1

Cited by 2 publications

(1 citation statement)

References 19 publications

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“…Provided that the sample is representative, the global average density (bulk density) of Ryugu is 1190 ± 20 kg m -3 [8] , and indicates macro-porosity of ~10% which is contrary to large macro-porosities required for primitive asteroids when typical meteoritic density is assumed 28 , provided that the returned samples collected from the two sampling sites on the surface of Ryugu represent the entire materials of Ryugu. The low macro-porosity of Ryugu is probably consistent with the packing model using the size-frequency distribution of Ryugu 29 . A difference in density distribution is found between Chambers A and C, with particles denser than 1800 kg m -3 [9] (> 2σ) only found in Chamber A, that being within the density range of typical meteorites found on Earth 12 , and indicating Ryugu might consist of a mixture of particles from different origins 30 or different degree of alteration processes in the parent bodies 5,31 .…”

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confidence: 76%

Ryugu: A brand-new planetary sample returned from a C-type asteroid

Yada

Abe

Okada

et al. 2021

Preprint

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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 samples. Here we describe the bulk sample 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 samples 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 sample’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.

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Section: Main Textsupporting

confidence: 76%

Ryugu: A brand-new planetary sample returned from a C-type asteroid

Yada

Abe

Okada

et al. 2021

Preprint

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On the Stability of Spinning Asteroids

Persson

Biele

2022

Tribol Lett

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Most asteroids with a diameter larger than $$\sim 300 \ {\mathrm{m}}$$ ∼ 300 m are rubble piles, i.e., consisting of more than one solid object. All asteroids are rotating but almost all asteroids larger than $$\sim 300 \ \mathrm{m}$$ ∼ 300 m rotate with a period longer than $$2.3 \ {\text{hours}}$$ 2.3 hours , which is the critical period where the centrifugal force equals the gravitational force. This indicates that there are nearly no adhesive interaction forces between the asteroid fragments. We show that this is due to the surface roughness of the asteroid particles which reduces the van der Waals interaction between the particles by a factor of 100 for micrometer sized particles and even more for larger particles. We show that surface roughness results in an interaction force which is independent of the size of the particles, in contrast to the linear size dependency expected for particles with smooth surfaces. Thus, two stone fragments of size $$100 \ {\mathrm{nm}}$$ 100 nm attract each other with the same non-gravitational force as two fragments of size $$10 \ {\mathrm{m}}$$ 10 m .

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Macroporosity and Grain Density of Rubble Pile Asteroid (162173) Ryugu

Cited by 2 publications

References 19 publications

Ryugu: A brand-new planetary sample returned from a C-type asteroid

Ryugu: A brand-new planetary sample returned from a C-type asteroid

On the Stability of Spinning Asteroids

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