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Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

 Times Cited Count:30 Percentile:96.87(Astronomy & Astrophysics)

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

Journal Articles

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.

Science, 364(6437), p.272 - 275, 2019/04

 Times Cited Count:233 Percentile:99.74(Multidisciplinary Sciences)

The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

Journal Articles

Effect of citrate-based non-toxic solvents on poly(vinylidene fluoride) membrane preparation $$via$$ thermally induced phase separation

Sawada, Shinichi; Ursino, C.*; Galiano, F.*; Simone, S.*; Drioli, E.*; Figoli, A.*

Journal of Membrane Science, 493, p.232 - 242, 2015/11

 Times Cited Count:51 Percentile:88.47(Engineering, Chemical)

The replacement of commonly-used substances with non-toxic equivalents is attracting a great amount of attention in membrane preparation processes. In order to address this issue, we prepared porous poly(vinylidene fluoride) (PVDF) membranes via thermally-induced phase separation using the following non-toxic Citroflex as solvents: acetyl tributyl citrate (ATBC); acetyl triethyl citrate (ATEC); and triethyl citrate (TEC). The pore size of the membranes increased in the following solvent order of ATBC $$<$$ ATEC $$<$$ TEC, which is the same trend of the PVDF/solvent affinity. During the phase separation process, high-affinity solvent molecules should have enough molecular mobility and easily gather with each other to form the large solvent rich phases, thereby producing the large pores. In the pure water microfiltration test using the PVDF membranes, the water permeability can be controlled in the wide range, depending on the pore size.

Oral presentation

Preparation of poly(vinylidene fluoride) membranes via a thermally-induced phase separation method using citric acid esters as a solvent

Sawada, Shinichi; Ulsino, C.*; Galiano, F.*; Simone, S.*; Drioli, E.*; Figoli, A.*

no journal, , 

The replacement of commonly-used substances with non-toxic equivalents is attracting a great amount of attention in membrane preparation processes. In order to address this issue, we prepared poly(vinylidene fluoride) (PVDF) flat membranes via a thermally-induced phase separation method using non-toxic citrate-based solvents: acetyl tributyl citrate (ATBC); acetyl triethyl citrate (ATEC); and triethyl citrate (TEC). The pore size of the prepared PVDF membranes depended on the type of used solvents, and increased in the following solvent order of ATBC $$<$$ ATEC $$<$$ TEC. This order is the same as that of the affinity with PVDF. In the case of the high affinity solvent, the solvent molecules would have high molecular mobility in a polymer solution and easily gather with each other to form the large size solvent-rich phases, which turn to the large pores in the prepared membranes.

Oral presentation

Spectral characteristics of asteroid (162173) Ryugu with Hayabusa2 NIRS3

Takir, D.*; Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; et al.

no journal, , 

JAXA spacecraft and sample return mission Hayabusa2 has arrived at the near-Earth asteroid 162173 Ryugu, which is classified a primitive carbonaceous object. Here we report recent results of near-infrared spectrometer (NIRS3) on the Hayabusa2 spacecraft. The observations provide direct measurements of the surface composition of Ryugu and context for the returned samples. NIRS3 has detected a weak and narrow absorption feature centered at 2.72 micrometer across entire observed surface. This absorption feature is attributed to the presence of OH-bearing minerals. The NIRS3 observations also revealed that Ryugu is the darkest object to be observed up-close by a visiting spacecraft. The intensity of the OH feature and low albedo are consistent with thermally-and/or shock-metamorphosed, and/or carbon-rich space-weathered primitive and hydrated carbonaceous chondrites.

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