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

https://doi.org/10.1038/s41550-020-01271-2

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 C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 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.

scattering length from photoproduction on the proton near the reaction threshold

Ishikawa, Takatsugu*; Fujimura, Hisako*; Fukasawa, Hiroshi*; Hashimoto, Ryo*; He, Q.*; Honda, Yuki*; Hosaka, Atsushi; Iwata, Takahiro*; Kaida, Shun*; Kasagi, Jirota*; et al.

Physical Review C, 101(5), p.052201_1 - 052201_6, 2020/05

https://doi.org/10.1103/PhysRevC.101.052201

An Evaluation method of reflectance spectra to be obtained by Hayabusa2 Near-Infrared Spectrometer (NIRS3) based on laboratory measurements of carbonaceous chondrites

Matsuoka, Moe*; Nakamura, Tomoki*; Osawa, Takahito; Iwata, Takahiro*; Kitazato, Kohei*; Abe, Masanao*; Nakauchi, Yusuke*; Arai, Takehiko*; Komatsu, Mutsumi*; Hiroi, Takahiro*; et al.

Earth, Planets and Space (Internet), 69(1), p.120_1 - 120_12, 2017/12

AA2017-0327.pdf:1.53MB

https://doi.org/10.1186/s40623-017-0705-4

We have conducted ground-based performance evaluation tests of the Near-Infrared Spectrometer (NIRS3) onboard Hayabusa2 spacecraft and established a method for evaluating its measured reflectance spectra. Reflectance spectra of nine powdered carbonaceous chondrite samples were measured by both NIRS3 and a FT-IR spectrometer. Since raw data obtained by NIRS3 had considerable spectral distortion caused by systematic offsets in sensitivity of individual pixels, we have established two methods for correcting the NIRS3 data by comparing them with the corresponding FT-IR data. In order to characterize the absorption bands in NIRS3 spectra, the depth of each band component D is defined for each wavelength (m). Reflectance spectra of asteroid Ryugu, the target asteroid of Hayabusa2, to be recorded by the NIRS3 are expected to reveal the characteristics of the surface materials by using the evaluation technique.

Internal stress distribution for generating closure domains in laser-irradiated Fe-3%Si(110) steels

Iwata, Keiji*; Imafuku, Muneyuki*; Suzuki, Kanki*; Shobu, Takahisa; Orihara, Hideto*; Sakai, Yusuke*; Akita, Koichi; Oya, Shinichi*; Ishiyama, Kazushi*

Journal of Applied Physics, 117(17), p.17A910_1 - 17A910_4, 2015/03

https://doi.org/10.1063/1.4916183

Internal stress distribution for generating closure domains occurring in laser-irradiated Fe-3%Si(110) steels was investigated using high-energy X-ray analysis and domain theory based on the variational principle. The measured triaxial stresses inside the specimen were compressive and the stress in the rolling direction became more dominant than stresses in the other directions. The calculations based on the variational principle of magnetic energy for closure domains showed that the measured triaxial stresses made the closure domains more stable than the basic domain without closure domains. The experimental and calculation results reveal that the laser-introduced internal stresses result in the occurrence of the closure domains.

Multiferroic -type hexaferrites with a room-temperature conical state and magnetically controllable spin helicity

Tokunaga, Yusuke*; Kaneko, Yoshio*; Okuyama, Daisuke*; Ishiwata, Shintaro*; Arima, Takahisa*; Wakimoto, Shuichi; Kakurai, Kazuhisa; Taguchi, Yasujiro*; Tokura, Yoshinori*

Physical Review Letters, 105(25), p.257201_1 - 257201_4, 2010/12

https://doi.org/10.1103/PhysRevLett.105.257201

Neutron scattering activities on multiferroic systems; Neutron diffraction experiments on hexaferrites

Kakurai, Kazuhisa; Wakimoto, Shuichi; Ishiwata, Shintaro*; Okuyama, Daisuke*; Nishi, Masakazu*; Tokunaga, Yusuke*; Arima, Takahisa*; Taguchi, Yasujiro*; Tokura, Yoshiki*

no journal, , 

Methane uptake in a black spruce forest underlain by discontinuous permafrost

Harazono, Yoshinobu*; Futakuchi, Yusuke*; Yoshikawa, Kota*; Iwata, Hiroki*; Ueyama, Masahito*; Nagano, Hirohiko; Sakabe, Ayaka*; Kosugi, Yoshiko*

no journal, , 

no abstracts in English

Natural evidence for the cementation in bentonite buffer based on transmission electron microscopy observation of bentonite ores

Kikuchi, Ryosuke*; Horiuchi, Misato*; Saito, Masaki*; Ishiwata, Tobimaru*; Nishiki, Yuto*; Sato, Tsutomu*; Takayama, Yusuke; Mitsui, Seiichiro

no journal, , 

In geological disposal of high-level radioactive wastes, the use of swelling clay is intrinsic as a buffer around waste packages. In order to achieve long-term safety, longevity of montmorillonite, a major constituent of bentonite buffer, under disposal related conditions is important. One of the alteration processes of concern is cementation of clay layers due to precipitation of secondary minerals such as silica. In this study, we examined natural bentonite ores that could serve as natural analogues for the cementation process, especially focusing on microstructure of consolidated bentonite. Bentonite ores were collected from the Tsukinuno Mine in Yamagata Prefecture, Japan. This bentonite is thought to have been formed by the diagenesis of volcanic ash. A dry polishing technique was used to form a smooth surface that well shows the original microstructure of bentonite ores, allowing petrographic discussion as in the observation of non-clayey rocks. Besides coarse quartz (probably pyroclastic origin), fine silica with grain sizes ranging from a few microns to submicron is widely observed in bentonite ores. The distribution of fine silica is characterized by discrete grains or short chains or small clusters in the fine-grained montmorillonite matrix, suggesting that they formed in closed system diagenesis and a low mobility of silica in clay matrix. Thin foils including fine silica and montmorillonite were extracted from polished sections using a focused ion beam apparatus and observed by transmission electron microscopy (TEM). TEM observations demonstrated a microstructure where montmorillonite edge is directly bonded to the fine silica particles. The microstructure as seen in this study, is interpreted to be formed by the authigenic silica precipitation during diagenesis, not by a physical mixture. The silica coating of montmorillonite edge could prevent water access to its interlayer space and free swelling, which leads to a decrease in swelling pressure.

Relationship between petrographic texture and swelling property in cemented bentonite ores

Ishiwata, Tobimaru*; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*; Kawakita, Ryohei; Takayama, Yusuke; Mitsui, Seiichiro

no journal, , 

It is known that the cementation of bentontie may cause the reduction of swelling pressure. However, fundamental mechanism of this reducing swelling pressure has not been well understood. To understand the mechanism, it is essential to identify the cementitious materials and observe the changes in microstructure associated with cementation. In this study, the microstructural observation and swelling tests were conducted on several bentonite ores collected from Tsukinuno Mine in Yamagata Prefecture, Japan, as natural analog of cementation, and the relationship between petrographic texture and swelling pressure was discussed. Thin sections of bentonite ores were prepared by dry polishing technique to observe flat surfaces in micro scales. Scanning electron microscopy (SEM) demonstrated the widespread distribution of authigenic, a few micron silica in the matrix of montmorillonite. Transmission electron microscopy (TEM) revealed that the micro silica minerals (commonly quartz and less commonly amorphous silica) adhered to the edge of montmorillonite grains. These observations suggest that the adherence of these cementitious materials to montmorillonite prevents water access to the interlayer of montmorillonite and swelling, resulting in a decrease in swelling pressure. While these microstructures were observed commonly in all samples collected from several bentonite beds, the relative abundance of montmorillonite and micro silica minerals varied among different beds. It is possible that the swelling pressure in the cemented bentonite is affected by the relative abundance of montmorillonite and cementitious materials.