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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：44 Percentile：96.93(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 
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.
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：262 Percentile：99.73(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.
Horita, Masakuni*; Kinoshita, Naoto*; Yoshioka, Naoya*; Tsuchihara, H.*
JNC TJ7400 2005-014, 424 Pages, 1997/03
In this study, the excavation disturbed zone (EDZ) in deep rock is evaluated in the 250m-level drift st the Kamaishi Mine for the kamaishi In-situ Test Project, Phase II.
Yoshioka, Naoya*; Tsuchihara, H.*; Horita, M.*; Kinoshita, Naoto*
PNC TJ1449 96-007, 349 Pages, 1996/03
None
; Yoshioka, Naoya; ; Sato, Toshinori
Engineering Geology, 35, p.223 - 228, 1996/00
Times Cited Count：3 Percentile：19.36(Engineering, Geological)None
Hata, Koji*; Michihiro Kazutoshi*; Yoshioka, Naoya*; Sugihara, Kozo
Zairyo, 44(502), p.885 - 890, 1995/07
None
Horita, Masakuni*; Kinoshita, Naoto*; Yoshioka, Naoya*; Nagahisa, K.*
JNC TJ7400 2005-013, 445 Pages, 1995/03
JNC-TJ7400-2005-013.PDF:15.85MB
The characteristics and extend of EDZ around an exting drift are evaluated by means of several investigation techniques and test in the drift and borehole.
Yamamoto, Takuya*; Yoshioka, Naoya*
JNC TJ7400 2005-045, 125 Pages, 1994/06
JNC-TJ7400-2005-045.pdf:11.04MB
The objective of the investigation before the drift excavation is to identify rock mass properties and initial condition of the rock mass around the planned drift.
Yamamoto, Takuya*; Yoshioka, Naoya*
JNC TJ7400 2005-043, 287 Pages, 1994/06
JNC-TJ7400-2005-043.pdf:31.72MB
The objective of the investigation before the drift excavation is to identify rock mass properties and initial condition of the rock mass around the planned drift.
Yoshioka, Naoya; Sugihara, Kozo; Kinashi, Hideo*; Hata, Koji*; Maruyama, Makoto*
Zairyo, 42(474), p.324 - 328, 1993/03
None
Sato, Toshinori; ; ; Yoshioka, Naoya
PNC TN7410 92-051, 56 Pages, 1992/12
Excavation of a shaft or a drift in rock mass influences the rock mass around a shaft or a drift mechanically and hydraulically. In Chubu Works, we excavated a shaft having a diameter of 6 m and a depth of 150 m at the Tono Mine, and studied the excavation effects. We call this study Shaft Excavation Effects Project (SEE Project). Measurements with extensometers were carried out at four sections during the shaft excavation to understand the behavior of rock mass around the shaft. The displacement was locally occurred and it's amount depends on geology and presence of a fault and fractures. Numerical analysis was performed to understand the observed phenomena and the excavation effects. It was suggested that the deformation of rock mass around the shaft was within elastic limit and the numerical simulations could describe time-dependent behavior of the measured displacement.
; ; Sato, Toshinori; Yoshioka, Naoya
PNC TN7410 92-046, 56 Pages, 1992/12
As a result of underground excavation to construct an underground facility, an excavation disturbed zone (EDZ) is often generated in rock mass around a shaft and a drift. In order to design and construct an underground facility, and to evaluate its long-term stability, it is necessary to understand the phenomena related to excavation disturbance. PNC (Power Reacter and Nuclear Fuel Development Corporation) excavated a shaft of 6m diameter and 152.3m depth in Neogene sedimentary rocks, and studied the influence induced by the shaft excavation on rock mass and groundwater flow around the shaft. This project was named SEE (Shaft Excavation Effects) project, and was carried out from 1978 to 1991. This report described a part of the SEE Project, focusing on mechanical and hydrological variation of rock mass around the shaft. The current conclusions were su㎜arized as follows: (1)Mechanical and hydrological variation of rock mass around the shaft was induced by stress redistribution and fracturing around the shaft. (2)The zone where mechanical and hydrological characteristics were varied was extended about 1m from shaft wall. (3)It is considered that unrecoverable deformation is generated in rock mass around a shaft because of fracturing and plastic deformation. We introduced a concept of permanent deformation modulus to take account of the unrecoverable deformation, and estimated the results of borehole jack tests. Consequently, we found the permanent deformation modulus was useful to identify the EDZ.
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.
