研究者業績

坂谷 尚哉

サカタニ ナオヤ  (Naoya Sakatani)

基本情報

所属
国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 太陽系科学研究系 特任助教

連絡先
sakatani.naoyajaxa.jp
研究者番号
70795187
J-GLOBAL ID
201901019739774118
researchmap会員ID
B000365669

主要な論文

 80
  • Naoya Sakatani, Satoshi Tanaka, Sota Arakawa
    INTERNATIONAL JOURNAL OF THERMOPHYSICS 43(6) 2022年6月  
    The thermal conductivity of planetary soils, or regolith, is essential for understanding the present global thermal state of bodies. The thermal conductivity of lunar soils is important with respect to lunar crustal heat flow. Although in situ measurements were performed by the Apollo 15 and 17 missions, laboratory measurements of the returned lunar samples have not reproduced the estimated subsurface values. Since the amount of extraterrestrial soil samples is limited, a small apparatus is needed to measure their thermal conductivity. In this study, we developed an apparatus enabling the measurement of the thermal conductivity of a small amount of soil (< 10 g) via the line heat source method as a function of compressional pressure under vacuum conditions. The thermal conductivity of glass beads and lunar regolith simulant derived by the new apparatus is higher than that obtained from the larger line heat source, and then, reliable apparatus. To evaluate the experimental results, we performed numerical simulation of the temperature evolution during the line heat source measurement, and found that the thermal conductivity derived from the simulation data is higher than the input thermal conductivity. This is consistent with the experimental results and is caused by the heat loss through a line heat source with a limited length. The difference depends on the contact conductance between the sample and the line heat source, and the calibration factors for each sample are determined.
  • N. Sakatani, S. Tanaka, T. Okada, T. Fukuhara, L. Riu, S. Sugita, R. Honda, T. Morota, S. Kameda, Y. Yokota, E. Tatsumi, K. Yumoto, N. Hirata, A. Miura, T. Kouyama, H. Senshu, Y. Shimaki, T. Arai, J. Takita, H. Demura, T. Sekiguchi, T. G. Müller, A. Hagermann, J. Biele, M. Grott, M. Hamm, M. Delbo, W. Neumann, M. Taguchi, Y. Ogawa, T. Matsunaga, T. Wada, S. Hasegawa, J. Helbert, N. Hirata, R. Noguchi, M. Yamada, H. Suzuki, C. Honda, K. Ogawa, M. Hayakawa, K. Yoshioka, M. Matsuoka, Y. Cho, H. Sawada, K. Kitazato, T. Iwata, M. Abe, M. Ohtake, S. Matsuura, K. Matsumoto, H. Noda, Y. Ishihara, K. Yamamoto, A. Higuchi, N. Namiki, G. Ono, T. Saiki, H. Imamura, Y. Takagi, H. Yano, K. Shirai, C. Okamoto, S. Nakazawa, Y. Iijima, M. Arakawa, K. Wada, T. Kadono, K. Ishibashi, F. Terui, S. Kikuchi, T. Yamaguchi, N. Ogawa, Y. Mimasu, K. Yoshikawa, T. Takahashi, Y. Takei, A. Fujii, H. Takeuchi, Y. Yamamoto, C. Hirose, S. Hosoda, O. Mori, T. Shimada, S. Soldini, R. Tsukizaki, M. Ozaki, S. Tachibana, H. Ikeda, M. Ishiguro, H. Yabuta, M. Yoshikawa, S. Watanabe, Y. Tsuda
    Nature Astronomy 5(8) 766-774 2021年8月24日  
    Planetesimals—the initial stage of the planetary formation process—are considered to be initially very porous aggregates of dusts1,2, and subsequent thermal and compaction processes reduce their porosity3. The Hayabusa2 spacecraft found that boulders on the surface of asteroid (162173) Ryugu have an average porosity of 30–50% (refs. 4–6), higher than meteorites but lower than cometary nuclei7, which are considered to be remnants of the original planetesimals8. Here, using high-resolution thermal and optical imaging of Ryugu’s surface, we discovered, on the floor of fresh small craters (<20 m in diameter), boulders with reflectance (~0.015) lower than the Ryugu average6 and porosity >70%, which is as high as in cometary bodies. The artificial crater formed by Hayabusa2’s impact experiment9 is similar to these craters in size but does not have such high-porosity boulders. Thus, we argue that the observed high porosity is intrinsic and not created by subsequent impact comminution and/or cracking. We propose that these boulders are the least processed material on Ryugu and represent remnants of porous planetesimals that did not undergo a high degree of heating and compaction3. Our multi-instrumental analysis suggests that fragments of the highly porous boulders are mixed within the surface regolith globally, implying that they might be captured within collected samples by touch-down operations10,11.
  • Naoya Sakatani, Kazunori Ogawa, Masahiko Arakawa, Satoshi Tanaka
    ICARUS 309 13-24 2018年7月  
    Many air-less planetary bodies, including the Moon, asteroids, and comets, are covered by regolith. The thermal conductivity of the regolith is an essential parameter controlling the surface temperature variation. A thermal conductivity model applicable to natural soils as well as planetary surface regolith is required to analyze infrared remote sensing data. In this study, we investigated the temperature and compressional stress dependence of the thermal conductivity of the lunar regolith simulant JSC-1A, and the temperature dependence of sieved JSC-1A samples under vacuum conditions. We confirmed that a series of the experimental data for JSC-1A are fitted well by our analytical model of the thermal conductivity (Sakatani et al., 2017). Comparison with the calibration data of the sieved samples with those for original JSC-1A indicates that the thermal conductivity of natural samples with a wide grain size distribution can be modeled as mono-sized grains with a volumetric median size. The calibrated model can be used to estimate the volumetric median grain size from infrared remote sensing data. Our experiments and the calibrated model indicates that uncompressed JSC-1A has similar thermal conductivity to lunar top surface materials, but the lunar subsurface thermal conductivity cannot be explained only by the effects of the density and self-weighted compressional stress. We infer that the nature of the lunar subsurface regolith grains is much different from JSC-1A and lunar top-surface regolith, and/or the lunar subsurface regolith is over-consolidated and the compressional stress higher than the hydrostatic pressure is stored in the lunar regolith layer. (C) 2018 Elsevier Inc. All rights reserved.
  • N. Sakatani, K. Ogawa, Y. Iijima, M. Arakawa, R. Honda, S. Tanaka
    AIP Advances 7(1) 2017年1月1日  
    The thermal conductivity of powdered media is characteristically very low in vacuum, and is effectively dependent on many parameters of their constituent particles and packing structure. Understanding of the heat transfer mechanism within powder layers in vacuum and theoretical modeling of their thermal conductivity are of great importance for several scientific and engineering problems. In this paper, we report the results of systematic thermal conductivity measurements of powdered media of varied particle size, porosity, and temperature under vacuum using glass beads as a model material. Based on the obtained experimental data, we investigated the heat transfer mechanism in powdered media in detail, and constructed a new theoretical thermal conductivity model for the vacuum condition. This model enables an absolute thermal conductivity to be calculated for a powder with the input of a set of powder parameters including particle size, porosity, temperature, and compressional stress or gravity, and vice versa. Our model is expected to be a competent tool for several scientific and engineering fields of study related to powders, such as the thermal infrared observation of air-less planetary bodies, thermal evolution of planetesimals, and performance of thermal insulators and heat storage powders.
  • Naoya Sakatani, Kazunori Ogawa, Yu-ichi Iijima, Masahiko Arakawa, Satoshi Tanaka
    ICARUS 267 1-11 2016年3月  
    Thermal conductivity of powdered materials under vacuum conditions is a valuable physical parameter in the context of planetary sciences. We report results of thermal conductivity measurements of 90-106 mu m and 710-1000 mu m glass beads, and lunar regolith simulant using two different experimental setups for varying the compressional stress and the temperature, respectively. We found the thermal conductivity increase with the compressional stress, for example, from 0.003 to 0.008 W m(-1) K-1 for the glass beads of 90-106 mu m in diameter at the compressional stress less than 20 kPa. This increase of the thermal conductivity is attributed the areal enlargement of the contacts between particles due to their elastic deformation. The thermal conductivity increased also with temperature, which primarily represented enhancement of the radiative heat conduction between particles. Reduction of the estimated radiative conductivity from the effective thermal conductivity obtained in the first experiment yields the relation between the solid conductivity (conductive contribution through inter-particle contacts) and the compressional stress. We found that the solid conductivity is proportional to approximately 1/3 power of the compressional stress for the glass beads samples, while the regolith simulant showed a weaker exponent than that of the glass beads. We developed a) semi-empirical expression of the thermal conductivity of the lunar regolith using our data on the lunar regolith simulant. This model enabled us to estimate a vertical distribution of the lunar subsurface thermal conductivity. Our model provides an examination for the density and compressional stress relationships to thermal conductivity observed in the in-situ measurements in Apollo 15 and 17 Heat Flow Experiments. (C) 2015 Elsevier Inc. All rights reserved.
  • Naoya Sakatani, Kazunori Ogawa, Yu-ichi Iijima, Rie Honda, Satoshi Tanaka
    ICARUS 221(2) 1180-1182 2012年11月  
    We measured the thermal conductivity of glass beads as a simple model material in order to investigate the compressional stress dependence of the thermal conductivity of powder materials. The measurements were conducted in a vertically elongated cylindrical sample container under vacuum conditions. Our results suggest that the compressional stress is one of the essential factors to understand the thermal conductivity structure in the regolith layer. (C) 2012 Elsevier Inc. All rights reserved.

MISC

 21
  • B. E. Clark, A. Sen, X. D. Zou, D. N. DellaGiustina, S. Sugita, N. Sakatani, M. Thompson, D. Trang, E. Tatsumi, M. A. Barucci, M. Barker, H. Campins, T. Morota, C. Lantz, A. R. Hendrix, F. Vilas, L. Keller, V. E. Hamilton, K. Kitazato, S. Sasaki, M. Matsuoka, T. Nakamura, A. Praet, S. M. Ferrone, T. Hiroi, H. H. Kaplan, W. F. Bottke, J. Y. Li, L. Le Corre, J. L. Molaro, R. L. Ballouz, C. W. Hergenrother, B. Rizk, K. N. Burke, C. A. Bennett, D. R. Golish, E. S. Howell, K. Becker, A. J. Ryan, J. P. Emery, S. Fornasier, A. A. Simon, D. C. Reuter, L. F. Lim, G. Poggiali, P. Michel, M. Delbo, O. S. Barnouin, E. R. Jawin, M. Pajola, L. Riu, T. Okada, J. D.P. Deshapriya, J. R. Brucato, R. P. Binzel, D. S. Lauretta
    Icarus 400 2023年8月  
    This paper summarizes the evidence for the optical effects of space weathering, as well as the properties of the surface that control optical changes, on asteroid (101955) Bennu. First, we set the stage by briefly reviewing what was known about space weathering of low-albedo materials from telescopic surveys, laboratory simulations, and sample return analysis. We then look at the evidence for the nature of space weathering on Bennu from recent spacecraft imaging and spectroscopy observations, including the visible to near-infrared and thermal infrared wavelengths, followed by other measurements such as normal albedo measurements from LIDAR scans. We synthesize these different lines of evidence in an effort to describe a general model of space weathering processes and resulting color effects on dark C-complex asteroids, with hypotheses that can be tested by analyzing samples returned by the mission. A working hypothesis that synthesizes findings thus far is that the optical effects of maturation in the space environment depend on the level of hydration of the silicate/phyllosilicate substrate. Subsequent variations in color depend on surface processes and exposure age. On strongly hydrated Bennu, in color imaging data, very young craters are darker and redder than their surroundings (more positive spectral slope in the wavelength range 0.4–0.7μm) as a result of their smaller particle sizes and/or fresh exposures of organics by impacts. Solar wind, dehydration, or migration of fines may cause intermediate-age surfaces to appear bluer than the very young craters. Exposed surfaces evolve toward Bennu's moderately blue global average spectral slope. However, in spectroscopic and LIDAR data, the equator, the oldest surface on Bennu, is darker and redder (wavelength range 0.55–2.0μm) than average and has shallower absorption bands, possibly due to dehydration and/or nanophase and/or microphase opaque production. Bennu is a rubble pile with an active surface, making age relationships, which are critical for determining space weathering signals, difficult to locate and quantify. Hence, the full story ultimately awaits analyses of the Bennu samples that will soon be delivered to Earth.
  • 岡田達明, 岡田達明, 田中智, 坂谷尚哉, 嶌生有理, 石崎拓也, 吉川真, 竹内央, 山本幸生, 荒井武彦, 千秋博紀, 出村裕英, 関口朋彦, 神山徹, 金丸仁明
    日本地球惑星科学連合大会予稿集(Web) 2023 2023年  
  • 黒川宏之, 嶌生有理, 岡田達明, 佐伯孝尚, 津田雄一, 森治, 坂谷尚哉, 深井稜汰, 青木順, 癸生川陽子, 熊本篤志, 田中智, 川村太一, 浦川聖太郎, 巽瑛理, 高尾勇輝, 菊地翔太, 瀧川晶, 奥住聡, 古家健次, 金丸仁明, 荒川創太
    日本惑星科学会秋季講演会予稿集(Web) 2023 2023年  
  • 佐伯孝尚, 津田雄一, 森治, 高尾勇輝, 菊地翔太, 黒川宏之, 岡田達明, 嶌生有理, 深井稜汰, 坂谷尚哉, 田中智
    日本惑星科学会秋季講演会予稿集(Web) 2023 2023年  
  • 熊本篤志, 宮本英昭, 坂谷尚哉, 嶌生有理, 黒川宏之, 佐伯孝尚, 津田雄一, 菊地翔太
    日本惑星科学会秋季講演会予稿集(Web) 2023 2023年  
  • 高尾勇輝, 菊地翔太, 佐伯孝尚, 津田雄一, 森治, 嶌生有理, 坂谷尚哉, 深井稜汰, 岡田達明, 黒川宏之, 大木春仁, 中川雄登, 西村尚, 鶴谷柊朔
    宇宙科学技術連合講演会講演集(CD-ROM) 67th 2023年  
  • 田中智, 三桝裕也, 神山徹, 坂谷尚哉, 北里宏平, 鎌田俊一, 平林正稔, 中澤暁, 吉川真, 津田雄一
    宇宙科学技術連合講演会講演集(CD-ROM) 67th 2023年  
  • 佐伯孝尚, 津田雄一, 森治, 丸祐介, 高尾勇輝, 菊地翔太, 黒川宏之, 嶌生有理, 坂谷尚哉, 深井稜汰, 岡田達明
    宇宙科学技術連合講演会講演集(CD-ROM) 67th 2023年  
  • 深井稜汰, 黒川宏之, 嶌生有理, 坂谷尚哉, 癸生川陽子, 青木順, 巽瑛理, 脇田茂, 牛久保孝行, 熊本篤志, 宮本英昭, 川村太一, 田中智, 辻健, 浦川聖太郎, 大澤亮, 津田雄一, 森治, 丸祐介, 佐伯孝尚, 岡田達明
    宇宙科学技術連合講演会講演集(CD-ROM) 67th 2023年  
  • Tatsuaki Okada, Satoshi Tanaka, Naoya Sakatani, Yuri Shimaki, Takehiko Arai, Hiroki Senshu, Hirohide Demura, Tomohiko Sekiguchi, Toru Kouyama, Masanori Kanamaru, Takuya Ishizaki
    16th Europlanet Science Congress 2022 16 EPSC2022-1191 2022年9月23日  
  • Tatsuaki Okada, Satoshi Tanaka, Naoya Sakatani, Yuri Shimaki, Takehiko Arai, Hiroki Senshu, Hirohide Demura, Tomohiko Sekiguchi, Toru Kouyama, Masanori Kanamaru, Takuya Ishizaki
    16th Europlanet Science Congress 2022 16 EPSC2022-1187 2022年9月23日  招待有り
  • 宮本英昭, MICHEL Patrick, MICHEL Patrick, 和田浩二, 逸見良道, 小川和律, 新原隆史, 坂谷尚哉, 大槻真嗣, 臼井寛裕, 菊地紘, 平田直之, 亀田真吾, 中村智樹, 諸田智克, 寺田直樹, 佐々木晶, 千秋博紀, 横田勝一郎, 木村智樹, 臼井英之, 三宅洋平, 西野真木, 長勇一郎, 二穴喜文, ASPHAUG Erik, BALLOUZ Ronald-Louis, BIELE Jens, BOETTGER Ute, ERNST Carolyn, BARNOUIN Olivier, GROTT Matthias, 小林真輝人, 清水雄太, 竹村知洋, 清水俊輔
    宇宙科学技術連合講演会講演集(CD-ROM) 66th 2022年  
  • 岡田達明, 田中智, 坂谷尚哉, 嶌生有理, 石崎拓也, 吉川真, 竹内央, 山本幸生, 千秋博紀, 荒井武彦, 出村裕英, 関口朋彦, 神山徹, 金丸仁明
    宇宙科学技術連合講演会講演集(CD-ROM) 66th 2022年  
  • 千秋博紀, 坂谷尚哉, 諸田智克, 横田康弘, 嶌生有理, HAMM Maximilian, 田中智, 岡田達明, 荒井武彦, 金丸仁明, 竹内央
    日本惑星科学会秋季講演会予稿集(Web) 2022 2022年  
  • 嶌生有理, 坂谷尚哉, 深井稜汰, 兵頭龍樹, 巽瑛理, 脇田茂, 浦川聖太郎, 末次竜, 岡田達明, 田中智, 渡邊誠一郎, 森治, 佐伯孝尚, 津田雄一
    日本惑星科学会秋季講演会予稿集(Web) 2022 2022年  
  • 荒井武彦, 岡田達明, 田中智, 福原哲哉, 出村裕英, 神山徹, 坂谷尚哉, 嶌生有理, 千秋博紀, 関口朋彦, 滝田隼
    日本地球惑星科学連合大会予稿集(Web) 2021 2021年  
  • Tatsuaki Okada, Satoshi Tanaka, Yuri Shimaki, Naoya Sakatani, Takehiko Arai, Hiroki Senshu, Hirohide Demura, Toru Kouyama, Tomohiko Sekiguchi, Tetsuya Fukuhara
    Europlanet Science Congress 2020 EPSC2020-12 2020年10月8日  招待有り
    &amp;lt;p&amp;gt;Thermal imaging, or thermography, has revealed the surface physical state of the C-type near-Earth asteroid 162173 Ryugu (Okada et al., 2020). The asteroid is the target body of JAXA Hayabsua2 asteroid sample return mission, and it has been characterized through remote sensing and surface experiments, and will be deeply and accurately investigated by analysis of returned sample. Thermal observations are among such multi-scale observations, providing a new insight into understanding planetary evolution process.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;Thermal infrared imager TIR (Okada et al., 2017; 2020) was used to take one-rotation global thermal images of Ryugu at every 6&amp;amp;#176; step, from the home position (20 km altitude) or from the Mid-Altitude (5 km altitude). There were two big surprises contrary to the predictions before arrival at Ryugu: i) flat diurnal temperature profiles compared to the case of non-rough surface, and ii) non-cold spots identified for most of boulders. The flat diurnal temperature profiles and its maximum temperature in a day indicate that Ryugu must have very rough surfaces made of highly porous materials, derived from the thermal inertia of 300 &amp;amp;#177; 100 J K&amp;lt;sup&amp;gt;-1&amp;lt;/sup&amp;gt;s&amp;lt;sup&amp;gt;-0.5&amp;lt;/sup&amp;gt;m&amp;lt;sup&amp;gt;-2&amp;lt;/sup&amp;gt; (hereafter, tiu). Non-cold boulders indicate that boulders are less consolidated or compacted than typical carbonaceous chondrite meteorites, and shows the same thermophysical properties as the surroundings. TIR was also used to take close-up thermal images during the descent operations, and to have proven that the surface of asteroid is covered with fragments of porous rocks, larger than several centimeters in diameter. The typical size of fragments larger than thermal skin depth (~35 mm) results in similar thermal properties between the boulders and their surroundings. We also consider the surface roughness effect (Shimaki et al., 2020) to obtain the maps of thermal inertia ( 225 &amp;amp;#177; 45 tiu) and the roughness (0.41 &amp;amp;#177; 0.05) at the same time, corresponding to very rough surfaces made of highly-porous materials. This thermal inertia is basically consistent with the value (282 +93/-35 tiu) by in situ measurement using a thermal radiometer MARA on MASCOT lander (Grott et al., 2019). Furthermore, in the close-up thermal images, there were found boulders colder by 20 &amp;amp;#176;C or more, indicating the thermal inertia of typical carbonaceous chondrite meteorites.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;Considering these results, we proposed a formation scenario of Ryugu: fluffy cosmic dusts gathered to form porous planetesimals, and then much larger sized but still porous bodies. A low degree of consolidation and alteration has occurred at most of the body, while a higher degree of consolidation or alteration proceeded at the deep interior. Huge meteoritic impacts destroyed and fragmented the bodies, and part of those fragments were re-accreted to form the next generation, rubble-pile bodies (asteroids). Boulders found on Ryugu might have originated from the deep interior of parent bodies, so that most of them are very porous and less consolidated but some of them are relatively dense materials similar to carbonaceous chondrites, which might have originated from the interior. Due to YORP effect, the rotation rate decreased to current one, and the current shape of a spinning top-shape were formed. Analysis of returned sample will make progress in our knowledge of the planetary formation process.&amp;lt;/p&amp;gt;
  • 門野敏彦, 嶌生有理, 小川和律, 白井慶, 石橋高, 和田浩二, 坂谷尚哉, 飯島祐一, 佐伯孝尚, 澤田弘崇, 杉田精司, 本田理恵, 荒川政彦
    日本惑星科学会秋季講演会予稿集(Web) 2019 2019年  
  • 小川和律, 和田浩二, 石橋高, 澤田弘崇, 荒川政彦, 本田理恵, 坂谷尚哉, 白井慶, 保井みなみ
    日本惑星科学会秋季講演会予稿集(Web) 2017 2017年  
  • 小川和律, 坂谷尚哉, 和田浩二, 保井みなみ, 荒川政彦
    日本惑星科学会秋季講演会予稿集(Web) 2015 2015年  
  • 千秋 博紀, 滝田 隼, 荒井 武彦, 福原 哲哉, 田中 智, 岡田 達明, 関口 朋彦, 坂谷 尚哉, はやぶさ2TIRチーム
    日本惑星科学会誌遊星人 24(2) 120-125 2015年  
    TIR(中間赤外カメラ)は,8から12ミクロンの波長帯で熱輻射の2次元イメージングを行う.ターゲット天体の1自転分の撮像から表層物質の熱履歴をもとめ,そこから熱物性を推定する.表層物質の熱物性は,ミッション遂行に必要な情報であるばかりでなく,その後の天体の運命を決める重要な情報である.

共同研究・競争的資金等の研究課題

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