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Last Updated :2024/07/26

研究者情報

マスター

アカウント（マスター）

  • 氏名

    倉本　圭(クラモト　キヨシ), クラモト　キヨシ

所属（マスター）

  • 理学研究院　地球惑星科学部門　宇宙惑星科学分野

所属（マスター）

  • 理学研究院　地球惑星科学部門　宇宙惑星科学分野

独自項目

syllabus

  • 2021, 宇宙理学特別講義１, Special Lecture of Cosmosciences 1, 修士課程, 理学院, 飛翔体技術，飛翔体観測，惑星探査，天文衛星
  • 2021, 宇宙理学特別講義１, Special Lecture of Cosmosciences 1, 修士課程, 理学院, 惑星科学、天文学、地球物理学
  • 2021, 宇宙理学特別講義２, Special Lecture of Cosmosciences 2, 修士課程, 理学院, 飛翔体技術，飛翔体観測，惑星探査，天文衛星
  • 2021, 宇宙理学特別講義２, Special Lecture of Cosmosciences 2, 修士課程, 理学院, 惑星科学、天文学、地球物理学
  • 2021, 惑星システム学特論１, Advanced Course on Planetary Systems 1, 修士課程, 理学院, 比較惑星学、地球、月、地球型惑星、木星型惑星、氷衛星、太陽系小天体、系外惑星
  • 2021, 大学院共通授業科目（一般科目）：自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, 宇宙、構造、形成・進化
  • 2021, 宇宙理学入門, Introduction to Cosmosciences, 修士課程, 理学院, 宇宙、構造、形成・進化
  • 2021, 地球惑星科学のための物理数学Ⅱ, Mathematics for Earth and Planetary Sciences II, 学士課程, 理学部, ベクトル解析 複素解析
  • 2021, 地球惑星科学のための物理数学Ⅱ演習, Exercises in Mathematics for Earth and Planetary Sciences II, 学士課程, 理学部, ベクトル解析 複素解析
  • 2021, 地球惑星科学Ⅱ, Basic Earth and Planetary Science Ⅱ, 学士課程, 全学教育, 宇宙，惑星，大気と海洋の運動と構造，気候変動，地球環境
  • 2021, 惑星大気構造学, Physics for Planetary Atmosphere, 学士課程, 理学部, 地球惑星大気、放射過程、静水圧平衡、熱力学、気体分子運動論、物質循環、エネルギー収支、大気の起源と進化、系外惑星
  • 2021, 情報実習, Exercises in Information Sciences, 学士課程, 理学部, 計算機ネットワーク、計算機、基本作法、基礎技術、情報科学、地球惑星情報学
  • 2021, 教科教育法（理科I）, Teaching Method of School Subjects(Science Ⅰ), 学士課程, 教育学部, 教員養成、理科教育法、指導法

researchmap

プロフィール情報

学位

  • 博士(理学)（東京大学）
  • 理学修士（東京大学）

プロフィール情報

  • 姓

    倉本, クラモト

  • 名

    圭, キヨシ

  • ID各種

    200901028967009342

対象リソース

業績リスト

研究キーワード

  • 物質進化   惑星大気   システム   現象   構造   進化   起源   地球   惑星   System   Phenomena   Structure   Evolution   Origin   Earth   Planets   

研究分野

  • 自然科学一般 / 天文学
  • 自然科学一般 / 宇宙惑星科学
  • 自然科学一般 / 大気水圏科学
  • 自然科学一般 / 固体地球科学

経歴

  • 2015年04月 - 現在 北海道大学 大学院理学研究院地球惑星科学部門 教授
  • 2007年04月 - 2015年03月 北海道大学 大学院理学研究院自然史科学部門 教授
  • 2012年08月 - 2014年07月 文部科学省 研究振興局 学術調査官
  • 2006年04月 - 2007年03月 北海道大学 大学院理学研究院自然史科学部門 助教授
  • 2001年04月 - 2006年03月 北海道大学 大学院理学研究科地球惑星科学専攻 助教授
  • 1998年11月 - 2001年03月 北海道大学 大学院理学研究科地球惑星科学専攻 助手
  • 1997年04月 - 1998年10月 北海道大学 低温科学研究所 日本学術振興会特別研究員
  • 1995年09月 - 1997年03月 東京大学 気候システム研究センター COE研究員
  • 1994年08月 - 1995年08月 東京工業大学 理学部一般教育等地学 技術補佐員

学歴

  •         - 1994年   東京大学   大学院 理学系研究科   地球惑星物理学専攻
  •         - 1991年   東京大学   大学院 理学系研究科   地球物理学専攻
  •         - 1989年   東京大学   理学部   地球物理学科

委員歴

  • 2023年10月 - 現在   日本学術会議   会員
  • 2017年04月 - 現在   文部科学省宇宙開発利用部会 国際宇宙ステーション・国際宇宙探査小委員会   委員
  • 2014年04月 - 現在   日本地球惑星科学連合   代議員
  • 2013年 - 現在   Progress of Earth and Planetary Science (日本地球惑星科学連合国際ジャーナル)   宇宙惑星科学分野編集長
  • 2022年05月 - 2024年04月   日本地球惑星科学連合   理事
  • 2019年05月 - 2023年04月   宇宙科学研究所宇宙理学委員会   委員長
  • 2019年01月 - 2022年12月   日本惑星科学会   運営委員
  • 2020年08月 - 2022年05月   日本地球惑星科学連合   宇宙惑星科学セクションプレジデント
  • 2016年04月 - 2020年07月   日本地球惑星科学連合   理事
  • 2015年04月 - 2019年03月   内閣府宇宙政策委員会 宇宙科学・探査小委員会   委員
  • 2017年01月 - 2018年12月   日本惑星科学会   副会長
  • 2015年01月 - 2016年12月   日本惑星科学会   会長
  • 2013年01月 - 2014年12月   日本惑星科学会   副会長
  • 2008年01月 - 2012年12月   日本惑星科学会   将来計画専門委員会委員長   日本惑星科学会
  • 1998年01月 - 2012年12月   日本惑星科学会   運営委員   日本惑星科学会
  • 2002年 - 2006年   日本惑星科学会   学会誌編集長   日本惑星科学会
  • 2003年 - 2004年   日本惑星科学会   2004年秋季講演会LOC総務   日本惑星科学会
  • 1998年 - 1999年   日本惑星科学会   学会誌編集幹事   日本惑星科学会

受賞

  • 2005年 日本気象学会 堀内賞
     地球および惑星における主要親気性元素の挙動に関する理論的研究 
    受賞者: 倉本 圭
  • 2005年 2005, Horiuchi Prize, Meteorological Society of Japan

論文

  • Hiroaki Saito, Kiyoshi Kuramoto
    The Astrophysical Journal 969 158 1 - 9 2024年07月10日 [査読有り]
  • Kiyoshi Kuramoto
    Annual Review of Earth and Planetary Sciences 52 1 2024年02月15日 [査読有り][招待有り]
     
    Two major hypotheses have been proposed for the origin of the Martian moons Phobos and Deimos: the in situ formation theory, supported by the fact that they have circular orbits nearly parallel to the Martian equator, and the asteroid capture theory, supported by the similarity of their reflectance spectra to those of carbonaceous asteroids. Regarding the in situ formation theory, recent theoretical studies have focused on the huge impact scenario, which proposes that debris ejected into orbits during the formation of a giant impact basin on Mars accumulated to form the Martian moons. On the other hand, gas drag from a Martian gas envelope composed of gravitationally attracted solar nebula gas has been proposed as a mechanism for trapping the approaching asteroidal objects in areocentric orbits. In particular, an object entering a temporarily captured orbit in the Martian gravitational sphere would easily evolve into a fully captured moon with a near-equatorial orbit under realistic gas densities. The upcoming Phobos sample return mission is expected to elucidate the origin of both moons, with implications for material transport in the early Solar System and the early evolution of Mars. ▪ The origin of Mars’ small moons, Phobos and Deimos, has long been an open question. ▪ The leading hypotheses are asteroid capture, inferred from their appearance like primitive asteroids, and giant impact, implied by the regularity of their orbits. ▪ The origin of Phobos will be precisely determined by a sample return mission to be conducted in the late 2020s to early 2030s. ▪ Determining the origin of the Martian moons will provide clues to clarifying how the parent planet Mars formed and came to have a habitable surface environment. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
  • Ryota Fukai, Tomohiro Usui, Wataru Fujiya, Yoshinori Takano, Ken‐ichi Bajo, Andrew Beck, Enrica Bonato, Nancy L. Chabot, Yoshihiro Furukawa, Hidenori Genda, Yuki Hibiya, Fred Jourdan, Thorsten Kleine, Mizuho Koike, Moe Matsuoka, Yayoi N. Miura, Frédéric Moynier, Ryuji Okazaki, Sara S. Russell, Hirochika Sumino, Michael E. Zolensky, Haruna Sugahara, Shogo Tachibana, Kanako Sakamoto, Masanao Abe, Yuichiro Cho, Kiyoshi Kuramoto
    Meteoritics & Planetary Science 2024年01月11日 [査読有り]
     
    Abstract Japan Aerospace Exploration Agency's Martian Moons eXploration (MMX) mission will launch a spacecraft in 2024 to return samples from Phobos in 2029. Curatorial work for the returned Phobos samples is critical for the sample allocation without degrading the sample integrity and subsequent sample analysis that will provide new constraints on the origin of Phobos and the evolution of the circum‐Mars environment. The Sample Analysis Working Team of the MMX is designing the sample curation protocol. The curation protocol consists of three phases: (1) quick analysis (extraction and mass spectrometry for gases), (2) pre‐basic characterization (bulk‐scale observation), and (3) basic characterization (grain‐by‐grain observation and allocation of the sample aliquots). Nondestructive analyses within the clean chamber (e.g., visible and near‐infrared spectral imaging) and outside the chamber (e.g., gas mass spectrometry) are incorporated into the curation flow in coordination with the MMX mission instrument teams for ground‐truthing the remote‐sensing data sets. The MMX curation/sample analysis flow enables the seamless integration between the sample and remote‐sensing data sets to maximize the scientific value of the collected Phobos samples.
  • Yoshiyuki O. TAKAHASHI, Yoshi-Yuki HAYASHI, George L. HASHIMOTO, Kiyoshi KURAMOTO, Masaki ISHIWATARI, Hiroki KASHIMURA
    Journal of the Meteorological Society of Japan. Ser. II 102 1 5 - 16 2024年
  • Yoshiyuki O. TAKAHASHI, Yoshi-Yuki HAYASHI, George L. HASHIMOTO, Kiyoshi KURAMOTO, Masaki ISHIWATARI
    Journal of the Meteorological Society of Japan. Ser. II 2023年 [査読有り]
  • Yasuhiro Kawakatsu, Kiyoshi Kuramoto, Tomohiro Usui, Haruna Sugahara, Hisashi Ootake, Ryoichiro Yasumitsu, Kent Yoshikawa, Stephane Mary, Markus Grebenstein, Hirotaka Sawada, Takane Imada, Takanobu Shimada, Kazunori Ogawa, Masatsugu Otsuki, Mitsuhisa Baba, Kazuhisa Fujita, Kris Zacny, Dylan van Dyne, Yasutaka Satoh, Ayumu Tokaji
    Acta Astronautica 202 715 - 728 2022年10月
  • Tatsuya Yoshida, Naoki Terada, Masahiro Ikoma, Kiyoshi Kuramoto
    The Astrophysical Journal 934 2 137 - 137 2022年08月01日 [査読有り]
     
    Abstract Terrestrial planets currently in the habitable zones around M dwarfs likely experienced a long-term runaway-greenhouse condition because of a slow decline in host-star luminosity in its pre-main-sequence phase. Accordingly, they might have lost significant portions of their atmospheres including water vapor at high concentration by hydrodynamic escape induced by the strong stellar X-ray and extreme ultraviolet (XUV) irradiation. However, the atmospheric escape rates remain highly uncertain due partly to a lack of understanding of the effect of radiative cooling in the escape outflows. Here we carry out 1D hydrodynamic escape simulations for an H2–H2O atmosphere on a planet with mass of 1M⊕ considering radiative and chemical processes to estimate the atmospheric escape rate and follow the atmospheric evolution during the early runaway-greenhouse phase. We find that the atmospheric escape rate decreases with the basal H2O/H2 ratio due to the energy loss by the radiative cooling of H2O and chemical products such as OH and OH+: the escape rate of H2 becomes one order of magnitude smaller when the basal H2O/H2 = 0.1 than that of the pure hydrogen atmosphere. The timescale for H2 escape exceeds the duration of the early runaway-greenhouse phase, depending on the initial atmospheric amount and composition, indicating that H2 and H2O could be left behind after the end of the runaway-greenhouse phase. Our results suggest that temperate and reducing environments with oceans could be formed on some terrestrial planets around M dwarfs.
  • Keigo Enya, Masanori Kobayashi, Jun Kimura, Hiroshi Araki, Noriyuki Namiki, Hirotomo Noda, Shingo Kashima, Shoko Oshigami, Ko Ishibashi, T. Yamawaki, Kazuyuki Tohara, Yoshifumi Saito, Masanobu Ozaki, Takahide Mizuno, Shunichi Kamata, Koji Matsumoto, Sho Sasaki, Kiyoshi Kuramoto, Yuki Sato, Takeshi Yokozawa, Tsutomu Numata, Satoko Mizumoto, Hiroyuki Mizuno, Kenta Nagamine, Akihiko Sawamura, Kazuo Tanimoto, Hisato Imai, Hiroyuki Nakagawa, Okiharu Kirino, David Green, Masayuki Fujii, Satoru Iwamura, Naofumi Fujishiro, Yoshiaki Matsumoto, Kay Lingenauber, Reinald Kallenbach, Christian Althaus, Thomas Behnke, Jan Binger, Anna Daurskikh, Henri Eisenmenger, Ulrich Heer, Christian Hüttig, Luisa M. Lara, Alexander Lichopoj, Horst Georg Lötzke, Fabian Lüdicke, Harald Michaelis, Juan Pablo Rodriguez Garcia, Kerstin Rösner, Alexander Stark, Gregor Steinbrügge, Pascal Thabaut, Nicolas Thomas, Simone del Togno, Daniel Wahl, Belinda Wendler, Kai Wickhusen, Konrad Willner, Hauke Hussmann
    Advances in Space Research 69 5 2283 - 2304 2022年03月01日 [査読有り]
     
    The Jupiter Icy Moons Explorer (JUICE) is a science mission led by the European Space Agency, being developed for launch in 2023. The Ganymede Laser Altimeter (GALA) is an instrument onboard JUICE, whose main scientific goals are to understand ice tectonics based on topographic data, the subsurface structure by measuring tidal response, and small-scale roughness and albedo of the surface. In addition, from the perspective of astrobiology, it is imperative to study the subsurface ocean scientifically. The development of GALA has proceeded through an international collaboration between Germany (the lead), Japan, Switzerland, and Spain. Within this framework, the Japanese team (GALA-J) is responsible for developing three receiver modules: the Backend Optics (BEO), the Focal Plane Assembly (FPA), and the Analog Electronics Module (AEM). Like the German team, GALA-J also developed software to simulate the performance of the entire GALA system (performance model). In July 2020, the Proto-Flight Models of BEO, FPA, and AEM were delivered from Japan to Germany. This paper presents an overview of JUICE/GALA and its scientific objectives and describes the instrumentation, mainly focusing on Japan's contribution.
  • Jooyeon Geem, Masateru Ishiguro, Yoonsoo P. Bach, Daisuke Kuroda, Hiroyuki Naito, Hidekazu Hanayama, Yoonyoung Kim, Yuna G. Kwon, Sunho Jin, Tomohiko Sekiguchi, Ryo Okazaki, Jeremie J. Vaubaillon, Masataka Imai, Tatsuharu Oono, Yuki Futamura, Seiko Takagi, Mitsuteru Sato, Kiyoshi Kuramoto, Makoto Watanabe
    Astronomy and Astrophysics 658 2022年02月01日 [査読有り]
     
    Context. Asteroids in comet-like orbits (ACOs) consist of asteroids and dormant comets. Due to their similar appearance, it is challenging to distinguish dormant comets from ACOs via general telescopic observations. Surveys for discriminating dormant comets from the ACO population have been conducted via spectroscopy or optical and mid-infrared photometry. However, they have not been conducted through polarimetry. Aims. We conducted the first polarimetric research of ACOs. Methods. We conducted a linear polarimetric pilot survey for three ACOs: (944) Hidalgo, (3552) Don Quixote, and (331471) 1984 QY1. These objects are unambiguously classified into ACOs in terms of their orbital elements (i.e., the Tisserand parameters with respect to Jupiter TJ significantly less than 3). Three ACOs were observed by the 1.6 m Pirka Telescope from UT 2016 May 25 to UT 2019 July 22 (13 nights). Results. We found that Don Quixote and Hidalgo have polarimetric properties similar to comet nuclei and D-type asteroids (optical analogs of comet nuclei). However, 1984 QY1 exhibited a polarimetric property consistent with S-type asteroids. We conducted a backward orbital integration to determine the origin of 1984 QY1, and found that this object was transported from the main belt into the current comet-like orbit via the 3:1 mean motion resonance with Jupiter. Conclusions. We conclude that the origins of ACOs can be more reliably identified by adding polarimetric data to the color and spectral information. This study would be valuable for investigating how the ice-bearing small bodies distribute in the inner Solar System.
  • Masateru Ishiguro, Yoonsoo P. Bach, Jooyeon Geem, Hiroyuki Naito, Daisuke Kuroda, Myungshin Im, Myung Gyoon Lee, Jinguk Seo, Sunho Jin, Yuna G. Kwon, Tatsuharu Oono, Seiko Takagi, Mitsuteru Sato, Kiyoshi Kuramoto, Takashi Ito, Sunao Hasegawa, Fumi Yoshida, Tomoko Arai, Hiroshi Akitaya, Tomohiko Sekiguchi, Ryo Okazaki, Masataka Imai, Katsuhito Ohtsuka, Makoto Watanabe, Jun Takahashi, Maxime Devogèle, Grigori Fedorets, Lauri Siltala, Mikael Granvik
    Monthly Notices of the Royal Astronomical Society 509 3 4128 - 4142 2022年01月01日 [査読有り]
     
    The investigation of asteroids near the Sun is important for understanding the final evolutionary stage of primitive Solar system objects. A near-Sun asteroid (NSA), (155140) 2005 UD, has orbital elements similar to those of (3200) Phaethon (the target asteroid for the JAXA's DESTINY+ mission). We conducted photometric and polarimetric observations of 2005 UD and found that this asteroid exhibits a polarization phase curve similar to that of Phaethon over a wide range of observed solar phase angles (α = 20-105°) but different from those of (101955) Bennu and (162173) Ryugu (asteroids composed of hydrated carbonaceous materials). At a low phase angle (α 30°), the polarimetric properties of these NSAs (2005 UD and Phaethon) are consistent with anhydrous carbonaceous chondrites, while the properties of Bennu are consistent with hydrous carbonaceous chondrites. We derived the geometric albedo, pV ∼0.1 (in the range of 0.088-0.109); mean V-band absolute magnitude, HV = 17.54 ± 0.02; synodic rotational period, $T_mathrm{rot} = 5.2388 pm 0.0022 , mathrm{h}$ (the two-peaked solution is assumed); and effective mean diameter, $D_mathrm{eff} = 1.32 pm 0.06 , mathrm{km}$. At large phase angles (α 80°), the polarization phase curve are likely explained by the dominance of large grains and the paucity of small micron-sized grains. We conclude that the polarimetric similarity of these NSAs can be attributed to the intense solar heating of carbonaceous materials around their perihelia, where large anhydrous particles with small porosity could be produced by sintering.
  • Patrick Michel, Stephan Ulamec, Ute Boettger, Matthias Grott, Naomi Murdoch, Pierre Vernazza, Cecily Sunday, Yun Zhang, Rudy Valette, Romain Castellani, Jens Biele, Simon Tardivel, Olivier Groussin, Laurent Jorda, Joerg Knollenberg, Jan Thimo Grundmann, Denis Arrat, Gabriel Pont, Stephane Mary, Markus Grebenstein, Hirdy Miyamoto, Tomoki Nakamura, Koji Wada, Kent Yoshikawa, Kiyoshi Kuramoto
    EARTH PLANETS AND SPACE 74 1 2022年01月 [査読有り]
     
    The Japanese MMX sample return mission to Phobos by JAXA will carry a rover developed by CNES and DLR that will be deployed on Phobos to perform in situ analysis of the Martian moon's surface properties. Past images of the surface of Phobos show that it is covered by a layer of regolith. However, the mechanical and compositional properties of this regolith are poorly constrained. In particular, from current remote images, very little is known regarding the particle sizes, their chemical composition, the packing density of the regolith as well as other parameters such as friction and cohesion that influence surface dynamics. Understanding the properties and dynamics of the regolith in the low-gravity environment of Phobos is important to trace back its history and surface evolution. Moreover, this information is also important to support the interpretation of data obtained by instruments onboard the main MMX spacecraft, and to minimize the risks involved in the spacecraft sampling operations. The instruments onboard the Rover are a Raman spectrometer (RAX), an infrared radiometer (miniRad), two forward-looking cameras for navigation and science purposes (NavCams), and two cameras observing the interactions of regolith and the rover wheels (WheelCams). The Rover will be deployed before the MMX spacecraft samples Phobos' surface and will be the first rover to drive on the surface of a Martian moon and in a very low gravity environment.
  • Kiyoshi Kuramoto, Yasuhiro Kawakatsu, Masaki Fujimoto, Akito Araya, Maria Antonietta Barucci, Hidenori Genda, Naru Hirata, Hitoshi Ikeda, Takeshi Imamura, Jörn Helbert, Shingo Kameda, Masanori Kobayashi, Hiroki Kusano, David J. Lawrence, Koji Matsumoto, Patrick Michel, Hideaki Miyamoto, Tomokatsu Morota, Hiromu Nakagawa, Tomoki Nakamura, Kazunori Ogawa, Hisashi Otake, Masanobu Ozaki, Sara Russell, Sho Sasaki, Hirotaka Sawada, Hiroki Senshu, Shogo Tachibana, Naoki Terada, Stephan Ulamec, Tomohiro Usui, Koji Wada, Sei-ichiro Watanabe, Shoichiro Yokota
    Earth, Planets and Space 74 1 2022年01月 [査読有り][招待有り]
     
    Martian moons exploration, MMX, is the new sample return mission planned by the Japan Aerospace Exploration Agency (JAXA) targeting the two Martian moons with the scheduled launch in 2024 and return to the Earth in 2029. The major scientific objectives of this mission are to determine the origin of Phobos and Deimos, to elucidate the early Solar System evolution in terms of volatile delivery across the snow line to the terrestrial planets having habitable surface environments, and to explore the evolutionary processes of both moons and Mars surface environment. To achieve these objectives, during a stay in circum-Martian space over about 3 years MMX will collect samples from Phobos along with close-up observations of this inner moon and carry out multiple flybys of Deimos to make comparative observations of this outer moon. Simultaneously, successive observations of the Martian atmosphere will also be made by utilizing the advantage of quasi-equatorial spacecraft orbits along the moons' orbits.
  • Tomoki Nakamura, Hitoshi Ikeda, Toru Kouyama, Hiromu Nakagawa, Hiroki Kusano, Hiroki Senshu, Shingo Kameda, Koji Matsumoto, Ferran Gonzalez-Franquesa, Naoya Ozaki, Yosuke Takeo, Nicola Baresi, Yusuke Oki, David J. Lawrence, Nancy L. Chabot, Patrick N. Peplowski, Maria Antonietta Barucci, Eric Sawyer, Shoichiro Yokota, Naoki Terada, Stephan Ulamec, Patrick Michel, Masanori Kobayashi, Sho Sasaki, Naru Hirata, Koji Wada, Hideaki Miyamoto, Takeshi Imamura, Naoko Ogawa, Kazunori Ogawa, Takahiro Iwata, Takane Imada, Hisashi Otake, Elisabet Canalias, Laurence Lorda, Simon Tardivel, Stephane Mary, Makoto Kunugi, Seiji Mitsuhashi, Alain Doressoundiram, Frederic Merlin, Sonia Fornasier, Jean-Michel Reess, Pernelle Bernardi, Shigeru Imai, Yasuyuki Ito, Hatsumi Ishida, Kiyoshi Kuramoto, Yasuhiro Kawakatsu
    EARTH PLANETS AND SPACE 73 1 2021年12月 [査読有り]
     
    The science operations of the spacecraft and remote sensing instruments for the Martian Moon eXploration (MMX) mission are discussed by the mission operation working team. In this paper, we describe the Phobos observations during the first 1.5 years of the spacecraft's stay around Mars, and the Deimos observations before leaving the Martian system. In the Phobos observation, the spacecraft will be placed in low-altitude quasi-satellite orbits on the equatorial plane of Phobos and will make high-resolution topographic and spectroscopic observations of the Phobos surface from five different altitudes orbits. The spacecraft will also attempt to observe polar regions of Phobos from a three-dimensional quasi-satellite orbit moving out of the equatorial plane of Phobos. From these observations, we will constrain the origin of Phobos and Deimos and select places for landing site candidates for sample collection. For the Deimos observations, the spacecraft will be injected into two resonant orbits and will perform many flybys to observe the surface of Deimos over as large an area as possible.
  • 吉田 辰哉, 倉本 圭
    遊星人 30 2 52 - 63 2021年06月 [査読有り][招待有り]
  • Hydrodynamic escape of an impact-generated reduced proto-atmosphere on Earth
    Tatsuya Yoshida, Kiyoshi Kuramoto
    Monthly Notices of the Royal Astronomical Society 505 2 2941 - 2953 2021年05月 [査読有り]
  • Kuroda, D., Geem, J., Akitaya, H., Jin, S., Takahashi, J., Takahashi, K., Naito, H., Makino, K., Sekiguchi, T., Bach, Y.P., Seo, J., Sato, S., Sasago, H., Kawabata, K.S., Kawakami, A., Tozuka, M., Watanabe, M., Takagi, S., Kuramoto, K., Yoshikawa, M., Hasegawa, S., Ishiguro, M.
    Astrophysical Journal Letters 911 2 2021年04月 [査読有り][通常論文]
     
    The asteroid exploration project "Hayabusa2" has successfully returned samples from the asteroid (162173) Ryugu. In this study, we measured the linear polarization degrees of Ryugu using four ground-based telescopes from 2020 September 27 to December 25, covering a wide-phase angle (Sun-target-observer's angle) range from 28 degrees to 104 degrees. We found that the polarization degree of Ryugu reached 53% around a phase angle of 100 degrees, the highest value among all asteroids and comets thus far reported. The high polarization degree of Ryugu can be attributed to the scattering properties of its surface layers, in particular the relatively small contribution of multiply scattered light. Our polarimetric results indicate that Ryugu's surface is covered with large grains. On the basis of a comparison with polarimetric measurements of pulverized meteorites, we can infer the presence of submillimeter-sized grains on the surface layer of Ryugu. We also conjecture that this size boundary represents the grains that compose the aggregate. It is likely that a very brittle structure has been lost in the recovered samples, although they may hold a record of its evolution. Our data will be invaluable for future experiments aimed at reproducing the surface structure of Ryugu.
  • Daisuke Kuroda, Masateru Ishiguro, Hiroyuki Naito, Makoto Watanabe, Sunao Hasegawa, Seiko Takagi, Kiyoshi Kuramoto
    ASTRONOMY & ASTROPHYSICS 646 2021年02月 [査読有り]
     
    Context. To investigate the physical properties of the surface layers of small Solar System objects, we take advantage of the phase-angle dependence of the linear polarization degree, which varies with albedo, composition, and other factors. In particular, the angle at which the positive and negative are reversed is a polarimetric parameter known as inversion angle. A group with large inversion angles (the so-called Barbarians) is unusual and is also noteworthy because of their association with meteorites.Aims. We identified an object with such a large inversion angle in the near-Earth asteroids and derived previously unknown parameters, including the maximum polarization degree. By comparing the polarimetric parameters and spectral properties of meteorites, we inferred the surface conditions based on the degree of polarization of the asteroid.Methods. We carried out multiband polarization imaging observations of an L-type near-Earth asteroid, (85989) 1999 JD(6), at the Hokkaido University Observatory in 2015 and 2019, covering a wide range of phase angles 30 degrees -105 degrees. Of the polarimetric parameters, we derived the maximum value, inversion angle, and the slope at that angle from the phase angle-polarization degree curve.Results. We found that the inversion angle and the maximum polarization degree of 1999 JD(6) are 27 degrees and 13%. The inversion angle is significantly larger than those of the majority of all asteroids observed before, but is consistent with that of Barbarian asteroids. 1999 JD(6) is the first example belonging to this group that is also among the near-Earth asteroids.Conclusions. We claim that 1999 JD(6) is a member of the Barbarians and has rougher surface particles than lunar regolith.
  • Saito, H., Yamamoto, T., Nakajima, K., Kuramoto, K., Yamamoto, M.-Y.
    Journal of the Acoustical Society of America 149 1 591 - 598 2021年01月 [査読有り]
  • Ito, Y., Hashimoto, G.L., Takahashi, Y.O., Ishiwatari, M., Kuramoto, K.
    Astrophysical Journal 893 2 2020年04月28日 [査読有り][通常論文]
     
    The existence of liquid water within an oxidized environment on early Mars has been inferred by the Mn-rich rocks found during recent explorations on Mars. The oxidized atmosphere implied by the Mn-rich rocks would basically be comprised of CO2 and H2O without any reduced greenhouse gases such as H-2 and CH4. So far, however, it has been thought that early Mars could not have been warm enough to sustain water in liquid form without the presence of reduced greenhouse gases. Here, we propose that H2O2 could have been the gas responsible for warming the surface of the oxidized early Mars. Our one-dimensional atmospheric model shows that only 1 ppm of H2O2 is enough to warm the planetary surface because of its strong absorption at far-infrared wavelengths, in which the surface temperature could have reached over 273 K for a CO2 atmosphere with a pressure of 3 bar. A wet and oxidized atmosphere is expected to maintain sufficient quantities of H2O2 gas in its upper atmosphere due to its rapid photochemical production in slow condensation conditions. Our results demonstrate that a warm and wet environment could have been maintained on an oxidized early Mars, thereby suggesting that there may be connections between its ancient atmospheric redox state and possible aqueous environment.
  • Yasuhiro Kawakatsu, Kiyoshi Kuramoto, Tomohiro Usui, Hitoshi Ikeda, Kent Yoshikawa, Hirotaka Sawada, Naoya Ozaki, Takane Imada, Hisashi Otake, Kenichiro Maki, Masatsugu Otsuki, Robert Muller, Kris Zacny, Yasutaka Satoh, Stephane Mary, Markus Grebenstein, Ayumu Tokaji, Liang Yuying, Ferran Gonzalez Franquesa, Nishanth Pushparaj, Takuya Chikazawa
    Proceedings of the International Astronautical Congress, IAC 2020-October 2020年 [査読有り]
     
    Martian Moons eXploration (MMX) is a mission to Martian moons under development in JAXA with international partners to be launched in 2024. This paper introduces the system definition and the latest status of MMX program. “How was water delivered to rocky planets and enabled the habitability of the solar system?” This is the key question to which MMX is going to answer in the context of our minor body exploration strategy preceded by Hayabusa and Hayabusa2. Solar system formation theories suggest that small bodies as comets and asteroids were delivery capsules of water, volatiles, organic compounds etc. from outside of the snow line to entitle the rocky planet region to be habitable. Mars was at the gateway position to witness the process, which naturally leads us to explore two Martian moons, Phobos and Deimos, to answer to the key question. The goal of MMX is to reveal the origin of the Martian moons, and then to make a progress in our understanding of planetary system formation and of primordial material transport around the border between the inner- and the outer-part of the early solar system. The mission is to survey two Martian moons, and return samples from one of them, Phobos. In view of the launch in 2024, the phase-A study was completed in February, 2020. The mission definition, mission scenario, system definition, critical technologies and programmatic framework are introduced int this paper.
  • Usui, T., Bajo, K.-I., Fujiya, W., Furukawa, Y., Koike, M., Miura, Y.N., Sugahara, H., Tachibana, S., Takano, Y., Kuramoto, K.
    Space Science Reviews 216 4 2020年04月 [査読有り][通常論文]
     
    Phobos and Deimos occupy unique positions both scientifically and programmatically on the road to the exploration of the solar system. Japan Aerospace Exploration Agency (JAXA) plans a Phobos sample return mission (MMX: Martian Moons eXploration). The MMX spacecraft is scheduled to be launched in 2024, orbit both Phobos and Deimos (multiple flybys), and retrieve and return >10 g of Phobos regolith back to Earth in 2029. The Phobos regolith represents a mixture of endogenous Phobos building blocks and exogenous materials that contain solar system projectiles (e.g., interplanetary dust particles and coarser materials) and ejecta from Mars and Deimos. Under the condition that the representativeness of the sampling site(s) is guaranteed by remote sensing observations in the geologic context of Phobos, laboratory analysis (e.g., mineralogy, bulk composition, O-Cr-Ti isotopic systematics, and radiometric dating) of the returned sample will provide crucial information about the moon's origin: capture of an asteroid or in-situ formation by a giant impact. If Phobos proves to be a captured object, isotopic compositions of volatile elements (e.g., D/H, C-13/C-12, N-15/N-14) in inorganic and organic materials will shed light on both organic-mineral-water/ice interactions in a primitive rocky body originally formed in the outer solar system and the delivery process of water and organics into the inner rocky planets.
  • Yoshida, T., Kuramoto, K.
    Icarus 345 2020年07月 [査読有り][通常論文]
     
    Proto-Mars growing within the solar nebula may have maintained both the hydrogen-dominated solar component and the impact degassed component enriched in H-2, CH4 and CO as a proto-atmosphere. Such a protoatmosphere would experience hydrodynamic escape early in the history of Mars but its flux and duration of reduced composition remain highly uncertain. Here we develop a one-dimensional hydrodynamic escape model which includes radiative cooling processes and photochemical processes for a multi-component atmosphere and estimate the amount of atmosphere lost by hydrodynamic escape and the duration of early Martian atmosphere with reduced chemical compositions. The mass escape rate decreases more than one order of magnitude with increasing the mixing fraction of CH4 and CO >= 10% mainly because of the energy loss by radiative cooling by these infrared active chemical molecules. Concurrently, the mass fractionation between H-2 and other heavier species occurs more remarkably. Assuming that carbon species equivalent to 1 bar of CO2 was left behind when most H-2 completed its hydrodynamic escape, it possibly takes as long as 30 Myr for most H-2 to be lost by hydrodynamic escape. The total amount of CH4 and CO lost by hydrodynamic escape exceeds 10 bar, equivalent to 20 bar of CO2 when the initial atmosphere is hydrogen-rich, which may explain the paucity of CO2 on Mars compared to Earth and Venus. The isotopic fractionation during hydrodynamic escape is not enough to elevate the D/H ratio from the proto-solar value to the present value, but it can explain the C-13/C-12 ratio of present Mars. The reduced atmosphere with enriched in CH4 and CO may further continue until these species are almost fully oxidized through photolysis and hydrogen escape. Our result suggests that a reduced environment may have been kept and played an important role in producing warm and wet climate and serving organic matters on Mars.
  • Nakagawa, Y., Kodama, T., Ishiwatari, M., Kawahara, H., Suto, Y., Takahashi, Y.O., Hashimoto, G.L., Kuramoto, K., Nakajima, K., Takehiro, S.-I., Hayashi, Y.-Y.
    Astrophysical Journal 898 2 2020年07月28日 [査読有り][通常論文]
     
    Direct-imaging techniques of exoplanets have made significant progress recently and will eventually enable monitoring of photometric and spectroscopic signals of Earth-like habitable planets. The presence of clouds, however, would remain as one of the most uncertain components in deciphering such direct-imaged signals of planets. We attempt to examine how the planetary obliquity produces different cloud patterns by performing a series of general circulation model simulation runs using a set of parameters relevant for our Earth. Then we use the simulated photometric lightcurves to compute their frequency modulation that is due to the planetary spin-orbit coupling over an entire orbital period, and we attempt to see to what extent one can estimate the obliquity of an Earth twin. We find that it is possible to estimate the obliquity of an Earth twin within the uncertainty of several degrees with a dedicated 4 m space telescope at 10 pc away from the system if the stellar flux is completely blocked. While our conclusion is based on several idealized assumptions, a frequency modulation of a directly imaged Earth-like planet offers a unique methodology to determine its obliquity.
  • Saito, H., Kuramoto, K.
    Astrophysical Journal 889 1 2020年01月23日 [査読有り][通常論文]
     
    The deuterium/hydrogen (D/H) ratio of primordial water partitioned into a planetary interior seems to be different on Earth and Mars. Water from volcanic rocks originating from Earth's deep mantle has a low D/H ratio with high He-3/He-4 ratios, implying that it was inherited partially from the solar nebula. In contrast, the D/H ratio of water in the Martian meteorites considered to represent the mantle does not trend toward that of the solar nebula. These differences may be owing to differences in the types of atmospheric structures formed on protoplanets accreting in the solar nebula. Using a 1D radiative-equilibrium model, we analyze the thermal structure of a hybrid-type protoatmosphere in which the solar nebula component dominates the upper layer while a degassed component dominates the lower layer. Our analysis implies Mars-sized protoplanets maintain a hybrid-type protoatmosphere and the D/H ratio of the lower atmosphere resembles that of the building blocks. Conversely, when the mass is larger than Mars-sized, the compositional stratification is collapsed by convective mixing of the solar nebula component with the degassed component, and the D/H ratio approaches that of the solar nebula. This tendency becomes stronger when the planetary mass is larger. If water vapor is distributed through a magma ocean into the planetary interior, Mars-sized protoplanets are likely to reflect the D/H ratios of the building blocks, while larger protoplanets are likely to have acquired a solar-nebula-like D/H ratio.
  • Huang, P.C., Chen, W.P., Mugrauer, M., Bischoff, R., Budaj, J., Burkhonov, O., Ehgamberdiev, S., Errmann, R., Garai, Z., Hsiao, H.Y., Hu, C.L., Janulis, R., Jensen, E.L.N., Kiyota, S., Kuramoto, K., Lin, C.S., Lin, H.C., Liu, J.Z., Lux, O., Naito, H., Neuhaüser, R., Ohlert, J., Pakštienė, E., Pribulla, T., Qvam, J.K.T., Raetz, S., Sato, S., Schwartz, M., Semkov, E., Takagi, S., Wagner, D., Watanabe, M., Zhang, Y.
    Astrophysical Journal 871 2 2019年 [査読有り]
  • Stephan Ulamec, Patrick Michel, Matthias Grott, Ute Böttger, Heinz Wilhelm Hübers, Naomi Murdoch, Pierre Vernazza, Özgür Karatekin, Jörg Knollenberg, Konrad Willner, Markus Grebenstein, Stephane Mary, Pascale Chazalnoël, Jens Biele, Christian Krause, Tra Mi Ho, Caroline Lange, Jan Thimo Grundmann, Kaname Sasaki, Michael Maibaum, Oliver Küchemann, Josef Reill, Maxime Chalon, Stefan Barthelmes, Roy Lichtenheldt, Rainer Krenn, Michal Smisek, Jean Bertrand, Aurélie Moussi, Cedric Delmas, Simon Tardivel, Denis Arrat, Frans IJpelaan, Laurence Mélac, Laurence Lorda, Emile Remetean, Michael Lange, Olaf Mierheim, Siebo Reershemius, Tomohiro Usui, Moe Matsuoka, Tomoki Nakamura, Koji Wada, Hirdy Miyamoto, Kiyoshi Kuramoto, Julia LeMaitre, Guillaume Mas, Michel Delpech, Loisel Celine, Arthur Rafflegeau, Honorine Boirard, Roseline Schmisser, Cédric Virmontois, Celine Cenac-Morthe, Dominique Besson, Fernando Rull
    Proceedings of the International Astronautical Congress, IAC 2019-October 2019年 [査読有り]
     
    Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. The Martian Moons eXploration (MMX) is a mission by the Japan Aerospace Exploration Agency, JAXA, to the Martian moons Phobos and Deimos. It will primarily investigate the origin of this moon by bringing samples back from Phobos to Earth and deliver a small (about 25 kg) Rover to the surface. The Rover is a contribution by the Centre National d'Etudes Spatiales (CNES) and the German Aerospace Center (DLR). Its currently considered scientific payload consists of a thermal mapper (miniRAD), a Raman spectrometer (RAX) a stereo pair of cameras looking forward (NavCAM) and two cameras looking at the interface wheel-surface (WheelCAM) and consequent Phobos' regolith mechanical properties. The cameras will serve for both, technological and scientific needs. The MMX rover will be delivered from an altitude of <100 m and start uprighting and deploying wheels and a solar generator after having come to rest on the surface. It is planned to operate for three months on Phobos and provide unprecedented science while moving for a few meters to hundreds of meters. MMX will be launched in September 2024 and inserted into Mars orbit in 2025, the Rover delivery and operations are planned for 2026-2027.
  • Yasuhiro Kawakatsu, Kiyoshi Kuramoto, Naoko Ogawa, Hitoshi Ikeda, Go Ono, Hirotaka Sawada, Takane Imada, Masatsugu Otsuki, Hisashi Otake, Robert Muller, Kris Zacny, Yasutaka Satoh, Kazuhiko Yamada, Stephane Mary, Markus Grebenstein, Kento Yoshikawa
    Proceedings of the International Astronautical Congress, IAC 2019-October 2019年 [査読有り]
     
    Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. Martian Moons eXploration (MMX) is a mission to Martian moons under study in JAXA with international partners to be launched in 2024. This paper introduces the mission definition and the latest status of MMX program. “How was water delivered to rocky planets and enabled the habitability of the solar system?” This is the key question to which MMX is going to answer in the context of our minor body exploration strategy preceded by Hayabusa and Hayabusa2. Solar system formation theories suggest that small bodies as comets and asteroids were delivery capsules of water, volatiles, organic compounds etc. from outside the snow line to entitle the rocky planet region to be habitable. Mars was at the gateway position to witness the process, which naturally leads us to explore two Martian moons, Phobos and Deimos, to answer to the key question. The goal of MMX is to reveal the origin of the Martian moons, and then to make a progress in our understanding of planetary system formation and of primordial material transport around the border between the inner- and the outer-part of the early solar system. The mission is to survey two Martian moons, and return samples from one of them. In view of the launch in 2024, the phase-A study is to be completed in this year. The mission definition, mission scenario, system description, and programmatic framework are introduced int this paper.
  • Jun KIMURA, Hauke HUSSMANN, Shunichi KAMATA, Koji MATSUMOTO, Jürgen OBERST, Gregor STEINBRÜGGE, Alexander STARK, Klaus GWINNER, Shoko OSHIGAMI, Noriyuki NAMIKI, Kay LINGENAUBER, Keigo ENYA, Kiyoshi KURAMOTO, Sho SASAKI
    TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN 17 2 234 - 243 2019年 [査読有り][通常論文]
  • Kamata, S., Nimmo, F., Sekine, Y., Kuramoto, K., Noguchi, N., Kimura, J., Tani, A.
    Nature Geoscience 12 6 407 - 410 2019年06月20日 [査読有り][通常論文]
     
    Many icy Solar System bodies possess subsurface oceans. On Pluto, Sputnik Planitia's location near the equator suggests the presence of a subsurface ocean and a locally thinned ice shell. To maintain an ocean, Pluto needs to retain heat inside. On the other hand, to maintain large variations in its thickness, Pluto's ice shell needs to be cold. Here we show, by thermal evolution and viscous relaxation calculations, that the presence of a thin layer of clathrate hydrates (gas hydrates) at the base of the ice shell can explain both the long-term survival of the ocean and the maintenance of shell thickness contrasts. Clathrate hydrates act as a thermal insulator, preventing the ocean from completely freezing while keeping the ice shell cold and immobile. The most likely clathrate guest gas is methane, derived from precursor bodies and/or cracking of organic materials in the hot rocky core. Nitrogen molecules initially contained and/or produced later in the core would probably not be trapped as clathrate hydrates, instead supplying the nitrogen-rich surface and atmosphere. The formation of a thin clathrate hydrate layer cap to a subsurface ocean may be an important generic mechanism to maintain long-lived subsurface oceans in relatively large but minimally heated icy satellites and Kuiper belt objects.
  • Daisuke Kuroda, Masateru Ishiguro, Makoto Watanabe, Sunao Hasegawa, Tomohiko Sekiguchi, Hiroyuki Naito, Fumihiko Usui, Masataka Imai, Mitsuteru Sato, Kiyoshi Kuramoto
    ASTRONOMY & ASTROPHYSICS 611 2018年03月 [査読有り][通常論文]
     
    We present a unique and significant polarimetric result regarding the near-Earth asteroid (152679) 1998 KU2, which has a very low geometric albedo. From our observations, we find that the linear polarization degrees of 1998 KU2 are 44.6 +/- 0.5% in the R-C band and 44.0 +/- 0.6% in the V band at a solar phase angle of 81.0 degrees. These values are the highest of any known airless body in the solar system (i.e., high-polarization comets, asteroids, and planetary satellites) at similar phase angles. This polarimetric observation is not only the first for primitive asteroids at large phase angles, but also for low-albedo (<0.1) airless bodies. Based on spectroscopic similarities and polarimetric measurements of materials that have been sorted by size in previous studies, we conjecture that 1998 KU2 has a highly microporous regolith structure comprising nano-sized carbon grains on the surface.
  • Yasuhiro Kawakatsu, Kiyoshi Kuramoto, Tomohiro Usui, Hitoshi Ikeda, Naoya Ozaki, Nicola Baresi, Go Ono, Takane Imada, Takanobu Shimada, Hiroki Kusano, Hirotaka Sawada, Takashi Ozawa, Mitsuhisa Baba, Hisashi Otake
    Proceedings of the International Astronautical Congress, IAC 2018-October 2018年 
    Martian Moons eXploration (MMX) is a mission under study in ISAS/JAXA to be launched in 2024. This paper introduces the mission design of MMX mission. “How was water delivered to rocky planets and enabled the habitability of the solar system?” This is the key question to which MMX is going to answer. Solar system formation theories suggest that rocky planets must have been born dry. Delivery of water, volatiles, organic compounds etc. from outside the snow line entitles the rocky planet region to be habitable. Small bodies as comets and asteroids play the role of delivery capsules. Then, dynamics of small bodies around the snow line in the early solar system is the issue that needs to be understood. Mars was at the gateway position to witness the process, which naturally leads us to explore two Martian moons, Phobos and Deimos, to answer to the key question. The goal of MMX is to reveal the origin of the Martian moons, and then to make a progress in our understanding of planetary system formation and of primordial material transport around the border between the inner- and the outer-part of the early solar system. The mission is to survey two Martian moons, and return samples from one of them. Following the mission concepts study results presented in the previous conference, the following items will be reported in this paper. First, based on the mission goals and objectives defined, the requirements to the systems and operations are derived and their feasibility is evaluated. Second, as to the key technologies issues identified, partial models are built and their performance is evaluated. And third, collaborations with overseas space agency are discussed and the programmatic framework is defined.
  • Henze, M., Henze, M., Darnley, M.J., Williams, S.C., Kato, M., Hachisu, I., Anupama, G.C., Arai, A., Boyd, D., Burke, D., Ciardullo, R., Chinetti, K., Cook, L.M., Cook, M.J., Erdman, P., Gao, X., Harris, B., Hartmann, D.H., Hornoch, K., Horst, J.C., Hounsell, R., Husar, D., Itagaki, K., Kabashima, F., Kafka, S., Kaur, A., Kiyota, S., Kojiguchi, N., Kučáková, H., Kuramoto, K., Maehara, H., Mantero, A., Masci, F.J., Matsumoto, K., Naito, H., Ness, J.-U., Nishiyama, K., Oksanen, A., Osborne, J.P., Page, K.L., Paunzen, E., Pavana, M., Pickard, R., Prieto-Arranz, J., Rodríguez-Gil, P., Sala, G., Sano, Y., Shafter, A.W., Sugiura, Y., Tan, H., Tordai, T., Vraštil, J., Wagner, R.M., Watanabe, F., Williams, B.F., Bode, M.F., Bruno, A., Buchheim, B., Crawford, T., Goff, B., Hernanz, M., Igarashi, A.S., José, J., Motta, M., O'Brien, T.J., Oswalt, T., Poyner, G., Ribeiro, V.A.R.M., Sabo, R., Shara, M.M., Shears, J., Starkey, D., Starrfield, S., Woodward, C.E.
    Astrophysical Journal 857 1 2018年 [査読有り]
  • Young, E.D., Kuramoto, K., Marcus, R.A., Yurimoto, H., Jacobsen, S.B.
    Oxygen in the Solar System 68 1 187 - 218 2018年 [査読有り][通常論文]
     
    In this chapter we compare and contrast chemical and photochemical pathways for mass-independent fractionation (MIF) of oxygen isotopes in the solar nebula. We begin by assessing the galactic evolution model for oxygen isotope variation in the Solar System in order to compare the predictions of a leading nucleosynthetic model with those of the chemical models. There are two fundamentally different classes of possible chemical mechanisms for mass-independent oxygen isotope fractionation in the early Solar System. One is symmetry-induced intramolecular vibrational disequilibrium of vibrationally excited reactant oxygen-bearing molecules. The other is isotope selective photodissociation of CO coupled with self-shielding and formation of H(2)O- Symmetry-induced fractionation is an experimentally verified process with solid theoretical foundations. It is observed to occur in Earth's atmosphere. It could have resulted in preservation of oxygen MIF effects only if mediated by dust grain surfaces. CO self-shielding is an attractive hypothesis for the origin of mass-independent oxygen isotope fractionation in the early Solar System because it appeals to a process that apparently occurs in the interstellar medium, but it lacks experimental verification. Three astrophysical settings for CO self-shielding are proposed as sites for generating Delta(17)O variability in the early Solar System. One is the inner annulus of the protostellar disk at relatively high temperature. Another is the surface of the disk high above the midplane where light from the central star grazes theas and dust of the disk, resulting in a zone of active CO predissociation and self-shielding. Interstellar light illuminating the disk at high incident angles causes a similar horizon of CO photodestruction. Variations in (16)O could also have been inherited from self-shielding by CO in the molecular cloud that gave rise to the protosun. The overall consequence of CO self-shielding is conversion of CO gas to (16)O-poor H(2)O. A key difference between galactic evolution, chemically-induced MIF effects, and CO self-shielding is the predicted relative oxygen isotopic compositions of primeval dust and the Sun. Therefore, the oxygen isotopic composition of the Sun will be a crucial arbiter that may permit us to narrow the list of possible origins for oxygen MIF in the early Solar System.
  • Ito, T., Ishiguro, M., Arai, T., Imai, M., Sekiguchi, T., Bach, Y.P., Kwon, Y.G., Kobayashi, M., Ishimaru, R., Naito, H., Watanabe, M., Kuramoto, K.
    Nature Communications 9 1 2486  2018年06月 [査読有り][通常論文]
     
    The near-Earth asteroid (3200) Phaethon is the parent body of the Geminid meteor stream. Phaethon is also an active asteroid with a very blue spectrum. We conducted polarimetric observations of this asteroid over a wide range of solar phase angles a during its close approach to the Earth in autumn 2016. Our observation revealed that Phaethon exhibits extremely large linear polarization: P = 50.0 +/- 1.1% at a = 106.5 degrees, and its maximum is even larger. The strong polarization implies that Phaethon's geometric albedo is lower than the current estimate obtained through radiometric observation. This possibility stems from the potential uncertainty in Phaethon's absolute magnitude. An alternative possibility is that relatively large grains (similar to 300 mu m in diameter, presumably due to extensive heating near its perihelion) dominate this asteroid's surface. In addition, the asteroid's surface porosity, if it is substantially large, can also be an effective cause of this polarization.
  • 齊藤 大晶, 倉本 圭
    日本惑星科学会誌遊星人 27 3 229 - 234 日本惑星科学会 2018年 [査読有り][通常論文]
     

    形成期の惑星内部に取り込まれた初生水の D/H 比は地球と火星で異なるらしい．始原マントルにソースを持つと考えられる噴出岩中のメルト包有物中の H2O は，地球試料においては，星雲ガスを取り込んだことを示唆する低い D/H 比を示す一方で，火星試料においては，炭素質コンドライトに近い D/H 比を示す．両者の D/H 比の差異は，星雲内で集積する原始惑星上における原始大気の構造が惑星質量に依存しているためであるかもしれない．新たな一次元大気構造数値モデリングの結果によれば， 火星質量程度の原始惑星の場合，上層に星雲ガス成分，下層に衝突脱ガス成分からなる成層した混成型原始大気が形成し，接している原始マントルは材料物質に含まれる H2O の D/H 比を獲得することができる．これに対して，火星質量以上の原始惑星の場合，対流により起源の異なる両成分が混合し，下層大気の D/H 比は星雲ガスの値に接近する．これによって大質量の惑星の始原マントルは，星雲ガスに近い値の D/H 比を獲得できた可能性がある．

  • 倉本 圭, 諸田 智克, 長岡 央, 中川 広務, 中村 智樹, 小川 和律, 大嶽 久志, 尾崎 正伸, 佐々木 晶, 千秋 博紀, 橘 省吾, 川勝 康弘, 寺田 直樹, 臼井 寛裕, 和田 浩二, 渡邊 誠一郎, MMX study team, 藤本 正樹, 玄田 英典, 平田 成, 今村 剛, 亀田 真吾, 松本 晃治, 宮本 英昭
    日本惑星科学会誌遊星人 27 3 207 - 215 日本惑星科学会 2018年 [査読有り][通常論文]
     

    火星衛星Phobosからのサンプルリターンに挑む火星衛星探査計画 (Martian Moons eXploration: MMX) は，現在，宇宙航空研究開発機構 (JAXA) プリプロジェクトとして，2024年の打ち上げと5年の往還期間を設定し，精力的な検討・初期開発が進められている．MMXは，サンプル分析，Deimosを加えた火星衛星の近接観測，そして火星大気および火星圏のモニタリング観測を組み合わせることにより，惑星に寄りそう衛星という切り口と視座から，太陽系における大気と水を湛えたハビタブル惑星の形成と進化の解明に迫ろうとしている．

  • Daisuke Kuroda, Masateru Ishiguro, Makoto Watanabe, Sunao Hasegawa, Tomohiko Sekiguchi, Hiroyuki Naito, Fumihiko Usui, Masataka Imai, Mitsuteru Sato, Kiyoshi Kuramoto
    Astronomy & Astrophysics 611 2017年11月 [査読有り][通常論文]
     
    We present a unique and significant polarimetric result regarding the near-Earth asteroid (152679) 1998 KU2, which has a very low geometric albedo. From our observations, we find that the linear polarization degrees of 1998 KU2 are 44.6 ± 0.5% in the RC band and 44.0 ± 0.6% in the V band at a solar phase angle of 81.0°. These values are the highest of any known airless body in the solar system (i.e., high-polarization comets, asteroids, and planetary satellites) at similar phase angles. This polarimetric observation is not only the first for primitive asteroids at large phase angles, but also for low-albedo (< 0.1) airless bodies. Based on spectroscopic similarities and polarimetric measurements of materials that have been sorted by size in previous studies, we conjecture that 1998 KU2 has a highly microporous regolith structure comprising nano-sized carbon grains on the surface.
  • Masateru Ishiguro, Daisuke Kuroda, Makoto Watanabe, Yoonsoo P. Bach, Jooyeon Kim, Mingyeong Lee, Tomohiko Sekiguchi, Hiroyuki Naito, Katsuhito Ohtsuka, Hidekazu Hanayama, Sunao Hasegawa, Fumihiko Usui, Seitaro Urakawa, Masataka Imai, Mitsuteru Sato, Kiyoshi Kuramoto
    The Astronomical Journal 154 5 180 - 180 2017年10月 [査読有り][通常論文]
  • Hiroaki Saito, Kiyoshi Kuramoto
    Monthly Notices of the Royal Astronomical Society 475 1 1274 - 1287 2017年 [査読有り][通常論文]
     
    Recent studies of the chronology of Martian meteorites suggest that the growth of Mars was almost complete within a few Myr after the birth of the Solar system. During such rapid accretion, proto-Mars likely gravitationally maintained both the solar nebula component and the impact degassing component, containing H2O vapour and reduced gas species, as a proto-atmosphere to be called a hybrid-type proto-atmosphere. Here we numerically analyse the mass and composition of the degassed component and the atmospheric thermal structure sustained by accretional heating. Our results predict that a growing Mars possibly acquired a massive and hot hybrid-type proto-atmosphere with surface pressure and temperature greater than several kbar and 2000 K, respectively, which is sufficient to produce a deep magma ocean. In such a high-temperature and high-pressure environment, a significant amount of H2O, CH4, CO, and H-2 is expected to be partitioned into the planetary interior, although this would strongly depend on the dynamics of the magma ocean and mantle solidification. The dissolved H2O may explain the wet Martian mantle implied from basaltic Martian meteorites. Along with the remnant reduced atmosphere after the hydrodynamic atmospheric escape, dissolved reduced gas species may have maintained an earliest Martian surface environment that allowed prebiotic chemical evolution and liquid H2O activities.
  • Noda, S., Ishiwatari, M., Nakajima, K., Takahashi, Y.O., Takehiro, S., Onishi, M., Hashimoto, G.L., Kuramoto, K., Hayashi, Y.-Y.
    Icarus 282 1 - 18 2017年 [査読有り][通常論文]
     
    In order to investigate a possible variety of atmospheric states realized on a synchronously rotating aqua planet, an experiment studying the impact of planetary rotation rate is performed using an atmospheric general circulation model (GCM) with simplified hydrological and radiative processes. The entire planetary surface is covered with a swamp ocean. The value of planetary rotation rate is varied from zero to the Earth's, while other parameters such as planetary radius, mean molecular weight and total mass of atmospheric dry components, and solar constant are set to the present Earth's values. The integration results show that the atmosphere reaches statistically equilibrium states for all runs; none of the calculated cases exemplifies the runaway greenhouse state. The circulation patterns obtained are classified into four types: Type-I characterized by the dominance of a day-night thermally direct circulation, Type-II characterized by a zonal wave number one resonant Rossby wave over a meridionally broad westerly jet on the equator, Type-III characterized by a long time scale north-south asymmetric variation, and Type-IV characterized by a pair of mid-latitude westerly jets. With the increase of planetary rotation rate, the circulation evolves from Type-I to Type-II and then to Type-III gradually and smoothly, whereas the change from Type-Ill to Type-IV is abrupt and discontinuous. Over a finite range of planetary rotation rate, both Types-III and -IV emerge as statistically steady states, constituting multiple equilibria. In spite of the substantial changes in circulation, the net energy transport from the day side to the night side remains almost insensitive to planetary rotation rate, although the partition into dry static energy and latent heat energy transports changes. The reason for this notable insensitivity is that the outgoing longwave radiation over the broad area of the day side is constrained by the radiation limit of a moist atmosphere, so that the transport to the night side, which is determined as the difference between the incoming solar radiation and the radiation limit, cannot change greatly. (C) 2016 The Authors. Published by Elsevier Inc.
  • Yasuhiro Kawakatsu, Kiyoshi Kuramoto, Naoko Ogawa, Hitoshi Ikeda, Yuya Mimasu, Go Ono, Hirotaka Sawada, Kento Yoshikawa, Takane Imada, Hisashi Otake, Hiroki Kusano, Kazuhiko Yamada, Masatsugu Otsuki, Mitsuhisa Baba
    Proceedings of the International Astronautical Congress, IAC 5 2732 - 2740 2017年 [査読有り][通常論文]
     
    © Copyright 2017 by the International Astronautical Federation (IAF). All rights reserved. Martian Moons eXploration (MMX) is a mission under study in ISAS/JAXA to be launched in 2020s. This paper introduces the concept of MMX mission. "How was water delivered to rocky planets and enabled the habitability of the solar system?" This is the key question to which MMX is going to answer. Solar system formation theories suggest that rocky planets must have been born dry. Delivery of water, volatiles, organic compounds etc. from outside the snow line entitles the rocky planet region to be habitable. Small bodies as comets and asteroids play the role of delivery capsules. Then, dynamics of small bodies around the snow line in the early solar system is the issue that needs to be understood. Mars was at the gateway position to witness the process, which naturally leads us to explore two Martian moons, Phobos and Deimos, to answer to the key question. The goal of MMX is to reveal the origin of the Martian moons, and then to make a progress in our understanding of planetary system formation and of primordial material transport around the border between the inner- and the outer-part of the early solar system. On the origin of Martian moons, there are two leading hypotheses, "Captured primordial asteroid" and "Giant Impact". We decide to collect samples from a Martian moon to conclude this discussion, and on the conclusion, to investigate further to improve our understanding of material distributions and transports at the edge of the inner part of the early solar system as well as of planetary formations. Moreover, circum-Martian environment will be measured and Martian atmosphere will be observed to improve our views of evolutions of Martian moons as well as Mars surface environmental transition. In the conceptual design phase, the goals and objectives of the mission are defined, and the feasibility of the mission is evaluated. Fundamental engineering options are listed up, and trade-off studies are conducted to define baseline plan. Key technology issues are identified and their technology readiness is evaluated. The results will be shown in the paper.
  • Shunichi Kamata, Jun Kimura, Koji Matsumoto, Francis Nimmo, Kiyoshi Kuramoto, Noriyuki Namiki
    Journal of Geophysical Research: Planets 121 7 1362 - 1375 2016年07月 [査読有り][通常論文]
  • Kamata, S., Kimura, J., Matsumoto, K., Nimmo, F., Kuramoto, K., Namiki, N.
    Journal of Geophysical Research: Planets 121 7 1362 - 1375 2016年 [査読有り][通常論文]
     
    Tidal deformation of icy satellites provides crucial information on their subsurface structures. In this study, we investigate the parameter dependence of the tidal displacement and potential Love numbers (i.e., h(2) and k(2), respectively) of Ganymede. Our results indicate that Love numbers for Ganymede models without a subsurface ocean are not necessarily smaller than those with a subsurface ocean. The phase lag, however, depends primarily on the presence/absence of a subsurface ocean. Thus, the determination of the phase lag would be of importance to infer whether Ganymede possesses a subsurface ocean or not based only on geodetic measurements. Our results also indicate that the major control on Love numbers is the thickness of the ice shell if Ganymede possesses a subsurface ocean. This result, however, does not necessarily indicate that measurement of either of h(2) or k(2) alone is sufficient to estimate the shell thickness; while a thin shell leads to large h(2) and k(2) independent of parameters, a thick shell does not necessarily lead to small h(2) and k(2). We found that to reduce the uncertainty in the shell thickness, constraining k(2) in addition to h(2) is necessary, highlighting the importance of collaborative analyses of topography and gravity field data.
  • Yasufumi Iryu, Kiyoshi Kuramoto, Masaki Satoh, Jun Matsumoto, Shoichi Yoshioka, Hodaka Kawahata, Ryuji Tada
    Progress in Earth and Planetary Science 3 1 2016年01月 [査読有り][通常論文]
  • Kamata, S., Sugita, S., Abe, Y., Ishihara, Y., Harada, Y., Morota, T., Namiki, N., Iwata, T., Hanada, H., Araki, H., Matsumoto, K., Tajika, E., Kuramoto, K., Nimmo, F.
    Icarus 250 492 - 503 2015年 [査読有り][通常論文]
     
    The solidification of the Lunar Magma Ocean (LMO) and formation of impact basins are important events that took place on the early Moon. The relative timing of these events, however, is poorly constrained. The aim of this study is to constrain the formation ages of old impact basins based on inferences of their thermal state. Most proposed basins formed before Pre-Nectarian (PN) 5 stage do not exhibit clear concentric features in either topography or gravity, suggesting substantial viscous lateral flow in the crust. Recent geodetic measurements reveal that the lunar crust is thinner than previously estimated, indicating that an extremely high crustal temperature is required for lateral flow to occur. In this study, we calculate lunar thermal evolution and viscoelastic deformation of basins and investigate the thermal state at the time of basin formation using recent crustal thickness models. We find that a Moho temperature >1300-1400 K at the time of basin formation is required for substantial viscous relaxation of topography to occur; the implied elastic thickness at the time of loading is <30 km. Such a high temperature can be maintained only for a short time (i.e., <50 Myr for most conditions) after solidification of the LMO or after mantle overturn if it took place; relaxed impact basins forming >= 150 Myr later than LMO solidification are unlikely. This result is in conflict with an intensive Late Heavy Bombardment (LHB) model, which assumes that most impact basins were formed at similar to 3.9 Ga, since it requires LMO solidification time much later than previous theoretical estimates. Either the LHB was moderate, or the majority of proposed early PN basins were not in fact formed by impacts. (C) 2014 Elsevier Inc. All rights reserved.
  • Sugiyama, K., Nakajima, K., Odaka, M., Kuramoto, K., Hayashi, Y.-Y.
    Icarus 229 71 - 91 2014年 [査読有り][通常論文]
     
    A series of long-term numerical simulations of moist convection in Jupiter's atmosphere is performed in order to investigate the idealized characteristics of the vertical structure of multi-composition clouds and the convective motions associated with them, varying the deep abundances of condensable gases and the autoconversion time scale, the latter being one of the most questionable parameters in cloud microphysical parameterization. The simulations are conducted using a two-dimensional cloud resolving model that explicitly represents the convective motion and microphysics of the three cloud components, H2O, NH3, and NH4SH imposing a body cooling that substitutes the net radiative cooling. The results are qualitatively similar to those reported in Sugiyama et al. (Sugiyama, K. et al. [2011]. Intermittent cumulonimbus activity breaking the three-layer cloud structure of Jupiter. Geophys. Res. Lett. 38, L13201. doi:10.1029/2011GL047878): stable layers associated with condensation and chemical reaction act as effective dynamical and compositional boundaries, intense cumulonimbus clouds develop with distinct temporal intermittency, and the active transport associated with these clouds results in the establishment of mean vertical profiles of condensates and condensable gases that are distinctly different from the hitherto accepted three-layered structure (e.g., Atreya, S.K., Romani, P.N. [1985]. Photochemistry and clouds of Jupiter, Saturn and Uranus. In: Recent Advances in Planetary Meteorology. Cambridge Univ. Press, London, pp. 17-68). Our results also demonstrate that the period of intermittent cloud activity is roughly proportional to the deep abundance of H2O gas. The autoconversion time scale does not strongly affect the results, except for the vertical profiles of the condensates. Changing the autoconversion time scale by a factor of 100 changes the intermittency period by a factor of less than two, although it causes a dramatic increase in the amount of condensates in the upper troposphere. The moist convection layer becomes potentially unstable with respect to an air parcel rising from below the H2O lifting condensation level (LCL) well before the development of cumulonimbus clouds. The instability accumulates until an appropriate trigger is provided by the H2O condensate that falls down through the H2O LCL; the H2O condensate drives a downward flow below the H2O LCL as a result of the latent cooling associated with the re-evaporation of the condensate, and the returning updrafts carry moist air from below to the moist convection layer. Active cloud development is terminated when the instability is completely exhausted. The period of intermittency is roughly equal to the time obtained by dividing the mean temperature increase, which is caused by active cumulonimbus development, by the body cooling rate. 2013 The Authors. Published by Elsevier Inc. All rights reserved.
  • Sugiyama, K., Nakajima, K., Odaka, M., Kuramoto, K., Hayashi, Y.-Y.
    Icarus 231 407 - 408 2014年 [査読有り][通常論文]
  • Tsumura, K., Arimatsu, K., Egami, E., Hayano, Y., Honda, C., Kimura, J., Kuramoto, K., Matsuura, S., Minowa, Y., Nakajima, K., Nakamoto, T., Shirahata, M., Surace, J., Takahashi, Y., Wada, T.
    Astrophysical Journal 789 2 2014年 [査読有り][通常論文]
     
    Based on observations from the Hubble Space Telescope and the Subaru Telescope, we have discovered that Europa, Ganymede, and Callisto are bright around 1.5 μm even when not directly lit by sunlight. The observations were conducted with non-sidereal tracking on Jupiter outside of the field of view to reduce the stray light subtraction uncertainty due to the close proximity of Jupiter. Their eclipsed luminosity was 10 -6 -10 -7 of their uneclipsed brightness, which is low enough that this phenomenon has been undiscovered until now. In addition, Europa in eclipse was < 1/10 of the others at 1.5 μm, a potential clue to the origin of the source of luminosity. Likewise, Ganymede observations were attempted at 3.6 μm by the Spitzer Space Telesc ope, but it was not detected, suggesting a significant wavelength dependence. It is still unknown why they are luminous even when in the Jovian shadow, but forward-scattered sunlight by hazes in the Jovian upper atmosphere is proposed as the most plausible candidate. If this is the case, observations of these Galilean satellites while eclipsed by the Jovian shadow provide us with a new technique to investigate the Jovian atmospheric composition. Investigating the transmission spectrum of Jupiter by this method is important for investigating the atmosphere of extrasolar giant planets by transit spectroscopy. © 2014. The American Astronomical Society. All rights reserved.
  • Kiyoshi Kuramoto, Takafumi Umemoto, Masaki Ishiwatari
    Earth and Planetary Science Letters 375 312 - 318 2013年08月 [査読有り][通常論文]
     
    Hydrodynamic escape of hydrogen driven by solar extreme ultraviolet (EUV) radiation heating is numerically simulated by using the constrained interpolation profile scheme, a high-accuracy scheme for solving the one-dimensional advection equation. For a wide range of hydrogen number densities at the lower boundary and solar EUV fluxes, more than half of EUV heating energy is converted to mechanical energy of the escaping hydrogen. Less energy is lost by downward thermal conduction even giving low temperature for the atmospheric base. This result differs from a previous numerical simulation study that yielded much lower escape rates by employing another scheme in which relatively strong numerical diffusion is implemented. Because the solar EUV heating effectively induces hydrogen escape, the hydrogen mixing ratio was likely to have remained lower than 1 vol% in the anoxic Earth atmosphere during the Archean era. (C) 2013 Elsevier B.V. All rights reserved.
  • 木星の大気構造と雲対流
    杉山 耕一朗, 中島 健介, 小高 正嗣, 石渡 正樹, 倉本 圭, 高橋 芳幸, 林 祥介
    遊・星・人 21 1 39 - 44 2012年03月 [査読有り][通常論文]
  • 関根 康人, 薮田 ひかる, 木村 淳, 古川 善博, 高野 淑識, 矢野 創, 船瀬 龍, 高井 研, 石原 盛男, 渋谷 岳造, 橘 省吾, 倉本 圭
    日本惑星科学会誌遊星人 21 3 229 - 238 日本惑星科学会 2012年 [査読無し][通常論文]
     
    エンセラダスの南極付近から噴出するプリュームの発見は,氷衛星の内部海の海水や海中の揮発性成分や固体成分の直接サンプリングの可能性を示した大きなブレイクスルーであるといえる.これまでカッシーニ探査によって,プリューム物質は岩石成分と相互作用する液体の内部海に由来していることが明らかになったが,サンプリング時の相対速度が大きいこと,質量分析装置の分解能が低いことなどの問題があり,内部海の化学組成や温度条件,海の存続時間など,生命存在の可能性を制約できる情報は乏しい.本論文では,エンセラダス・プリューム物質の高精度その場質量分析とサンプルリターンによる詳細な物質分析を行うことで,内部海の化学組成の解明,初期太陽系物質進化の制約,そして生命存在可能性を探ることを目的とする探査計画を提案する.本提案は,"宇宙に生命は存在するのか"という根源的な問いに対して,理・工学の様々な分野での次世代を担う若手研究者が惑星探査に参入し結集する点が画期的であり,我が国の科学・技術界全体に対しても極めて大きな波及効果をもつ.
  • 杉山 耕一朗, 谷 伊織, 加藤 則行, 梅本 隆史, 押川 智美, 三上 峻, 倉本 圭, 林 祥介, 中川 義次, 惑星科学研究センター, 鈴木 絢子, 高橋 隼, 中村 友昭, 真鍋 翔, 堺 正太朗, 鶴巻 亮一, 中岡 礼奈, 辰巳 信平
    日本惑星科学会誌遊星人 21 4 368 - 376 日本惑星科学会 2012年 [査読無し][通常論文]
     
    惑星科学研究センター(CPS)では,国内外の惑星科学研究者の教育研究活動を広く支援する「場」の1つとして,先端的な知見の共有を容易にするための知見アーカイブを構築している.この取り組みは, 2000年に発足した北海道大学理学部の有志活動であるmosirプロジェクトを継承・発展させたものであり,現在に至るまでの活動で蓄積した研究会やセミナーでの研究発表を始めとするコンテンツは1,100本以上にのぼる.本稿ではCPSの知見アーカイブの概要を示すと共に,知見アーカイブの利便性を向上させるための取り組みや作業コストの低減を図るための取り組みを解説する.
  • Youhei Sasaki, Shin-ichi Takehiro, Kiyoshi Kuramoto, Yoshi-Yuki Hayashi
    Physics of the Earth and Planetary Interiors 188 3-4 203 - 213 2011年10月 [査読有り][通常論文]
     
    Numerical experiments are performed in order to investigate an MHD dynamo in a rotating spherical shell with stress-free top and no-slip bottom boundaries. The Ekman number, the Prandtl number, and the ratio of inner to outer radii are fixed as 10(-3), 1, and 0.35, respectively. The magnetic Prandtl number is varied from 5 to 50, and the modified Rayleigh number is increased from 1.5 to 10 times the critical Rayleigh number. The initial imposed magnetic field is either a weak or strong magnetic field, where the magnetic energy of the initial field is approximately two orders of magnitude smaller or larger than the kinetic energy of the quasi-steady state of non-magnetic thermal convection.For cases involving a weak initial magnetic field, self-sustained dynamo solutions are established when the magnetic Prandtl number is larger than or equal to 5, and the modified Rayleigh number is larger than or equal to 5 times the critical Rayleigh number. The solutions are categorized as a weak field-dynamo, where the mean magnetic energy is one order of magnitude smaller than the mean kinetic energy. The dynamo solutions are characterized by a radially two-layer spatial structure. The upper layer is dominated by a strong prograde zonal mean zonal flow with large-scale prograde propagating spiral vortices having a longitudinal wavenumber of 3. Toroidal kinetic energy is converted to toroidal magnetic energy through stretching of the field lines by large-scale prograde propagating spiral vortices. On the other hand, the lower layer contains small-scale retrograde propagating columnar convective vortices having a longitudinal wavenumber of 8. The magnetic field lines are not concentrated in the vortices, but rather wind around the vortices in each layer. Poloidal kinetic energy is converted to poloidal magnetic energy through winding of the field lines around small-scale retrograde propagating columnar convective vortices.For cases involving a strong initial magnetic field, self-sustained dynamo solutions are established when the magnetic Prandtl number is greater than or equal to 4 and the modified Rayleigh number is greater than or equal to 3 times the critical Rayleigh number. In contrast with the cases involving a weak initial magnetic field, all of the dynamo solutions are strong-field solutions.Bistability is observed when the magnetic Prandtl number is 5, and the modified Rayleigh number is approximately equal to 10 times the critical Rayleigh number, where weak-field and strong-field dynamo solutions coexist. However, transition between the weak-field and strong-field solutions does not occur in this case. (C) 2011 Elsevier B.V. All rights reserved.
  • Jun Kimura, Taichi Kawamura, Hisataka Morito, Tomokatsu Morota, Chikatoshi Honda, Kiyoshi Kuramoto, Tatsuaki Okada
    Icarus 214 2 596 - 605 2011年08月 [査読有り][通常論文]
     
    Iapetus, one of the saturnian moons, has an extreme albedo contrast between the leading and trailing hemispheres. The origin of this albedo dichotomy has led to several hypotheses, however it remains controversial. To clarify the origin of the dichotomy, the key approach is to investigate the detailed distribution of the dark material. Recent studies of impact craters and surface temperature from Cassini spacecraft data implied that sublimation of H(2)O ice can occur on Iapetus' surface. This ice sublimation can change the albedo distribution on the moon with time.In this study, we evaluate the effect of ice sublimation and simulate the temporal change of surface albedo. We assume the dark material and the bright ice on the surface to be uniformly mixed with a certain volume fraction, and the initial albedo distribution to incorporate the dark material deposits on the surface. That is, the albedo at the apex is lowest and concentrically increases in a sinusoidal pattern. This situation simulates that dark materials existed around the Iapetus' orbit billions of years ago, and the synchronously rotating Iapetus swept the material and then deposited it on its surface. The evolution of the surface albedo during 4.0 Gyr is simulated by estimating the surface temperature from the insolation energy on Iapetus including the effect of Saturn's eccentricity and Iapetus' obliquity precession, and evaluating the sublimation rate of H(2)O ice from the Iapetus' surface.As a result, we found that the distribution of the surface albedo changed dramatically after 4.0 Gyr of evolution. The sublimation has three important effects on the resultant surface albedo. First, the albedo in the leading hemisphere has significantly decreased to approach the minimum value. Second, the albedo distribution has been elongated along the equator. Third, the edge of the low albedo region has become clear. Considering the effect of ice sublimation, the current albedo distribution can be reconstructed from the sinusoidal albedo distribution, suggesting the apex-antapex cratering asymmetry as a candidate for the origin of the albedo dichotomy. From the model analysis, we obtained an important aspect that the depth of the turn-over layer where the darkening process proceeded for 4 Gyr should be an order of 10 cm, which is consistent with evaluation from the Cassini radar observations. (C) 2011 Elsevier Inc. All rights reserved.
  • Sugiyama, K., Nakajima, K., Odaka, M., Ishiwatari, M., Kuramoto, K., Morikawa, Y., Nishizawa, S., Takahashi, Y.O., Hayashi, Y.-Y.
    Geophysical Research Letters 38 13 L13201, 5 PP., 2011 doi:10.1029/2011GL047878  2011年 [査読有り][通常論文]
     
    A long-term numerical simulation is performed to investigate idealized characteristics of the cloud layer of Jupiter's atmosphere using a two-dimensional cloud convection model that treats thermodynamics and microphysics of the three cloud components, H(2)O, NH(3), and NH(4)SH. A prominent result obtained is intermittent emergence of vigorous cumulonimbus clouds rising from the H(2)O condensation level to the tropopause. Due to the active transport associated with these clouds, the mean vertical distributions of cloud particles and condensible gases are distinctly different from the hitherto accepted three-layered structure; considerable amounts of H(2)O and NH(4)SH cloud particles exist above the NH(3) condensation level, while the mixing ratios of all condensible gases decrease with height from the H(2)O condensation level. The mean vertical profile of NH(3) vapor is consistent with the results of radio observations in that the abundance of NH(3) is subsolar below the NH(3) cloud base. Citation: Sugiyama, K., K. Nakajima, M. Odaka, M. Ishiwatari, K. Kuramoto, Y. Morikawa, S. Nishizawa, Y. O. Takahashi, and Y.-Y. Hayashi (2011), Intermittent cumulonimbus activity breaking the three-layer cloud structure of Jupiter, Geophys. Res. Lett., 38, L13201, doi: 10.1029/2011GL047878.
  • 「月惑星探査の来たる10年」検討・第一段階報告
    大谷栄治, 倉本圭, 今村剛, 寺田直樹, 渡部重十, 荒川政彦, 伊藤孝士, 圦本尚義, 渡部潤一, 木村淳, 高橋幸弘, 中島健介, 中本泰史, 三好由純, 小林憲正, 山岸明彦, 並木則行, 小林直樹, 出村裕英, 大槻圭史
    日本惑星科学会誌 20 350 - 366 2011年 [査読有り][通常論文]
  • 上端応力無し, 下端滑り無し条件を課した回転球殻中に出現する弱磁場ダイナモ
    佐々木 洋平, 竹広 真一, 林 祥介, 倉本 圭
    ながれ 別冊 29221 2010年 [査読無し][通常論文]
  • 今村 剛, 笹井 康子, 佐川 英夫, 黒田 剛史, 佐藤 毅彦, 上野 宗孝, 鈴木 睦, 高橋 幸弘, 高橋 芳幸, はしもと じょーじ, 倉本 圭
    遊・星・人 : 日本惑星科学会誌 18 2 76 - 78 日本惑星科学会 2009年06月25日 [査読無し][通常論文]
     
    火星表層の水循環や気象学の理解を目的とする火星周回衛星の検討を進めている.可視〜赤外域での高解像度の分光撮像による水蒸気マッピングと大気力学場モニター,そしてサブミリ波サウンダーによる水蒸気やその他微量ガスの3次元分布の観測が,二つの柱である.着陸機による局地気象の直接観測や大気電気観測との連携についても検討中である.
  • 倉本 圭, 阿部 豊, はしもと じょーじ, 林 祥介, 関根 康人, 佐藤 光輝
    天文月報 102 3 184 - 189 日本天文学会 2009年02月20日 [査読無し][通常論文]
  • 杉山 耕一朗, 小高 正嗣, 佐野 康男, 大石 憲且, 馬場 聡, 高井 昌彰, 大石 尊久, 林 祥介, 倉本 圭, 渡部 重十
    遊・星・人 : 日本惑星科学会誌 17 2 123 - 129 日本惑星科学会 2008年06月25日 [査読無し][通常論文]
     
    北海道大学と名寄市立木原天文台とを接続する広帯域ネットワークを構築し,研究と教育の連携のための実験を行った.広帯域ネットワークを用いる最大の利点は,地理的に離れた両拠点の既存の機材とソフトウェア環境を現地まで移動することなく相互に利用できるようになり,両拠点が一体の遠隔天文台として機能できることである.実際に,北海道大学から木原天文台の望遠鏡を遠隔操作して天体の操像観測を試み,遠隔天文台としての機能の検証を行った.また,両拠点の観望映像のどちらか条件の良い映像をインターネット中継映像として配信する実験を行い,今回我々の構築したネットワーク環境が天文現象のインターネット中継の成功率向上に資することを確認した.
  • Mass-independent oxygen isotope variation in the solar nebula
    Young, Edward D, Kuramoto, Kiyoshi, Marcus, Rudolph A, Yurimoto, Hisayoshi, Jacobsen, Stein B
    Reviews in Mineralogy and Geochemistry 68 1 187 - 218 2008年
  • 氷が担う原始太陽系星雲のグローバル物質輸送
    低温科学 66 83 - 88 2008年 [査読無し][通常論文]
  • Takashi Fukui, Kiyoshi Kuramoto
    ORIGIN OF MATTER AND EVOLUTION OF GALAXIES 1016 409 - 411 2008年 [査読有り][通常論文]
     
    We perform a numerical simulation on the global transport process of O-16-poor H2O and silicate in a protoplanetary disk to examine whether the process is responsible for the oxygen isotopic systematics observed in chondritic components without conflicting with observation of protoplanetary disks and theory of planet formation.
  • 倉本 圭, 玄田 英典, 荒井 朋子, 岡田 達明, 杉田 精司
    遊・星・人 : 日本惑星科学会誌 16 3 197 - 207 日本惑星科学会 2007年09月25日 [査読無し][通常論文]
     
    惑星内部の進化の実証的研究は惑星科学の萌芽的分野であり,「かぐや」をはじめとする月の新たな探査はその前進のための大きな一歩となる.本論文では,これまでの月内部進化についての理解とそれにまっわる謎について,月の熱進化の観点からレビューする.そして今後どのような着眼点で何を調べると月内部進化の理解に有益なのか,考えるためのヒントを提供したい.
  • Sakamoto, N., Seto, Y., Itoh, S., Kuramoto, K., Fujino, K., Nagashima, K., Krot, A.N., Yurimoto, H.
    Science 317 5835 231 - 233 2007年 [査読有り][通常論文]
     
    Oxygen isotopic composition of our solar system is believed to have resulted from mixing of two isotopically distinct nebular reservoirs, O-16-rich and O-17,O-18-rich relative to Earth. The nature and composition of the O-17,O-18-rich reservoir are poorly constrained. We report an in situ discovery of a chemically and isotopically unique material distributed ubiquitously in fine-grained matrix of a primitive carbonaceous chondrite Acfer 094. This material formed by oxidation of Fe, Ni-metal and sulfides by water either in the solar nebula or on a planetesimal. Oxygen isotopic composition of this material indicates that the water was highly enriched in O-17 and O-18 (delta O-17,18(SMOW) = + 180 parts per thousand per mil), providing the first evidence for an extremely O-17,O-18-rich reservoir in the early solar system.
  • 圦本 尚義
    Protostars and Planets V 849 - 862 2007年 [査読有り][通常論文]
  • Sugiyama, K.-I., Odaka, M., Kuramoto, K., Hayashi, Y.-Y.
    Geophysical Research Letters 33 3 L03201 - L03201 2006年 [査読有り][通常論文]
     
    The dependency of static stability N-2 of the Jovian atmospheres on the abundances of condensible elements is considered by calculating the moist adiabatic profiles. An optimal minimization method of the Gibbs free energy is utilized to obtain equilibrium compositions in order to cover a variety of basic elements. It is shown that CH4 is one of the dominant contributors to producing a stable layer in the Uranian atmosphere. On Jupiter, R. K. Achterberg and A. P. Ingersoll (1989) have shown that, at low water abundances, N-2 is proportional to the H2O abundance. In the present study, we show that this relationship does not hold when the H2O abundance is larger than approximately 5 x solar. A rough estimation of wave speed indicates that the abundance of 10 x solar is marginal to explain the SL9-induced wave speed as that of an internal gravity wave.
  • 倉本 圭, 圦本 尚義
    遊・星・人 : 日本惑星科学会誌 14 4 193 - 200 日本惑星科学会 2005年12月25日 [査読無し][通常論文]
  • Kuramoto Kiyoshi, Yurimoto Hisayoshi
    Chondrites and the Protoplanetary Disk 341 181 - 192 2005年 [査読有り][通常論文]
  • Yurimoto, H., Kuramoto, K.
    Science 305 5691 1763 - 6 2004年 [査読有り][通常論文]
     
    Meteorites and their components have anomalous oxygen isotopic compositions characterized by large variations in 18O/16O and 17O/16O ratios. On the basis of recent observations of star-forming regions and models of accreting protoplanetary disks, we suggest that these variations may originate in a parent molecular cloud by ultraviolet photodissociation processes. Materials with anomalous isotopic compositions were then transported into the solar nebula by icy dust grains during the collapse of the cloud. The icy dust grains drifted toward the Sun in the disk, and their subsequent evaporation resulted in the 17O- and 18O-enrichment of the inner disk gas.
  • 中神 雄一, 大島 修, 杉山 耕一朗, 川端 善仁, 佐藤 光一郎, 小林 和真, 笹川 浩達, 小高 正嗣, 倉本 圭, Mosir プロジェクト
    遊・星・人 : 日本惑星科学会誌 12 2 80 - 88 日本惑星科学会 2003年06月25日 [査読無し][通常論文]
  • Yokohata, T., Odaka, M., Kuramoto, K.
    Icarus 159 2 439 - 448 2002年 [査読有り][通常論文]
     
    In order to study the stability of martian climate, we constructed a two-dimensional (horizontal-vertical) energy balance model. The long-term CO2 mass exchange process between the atmosphere and CO2 ice caps is investigated with particular attention to the effect of planetary ice distribution on the climate stability. Our model calculation suggests that high atmospheric pressure presumed for past Mars would be unstabilized if H2O ice widely prevailed. As a result, a cold climate state might have been achieved by the condensation of atmospheric CO2 onto ice caps. On the other hand, the low atmospheric pressure, which is buffered by the CO2 ice cap and likely close to the present pressure, would be unstabilized if the CO2 ice albedo decreased. This may have led the climate into a warm state with high atmospheric pressure owing to complete evaporation of CO2 ice cap. Through the albedo feedback mechanisms of H2O and CO2 ices in the atmosphere-ice cap system, Mars may have experienced warm and cold climates episodically in its history. (C) 2002 Elsevier Science (USA).
  • Hiroki Senshu, Kiyoshi Kuramoto, Takafumi Matsui
    Journal of Geophysical Research: Planets 107 E12 1 - 1 2002年
  • 横畠 徳太, 倉本 圭
    遊・星・人 : 日本惑星科学会誌 10 2 64 - 74 日本惑星科学会 2001年06月25日 [査読無し][通常論文]
  • 千秋 博紀, 倉本 圭, 松井 孝典
    遊・星・人 : 日本惑星科学会誌 9 1 17 - 32 日本惑星科学会 2000年03月25日 [査読無し][通常論文]
  • エウロパの海
    天気 (日本気象学会誌) 47 39 - 40 2000年 [査読無し][通常論文]
  • 倉本 圭
    号外地球 23 25 - 29 海洋出版 1999年02月 [査読無し][通常論文]
  • 鉄のコアの観測可能性
    遊・星・人 (日本惑星科学会誌) 7 218 - 220 1998年 [査読無し][通常論文]
  • Kuramoto Kiyoshi, Saiganji Yoshihiko, Yamamoto Tetsuo
    Lunar and Planetary Science Conference 29 1998年 [査読有り][通常論文]
  • 倉本 圭
    遊・星・人 : 日本惑星科学会誌 6 3 196 - 198 日本惑星科学会 1997年09月25日 [査読無し][通常論文]
  • Kiyoshi Kuramoto
    Physics of the Earth and Planetary Interiors 100 1-4 3 - 20 1997年 [査読無し][通常論文]
     
    Recent understandings of planetary accretion have suggested that accumulation of a small number of large planetesimals dominates intermediate to final growth stages of the terrestrial planets, with impact velocity high enough to induce extensive melting of the planetesimal and target materials, resulting in formation of a large molten region in which gravitational segregation of silicate and metal, that is, core formation proceeds. In case of homogeneous accretion, volatiles contained in each planetesimal are likely subjected to partitioning among gas, silicate melt, and molten metallic iron at significantly high temperatures and pressures in such a massive molten region. Each phase would subsequently form the proto-atmosphere, -mantle, or -core, respectively. Such chemical reprocessing of H and C associated with core formation, which is followed by both degassing from mantle and atmospheric escape, may result in a diverse range of H2O/CO2 in planetary surface environments, which mainly depends on the H and C content relative to metallic iron in planetary building stones. This may explain inferred difference in volatile distribution between the Earth's (relatively H2O-rich, CO2-poor) and the martian (H2O-poor, CO2-rich) surface environments. Such volatile redistribution may be systematically described by using the retentivity of H2O, ξ, defined as follows: ξ = 1 - ([CO]0 + 2[CH4]0 + 2[C(gr)]0)/[H2O]0, where [i]0 represents mol number of species i partitioned into non-metallic phases, that is, gas and silicate melt in impact-induced molten region. When ξ > 0.5, relatively H2O-rich and CO2-poor surface environment may eventually evolve, although a small portion of H2O partitioned into the non-metallic phases are possibly consumed by subsequent chemical reactions with reduced C-species with producing CO2 and H2. When ξ < 0.5, on the contrary, H2O consumption by the above reactions and selective loss of H2 to space may result in relative H2O-depleted and CO2-rich surface environment. Given the building stone composition by the two-component model by Ringwood (1977) and Wänke (1981), ξ is found to decrease with increasing the mixing fraction of the volatile-rich component: ξ > 0.5 for the mixing fraction smaller than about 15-20% and, ξ < O for the mixing fraction larger than about 20-30%. This is not significantly dependent on temperature and pressure in molten region and H/C ratio in the building stone. The estimated mixing fraction of the volatile-rich component, about 10% for the Earth and 35% for Mars, is consistent with the observed difference in volatile distribution between the surfaces of both planets. © 1997 Elsevier Science B.V.
  • Kiyoshi Kuramoto, Takafumi Matsui
    Journal of Geophysical Research: Planets 101 E6 14909 - 14932 1996年06月01日 [査読有り][通常論文]
     
    Partitioning of H and C among fluid, silicate melt, and molten metallic iron within a growing Earth at temperatures 2000-2500 K and pressures 0.2-5 GPa is estimated by using a thermodynamic model based on the recent knowledge on gas solubility into silicate melts and molten metallic iron. The repulsive interactions among H, C, and S dissolved in molten metallic iron are taken into account. It is shown that partition coefficient of H between molten metallic iron and silicate melt increases with pressure and temperature. Under the presence of Fe-rich metal, CO2 content in silicate melt is suggested to be very low because of low oxygen fugacity under such condition. Assuming a homogeneous accretion of planetesimals with the composition given by the two-component model slightly modified from Ringwood [1977] and Wanke [1981], it is shown that C is preferentially partitioned to molten metallic iron and quite less to silicate melt, whereas a substantial proportion of H is partitioned to silicate melt as H2O and also to molten metallic iron as interstitial atoms. For such concentrations of H, C, and S, the effect of thermodynamic interaction among them in molten metallic iron is not strong enough to cause the oversaturation of graphite. H and C partitioned to molten metallic iron may account for a significant portion of the density deficit in Earth's core. The estimated amount of H2O partitioned to silicate melt is possibly large enough to explain the sources for (1) H2O in the hydrosphere and mantle, (2) oxygen which partially oxidizes ferrous iron to ferric iron in the mantle, and (3) oxidant for metals which may fail to segregate to the core and act as the source of the highly siderophile elements in the mantle of the present Earth. The higher H/C and the lower C/(36) Ar ratios in the silicate Earth including the hydrosphere compared to various classes of meteorites are possibly explained if these elements are derived from the early mantle material after the H and C partitioning to molten metallic iron and core segregation. Accretion of the late veneer material such as the highly oxidized, CI chondrite-like material seems difficult to explain such elemental abundance pattern without invoking unknown large volatile reservoir in the mantle.
  • 倉本 圭, 松井 孝典
    科学 66 3 193 - 201 岩波書店 1996年03月 [査読無し][通常論文]
  • Kiyoshi Kuramoto, Takafumi Matsui
    Journal of Geophysical Research E: Planets 101 6 14909 - 14932 1996年 [査読無し][通常論文]
     
    Partitioning of H and C among fluid, silicate melt, and molten metallic iron within a growing Earth at temperatures 2000-2500 K and pressures 0.2-5 GPa is estimated by using a thermodynamic model based on the recent knowledge on gas solubility into silicate melts and molten metallic iron. The repulsive interactions among H, C, and S dissolved in molten metallic iron are taken into account. It is shown that partition coefficient of H between molten metallic iron and silicate melt increases with pressure and temperature. Under the presence of Fe-rich metal, CO2 content in silicate melt is suggested to be very low because of low oxygen fugacity under such condition. Assuming a homogeneous accretion of planetesimals with the composition given by the two-component model slightly modified from Ringwood [1977] and Wänke [1981], it is shown that C is preferentially partitioned to molten metallic iron and quite less to silicate melt, whereas a substantial proportion of H is partitioned to silicate melt as H2O and also to molten metallic iron as interstitial atoms. For such concentrations of H, C, and S, the effect of thermodynamic interaction among them in molten metallic iron is not strong enough to cause the oversaturation of graphite. H and C partitioned to molten metallic iron may account for a significant portion of the density deficit in Earth's core. The estimated amount of H2O partitioned to silicate melt is possibly large enough to explain .the sources for (1) H2O in the hydrosphere and mantle, (2) oxygen which partially oxidizes ferrous iron to ferric iron in the mantle, and (3) oxidant for metals which may fail to segregate to the core and act as the source of the highly siderophile elements in the mantle of the present Earth. The higher H/C and the lower C/36 Ar ratios in the silicate Earth including the hydrosphere compared to various classes of meteorites are possibly explained if these elements are derived from the early mantle material after the H and C partitioning to molten metallic iron and core segregation. Accretion of the late veneer material such as the highly oxidized, CI chondrite-like material seems difficult to explain such elemental abundance pattern without invoking unknown large volatile reservoir in the mantle. Copyright 1996 by the American Geophysical Union.
  • 倉本 圭
    遊・星・人 : 日本惑星科学会誌 4 4 201 - 214 日本惑星科学会 1995年12月01日 [査読無し][通常論文]
  • KURAMOTO K, MATSUI T
    Journal of Geophysical Research 99 E10 21183 - 21200 1994年 [査読無し][通常論文]

MISC

書籍等出版物

  • 倉本, 圭, 藤倉, 克則 
    ニュートンプレス 2022年05月 (ISBN: 9784315525465) 205p
  • 倉本, 圭 
    ニュートンプレス 2021年05月 (ISBN: 9784315523737) 205p
  • 在田 一則, 池田 元美, 倉本 圭, 小笹 隆司, 佐藤 光輝, 沢田 健, 白岩 孝行, 杉山 慎, 鈴木 徳行, 高波 鐵夫, 竹下 徹, 谷岡 勇一郎, 池田 隆司, 谷本 陽一, 知北 和久, 角皆 潤, 永井 隆哉, 中川 光弘, 新井田 清信, 長谷部 文雄 (担当:共著)
    北海道大学出版会 2010年11月 (ISBN: 4832981951) 427
  • 沢田 健, 西 弘嗣, 栃内 新, 馬渡 峻輔, 綿貫 豊, 秋元 信一, 阿波根 直一, 大原 昌宏, 柁原 宏, 片倉 春雄, 倉本 圭, 小林 快次, 鈴木 徳行, 高橋 英樹, 堀口 健雄, 前川 光司, 増田 道夫, 増田 隆一, 沢田 健, 西 弘嗣, 馬渡 峻輔, 綿貫 豊 (担当:共著)
    北海道大学図書刊行会 2008年03月 (ISBN: 4832981838) 272
  • 松田, 准一, 圦本, 尚義, 日本地球化学会, 木多, 紀子, 橘, 省吾, 倉本, 圭, 中村, 智樹, 香内, 晃, 平原, 靖大, 村江, 達士 
    培風館 2008年02月 (ISBN: 9784563049027) vii, 291p

所属学協会

  • 日本地球惑星科学連合   日本惑星科学会   

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2022年04月 -2027年03月 
    代表者 : 寺田 直樹, 古川 善博, 黒田 剛史, 三宅 洋平, 関 華奈子, 青木 翔平, 横田 勝一郎, 倉本 圭
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2021年04月 -2025年03月 
    代表者 : 竹広 真一, 高橋 芳幸, 中島 健介, 倉本 圭, 佐藤 隆雄, 杉山 耕一朗
     
    今年度は, 木星型惑星大気の表層ジェット生成のメカニズムの研究に用いられいる「浅いモデル」と「深いモデル」の 2 系統のモデルについて, 数値実験の設計と系統的なパラメター数値実験のための予備的なテスト計算を行った. 「浅いモデル」は当初予定していた惑星表面の薄い大気層の 3 次元流体運動を考えたモデルに取り掛かる準備として, 回転球面上の 1 層浅水モデルに小規模対流運動の効果を表す渦度強制を導入してパラメター実験を行った. この数値実験の先行研究である Scott and Polvani (2008) の設定をもとに, モデル解像度を高く, 渦度強制スケールを小さくしたところ, 木星および土星大気にみられるような赤道域の強い順行ジェットと中高緯度域の弱い縞状構造が出現する状況が見出された. このモデルでのパラメター実験は, 今後の3 次元モデルによる数値実験での木星土星大気に相当するようなパラメターを制限する際に役立つと期待される. 「深いモデル実験」は Heimpel and Aurnou (2007) の設定に基づいて, 研究代表者が開発し研究してきた地球流体電脳倶楽部の回転球殻熱対流モデル(http://www.gfd‐dennou.org/library/spmodel/) を用いて, 経度方向の対称性を仮定せず計算領域を全球に広げ, 粘性拡散係数を高次で増加させるパラメターをさまざまに変化させて時間積分を行った. その結果, Heimpel らが見出した, 木星土星大気にみられる赤道順行ジェットと中高緯度縞状ジェットが出現するのは高次の粘性が強い設定の場合のみであり, 高次粘性効果を弱めていくと中高緯度の縞状ジェットが消失してしまうことが見出された.
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2021年04月 -2024年03月 
    代表者 : 倉本 圭
     
    [揮発性物質の原始大気・惑星内部分配モデルの構築]マグマオーシャン、金属鉄、富水素原始大気間の水素、炭素等の揮発性元素の分配を、原始惑星の集積成長過程と同時に解く数値シミュレーションコードの開発を進めた。近年の地震学的探査によって理解が急速に進展している火星内部の揮発性物質量と対比できるアウトプットを得つつある。 [多成分大気散逸モデルの拡張]新たにH2Oとその光化学生成物を放射冷却材として加えた流体力学的散逸モデルを構築した。モデル計算の結果、放射活性の高いH2Oならびにその光分解生成物にも、その放射冷却効果によって原始大気からの水素流出を大幅に抑制する働きがあることが明らかになってきた。これは還元的原始大気が、惑星集積期を含め数億年の時間スケールで持続しうることを示す。 [原始大気海洋系の化学進化モデルの構築]光化学過程と水溶液反応に駆動される、原始大気-原始海洋の結合進化モデルのひな型を構築した。富水素大気から出発した場合、非水溶性の高分子炭化水素が大量に生じ、原始海洋表層に油質層を形成する可能性が明らかになってきた。また、NH3の貯蔵庫としての海洋の役割について理論的に解析を進めた。炭酸塩との化学平衡状態にある海洋を想定すると、NH4+を含む溶存NH3量は気相中のNH3量を大幅に上回りうることが分かった。これは原始地球表層でアミノ酸の無生物学的な合成が可能とされる大気NH3分圧レベルが、従来の大気光化学モデルからの推定よりも大幅に伸びる可能性を示している。
  • 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2017年06月 -2022年03月 
    代表者 : 玄田 英典, 高橋 芳幸, 鎌田 俊一, 倉本 圭, 黒川 宏之, 市川 浩樹
     
    本研究では、太陽系天体における水・物質循環に関する実証可能な物理モデルを構築し、多様な水環境を有する太陽系天体が、いかにして作られたのかを明らかにする。最終的には、実験班により定量化された化学過程を、各天体の物理モデルに組み込み、探査・分析データを実証として、太陽系天体の水・物質循環の歴史を紐解くことを目的とする。 多様な小天体の水・揮発性元素量解明を目的とし、小天体内部の水岩石反応から予想される鉱物組み合わせに対して理論スペクトル計算を行い、近赤外リモセンデータから母天体組成を制約する理論的枠組みを構築した。また、衝突計算を行い、リュウグウを形成した母天体の破壊的な衝突によって一部の含水鉱物が脱水するが、一部は生き残ることを明らかにした。はやぶさ２に続くミッションである火星衛星探査計画も推進している。 氷天体の内部海の維持に関しては、特に冥王星を対象にした研究を進めた。ガスハイドレートの薄い層が内部海の凍結を防ぐことがわかった。同時に、巨大盆地の安定性や、窒素に富む表層などといった冥王星の謎も解明できることを明らかにした。 金星の大気大循環モデル実験および、古火星大気を想定した大気放射モデルの構築を行った。金星大気実験からは、金星探査機あかつきが発見した惑星規模筋状構造の成因を明らかにした。火星に関しては、酸化的大気組成下での太古の流水活動を示す火星探査データを受け、過酸化水素による温暖化機構を提唱した。 地球型惑星の大気と水の起源解明を目的とし、揮発性元素供給・分配・散逸の理論モデル構築を行った。その成果として、原始惑星円盤内のダスト進化・小天体組成に応じた初期惑星の水量・大気組成の予想が可能となった。また、集積期の火星大気形成と進化を、脱ガス成分と原始太陽系星雲ガス成分の成層性を考慮し、含水素大気の長寿命化の可能性を示した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2018年04月 -2021年03月 
    代表者 : 倉本 圭
     
    微惑星集積期の原始惑星上における脱ガス大気成分と原始太陽系星雲ガス成分の混合過程について数値的に調査した。これは、微惑星衝突による惑星表面からの集積熱ならびに脱ガス成分の供給と、惑星周囲からの原始太陽系星雲ガスの重力束縛を考慮し、大気の放射対流平衡構造の進化を数値的に求め、両成分の密度成層の安定性を追跡したものである。火星材料物質を想定した脱ガス成分を与えた場合、0.1地球質量を上回る原始惑星では両成分の混合が起き、惑星内部に原始太陽系星雲ガス成分が取り込まれるようになる可能性を示した。太陽極端紫外線の照射によって駆動される、水素に富む初期大気の流体力学的散逸モデルの構築を進め、光学活性分子種による放射冷却と分離の光解離の効果を取り込んだ。手始めとして、火星質量の惑星に対して、紫外線強度や下層大気の重元素濃度などの諸条件を変えた数値シミュレーションを実施した。数値モデルが順調かつ物理的に整合的な動作をすることを確認することができ、また、メタンの光解離と赤外熱放射によるエネルギー消費が、散逸流速を著しく低下させることが示された。初期太陽に推定される紫外線強を当てはめた場合、惑星形成後数億年間に渡って原始大気に水素分子が高濃度で残存する可能性が示唆された。集積期の惑星における揮発性元素のガス・シリケイトメルト・金属鉄間の分配の熱力学モデル構築の検討を進め、水素・炭素に加えて、窒素の取り込みに向けた定式化を進めた。
  • 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2016年04月 -2017年03月 
    代表者 : 林 正彦, 倉本 圭, 百瀬 宗武, 井田 茂, 左近 樹
     
    これまでの新学術領域研究5年の取りまとめとして、計画研究代表者及び公募研究代表者のすべてから研究成果に関する情報を包括的に収集し、最終的に研究成果報告書（冊子体）を作成した。 得られた成果をさらに今後の系外惑星研究に生かしていきたい。
  • 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2011年04月 -2016年03月 
    代表者 : 林 正彦, 百瀬 宗武, 倉本 圭, 井田 茂, 左近 樹
     
    総括班は４件の計画研究を有機的な連携のもとに推進する事を主な目的としている。領域全体の情報交換を促進する為、国際研究集会を９回開催し、その参加者は国内外合わせて８００名を数えた。同じく研究で得られた成果を広く国内外に発信し、若手育成の為に措置を講じ、領域ホームページを作成し情報発信をした。公募研究では２度の募集を行い全１４件を採択。参加者は全国の大学・研究機関に分布している。
  • 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2011年04月 -2016年03月 
    代表者 : 倉本 圭, 林 祥介, 阿部 豊, はしもと じょーじ, 関根 康人, 石渡 正樹, 玄田 英典, 竹広 真一, 佐々木 洋平, 中島 健介, 濱野 景子, 大西 将徳
     
    地球類似惑星の巨大衝突後の水蒸気大気の進化を求め、海洋が速やかに形成される惑星とマグマオーシャンが長期間保持される惑星に大別されることを示し、それらの観測可能性を明らかにした。多様な境界条件を与えた大気大循環シミュレーションにより、同期回転惑星や表層H2O保有量の少ない陸惑星ではハビタブルゾーンが拡大する可能性があることを示し、長期大気散逸によって表層水が減少すると、むしろ表層水が安定に存在できるようになる進化経路があることを見出した。巨大ガス惑星の雲対流シミュレーションと放射輸送モデリングを進め、ガス惑星大気の対流活動の間欠性の成因とガス惑星の熱放射に及ぼす雲層の役割について明らかにした。
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2010年 -2012年 
    代表者 : 倉本 圭, 竹広 真一, 福井 隆, 安達 俊貴
     
    月および小型惑星を構成する物質組成の多様性を原始惑星系円盤の形成進化モデルを用いて推定し,これら天体の内部構造の進化ついて数値的・理論的解析を行った.月マグマオーシャンの固化に伴い形成される不安定に成層した一連の沈積岩は,地質学的に短時間で安定な配置に向かい転倒する.転倒時にMgに富む橄欖岩沈積層は再融解を引き起こすと予想される.この結果は月の裏側にMgに富む苦鉄質鉱物が存在することと調和する.また安定な配置に達した後の月慣性能率因子は現在の月の観測値とほぼ一致する.一方,水星に予想される還元的な化学組成が、水星探査機の最新の観測によって確認され,さらに重力場データからケイ酸塩マントルの厚さが極めて薄いことが示唆された.これらを反映した水星構造を想定し,熱史シミュレーションを行ったところ,液体核は現在でも十分熱対流を起こし,ダイナモ活動を容易に維持できる可能性が示された.
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2008年 -2011年 
    代表者 : 石渡 正樹, 倉本 圭, 小高 正嗣, 中島 健介
     
    本研究では,水蒸気を含む同期回転惑星大気の循環構造に関するパラメータ実験,及び現実的なシミュレーションをめざしたモデル開発を行った.自転角速度変更実験により,振動する南北非対称状態が出現する場合や多重平衡解が得られる場合があることがわかった.太陽定数変更実験により,暴走温室状態が発生する太陽定数の値は,自転角速度の値に応じて100W/m^2程度の差が生じることがわかった.これらに加え,水素大気用放射スキームや数値モデル用データ入出力ライブラリの整備も行った.
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2007年 -2009年 
    代表者 : 倉本 圭, 佐々木 洋平, 福井 隆, 岩堀 智子
     
    水星を構成する物質の組成を原始太陽系星雲の進化モデルから推定し、その結果に基づいた物性値を用いて、水星の内部熱構造の進化ならびに固有磁場の起源について数値的・理論的解析を行った。水星のマントル物質は従来の推定よりも流動性が低く、そのために惑星中心部の冷却が妨げられ、固体内核の成長が鈍る。また液体核は内核からの軽元素放出によって対流し、それを駆動力とする穏やかな発電作用が生じて現在の弱い固有磁場が形成される可能性があることが分かった。これらは現在進みつつある水星探査の獲得データを解釈する基盤となる。
  • 日本学術振興会：科学研究費助成事業 基盤研究(S)
    研究期間 : 2005年 -2008年 
    代表者 : 圦本 尚義, 榎森 啓元, 倉本 圭
     
    最近,申請者達は『太陽系固体惑星の起源物質(Nature 428,921:2004)』,『酸素同位体的に不均一な太陽系の謎(Science 305,1763:2004)』,『太陽系の形成順序(Nature 423,728;2003)』を解明する重要な発見や仮説を提唱し,太陽系の新しい起源論を展開し始めた。本研究では,これらの発見に対応する太陽系創成期とそれに直接つながる先太陽系史に焦点を当て,これらの発見を進展させるための新しい証拠を隕石から探索する。この探索結果を取り入れ,現在提唱中の仮説を検証・発展させることにより新しい太陽系起源論を構築することを目的とする。 今年度は以下の研究を行い,今年度より採択された特別推進研究に研究を発展させた。 ●隕石中における先太陽系物質の系統的な探査 1.同位体顕微鏡を用いて隕石研磨片のマトリックス中の同位体異常を精査した。 2.同位体異常があった領域を電界放出型走査電子顕微鏡によりナノメートル分解能で観察し,同位体異常を持つ物質を同定した。 3.同定粒子を現有の分析走査電子顕微鏡により化学分析し,鉱物名と組成を決定した。 4.隕石の種類毎に先太陽系物質の特徴および存在度についてデータベースを作成した。 ●太陽系内の酸素同位体異常の起源と大きさ 1.隕石試料の中に含まれている46億年前の太陽風成分酸素の同位体比を同位体顕微鏡により測定した。 2.測定値に数値計算による補正を加え,46億年前誕生時の太陽の酸素同位体比を決定した。 ●始原隕石構成物質の形成と進化 1.先太陽系物質の系統的な探査のため作成した隕石試料から難揮発性包有物(CAI)とコンドリュールを選別した。 2.選別したCAIとコンドリュールに短寿命核種を用いた年代測定を同位体顕微鏡により行った。 3.色々な隕石毎のCAI,コンドリュール形成時期と形成期間をデータベース化した。
  • 日本学術振興会：科学研究費助成事業 学術創成研究費
    研究期間 : 2004年 -2008年 
    代表者 : 石原 盛男, 豊田 岐聡, 植田 千秋, 内野 喜一郎, 圦本 尚義, 倉本 圭, 松本 拓也
     
    まず新規に開発する超高感度極微量質量分析システムの構想決定を行い,その検討結果をもとに装置の製作を行った。その後,質量分析部,1次イオン照射系,レーザーイオン化について,それぞれ装置性能評価を行った。
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2004年 -2007年 
    代表者 : 林 祥介, 渡部 重十, 倉本 圭, 石渡 正樹, 小高 正嗣, 中島 健介
     
    木星型惑星大気の力学的構造・熱的構造・物質分布の関連を明らかにするために、関連する知見の集積と時空間対象の異なる複数のモデル群の開発を行い、それらによる数値実験を実行した。主な研究成果は以下の通りである。 1.木星型惑星大気に可能な組成をカバーできる汎用鉛直一次元熱力学平衡大気モデルを開発し、雲層における静的安定度の凝結成分存在度に対する依存性を調査する数値計算を行った。NH_3の凝結とNH_4SHの生成反応に伴う成層安定度への寄与はH_2Oの凝結に伴う成層安定度への寄与に比べ無視できない場合があることを指摘した。 2.木星大気中の凝結性成分H_2O,NH_3,H_2Sを考慮した二次元雲対流モデルの開発を行い、対流運動によって決まる木星大気中の平均的な鉛直雲分布と流れ場の様相を数値計算によって調べた。その結果、流れの場はH_2O凝結高度を境にして凝結を伴う上層の湿潤対流領域、凝結を伴わない下側の乾燥対流領域に分割されること、H_2O凝結に伴うプリュームはNH_3,H_2Sによる安定層を貫入し雲層全体の混合に寄与することを示した。 3.木星大気を念頭においた球殻内の3次元循環構造を考察することを目指して、ブシネスク球殻対流モデルを用いた赤道加速機構に関する数値的研究を行った。その結果、上層に安定成層を伴う高速に回転する球殻内の有限振幅熱対流を調べた。一連の数値実験の結果から、強い安定成層の存在が赤道逆行流の生成を助長することが示された。このことは球殻対流による木星・土星の赤道西風成因説に重要な疑問を投げかける。 4.これらの数値モデル群に共通して必要となる基盤ソフトウエアの整備を行った。数値モデルのためのデータ入出力ライブラリ(gt4f90io)の整備、モデルの解説文書の生成ツール(Rdoc)等の開発を進めた。また、数値モデルを作成する上でのプログラム書法や基礎演算Fortran90の関数群を整備し、それらを用いて作成したスペクトル計算プログラム集(spmodel)を開発した。これらは広くインターネット上に公開した。
  • 日本学術振興会：科学研究費助成事業 若手研究(B)
    研究期間 : 2004年 -2006年 
    代表者 : 倉本 圭
     
    古火星に想定される高圧の二酸化炭素大気の鉛直一次元大気熱収支・放射対流平衡モデルの開発は,多方向・高波長分解計算の厳密化,ならびに,散乱温室効果をもたらす二酸化炭素氷雲の鉛直プロファイル決定機構の導入を行い,ほぼ満足のできるレベルに到達した. このモデルを用いて,古火星大気の放射対流平衡構造・熱収支・二酸化氷雲による温室効果についての境界条件を変化させたパラメタスタディを進め,3気圧以上の大気圧と10^5-10^7kg^<-1>の範囲の凝結核混合比があれば,38億年前の火星において全球平均気温がH_2Oの融点を超える温暖な気候が実現されることが分かった. 一方,凝結核混合比が極めて小さい,あるいは大きい場合には,大気圧を増加させてゆくと,やがては地表面へのCO_2凝結が起こり,いわゆる大気崩壊が起こることがわかった.地球大気を参考にすると凝結核混合比は数桁の範囲で変動することが予想される.温室効果の強さが凝結核混合比に強く依存することは,火星の高クレーター密度地域の地形侵食が著しくは進んでいない,つまり温暖湿潤な気候の出現が間欠的であったと示唆されるここと調和する. 大気の地表面への凝結によって形成される二酸化炭素氷床の流動過程について,その数値計算のための流動則と涵養消耗過程についての基礎的な定式化を行った。完成した大気放射モデルから凝結核の挙動が重要なことが判明し,凝結核の移流を考慮した大気-氷床結合モデルが火星の気候変動の理解に有益であることが分かった.
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2004年 -2004年 
    代表者 : 林 祥介, 倉本 圭, 小高 正嗣, 石渡 正樹, 竹広 真一, 中島 健介
     
    予備的な国内検討会を実施後,米国への調査旅行を企画し,UNIDATAならびPrinceton大のGFDL/NOAAを訪問,情報技術の進展とそれによる当該分野の教育・研究活動への影響等に関して意見交換を行った.調査の結果を受け,さらに国内検討会を開催し,現在の情勢と当該分野でなされるべき今後の対応について議論を進めた.これらの資料は「地球流体電脳倶楽部」のWEBサーバ上に掲載し公開されており,http://www.gfd-dennou.org/arch/davis/workshop/から適宜たどることができる. UNIDATAは1983年に設立され,米国の大気科学関連大学連合によって運営される,当該分野の研究教育のための情報基盤を支えるための組織である.データのアーカイブ,必要となるファイル形式の提供(netCDF),データハンドリングと可視化ツールの開発と提供で知られており,また,様々な情報技術開発のコーディネーションを行う.現在,UNIDATAが中心となって,各地に分散しているデータサーバをインターネット上に統合,一つの仮想的なデータベースとして機能せしめ,情報をリアルタイムで提供(OPeNDAP/THREDDS),数値予報モデルと有機的に組み合わし,研究のみならず教育の現場で利用する実験が進められている.残念ながらわが国では気象業務法の縛りがあり,かつ,気象庁が研究教育活動に対してデータを提供する枠組の整備が不十分で,同種の試みを実行することは不可能である.様々な制度がインターネット以前の時代のままであることが問題であり,情報基盤構築をリードするUNIDATAのような組織がないことが状況の改善を困難にしている.
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2001年 -2004年 
    代表者 : 圦本 尚義, 井田 茂, 藤本 正樹, 倉本 圭, 榎森 啓元
     
    惑星や隕石の平均化学組成は太陽系平均組成とすこしずつ異なり、それぞれ独自の値をもつことが知られている。この隕石や惑星の化学組成の変動は、原始惑星系円盤において太陽近傍まで落下したダストが太陽系外縁部に還流した結果であると考えられる。本研究では、この原始太陽系中心から外縁部まで達する原始太陽系における物質大循環に関するモデルを、隕石中の物質の分析結果と惑星系円盤中の電磁気学的・力学的・化学的シミュレーションを結合させ、定量化することにある。 この研究では数値シミュレーションと隕石中の同位体分布の研究を発展させ,以下のような成果を得た。 1.太陽系の酸素同位体異常の起源が母星間雲におけるCOの自己遮蔽効果を起源とすることを決定した。 2.母星間雲の酸素同位体異常は星間ガスと氷成分により相分離され,原始惑星円盤中に導入されることを決定した。 3.惑星の酸素同位体組成は原始惑星系円盤中のダスト濃縮と氷の蒸発により支配されることを突き止めた。 4.原始惑星系のガス・ダスト比が変化すると形成される木星型惑星の質量,軌道半径分布がどのように変わるか数値シミュレーションにより求めた。その結果は天体観測による系外惑星の存在確率をよく説明した。これは,円盤ガス量は星形成プロセスで決まるが惑星形成はガス・ダスト比により支配されることを意味している。 5.宇宙空間を満たすプラズマ中における大規模渦の振舞いを数値計算で調査した。渦が巻上がるにつれてその内部で電子慣性効果が発動し、その結果、出現した小渦が元の大渦の素早い崩壊をひきおこすことを発見した。これは、宇宙空間において従来よりも効率よく物質混合が起きていることを示唆する。
  • 日本学術振興会：科学研究費助成事業 萌芽研究
    研究期間 : 2001年 -2003年 
    代表者 : 林 祥介, 小高 正嗣, 倉本 圭, 渡部 重十
     
    今年度はこれまでの火星大気二次元対流計算の延長線上に計算領域の拡張と放射・光化学プロセスの導入を試みた. 計算領域の拡張は,分解脳100mを維持したまま,まず鉛直方向に高度100kmまで拡張することを行い,ついで水平方向にできるだけ広い領域を並列計算技術等を用いて確保することとした.これまでの計算により,対流圏の鉛直対流によって生成される重力波は高度とともにその卓越波数が小さくなることがわかっており,高高度領域での内部重力波による混合の影響を計算するためには同時に水平方向にも十分な計算領域が必要となる. 領域拡張において判明したことは,これまで我々が用いてきた非弾性方程式系の問題点である.非弾性系では音波を含まないため,圧力を求める際には楕円型の微分方程式を解く必要があったが,これは並列化計算における効率を低下させる要素となる.我々は数値コードを再検討した結果,基礎方程式系の見直しを行い新たに音波を考慮した準圧縮方程式系に基づく対流数値モデルの開発を行うことにした.開発中のモデルと関連文書はhttp://www.gfd-dennou.org/arch/deepconv以下に公開している. 放射・光化学プロセスの導入に関しては極めて単純な二酸化炭素の吸収射出ならびに二酸化炭素の光分解過程を組み込み,高高度での物質分布の時間発展を追うことにした.高高度領域を確保するべく水平32kmの狭い領域に限定し,非弾性系モデルを用いた予備的な計算を実行した.残念ながら,二酸化炭素の光分解に対して重力波の砕破混合が働き分解を阻害する傾向を見極めるための十分なパラメタ実験を行うまでには到らなかった.今後準圧縮方程式系によるモデルを用いて計算を継続する予定である.
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2000年 -2001年 
    代表者 : 渡部 重十, 高橋 幸弘, 倉本 圭, 林 祥介
     
    高速高感度CCDカメラと狭帯域干渉フィルターを用いた木星可視オーロラ・大気光観測システムを設計・開発した.木星可視光オーロラ・大気光は地上から観測された例はなく,初めての試みである.北海道陸別町の「銀河の森天文台」の口径115cm反射望遠鏡,東北大学付属飯舘観測所の口径60cm反射望遠鏡,北海道大学理学部にて口径10cm小型望遠鏡を用いて,1999年11月から2001年11月まで3シーズンに渡り観測を実施した.水素ランプを用いて干渉フリンジを撮像することにより,観測波長域の異なる画像を減算処理し,観測波長での発光・変動を検出するという新しい観測・解析手法を開発した.地球大気の揺らぎを除くために露出時間の短い複数の画像の重ね合わせから発光・変動を検出するという手法も開発した.その結果,木星北極域に発光現象を捉えた.この手法による連続観測が今後実施されると,木星研究にとって非常に大きなインパクトになる.本研究で開発した微弱な発光を検出するという観測・画像処理手法は,木星可視オーロラ・大気光以外にも,惑星大気やその他微弱な発光を捕らえるようなさまざまな観測対象にも応用できる. 理論的な研究は,木星大気だけでなく比較惑星学的に火星・金星・地球に対しても実施した.その結果は,木星大気では大気・雲・光化学・プラズマ相互作用の重要性,特に高高度ではイオン抗力による大気・プラズマ相互作用が重要であることを指摘した.
  • 日本学術振興会：科学研究費助成事業 奨励研究(A)
    研究期間 : 1999年 -2000年 
    代表者 : 倉本 圭
     
    集積期の火星熱史について現実的な微惑星サイズ分布を与えた数値シミュレーションを行うと同時に,火星CO_2大気-極冠システムの安定性解析を行った. 熱史の数値シミュレーションから得られた結果は以下の通りである. 1)火星半径が約3000kmに達すると微惑星衝突点の融解が起こり始める. 2)融解開始後,半径がさらに300km成長するまで,サイズの大きな微惑星のみが融解に寄与する. 以上の結果は,火星の大気,マントル,金属核の分化が集積過程の末期に起こり始めることを意味する. 火星において実現し得る大気状態を明らかにするには,大気-極冠システムの安定性の解析が必要である.そのために大気-極冠間の質量交換を考慮した2次元エネルギーバランスモデルを構築した.このモデルは,与えられた日射の緯度分布に対し,大気-地表システムのエネルギー・質量バランスの南北・鉛直構造を解くものである.そこにはCO_2大気の温室効果,緯度間の熱輸送,地表-大気間の熱およびCO_2交換(極冠における凝縮,蒸発)過程が組み込まれている. このモデルを用いた安定性解析の結果を以下に説明する.大気-極冠システムが長期的な定常状態にあるためには,火星年で積分したCO_2凝結量と蒸発量が釣り合った状態になければならない.それには,大気圧が低く大部分のCO_2が極冠に凝結した"冷たい"定常状態と,極冠が完全に蒸発し大気圧が高い"熱い"定常状態,そしてこれらの中間の状態がありうる.中間状態は不安定であり,仮にこの状態から出発しても数十年で"冷たい"ないしは"熱い"定常状態に遷移する.宇宙空間への大気散逸などによって大気-極冠システムのCO_2量がある臨界量を下回ると,"冷たい"定常状態しか実現されなくなる.この臨界量は大気圧に換算しておよそ0.1-1気圧のオーダーであり,太陽定数,軌道要素,地表のアルベド分布に強く依存する.
  • 日本学術振興会：科学研究費助成事業 特別研究員奨励費
    研究期間 : 1998年 -1998年 
    代表者 : 倉本 圭

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