Researcher Database

Kiyoshi Kuramoto
Faculty of Science Earth and Planetary Sciences Cosmosciences
Professor

Researcher Profile and Settings

Affiliation

  • Faculty of Science Earth and Planetary Sciences Cosmosciences

Job Title

  • Professor

Degree

  • Ph.D(The University of Tokyo)
  • Master of Science(The University of Tokyo)

URL

J-Global ID

Research Interests

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

Research Areas

  • Natural sciences / Astronomy
  • Natural sciences / Space and planetary science
  • Natural sciences / Solid earth science
  • Natural sciences / Atmospheric and hydrospheric science
  • Natural sciences / Solid earth science

Academic & Professional Experience

  • 2015/04 - Today Hokkaido University Division of Earth and Planetary Sciences, Faculty of Science Professor
  • 2007/04 - 2015/03 Hokkaido University Division of Natural History Sciences, Faculty of Science Professor
  • 2012/08 - 2014/07 Ministry of Education,Culture,Sports,Science and Technology
  • 2006/04 - 2007/03 Hokkaido University Division of Natural History Sciences, Faculty of Science Associate Professor
  • 2001/04 - 2006/03 Hokkaido University Department of Earth and Planetary Sciences, Graduate Scool of ScienceGraduate School of Science Associate Professor
  • 1998/11 - 2001/03 Hokkaido Univeristy Department of Earth and Plantary Sciences, Graduate School of Science Research Associate
  • 1997/04 - 1998/10 Hokkaido University Institute of Low Temperature Sciences Post doctoral fellowships of JSPS
  • 1995/09 - 1997/03 University of Tokyo Center for Climate System Research COE researcher
  • 1994/08 - 1995/08 Tokyo Institute of Technology Undergraduate School of Science Technical Assistant

Education

  •        - 1994  The University of Tokyo  Graduate School of Science
  •        - 1994  The University of Tokyo  Graduate School, Division of Science
  •        - 1991  The University of Tokyo  Graduate School of Science
  •        - 1991  The University of Tokyo  Graduate School, Division of Science
  •        - 1989  The University of Tokyo  Faculty of Science
  •        - 1989  The University of Tokyo  Faculty of Science

Association Memberships

  • 日本地球惑星科学連合   日本惑星科学会   

Research Activities

Published Papers

  • Yuta Nakagawa, Takanori Kodama, Masaki Ishiwatari, Hajime Kawahara, Yasushi Suto, Yoshiyuki O. Takahashi, George L. Hashimoto, Kiyoshi Kuramoto, Kensuke Nakajima, Shin-ichi Takehiro, Yoshi-Yuki Hayashi
    ASTROPHYSICAL JOURNAL 898 (2) 0004-637X 2020/08 [Refereed][Not invited]
     
    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.
  • Tatsuya Yoshida, Kiyoshi Kuramoto
    ICARUS 345 0019-1035 2020/07 [Refereed][Not invited]
     
    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.
  • Tomohiro Usui, Ken-ichi Bajo, Wataru Fujiya, Yoshihiro Furukawa, Mizuho Koike, Yayoi N. Miura, Haruna Sugahara, Shogo Tachibana, Yoshinori Takano, Kiyoshi Kuramoto
    SPACE SCIENCE REVIEWS 216 (4) 0038-6308 2020/04 [Refereed][Not invited]
     
    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.
  • Yuichi Ito, George L. Hashimoto, Yoshiyuki O. Takahashi, Masaki Ishiwatari, Kiyoshi Kuramoto
    ASTROPHYSICAL JOURNAL 893 (2) 0004-637X 2020/04 [Refereed][Not invited]
     
    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.
  • Hiroaki Saito, Kiyoshi Kuramoto
    ASTROPHYSICAL JOURNAL 889 (1) 0004-637X 2020/01 [Refereed][Not invited]
     
    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.
  • Shunichi Kamata, Francis Nimmo, Yasuhito Sekine, Kiyoshi Kuramoto, Naoki Noguchi, Jun Kimura, Atsushi Tani
    NATURE GEOSCIENCE 12 (6) 407 - + 1752-0894 2019/06 [Refereed][Not invited]
     
    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.
  • 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 [Refereed][Not invited]
  • Edward D. Young, Kyoshi Kuramoto, Rudolph A. Marcus, Hisayoshi Yurimoto, Stein B. Jacobsen
    Oxygen in the Solar System 187 - 218 2018/11/15 [Refereed][Not invited]
     
    © 2008, the Mineralogical Society of America. All rights reserved. In this chapter we compare and contrast chemical and photochemical pathways for massindependent 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 massindependent 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 H2O. 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 δ170 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 the gas 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 16O 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 16O-poor H2O. 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.
  • Takashi Ito, Masateru Ishiguro, Tomoko Arai, Masataka Imai, Tomohiko Sekiguchi, Yoonsoo P. Bach, Yuna G. Kwon, Masanori Kobayashi, Ryo Ishimaru, Hiroyuki Naito, Makoto Watanabe, Kiyoshi Kuramoto
    NATURE COMMUNICATIONS 9 (1) 2486  2041-1723 2018/06 [Refereed][Not invited]
     
    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.
  • Daisuke Kuroda, Masateru Ishiguro, Makoto Watanabe, Sunao Hasegawa, Tomohiko Sekiguchi, Hiroyuki Naito, Fumihiko Usui, Masataka Imai, Mitsuteru Sato, Kiyoshi Kuramoto
    ASTRONOMY & ASTROPHYSICS 611 1432-0746 2018/03 [Refereed][Not invited]
     
    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.
  • Hiroaki Saito, Kiyoshi Kuramoto
    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 475 (1) 1274 - 1287 0035-8711 2018/03 [Refereed][Not invited]
     
    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.
  • Saito H., Kuramoto K.
    Planetary People - The Japanese Society for Planetary Sciences 日本惑星科学会 27 (3) 229 - 234 0918-273X 2018 [Not refereed][Not invited]
     
    <p>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.</p>
  • Kuramoto K., Morota T., Nagaoka H., Nakagawa H., Nakamura T., Ogawa K., Otake H., Ozaki M., Sasaki S., Senshu H., Tachibana S., Kawakatsu Y., Terada N., Usui T., Wada K., Watanabe S., MMX study team, Fujimoto M., Genda H., Hirata N., Imamura T., Kameda S., Matsumoto K., Miyamoto H.
    Planetary People - The Japanese Society for Planetary Sciences 日本惑星科学会 27 (3) 207 - 215 0918-273X 2018 [Not refereed][Not invited]
     
    <p>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.</p>
  • Daisuke Kuroda, Masateru Ishiguro, Makoto Watanabe, Sunao Hasegawa, Tomohiko Sekiguchi, Hiroyuki Naito, Fumihiko Usui, Masataka Imai, Mitsuteru Sato, Kiyoshi Kuramoto
    Astronomy & Astrophysics 611 0004-6361 2017/11 [Refereed][Not invited]
     
    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
    ASTRONOMICAL JOURNAL 154 (5) 180  0004-6256 2017/11 [Refereed][Not invited]
     
    We conducted a polarimetric observation of the fast-rotating near-Earth asteroid (1566) Icarus at large phase (Sun-asteroid-observer's) angles alpha = 57 degrees-141 degrees around the 2015 summer solstice. We found that the maximum values of the linear polarization degree are P-max = 7.32 +/- 0.25% at phase angles of alpha(max) = 124 degrees +/- 8 degrees in the V-band and P-max = 7.04 +/- 0.21% at alpha(max) = 124 degrees +/- 6 degrees in the RC-band. Applying the polarimetric slope-albedo empirical law, we derived a geometric albedo of p(V) = 0.25 +/- 0.02, which is in agreement with that of Q-type taxonomic asteroids. amax is unambiguously larger than that of Mercury, the Moon, and another near-Earth S-type asteroid (4179) Toutatis but consistent with laboratory samples with hundreds of microns in size. The combination of the maximum polarization degree and the geometric albedo is in accordance with terrestrial rocks with a diameter of several hundreds of micrometers. The photometric function indicates a large macroscopic roughness. We hypothesize that the unique environment (i.e., the small perihelion distance q = 0.187 au and a short rotational period of T-rot = 2.27 hr) may be attributed to the paucity of small grains on the surface, as indicated on (3200) Phaethon.
  • 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 1538-3881 2017/10 [Refereed][Not invited]
  • 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 0019-1035 2017 [Refereed][Not invited]
     
    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 0074-1795 2017 [Refereed][Not invited]
     
    © 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 2169-9097 2016/07 [Refereed][Not invited]
     
    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) 2197-4284 2016/01 [Refereed][Not invited]
  • Kamata, Shunichi, Kimura, Jun, Matsumoto, Koji, Nimmo, Francis, Kuramoto, Kiyoshi, Namiki, Noriyuki
    Journal of Geophysical Research-Planets 121 (7) 1362  2169-9097 2016 [Refereed][Not invited]
  • Shunichi Kamata, Seiji Sugita, Yutaka Abe, Yoshiaki Ishihara, Yuji Harada, Tomokatsu Morota, Noriyuki Namiki, Takahiro Iwata, Hideo Hanada, Hiroshi Araki, Koji Matsumoto, Eiichi Tajika, Kiyoshi Kuramoto, Francis Nimmo
    ICARUS 250 492 - 503 0019-1035 2015/04 [Refereed][Not invited]
     
    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 0019-1035 2014 [Refereed][Not invited]
     
    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 0019-1035 2014 [Refereed][Not invited]
  • 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) 0004-637X 2014 [Refereed][Not invited]
     
    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 0012-821X 2013/08 [Refereed][Not invited]
     
    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.
  • Atmospheric structure and cloud convection in Jupiter's atmosphere
    K. Sugiyama, K. Nakajima, M. Odaka, M. Ishiwatari, K. Kuramoto, Y. O. Takahashi, Y.-Y. Hayashi
    Planetary People 21 (1) 39 - 44 2012/03 [Refereed][Not invited]
  • Sekine Y., Yabuta H., Kimura J., Furukawa Y., Takano Y., Yano H., Funase R., Takai K., Ishihara M., Shibuya T., Tachibana S., Kuramoto K.
    Planetary People - The Japanese Society for Planetary Sciences 日本惑星科学会 21 (3) 229 - 238 0918-273X 2012 [Not refereed][Not invited]
     
    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.
  • Sugiyama K., Tani I., Katoh N., Umemoto T., Oshikawa T., Mikami T., Kuramoto K., Hayashi Y., Nakagawa Y., Center for Planetary Science, Suzuki A., Takahashi J., Nakamura T., Manabe S., Sakai S., Tsurumaki R., Nakaoka R., Tatsumi S.
    Planetary People - The Japanese Society for Planetary Sciences 日本惑星科学会 21 (4) 368 - 376 0918-273X 2012 [Not refereed][Not invited]
     
    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 0031-9201 2011/10 [Refereed][Not invited]
     
    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 0019-1035 2011/08 [Refereed][Not invited]
     
    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  0094-8276 2011 [Refereed][Not invited]
     
    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 [Refereed][Not invited]
  • 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, HAYASHI YOSHIYUKI, 倉本 圭
    ながれ 別冊 29221 2010 [Not refereed][Not invited]
  • IMAMURA Takeshi, KASAI Yasuko, SAGAWA Hideo, KURODA Takeshi, SATOH Takehiko, UENO Munetaka, SUZUKI Makoto, TAKAHASHI Yukihiro, TAKAHASHI Yoshiyuki, HASHIMOTO George L., KURAMOTO Kiyoshi
    Planetary people 日本惑星科学会 18 (2) 76 - 78 0918-273X 2009/06/25 [Not refereed][Not invited]
     
    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 日本天文学会 102 (3) 184 - 189 0374-2466 2009/02/20 [Not refereed][Not invited]
  • SUGIYAMA Ko-ichiro, ODAKA Masatsugu, SANO Yasuo, OHISHI Norikatsu, BABA Satoshi, TAKAI Yoshiaki, OHISHI Takahisa, HAYASHI Yoshi-Yuki, KURAMOTO Kiyoshi, WATANABE Shigeto
    Planetary people 日本惑星科学会 17 (2) 123 - 129 0918-273X 2008/06/25 [Not refereed][Not invited]
     
    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.
  • Global material transport in the solar nebula controlled by ice component
    Low Temperature Science 66 83 - 88 2008 [Not refereed][Not invited]
  • 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 [Not refereed][Not invited]
  • Young, Edward D, Kuramoto, Kiyoshi, Marcus, Rudolph A, Yurimoto, Hisayoshi, Jacobsen, Stein B
    Reviews in Mineralogy and Geochemistry 68 (1) 187 - 218 1529-6466 2008 [Refereed][Not invited]
     
    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.
  • Takashi Fukui, Kiyoshi Kuramoto
    ORIGIN OF MATTER AND EVOLUTION OF GALAXIES 1016 409 - 411 0094-243X 2008 [Refereed][Not invited]
     
    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.
  • KURAMOTO Kiyoshi, GENDA Hidenori, ARAI Tomoko, OKADA Tatsuaki, SUGITA Seiji
    Planetary people 日本惑星科学会 16 (3) 197 - 207 0918-273X 2007/09/25 [Not refereed][Not invited]
     
    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.
  • Naoya Sakamoto, Yusuke Seto, Shoichi Itoh, Kiyoshi Kuramoto, Kiyoshi Fujino, Kazuhide Nagashima, Alexander N. Krot, Hisayoshi Yurimoto
    SCIENCE 317 (5835) 231 - 233 0036-8075 2007/07 [Refereed][Not invited]
     
    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.
  • Yurimoto Hisayoshi, Kuramoto Kiyoshi, Krot Alexander N, Scott Edward RD, Cuzzi Jeffrey N, Thiemens Mark H, Lyons James R
    Protostars and planets V Citeseer 849 - 862 2007 [Refereed][Not invited]
  • K Sugiyama, M Odaka, K Kuramoto, YY Hayashi
    GEOPHYSICAL RESEARCH LETTERS 33 (3) L03201 - L03201 0094-8276 2006/02 [Refereed][Not invited]
     
    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.
  • K Sugiyama, M Odaka, K Kuramoto, YY Hayashi
    GEOPHYSICAL RESEARCH LETTERS 33 (3) 0094-8276 2006/02 [Refereed][Not invited]
     
    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.
  • KURAMOTO Kiyoshi, YURIMOTO Hisayoshi
    Planetary people 日本惑星科学会 14 (4) 193 - 200 0918-273X 2005/12/25 [Not refereed][Not invited]
  • Kuramoto Kiyohi, Yurimoto Hisayoshi
    Chondrites and the Protoplanetary Disk 341 181 - 192 2005 [Refereed][Not invited]
  • Hisayoshi Yurimoto, Kiyoshi Kuramoto
    Science (New York, N.Y.) 305 (5691) 1763 - 6 0036-8075 2004/09/17 [Refereed][Not invited]
     
    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.
  • NAKAGAMI Yuuichi, OHSHIMA Osamu, SUGIYAMA Ko-ichiro, KAWABATA Yoshihito, SATO Koichiro, KOBAYASHI Kazumasa, SASAGAWA Hirotatsu, ODAKA Masatsugu, KURAMOTO Kiyoshi, Mosir project
    Planetary people 日本惑星科学会 12 (2) 80 - 88 0918-273X 2003/06/25 [Not refereed][Not invited]
  • T Yokohata, M Odaka, K Kuramoto
    ICARUS 159 (2) 439 - 448 0019-1035 2002/10 [Refereed][Not invited]
     
    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).
  • SA Hauck, RJ Phillips
    JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 107 (E7) 5118  0148-0227 2002/07 [Refereed][Not invited]
     
    [1] We present a coupled thermal-magmatic model for the evolution of Mars' mantle and crust that may be consistent with estimates of the average crustal thickness and crustal growth rate. By coupling a simple parameterized model of mantle convection to a batch-melting model for peridotite, we can investigate potential conditions and evolutionary paths of the crust and mantle in a coupled thermal-magmatic system. On the basis of recent geophysical and geochemical studies, we constrain our models to have average crustal thicknesses between 50 and 100 km that were mostly formed by 4 Ga. Our nominal model is an attempt to satisfy these constraints with a relatively simple set of conditions. Key elements of this model are the inclusion of the energetics of melting, a wet (weak) mantle rheology, self-consistent fractionation of heat-producing elements to the crust, and a near-chondritic abundance of those elements. The latent heat of melting mantle material is a small (percent level) contributor to the total planetary energy budget over 4.5 Gyr but is crucial for constraining the thermal and magmatic history of Mars. Our nominal model predicts an average crustal thickness of similar to62 km that was 73% emplaced by 4 Ga. However, if Mars had a primary crust enriched in heat-producing elements, consistent with SNC meteorite geochemistry, then our models predict a considerably diminished amount of post 4 Ga crustal emplacement relative to the nominal model. The importance of a wet mantle in satisfying the basic constraints of Mars' thermal and crustal evolution suggests (independently from traditional geomorphology or meteorite geochemistry arguments) that early Mars had a wet environment. Extraction of water from the mantle of a one-plate planet such as Mars is found to be extremely inefficient, such that 90-95% of all water present in the mantle after the initial degassing event should still reside there currently. Yet extraction of even 5% of a modestly wet mantle (similar to36 ppm water) would result in a significant amount (6.4 m equivalent global layer) of water available to influence the early surface and climate evolution of the planet.
  • YOKOHATA, KURAMOTO Kiyoshi
    Planetary people 日本惑星科学会 10 (2) 64 - 74 0918-273X 2001/06/25 [Not refereed][Not invited]
  • Climate changes on Mars: CO2 polar cap and H2O ice sheet
    10 64 - 74 2001 [Not refereed][Not invited]
  • SENSHU Hiroki, KURAMOTO Kiyoshi, MATSUI Takafumi
    Planetary people 日本惑星科学会 9 (1) 17 - 32 0918-273X 2000/03/25 [Not refereed][Not invited]
  • Early thermal history of a proto-planet
    9 17 - 32 2000 [Not refereed][Not invited]
  • The ocean in Europa
    47 39 - 40 2000 [Not refereed][Not invited]
  • エウロパの海
    天気 (日本気象学会誌) 47 39 - 40 2000 [Not refereed][Not invited]
  • 倉本 圭
    号外地球 海洋出版 (23) 25 - 29 0916-9733 1999/02 [Not refereed][Not invited]
  • Feasibility of exploration of lunar iron core
    7 218 - 220 1998 [Not refereed][Not invited]
  • 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 [Not refereed][Not invited]
  • Kuramoto Kiyoshi, Saiganji Yoshihiko, Yamamoto Tetsuo
    Lunar and Planetary Science Conference 29 1998 [Refereed][Not invited]
  • KURAMOTO Kei
    Planetary people 日本惑星科学会 6 (3) 196 - 198 0918-273X 1997/09/25 [Not refereed][Not invited]
  • K Kuramoto
    PHYSICS OF THE EARTH AND PLANETARY INTERIORS 100 (1-4) 3 - 20 0031-9201 1997/03 [Refereed][Not invited]
     
    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, xi, defined as follows: xi = 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 xi > 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 H-2. When xi < 0.5, on the contrary, H2O consumption by the above reactions and selective loss of H-2 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 Wanke (1981), xi is found to decrease with increasing the mixing fraction of the volatile-rich component: xi > 0.5 for the mixing fraction smaller than about 15-20% and, xi < 0 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. (C) 1997 Elsevier Science B.V.
  • Special issue, Origin and evolution of the Moon
    6 196 - 198 1997 [Not refereed][Not invited]
  • Kiyoshi Kuramoto
    Physics of the Earth and Planetary Interiors 100 (1-4) 3 - 20 0031-9201 1997 [Not refereed][Not invited]
     
    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.
  • K Kuramoto, T Matsui
    JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 101 (E6) 14909 - 14932 0148-0227 1996/06 [Refereed][Not invited]
     
    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 岩波書店 66 (3) 193 - 201 0022-7625 1996/03 [Not refereed][Not invited]
  • Kiyoshi Kuramoto, Takafumi Matsui
    Journal of Geophysical Research E: Planets 101 (6) 14909 - 14932 0148-0227 1996 [Not refereed][Not invited]
     
    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.
  • KURAMOTO Kiyoshi
    Planetary People 日本惑星科学会 4 (4) 201 - 214 0918-273X 1995/12/01 [Not refereed][Not invited]
  • Earth and Mars: H, C, and early differentiation
    4 201 - 214 1995 [Not refereed][Not invited]
  • K KURAMOTO, T MATSUI
    JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 99 (E10) 21183 - 21200 0148-0227 1994/10 [Refereed][Not invited]
     
    Judging from accretion energy and accretion time for the giant icy satellites it is suggested that a proto-atmosphere is formed by the evaporation of icy materials during accretion of these bodies around the proto-gaseous giant planets. We study the blanketing effect of proto-atmosphere during accretion of these satellites in the gas-free environment. We use a gray atmosphere model in which the condensation of H2O in a convective atmosphere is taken into account. The numerical results strongly suggest that the accretion energy flux is large enough to increase the surface temperature higher than approximately 500 K during accretion due to the blanketing effect of proto-atmosphere as long as the accretion time is shorter than 10(5) years. Such a high surface temperature causes the formation of a deep water-rich ocean due to the melting of icy materials. Also a rocky core should be eventually formed by sinking of rocky materials through the water-rich ocean during accretion. Therefore, the apparent difference in the surface geologic features between Ganymede and Callisto can hardly be explained by whether or not these bodies have experienced the formation of rocky core. Stability of hydrostatic structure of the proto-atmosphere is also studied. Vigorous escape of the proto-atmosphere is likely to occur under high surface temperature. A large portion of accretional energy is possibly consumed by the vigorous escape during accertion. Thus, the giant icy satellites may lose a significant amount of icy materials during their accretions. This can explain the ice-depleted composition of Titan inferred from the observed mean densities of Saturnian satellites, if the accretion occurs within 10(4) - 10(5) years. Such a significant loss of icy materials is also expected for Ganymede and Callisto. The escape and catalytic reaction in the hot proto-atmosphere may play an important role in formation of the present N2-abundant and CO-depleted atmosphere of Titan.
  • KURAMOTO K, MATSUI T
    Journal of Geophysical Research 99 (E10) 21183 - 21200 0148-0227 1994 [Not refereed][Not invited]

Books etc

  • 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 (Joint work)
    北海道大学出版会 2010/11 (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 (Joint work)
    北海道大学図書刊行会 2008/03 (ISBN: 4832981838) 272

MISC

Awards & Honors

  • 2005 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 2005, Horiuchi Prize, Meteorological Society of Japan

Research Grants & Projects

  • Modeling of water and material circulations in the solar system objects
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    Date (from‐to) : 2017/06 -2022/03 
    Author : 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。
  • Formation and evolution of a reduced-type proto-atmosphere on early Earth
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2018/04 -2021/03 
    Author : 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。
  • 太陽系外惑星の新機軸:地球型惑星へ
    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)
    Date (from‐to) : 2016/04 -2017/03 
    Author : 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。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2013/05 -2017/03 
    Author : HATA Yutaka
     
    In this study, we obtained the following results:1. We proposed a fuzzy logic-based analysis method for human health checkup data. In it, we demonstrated the fuzzy normal degree for some diseases. 2. We calculated a risk factor for diabetes based on the health checkup data in health checkup data. 3. We investigated a relation between Hb-A1c and the other index of blood test by self-organizing map for investigating diabetics. 4. We detect the abnormal state of human body by measuring a daily life of humans by MEMS senor with ECG, temperature, humidity etc. 5. We developed a cerebral aneurysm outbreak prediction system by paying attention to a shape and a blood vessel divergence angle of vasculature provided from cerebral arterial circle three dimensional shape toward the initiative medical care realization of the cerebral aneurysm.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    Date (from‐to) : 2011/04 -2016/03 
    Author : HAYASHI Masahiko
     
    The managing team had an objective to promote the four pre-planned areas of research under close interaction one another. We encouraged active exchange of information among the researchers involved in this Grant-in-aid program, and organized nine international conferences with more than 800 participants in total. We also build a homepage dedicated for the program and released information and achievements to both inside and outside of the country. We worked to foster younger generation researchers by involving graduate students and hiring posdocs with the Grant. We approved a total of 14 open research proposals in two times, with the proposed researchers spreading over many Japanese universities and research organizations.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    Date (from‐to) : 2011/04 -2016/03 
    Author : Kuramoto Kiyoshi, ISHIWATARI Masaki, GENDA Hidenori, TAKEHIRO Shinichi, SASAKI Yohei, NAKAJIMA Kensuke, HAMANO Keiko, ONISHI Masanori
     
    Evolution of steam atmospheres on earth-like planets after each final giant impact event is theoretically solved with an analysis of its observability. Two types of evolutionary tracks are found: one is the rapid formation of a water ocean and another is the long-term persistence of the magma ocean state. The secular loss of surface water due to atmospheric escape driven by stellar UV irradiation may rather stabilize surface liquid water than merely produce an arid surface environment. General circulation experiments provided with various boundary conditions reveal that a synchronously rotating planet and a land planet may have wider habitable zones than previously thought. Numerical models to solve cloud convection and radiative transfer in gas giant planets are also developed, revealing the mechanisms for the intermittencies observed for cloud convection in the solar system gas planets as well as roles of cloud layers on controlling the thermal emission from gas giant atmospheres.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2010 -2012 
    Author : KURAMOTO Kiyoshi, TAKEHIRO Shin-ichi, FUKUI Takashi, ADACHI Toshitaka
     
    Theoretical and numerical studies on the evolution of the interiors of the Moon and small rocky planets were performed on the basis of the consideration about the variety of raw materials of these bodies by using a model of proto-planetary disk. A series of cumulate rock layers, formed in the early Moon due to cooling and solidification of a magma ocean, should have overturned toward stable structure. During the overturn process, Mg-rich olivine cumulate likely becomes to melt again, which is consistent with the exposure of Mg-rich mafic minerals on the lunar far-side. The present moment of inertia factor of the Moon is explained by the density profile after the completion of overturn. Recent spacecraft data shows that Mercury has a significantly reduced composition enriched in sulfur as well as E-chondrites, which is consistent with our disk model, and also has a thin silicate mantle with thickness less than about 400 km. We performed thermal history simulations considering such a new structure. It is suggested that the liquid core of Mercury is thermally convective until present, allowing dynamo action producing the intrinsic magnetic field of Mercury.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2009 -2011 
    Author : SAIKI Tsunemasa, UTSUMI Yuichi, KURAMOTO Kei
     
    Recently, micro total analysis systems(μTAS) have received a lot of attention for its efficiency in producing reactions and in reducing the used amount of reagents. In the area ofμTAS, s urface acoustic wave(SAW) actuators, because of their very simple structures, have studied. T he SAW is generated from an inter digital transduc er(IDT). We thus investigated t he relationship between IDT's shape s and liquid flows, in order to optimize the SAW actua tors. It was found that optimized IDT's pitch depends on viscosity of liquid. Then, in order to support de sign of the SAW actuators, we investigated the physical mechanism of the liquid flow by using numerical analysis of the moving parti cle semi-im plicit method. It was proven that the liquid flow is caused by t he energy of the SAW and is affected by the visco sity of the liquid and interaction between the liquid and a waved plate of a substance. Finally, on the knowledge obtained b y the experiment and the analysis, a micro chip for mixing and reacting 2 solutions was designed and fabricated. T he local and rapid mixing of conti nuous liquid flow was found to be pos sible by using the chip.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2008 -2011 
    Author : ISHIWATARI Masaki, KURAMOTO Kiyoshi, ODAKA Masatsugu, NAKAJIMA Kensuke
     
    In this study, parameter experiments on structures of moist atmospheres on synchronously rotating planets are performed, and model infrastructure needed for realistic simulations are developed. Parameter experiment with various planetary rotation rate show existence of oscillating north-south asymmetric states and occurence of multiple equilibrium. Parameter experiment with various solar constant show that the value of solar constant at which the runaway greenhouse states occur changes about 100W/m^2 according to the value of planetary rotation rate. Moreover, radiation scheme for hydrogen atmospheres and a data input/output library are developed.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2007 -2009 
    Author : KURAMOTO Kiyoshi, SASAKI Youhei, FUKUI Takashi, IWAHORI Tomoko
     
    The bulk composition of Mercury estimated from a model for the solar nebula evolution is adopted for the numerical and theoretical analysis of the thermal history and dynamo action of this innermost planet. The mantle components are probably more viscous than the previous estimates, which slows down the growth of solid inner core. The release of light element from the slowly growing inner core possibly induces the convection of outer liquid core with generating a moderate dynamo action and the present weak intrinsic magnetic field. These results provide a basis for the interpretation of data acquired by the current and future Mercury exploration missions.
  • 同位体による先太陽系史と太陽系創成期の解明
    日本学術振興会:科学研究費助成事業 基盤研究(S)
    Date (from‐to) : 2005 -2008 
    Author : 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。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Creative Scientific Research
    Date (from‐to) : 2004 -2008 
    Author : ISHIHARA Morio, TOYODA Michisato, UEDA Chiaki, UCHINO Kiichiro, YURIMOTO Hisayoshi, KURAMOTO Kiyoshi, MATSUMOTO Takuya
     
    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。
  • Theoretical and numerical study on Jovian atmospheres:their dynamics, matetialtrensport, and energetics.
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2004 -2007 
    Author : HAYASHI Yoshi-yuki, WATANABE Shigeto, KURAMOTO Kiyoshi, ISHIWATARI Masaki, ODAKA Masatsugu, NAKAJIMA Kensuke
     
    For the purpose of investigating the interplay among dynamical, thermal, and compositional structures of the atmospheres of Jovian planets, we compiled the current status of corresponding knowledge, developed a hierarchical modeling system, and conducted numerical experiments with those hierardical modeling systems. The main findings of our investigations are summarized as follows: 1. We developed a vertical one-dimensional equilibrium cloud condensation model, which enable us to cover possible atmospheric compositional varieties of the Jovian planets. We found that the contributions to the intensity of stability by the cloud layers associated with the condensation of NH_3 and formation of NH_4SH are not negligible compared with that of H_2O. 2. We developed a two-dimensional cloud convection model incorporating the condensation of NH_3 and H_2O and formation of NH_4SH. We conducted a series of numerical experiments, and found that the H_2O condensation level acts as a distinct dynamical boundary that separates the convective motions above and below it. The stable layers due to NH_3 and NH_4SH clouds cannot suppress the cloudy plumes driven by H_2O condensation healing, resulting in the mixing over the full depth of the atmosphere above the H_2O condensation level. 3. With the application to the Jovian atmosphere in mind, we performed a series of numerical studies on the equatorial acceleration using the three dimensional Bousinesq spherical shell convection model. We found that a strong stable layer in the outer layer helps the development of equatorial retrograde jet. This result may raise a question about the theory where rotating spherical thermal convection explains the cause of the equatorial westerly jets of Jupiter and Saturn. 4. A common software infrastructure, over which those numerical models were constructed, was developed. It contains "gt4f90io" which is a library for I/O of numerical data, and "Rdoc" which is an automatic documentation generator for numerical model codes. We also organized a standard style of Fortran90 programming and constructed a library of Fortran90 functions for basic mathematical manipulations, with which we developed 'Spmodel" which is a set of spectral models. All of the softwares mentioned are open to public on our web site.
  • 日本学術振興会:科学研究費助成事業 若手研究(B)
    Date (from‐to) : 2004 -2006 
    Author : 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.
  • 地球流体力学の知見情報をインターネット上に集積公開して行くための調査研究
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    Date (from‐to) : 2004 -2004 
    Author : 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.
  • GLOBAL DUST CIRCULATION IN THE PROTO-PLANETARY DISK
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2001 -2004 
    Author : YURIMOTO Hisayoshi, IDA Shigeru, FUJIMOTO Masaki, KURAMOTO Kiyoshi, EMORI Hiroyuki
     
    It is believed that bulk chemical compositions among planets and asteroids in the solar system is similar but slightly different from the solar abundance ratios one another. The variations of the bulk composition may result from a global circulation of dusts around the proto-planetary disk. The dusts spiral into the proto-sun from outer edge of the disk and some of them launched from the inner edge of the disk to the outer-edge. In this study, we made chemical analyses of meteorites and numerical simulations of electro-magnetic effects, dynamic effects and chemical reaction network estimated in the proto-planetary disk. We may conclude the subjects as follows : 1.Oxygen isotopic anomaly observed in the solar system was originated in the parent molecular cloud by a self-shielding effect of carbon monoxides by ultra-violet light irradiation. 2.The oxygen isotopic fractionation in the molecular cloud was separated into interstellar gas and ice phases. Differences of dynamics and chemistry in the disk introduced the anomaly of oxygen isotopes in the solar system. 3.oxygen isotopic compositions of planets were mainly determined by enrichment factor of dusts and evaporation of ice in a proto-planetary disk. 4.A numerical simulation suggests that trajectory around a central star and the mass of gas planets were controlled by gas-dust ratios in a proto-planetary disk. The results correspond to probabilities of extra-solar planets by astronomical observations. This conclusion suggests that amounts of proto-planetary disk are determined by star-formation process, but the planetary formation around the star is controlled by the gas-dust ratio in the disk. 5.Nature of electro-magneto vortex of interstellar plasma was simulated numerically. Inertia effects of electrons are important to the vortex evolution. Larger scale vortex is immediately fractionized to smaller scale ones. This process suggests that material mixing is promptly evolved in the space than ever thought.
  • 対流渦の直接数値計算による惑星CO_2大気の光化学安定性に関する研究
    日本学術振興会:科学研究費助成事業 萌芽研究
    Date (from‐to) : 2001 -2003 
    Author : 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.
  • Observation of Jovian Visible Aurora and its Generation Mechanism
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2000 -2001 
    Author : WATANABE Shigeto, TAKAHASHI Yukihiro, KURAMOTO Kiyoshi, HAYASHI Yoshiyuki
     
    We have built an optical observation system of Jovian visible aurora and airglow, which consists of CCD and narrow band filter on ground-based telescope. The emissions have never been measured from ground. We have carried out the observations by use of Rikubetsu 110cm telescope, lidate 60cm telescope and Hokkaido University 10cm telescope from 1999 to 2001. We have also developed an imaging processing system that analyzes the image of Jupiter taken with short exposure time and integrated. We found some emissions in the northern region of Jupiter. Our system may be able to apply to detect very weak signals from planets or airglow. We have investigated theoretically the atmosphere of Jupiter as well as Venus, Earth and Mars. The results suggested that the interactions with clouds and plasma are important to planetary atmospheres. Especially, at high altitudes the ion-drag effect must be considered in the planetary upper atmospheres.
  • 日本学術振興会:科学研究費助成事業 奨励研究(A)
    Date (from‐to) : 1999 -2000 
    Author : 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.
  • 原始太陽系星雲の物質進化に関する理論的研究
    日本学術振興会:科学研究費助成事業 特別研究員奨励費
    Date (from‐to) : 1998 -1998 
    Author : 倉本 圭
  • Material evolution from interstellar clouds to planetary systems
    Date (from‐to) : 1993
  • Planetary surface environment
    Date (from‐to) : 1988
  • Formation and evolution of the Earth and planets
    Date (from‐to) : 1988

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