Associate for Education and Public Outreach

兵頭 龍樹

ヒョウドウ リュウキ  (RYUKI HYODO)

基本情報

所属
国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 太陽系科学研究系 国際トップヤングフェロー (准教授相当)

連絡先
hyodoelsi.jp
研究者番号
20814693
ORCID ID
 https://orcid.org/0000-0003-4590-0988
J-GLOBAL ID
202001015221817161
researchmap会員ID
R000006549

外部リンク

About

惑星形成論および惑星探査を専門とし,JAXA 内部から積極的に次世代の惑星探査ミッションの構築を行なっている.ESA・NASA・JAXA の3機関の探査計画に参画.3-4ヶ月/年はパリ大学で活動.

 

個人ホームページ: https://members.elsi.jp/~hyodo/English/index.html (Here)

google scholar: https://scholar.google.co.jp/citations?user=IjqvVCwAAAAJ&hl=en (Here)

 

Research Interests

コンピュータシミュレーションと理論的手法を用いて, 多様な惑星系, 小天体, リングの形成と進化過程の理解(惑星形成論)を目指す.また科学的な側面から惑星探査ミッションを積極的に価値最大化・構築すること(惑星探査学)を目的とする.

 

Mission Involvements

NASA土星探査計画 Cassini / JAXA小惑星探査計画 Hayabusa2 / ESA水星探査計画 BepiColombo / JAXA火星衛星探査計画 MMX / JAXA次世代サンプルリターン計画 (彗星!?) / 深宇宙・超コンステレーション構想 (即応型小天体フライバイ探査構想) / JAXA外惑星探査計画 OPENS (日本初の外惑星探査計画 !?)

 

主なプレスリリース 

『新時代を迎える火星生命探査における火星衛星探査計画「MMX」の役割 (link)』

『後期集積が水星に与える影響 (link)』

『火星衛星、巨大衝突で形成される (link)』

『JAXA火星衛星サンプルリターン(MMX)計画で、火星の全歴史の解明が可能 (link)』

『土星の輪、誕生の謎を解明 (link)』

 

主な外部インタビュー記事

『日本惑星科学会最優秀研究者賞受賞インタビュー (link)』

『理論研究で月や火星探査の道筋をつける (link)』

『惑星形成論研究者はリュウグウサンプル分析結果のどこに注⽬するのか (link)』


受賞

 2

主要な論文

 45
  • Ryuki Hyodo, Tomohiro Usui
    SCIENCE 373(6556) 742-742 2021年8月  査読有り筆頭著者責任著者
  • Ryuki Hyodo, Tristan Guillot, Shigeru Ida, Satoshi Okuzumi, Andrew N. Youdin
    ASTRONOMY & ASTROPHYSICS 646 2020年12月12日  査読有り筆頭著者責任著者
    Around the snow line, icy pebbles and silicate dust may locally pile-up and form icy and rocky planetesimals via streaming instability and/or gravitational instability. We perform 1D diffusion-advection simulations that include the back-reaction to radial drift and diffusion of icy pebbles and silicate dust, ice sublimation, release of silicate dust, and their recycling through recondensation and sticking onto pebbles outside the snow line. We use a realistic description of the scale height of silicate dust obtained from Ida et al. and that of pebbles including the effects of a Kelvin-Helmholtz instability. We study the dependence of solid pile-up on distinct effective viscous parameters for turbulent diffusions in the radial and vertical directions ($\alpha_{\rm Dr}$ and $\alpha_{\rm Dz}$) and for the gas accretion to the star ($\alpha_{\rm acc}$) as well as that on the pebble-to-gas mass flux ($F_{\rm p/g}$). We derive the sublimation width of drifting icy pebbles which is a critical parameter to characterize the pile-up of silicate dust and pebbles around the snow line. We identify a parameter space (in the $F_{\rm p/g}-\alpha_{\rm acc}-\alpha_{\rm Dz}(=\alpha_{\rm Dr})$ space) where pebbles no longer drift inward to reach the snow line due to the back-reaction that slows down radial velocity of pebbles. We show that the pile-up of solids around the snow line occurs in a broader range of parameters for $\alpha_{\rm acc}=10^{-3}$ than for $\alpha_{\rm acc}=10^{-2}$. Above a critical $F_{\rm p/g}$ value, the runaway pile-up of silicate dust inside the snow line is favored for $\alpha_{\rm Dr}/\alpha_{\rm acc} \ll 1$, while that of pebbles outside the snow line is favored for $\alpha_{\rm Dr}/\alpha_{\rm acc} \sim 1$. Our results imply that a distinct evolutionary path could produce a diversity of outcomes in terms of planetesimal formation around the snow line.
  • Ryuki Hyodo, Kosuke Kurosawa, Hidenori Genda, Tomohiro Usui, Kazuhisa Fujita
    Scientific Reports 9(1) 2019年12月  査読有り筆頭著者責任著者
    Throughout the history of the solar system, Mars has experienced continuous asteroidal impacts. These impacts have produced impact-generated Mars ejecta, and a fraction of this debris is delivered to Earth as Martian meteorites. Another fraction of the ejecta is delivered to the moons of Mars, Phobos and Deimos. Here, we studied the amount and condition of recent delivery of impact ejecta from Mars to its moons. Using state-of-the-art numerical approaches, we report, for the first time, that materials delivered from Mars to its moons are physically and chemically different from the Martian meteorites, which are all igneous rocks with a limited range of ages. We show that Mars ejecta mixed in the regolith of its moons potentially covers all its geological eras and consists of all types of rocks, from sedimentary to igneous. A Martian moons sample-return mission will bring such materials back to Earth, and the samples will provide a wealth of "time-resolved" geochemical information about the evolution of Martian surface environments.
  • Ryuki Hyodo, Hidenori Genda, Sébastien Charnoz, Pascal Rosenblatt
    Astrophysical Journal 845(2) 125-125 2017年8月20日  査読有り筆頭著者責任著者
    Phobos and Deimos are the two small moons of Mars. Recent works have shown that they can accrete within an impact-generated disk. However, the detailed structure and initial thermodynamic properties of the disk are poorly understood. In this paper, we perform high-resolution SPH simulations of the Martian moon-forming giant impact that can also form the Borealis basin. This giant impact heats up the disk material (around ∼2000 K in temperature) with an entropy increase of ∼1500 J K-1 kg-1. Thus, the disk material should be mostly molten, though a tiny fraction of disk material () would even experience vaporization. Typically, a piece of molten disk material is estimated to be meter sized owing to the fragmentation regulated by their shear velocity and surface tension during the impact process. The disk materials initially have highly eccentric orbits (e ∼ 0.6-0.9), and successive collisions between meter-sized fragments at high impact velocity (∼1-5 km s-1) can grind them down to ∼100 μm sized particles. On the other hand, a tiny amount of vaporized disk material condenses into ∼0.1 μm sized grains. Thus, the building blocks of the Martian moons are expected to be a mixture of these different sized particles from meter-sized down to ∼100 μm sized particles and ∼0.1 μm sized grains. Our simulations also suggest that the building blocks of Phobos and Deimos contain both impactor and Martian materials (at least 35%), most of which come from the Martian mantle (50-150 km in depth at least 50%). Our results will give useful information for planning a future sample return mission to Martian moons, such as JAXA's MMX (Martian Moons eXploration) mission.
  • Ryuki Hyodo, Keiji Ohtsuki
    Nature Geoscience 8(9) 686-689 2015年10月1日  査読有り筆頭著者責任著者
    Saturn's F ring is a narrow ring of icy particles, located 3,400 km beyond the outer edge of the main ring system. Enigmatically, the F ring is accompanied on either side by two small satellites, Prometheus and Pandora, which are called shepherd satellites. The inner regular satellites of giant planets are thought to form by the accretion of particles from an ancient massive ring and subsequent outward migration. However, the origin of a system consisting of a narrow ring and shepherd satellites remains poorly understood. Here we present N-body numerical simulations to show that a collision of two of the small satellites that are thought to accumulate near the main ring's outer edge can produce a system similar to the F ring and its shepherd satellites. We find that if the two rubble-pile satellites have denser cores, such an impact results in only partial disruption of the satellites and the formation of a narrow ring of particles between two remnant satellites. Our simulations suggest that the seemingly unusual F ring system is a natural outcome at the final stage of the formation process of the ring-satellite system of giant planets.

MISC

 9

担当経験のある科目(授業)

 1

共同研究・競争的資金等の研究課題

 9

社会貢献活動

 5