小惑星の表面更新機構の解明

2022 Fiscal Year Research-status Report

• Project/Area Number: 21K03647
• Research Institution: The University of Aizu
• Principal Investigator: 北里 宏平 会津大学, コンピュータ理工学部, 准教授 (50550597)
• Co-Investigator(Kenkyū-buntansha): 平田 成 会津大学, コンピュータ理工学部, 上級准教授 (80372655)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 小惑星 / 表面更新 / イトカワ / はやぶさ / 熱風化 / 熱衝撃 / 熱疲労

Outline of Annual Research Achievements

本研究では，地球近傍小惑星に見られる表面更新の主要なメカニズムを解明することをめざし，宇宙空間に暴露された小惑星表面環境における熱風化の影響を評価するため，地球近傍小惑星の軌道計算，はやぶさが取得したイトカワの画像・分光データの解析，イトカワの熱解析を行う．

令和4年度は，主に小惑星イトカワの形状モデルを用いた輻射伝熱解析と熱応力解析に取り組んだ．イトカワの輻射伝熱解析は過去にも取り組んだ経験があり，イトカワのくびれ部分で表面更新を起こしたと見られる場所が，地形のつくる影によって急激な温度変化を経験するという結果を得ていた．その輻射伝熱解析には独自に開発した計算コードを使用していたが，従来の計算ではshadowingやself-heatingの効果によって生じる数値計算の不安定性から，対象領域の大きさに対して十分な解像度のモデルでの計算ができていなかった．そこで本研究では，Euler法で計算していた部分を陰解法の一種であるCrank-Nicolson法に置き換えることによって計算を安定化されることに成功した．そして，より精密な形状モデルを用いた解析を行い，熱衝撃が小惑星の表面更新を促進させた可能性があることを示すことができた．

また，イトカワのくびれ部分以外で表面更新を起こしたと考えられる複数箇所について，それらの成因が熱疲労であるかを定量的に評価するために，商用の有限要素法シミュレーションソフトCOMSOL Multiphysicsを用いて太陽輻射加熱によって生じる熱応力の計算を行った．現時点で熱応力の大きさと表面更新を起こした場所に明確な相関は見られていないが，いくつか検証課題が残っており，この熱応力解析は翌年度も継続して行うつもりである．

Current Status of Research Progress

2: Research has progressed on the whole more than it was originally planned.

Reason

イトカワの輻射伝熱解析と熱応力解析を計画通りに進めることができており，論文出版の準備を進めている．

Strategy for Future Research Activity

令和5年度は，イトカワ表面に生じる熱応力の追加解析に加えて，はやぶさのデータ解析から判明した近赤外分光器の迷光の影響について調査する．そして，近赤外分光計データの校正手法を確立し，イトカワ表面の表面更新の痕跡を明らかにする．

Causes of Carryover

COVID-19の影響で見送られ続けていた国際会議が翌年度に米国で開催されるという通知が年度途中にあり，その会議に参加する旅費を確保するために次年度使用額が生じた．

Research Products

• [Journal Article] Soluble organic molecules in samples of the carbonaceous asteroid (162173) Ryugu (2023)
  • Author(s): Naraoka, H. et al. (including Kitazato, K. & Hirata, N.)
  • Journal Title: Science Volume: 379 Pages: -
  • DOI: 10.1126/science.abn9033
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Formation and evolution of carbonaceous asteroid Ryugu: Direct evidence from returned samples (2023)
  • Author(s): Nakamura, T. et al. (including Kitazato, K. & Hirata, N.)
  • Journal Title: Science Volume: 379 Pages: -
  • DOI: 10.1126/science.abn8671
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Samples returned from the asteroid Ryugu are similar to Ivuna-type carbonaceous meteorites (2023)
  • Author(s): Yokoyama, T. et al. (including Hirata, N. & Kitazato, K.)
  • Journal Title: Science Volume: 379 Pages: -
  • DOI: 10.1126/science.abn7850
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution (2023)
  • Author(s): Okazaki, R. et al. (including Hirata, N. & Kitazato, K.)
  • Journal Title: Science Volume: 379 Pages: -
  • DOI: 10.1126/science.abo0431
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] A dehydrated space-weathered skin cloaking the hydrated interior of Ryugu (2023)
  • Author(s): Noguchi, T. et al. (including Hirata, N. & Kitazato, K.)
  • Journal Title: Nature Astronomy Volume: 7 Pages: 170-181
  • DOI: 10.1038/s41550-022-01841-6
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Macromolecular organic matter in samples of the asteroid (162173) Ryugu (2023)
  • Author(s): Yabuta, H. et al. (including Kitazato, K. & Hirata, N.)
  • Journal Title: Science Volume: 379 Pages: -
  • DOI: 10.1126/science.abn9057
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] First asteroid gas sample delivered by the Hayabusa2 mission: A treasure box from Ryugu (2022)
  • Author(s): Okazaki, R. et al. (including Hirata, N. & Kitazato, K.)
  • Journal Title: Science Advances Volume: 8 Pages: -
  • DOI: 10.1126/sciadv.abo7239
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Derivation of 1.064 µm normal albedos on the C-type asteroid Ryugu from laser pulse intensity measurement of the Hayabusa2 LIDAR (2022)
  • Author(s): Yamada, R. et al. (including Hirata, N.)
  • Journal Title: Earth, Planets and Space Volume: 74 Pages: -
  • DOI: 10.1186/s40623-022-01717-z
  • Peer Reviewed / Open Access
• [Journal Article] Martian moons exploration MMX: sample return mission to Phobos elucidating formation processes of habitable planets (2022)
  • Author(s): Kuramoto, K. et al. (including Hirata, N.)
  • Journal Title: Earth, Planets and Space Volume: 74 Pages: -
  • DOI: 10.1186/s40623-021-01545-7
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Photometric behavior of Ryugu’s NIR spectral parameters (2022)
  • Author(s): Longobardo, A. et al. (including Kitazato, K. & Hirata, N.)
  • Journal Title: Astronomy & Astrophysics Volume: 666 Pages: -
  • DOI: 10.1051/0004-6361/202244097
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Characterization of the MASCOT landing area by Hayabusa2 (2022)
  • Author(s): Schroder, S. et al. (including Kitazato, K.)
  • Journal Title: Astronomy & Astrophysics Volume: 666 Pages: -
  • DOI: 10.1051/0004-6361/202244059
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Clustering analysis of high spatial resolution spectra of asteroid (162173) Ryugu from Hayabusa2/NIRS3 (2022)
  • Author(s): Bott, N, Perna, D., Deshapriya, J. D. P., Hasselmann, P. H., Barucci, M. A., Domingue, D. L., Dotto, E., Kitazato, K., Matsuoka, M., Palomba, E., Usui, T. and Fulchignoni, M.
  • Journal Title: Planetary and Space Science Volume: 219 Pages: -
  • DOI: 10.1016/j.pss.2022.105530
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Site selection for the Hayabusa2 artificial cratering and subsurface material sampling on Ryugu (2022)
  • Author(s): Kikuchi, S. et al. (including Hirata, N. & Kitazato, K.)
  • Journal Title: Planetary and Space Science Volume: 219 Pages: -
  • DOI: 10.1016/j.pss.2022.105519
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] A pristine record of outer Solar System materials from asteroid Ryugu’s returned sample (2022)
  • Author(s): Ito, M. et al. (including Hirata, N. & Kitazato, K.)
  • Journal Title: Nature Astronomy Volume: 6 Pages: 1163-1171
  • DOI: 10.1038/s41550-022-01745-5
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] NIRS3 spectral analysis of the artificial Omusubi-Kororin crater on Ryugu (2022)
  • Author(s): Galiano, A. et al. (including Kitazato, K.)
  • Journal Title: Monthly Notices of the Royal Astronomical Society Volume: 514 Pages: 6173-6182
  • DOI: 10.1093/mnras/stac1547
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Three-axial shape distributions of pebbles, cobbles and boulders smaller than a few meters on asteroid Ryugu (2022)
  • Author(s): Michikami, T. et al. (including Hirata, N.)
  • Journal Title: Icarus Volume: 381 Pages: -
  • DOI: 10.1016/j.icarus.2022.115007
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Presentation] Analysis of disk-resolved photometric properties of local regions on asteroid 25143 Itokawa with a pixel-oriented image DB system (2022)
  • Author(s): Hirata, N., Kitazato, K., Tatsumi, E., Sato, H. and Kikuchi, H.
  • Organizer: American Geoscience Union fall meeting 2022
  • Int'l Joint Research
• [Presentation] Simulator for formation of rubble-pile asteroids using open-source physics simulation (2022)
  • Author(s): Tsunoda, T. and Hirata, N.
  • Organizer: American Geoscience Union fall meeting 2022
  • Int'l Joint Research
• [Presentation] AiGIS2, a Jupyter Notebook-based interactive analysis and visualization tool for asteroid exploration data (2022)
  • Author(s): Nagayoshi, T. and Hirata, N.
  • Organizer: American Geoscience Union fall meeting 2022
  • Int'l Joint Research
• [Presentation] Photometric correction of Hayabusa2’s NIRS3 spectra of asteroid 162173 Ryugu using empirical photometric models (2022)
  • Author(s): Williamson, L., Takir, D., Le Corre, K., Emery, J. and Kitazato, K.
  • Organizer: AAS Division of Planetary Science meeting #54
  • Int'l Joint Research