水星における磁気圏ー外気圏ー表層カップリングの研究

• Project/Area Number: 22KJ3187
• Project/Area Number (Other): 22J01606 (2022)
• Research Category: Grant-in-Aid for JSPS Fellows
• Allocation Type: Multi-year Fund (2023); Single-year Grants (2022)
• Section: 国内
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: Japan Aerospace EXploration Agency
• Principal Investigator: 相澤 紗絵 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, 特別研究員(PD)
• Project Period (FY): 2023-03-08 – 2024-03-31
• Project Status: Discontinued (Fiscal Year 2023)
• Budget Amount: ¥4,420,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥1,020,000); Fiscal Year 2024: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000); Fiscal Year 2023: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000); Fiscal Year 2022: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000)
• Keywords: 惑星磁気圏 / プラズマ / 数値計算 / BepiColombo / 太陽風ー惑星相互作用 / 水星磁気圏 / カップリングシステム

Outline of Research at the Start

太陽に最も近い惑星である水星は、過去の探査によって弱いながらも地球と似た固有磁場を持ち、太陽からの高速プラズマ流(太陽風)との相互作用によって小さな磁気圏を形成すること、また地球のような厚い大気は存在せず外気圏とよばれる薄い中性大気が広がっていることがわかっている。本研究では水星の地球とは異なるカップリングシステム、すなわち、太陽風ー磁気圏ー外気圏ー水星表層間の相互作用を理解することが不可欠である。本研究ではこの相互作用に数値計算とBepiColomboからの最新の科学データを用いてアプローチを行う。

Outline of Annual Research Achievements

厚い大気を持たない水星では、太陽からのプラズマ流である太陽風が惑星磁気圏（プラズマ）のみならず外気圏（中性大気）や表層（固体）と直接相互作用する環境にある。本研究は数値計算と最新のBepiColomboスイングバイデータを用いて、どのように各層が影響を及ぼし合っているかを明らかにすることを目的とし、その第一段階として太陽風プラズマー惑星磁気圏とそれらの外気圏および表層へのプラズマの降り込みについて研究を行った。数値計算では主に地表への惑星起源イオンの降り込みについて研究を行った。結果は学会等で発表済みであり、鋭意論文執筆中である。いくつか新たな計算を開発中であるがまだ中途であり、今後も開発を続けていく予定である。データ解析の観点では、BepiColomboのスイングバイの粒子データのキャリブレーションおよびデータ解析を行った。研究開始前および期間中に３回の水星フライバイが行われたが、特に第一回目のフライバイ結果から、数eVから数keVの電子およびイオンの観測を詳細に解析することにより、特に水星の朝側磁気圏において数keVのエネルギーを持つ電子が特定の周期をもって惑星表層へ降り込んでいる様子が初めて直接観測され、これらが過去のMESSENGER衛星によって観測された蛍光X線の分布とよく一致することがわかった。これらは水星の磁気圏サイクルと関連して磁気圏尾部での物理過程（ダイポラリゼーションやリコネクション）によるものであると推測される。過去の研究では磁気圏尾部での物理過程と蛍光X線分布の関係が指摘されてきたがこれまでその直接的な観測的証拠が得られておらず、史上初である。成果はNature Communicationsに発表され、各種国際学会で発表され、またプレスリリースも行った。第２回および３回のフライバイの成果は論文投稿中および解析中であり、順次発表される。

Research Products

• [Int'l Joint Research] LATMOS/IRAP(フランス)
• [Int'l Joint Research] University of Pisa(イタリア)
• [Int'l Joint Research] IRAP/LPP/LATMOS(フランス)
• [Int'l Joint Research] University of Pisa(イタリア)
• [Int'l Joint Research] University of Michigan/NASA(米国)
• [Int'l Joint Research] University of Leicester(英国)
• [Journal Article] BepiColombo observations of oxygen and carbon ions in the flank of Venus induced magnetosphere (2024)
  • Author(s): Hadid L., Delcourt D., Saito Y., Fraenz M., Yokota S, Fiethe B., Verdeil C., Katra B., Leblanc F., Fischer H., Persson M., Aizawa S, Andre N., Harada Y., Fedorov A., Fontaine D., Krupp N., Michalik H., Illiano J.-M., Berthelier J.-J., Krugger H., Murakami G., Matsuda S., Heyner D., Auster U., Richter I., Mieth J.
  • Journal Title: Nature Astronomy Volume: -
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] TARB書評:上出洋介『オーロラ 宇宙の渚をさぐる』 (2023)
  • Author(s): Aizawa Sae
  • Journal Title: Tokyo Academic Review of Books Volume: 52 Pages: 1
  • DOI: 10.52509/tarb0052
  • ISSN: 2435-5712
  • Year and Date: 2023-01-14
  • Peer Reviewed / Open Access
• [Journal Article] Influence of Solar Wind Variations on the Shapes of Venus’ Plasma Boundaries Based on Venus Express Observations (2023)
  • Author(s): Signoles C.、Persson M.、Futaana Y.、Aizawa S.、Andre N.、Bergman S.、Fedorov A.、Lindwall V.、Martinez N.、Mazelle C.、Rojas Mata S.、Wolff A.、Zhang T. L.
  • Journal Title: The Astrophysical Journal Volume: 954 Issue: 1 Pages: 95-95
  • DOI: 10.3847/1538-4357/ace7b1
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Direct evidence of substorm-related impulsive injections of electrons at Mercury (2023)
  • Author(s): Aizawa S.,Harada Y., Andre N., Saito Y., Barabash S., Delcourt D., Sauvaud J.-A., Barthe A., Fedorov A., Penou E., Yokota S., Miyake W., Persson M., Nenon Q., Rojo M., Futaana Y., Asamura K., Shimoyama M., Hadid L. Z., Fontaine D., Katra B., Fraenz M., Krupp N., Matsuda S., Murakami G.
  • Journal Title: Nature Communications Volume: 14 Issue: 1
  • DOI: 10.1038/s41467-023-39565-4
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Maps of Solar Wind Plasma Precipitation onto Mercury’s Surface: A Geographical Perspective (2023)
  • Author(s): Lavorenti Federico、Jensen Elizabeth A.、Aizawa Sae、Califano Francesco、D’Amore Mario、Domingue Deborah、Henri Pierre、Lindsay Simon、Raines Jim M.、Savin Daniel Wolf
  • Journal Title: The Planetary Science Journal Volume: 4 Issue: 9 Pages: 163-163
  • DOI: 10.3847/psj/acef15
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Forecasting Heliospheric CME Solar-Wind Parameters Using the UCSD Time-Dependent Tomography and ISEE Interplanetary Scintillation Data: The 10 March 2022 CME (2023)
  • Author(s): Jackson Bernard V.、Tokumaru Munetoshi、Iwai Kazumasa、Bracamontes Matthew T.、Buffington Andrew、Fujiki Ken’ichi、Murakami Go、Heyner Daniel、Sanchez-Cano Beatriz、Rojo Mathias、Aizawa Sae、Andre Nicolas、Barthe Alain、Penou Emmanuel、Fedorov Andrei、Sauvaud Jean-Andre、Yokota Shoichiro、Saito Yoshifumi
  • Journal Title: Solar Physics Volume: 298 Issue: 5 Pages: 74-74
  • DOI: 10.1007/s11207-023-02169-8
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] On the origins of backscattered solar wind energetic neutral hydrogen from the Moon and Mercury (2023)
  • Author(s): Leblanc F.、Deborde R.、Tramontina D.、Bringa E.、Chaufray J.Y.、Aizawa S.、Modolo R.、Morrissey L.、Woodson A.、Verkercke S.、Dukes C.
  • Journal Title: Planetary and Space Science Volume: 229 Pages: 105660-105660
  • DOI: 10.1016/j.pss.2023.105660
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Solar-wind electron precipitation on weakly magnetized bodies: The planet Mercury (2023)
  • Author(s): Lavorenti Federico、Henri Pierre、Califano Francesco、Deca Jan、Lindsay Simon、Aizawa Sae、Benkhoff Johannes
  • Journal Title: Astronomy and Astrophysics Volume: 674 Pages: A153-A153
  • DOI: 10.1051/0004-6361/202245711
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Electron moments derived from the Mercury Electron Analyzer during the cruise phase of BepiColombo (2023)
  • Author(s): M. Rojo, M. Persson, J.-A. Sauvaud, S. Aizawa, G. Nicolaou, E. Penou, A. Barthe, N. Andre, C. Mazelle, A. Fedorov, S. Yokota, Y. Saito, D. Heyner, I. Richter, U. Auster, D. Schmid, D. Fischer, T. Horbury, C.J. Owen, M. Maksimovic, Y. Khotyaintsev, P. Louarn, G. Murakami
  • Journal Title: Astronomy and Astrophysics Volume: -
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] LatHyS global hybrid simulation of the BepiColombo second Venus flyby (2022)
  • Author(s): Aizawa S.、Persson M.、Menez T.、Andre N.、Modolo R.、Genot V.、Sanchez-Cano B.、Volwerk M.、Chaufray J.-Y.、Baskevitch C.、Heyner D.、Saito Y.、Harada Y.、Leblanc F.、Barthe A.、Penou E.、Fedorov A.、Sauvaud J.-A.、Yokota S.、Auster U.、Richter I.、Mieth J.、Horbury T.S.、Louarn P.、Owen C.J.、Murakami G.
  • Journal Title: Planetary and Space Science Volume: 218 Pages: 105499-105499
  • DOI: 10.1016/j.pss.2022.105499
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] BepiColombo mission confirms stagnation region of Venus and reveals its large extend (2022)
  • Author(s): M. Persson, et al. (incl. K. Masunaga)
  • Journal Title: Nature Communications Volume: 13 Issue: 1 Pages: 7743-7743
  • DOI: 10.1038/s41467-022-35061-3
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] BepiColombo Mio Observations of Low-Energy Ions During the First Mercury Flyby: Initial Results (2022)
  • Author(s): Harada, Y., S. Aizawa, Y. Saito, N. Andre, M. Persson, D. Delcourt, L. Z. Hadid, M. Fraenz, S. Yokota, A. Fedorov, W. Miyake, E. Penou, A. Barthe, J. A. Sauvaud, B. Katra, S. Matsuda, G. Murakami
  • Journal Title: Geophys. Res. Lett. Volume: 49 Issue: 17
  • DOI: 10.1029/2022gl100279
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Dayside magnetopause reconnection and flux transfer events under radial interplanetary magnetic field (IMF): BepiColombo Earth-flyby observations (2022)
  • Author(s): Sun Weijie、Slavin James A.、Nakamura Rumi、Heyner Daniel、Trattner Karlheinz J.、Mieth Johannes Z. D.、Zhao Jiutong、Zong Qiu-Gang、Aizawa Sae、Andre Nicolas、Saito Yoshifumi
  • Journal Title: Annales Geophysicae Volume: 40 Issue: 2 Pages: 217-229
  • DOI: 10.5194/angeo-40-217-2022
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Electron dynamics in small magnetospheres (2022)
  • Author(s): Lavorenti Federico、Henri Pierre、Califano Francesco、Deca Jan、Aizawa Sae、Andre Nicolas、Benkhoff Johannes
  • Journal Title: Astronomy & Astrophysics Volume: 664 Pages: A133-A133
  • DOI: 10.1051/0004-6361/202243911
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Solar-wind-dependent streamline model for Mercury’s magnetosheath (2022)
  • Author(s): Schmid D.、Narita Y.、Plaschke F.、Volwerk M.、Nakamura R.、Baumjohann W.、Heyner D.、Pump K.、Aizawa S.
  • Journal Title: Astronomy & Astrophysics Volume: 668 Pages: A113-A113
  • DOI: 10.1051/0004-6361/202245008
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Presentation] Electron populations observed by Mercury Electron Analyzer onboard Mio/BepiColombo during its second Mercury flyby (2023)
  • Author(s): S. Aizawa
  • Organizer: European Geoscience Union General Assembly 2023
  • Int'l Joint Research
• [Presentation] Low-energy plasma observed by Mercury Plasma Particle Experiment onboard Mio/BepiColombo during its Mercury flybys (2023)
  • Author(s): S. Aizawa
  • Organizer: Asia Oceania Geoscience Society 2023
  • Int'l Joint Research / Invited
• [Presentation] Electron populations observed by Mercury Electron Analyzer onboard Mio/BepiColombo during Mercury flybys (2023)
  • Author(s): S. Aizawa
  • Organizer: Americal Geoscience Union fall meeting 2023
  • Int'l Joint Research
• [Presentation] Electron Acceleration observed by Mercury Electron Analyzer onboard Moi/BepiColombo during its second Mercury flyby (2022)
  • Author(s): Sae Aizawa
  • Organizer: AGU (American Geophysical Union) fall meeting 2022
  • Int'l Joint Research
• [Presentation] Escape and Precipitation of planetary ions at Mercury under different solar wind conditions (2022)
  • Author(s): Sae Aizawa
  • Organizer: EPSC (European Planetary Science Congress)
  • Int'l Joint Research
• [Presentation] Circulation and Escape of Planetary Ions at Mercury (2022)
  • Author(s): Sae Aizawa
  • Organizer: AOGS (Asia Oceania Geoscience Society)
  • Int'l Joint Research / Invited
• [Presentation] LatHyS hybrid simulation of the August, 10 2021 BepiColombo Venus flyby (2022)
  • Author(s): Sae Aizawa
  • Organizer: European Geoscience Union (EGU) General Assembly 2022
  • Int'l Joint Research / Invited
• [Presentation] The first simultaneous observation of low energy ions and electrons at Mercury during the first BepiColombo flyby (2022)
  • Author(s): Sae Aizawa
  • Organizer: JpGU (Japan Geoscience Union) Meeting 2022
  • Int'l Joint Research
• [Presentation] Low-energy plasma observed by MEA and MIA onboard Mio/BepiColombo during its second Mercury flyby (2022)
  • Author(s): Sae Aizawa
  • Organizer: SGEPSS (Society of Geomagnetism and Earth, Planetary and Space Sciences) meeting
• [Remarks] First BepiColombo Flyby of Mercury ...
  • URL: https://www.europlanet-society.org/first-bepicolombo-flyby-of-mercury-finds-electron-rain-triggers-x-ray-auroras/
• [Remarks] 水星へと降り込む電子を直接観測！「みお」水星スイングバイが明かす水星磁気圏
  • URL: https://www.isas.jaxa.jp/topics/003445.html
• [Remarks] 太陽風は金星大気に入り込めない！「みお」金星スイングバイが明らかにした太陽風 ― 金星圏境界構造 ―
  • URL: https://www.isas.jaxa.jp/topics/003293.html
• [Remarks] Europlanet Society news
  • URL: https://www.europlanet-society.org/bepicolombo-and-solar-orbiter-compare-notes-at-venus/