Roles of heliospheric boundaries in acceleration and transport of cosmic rays

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K03953
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: Kyushu University
• Principal Investigator: Matsukiyo Shuichi 九州大学, 総合理工学研究院, 准教授 (00380709)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 太陽圏境界 / 宇宙線 / 粒子加速・輸送 / 微物理特性 / MHD計算 / フル粒子計算 / テスト粒子計算

Outline of Final Research Achievements

Our research aimed to unravel the mechanisms of acceleration and transport of cosmic rays observed on Earth by focusing on the two crucial roles played by the heliospheric boundary. The first role is that of a fortress preventing the entering of cosmic rays from the external environment. We combined magnetohydrodynamic simulations and test particle calculations, to investigate this aspect. Through this approach, we successfully revealed the behavior of cosmic ray particles at the level of particle trajectories within the vast heliosphere for the first time.

The second role is that of a cosmic ray accelerator within the heliospheric boundary. We specifically focused on the anomalous cosmic rays believed to be generated at an important boundary structure known as the termination shock. By employing first-principles full particle simulations, we reproduced the termination shock and elucidated the relationship between its microstructure and particle acceleration.

Free Research Field

宇宙プラズマ物理学、宇宙流体環境学

Academic Significance and Societal Importance of the Research Achievements

太陽圏境界は米国のボイジャー探査機が今世紀に入って初めて直接探査に成功した。宇宙線の生成や輸送は、生命進化や惑星の気候変動にも重要な役割を果たすと考えられているものの、その詳細はほとんど不明なため、研究の進展への期待が大きい。宇宙線がどのようにして複雑な太陽圏内部を旅して地球にやってくるのか、どのような条件で終端衝撃波での加速機構が発現するのか、本研究では従来のモデルの制限を超えて粒子軌道レベルでの解明に取り組んだ。ボイジャーは広大な太陽圏境界をたった2本の経路上で探査したにすぎないため、本研究のような数値実験によるアプローチが本質的に重要で、ここで得た知見が次世代の探査計画にも生かされる。