Energetic Particle Acceleration and Modulation in the Heliosphere: The Role of ICMEs and Planetary Magnetospheres

This is a comprehensive review that examines Interplanetary Coronal Mass Ejections (ICMEs) as critical drivers of energetic particle dynamics across the heliosphere, influencing both solar energetic particle (SEP) acceleration at ICME-driven shocks and the modulation of galactic cosmic rays (GCRs). The interaction of these heliospheric transients with planetary magnetospheres provides a natural laboratory for studying acceleration and transport processes in complex plasma environments. Saturn’s magnetosphere, while internally dynamic, allows partial penetration of heliospheric energetic particles into the outer and middle magnetosphere, enabling indirect solar wind diagnostics and revealing ICME-induced variations such as Forbush decreases and SEP-driven transient radiation belts. In contrast, Jupiter’s much stronger and rapidly rotating magnetosphere presents a fundamentally different regime. External solar particles—particularly SEPs—encounter significant barriers to entry due to the planet’s intense magnetic field and dense, internally sourced plasma environment, limiting direct penetration into the inner magnetosphere. Instead, Jupiter sustains high-efficiency internal acceleration processes, including wave–particle interactions and rotationally driven transport. These mechanisms energize particles to MeV and, in some cases, relativistic energies, producing radiation belts and current systems that largely mask signatures of heliospheric transients. Comparative examination of these two systems provides insight into the regulation of energetic particle acceleration, transport, and modulation in strong-field planetary environments.