Electron Acceleration to MeV Energies at Jupiter and Saturn

Area of Science:

• Planetary Science
• Plasma Physics
• Astrophysics

Background:

• Jupiter and Saturn possess intense radiation belts with relativistic electrons up to tens of megaelectronvolts (MeV).
• The precise mechanisms accelerating these electrons to such high energies remain incompletely understood.
• A lack of high-quality MeV electron spectra has hindered model development and validation.

Purpose of the Study:

• To derive Jupiter's MeV electron spectra using reprocessed Galileo data.
• To systematically analyze Saturn's MeV electron spectra from Cassini data.
• To investigate the dominant acceleration mechanisms for MeV electrons in the outer magnetospheres of Jupiter and Saturn.

Main Methods:

• Reprocessing Galileo orbiter data to obtain Jupiter's MeV electron spectra.
• Systematic analysis of Cassini orbiter data for Saturn's MeV electron spectra.
• Focusing analysis on regions beyond typical radiation belt levels (L > 20 for Jupiter, L > 4 for Saturn).

Main Results:

• Wave-particle interactions do not appear to be the dominant acceleration mechanism for MeV electrons in the studied regions of both magnetospheres.
• Electron acceleration is consistent with adiabatic transport, a crucial confirmation for energetic particle studies.
• Radial diffusion is suggested as the primary acceleration process for Jupiter's MeV electrons, as injections were not observed at these energies.

Conclusions:

• Adiabatic transport is confirmed as a significant mechanism for accelerating relativistic electrons in Jupiter and Saturn's magnetospheres.
• The findings challenge the dominant role of wave-particle interactions in these regions.
• Radial diffusion is identified as a likely dominant acceleration process for MeV electrons in Jupiter's magnetosphere.