Radiation Belts of the Outer Planets

Abstract

Planets with an intrinsic magnetic field trap and accelerate charged particles, and form radiation belts. These belts exist in a permanent interplay of different physical processes: Particles are initially provided, e.g., through erupted moon material, and accelerated to high energies, e.g., through transport into the stronger parts of the planet’s magnetic field. Particle production is countered through the removal of particles, e.g., when they hit the planet. Particle acceleration in turn is balanced through slowing the particles down again, e.g., when emitting synchrotron radiation. The balance of the involved processes determines the structure and dynamics of the various radiation belts. This presentation will discuss the processes that are currently considered as most important at Jupiter and Saturn, and illustrate them through examples. We will briefly review the current state of the relative importance of these processes, although that topic is far from being closed, even at well-explored planets. Comparison with Earth will provide context and demonstrate how some physical processes are potentially better studied at one planet than another. We will discuss some of the limited data we have for the radiation belts of the moon Ganymede, as well as the Ice Giants. While these data are far from conclusive, they reveal open questions or even mysteries that are left for future missions, such as JUICE or an Ice Giant flagship. We will discuss how the study of radiation belts also has an impact on several other fields of planetary science and, e.g., how it informs on ring structure.