Science Seminars

Particle Acceleration and Deceleration at the Giant Planets

Speaker: Peter Kollmann (JHUAPL)
Date: Thursday, May 13, 2021
Time: 4:00 PM
Location: Zoom

Seminar Abstract:

Several radiation belt processes are more straightforward to study at the Giant Planets compared to the Earth – some processes because there is less ambiguity with competing processes, others because they only play a minor role at the Earth. Electron spectra at Jupiter and Saturn, measured by the Galileo and Cassini mission, show sharp cutoffs in the MeV energy range. These features can be robustly traced throughout planetary
magnetospheres, relatively independent of the magnetospheric dynamics. We find that the relation between cutoff energy and distance to the planet is consistent with adiabatic heating, at least at large planetary distances. It was also demonstrated that acceleration at smaller distances might occur locally through wave-particle interaction. These two findings suggests that giant magnetospheres spatially un-mix regions where local and adiabatic acceleration take place, allowing to study these processes with less ambiguity than in smaller magnetospheres.
Giant planet magnetospheres are surrounded by rings and gas tori produced by geologically active moons. This material means that not only acceleration but also deceleration occurs in Giant Planet radiation belts. Energetic particles passing through neutral material in the equatorial plane ionize it and lose energy in the process. This is most notable for the innermost ion radiation belt of Jupiter that was recently sampled by the Juno mission. Adiabatically heated protons, oxygen, and sulfur ions are decelerated in this belt through interaction with Jupiter’s ring halo, turning the initially peaked spectrum into a power law.