Comparisons between the diverse electron radiation belts of the solar system; Implications for radiation belt studies at Earth

Recent studies have demonstrated that several different processes limit the most intense relativistic electron intensities within the diverse radiation belts in the solar system. Specifically, the most intense radiation belt intensities at Earth, Uranus and Jupiter all appear to be limited by a differential and relativistic version of the so-called Kennel-Petschek limit, which relies on strong whistler-wave-stimulated losses acting in a non-linear feedback mode through reflection of the waves back into the system. The most intense observed intensities at Netune and Saturn reside below those allowed by the Kennel-Petschek limit. At Neptune the absence of dynamic injection phenomena may be limiting the acceleration of relativistic electrons. At Saturn, scattering and absorption by dense clouds of gas and dust from the plumes of the moon Enceladus appear to be responsible for limiting radiation belt intensities. Even given this diversity of behaviors within the solar system, the substantial consistency of electron spectral behaviors within the very different magnetospheres of Earth, Jupiter, and Uranus is rather remarkable. For Earth studies, the utilization of the Kennel-Petschek limit has fallen on disfavor as some of the simplifying assumptions that have gone into that original theory have been challenged by observations, specifically of the behavior of whistler waves within Earth’s inner and middle magnetosphere. Our results suggest strongly that the Kennel-Petschek theory is robust to the diversity of magnetospheric and whistler mode behaviors and that it still has important implications for the behavior of Earth’s radiation belts.