Turbulence in the Magnetospheres of the Outer Planets

TL;DR

This paper reviews turbulence phenomena in the magnetospheres of outer planets, highlighting differences from other space environments and summarizing observational findings, especially from Jupiter and Saturn, with implications for plasma heating.

Contribution

It provides a comprehensive overview of turbulence in outer planet magnetospheres, emphasizing the unique environment and recent spacecraft observations, and discusses the role of turbulence in plasma heating.

Findings

Turbulence in Jupiter's and Saturn's magnetospheres is well documented by spacecraft data.

Turbulent fluctuations are smaller than the background magnetic field but significant for plasma heating.

Uranus' and Neptune's magnetospheres are less understood due to limited data.

Abstract

The magnetospheres of the outer planets exhibit turbulent phenomena in an environment which is qualitatively different compared to the solar wind or the interstellar medium. The key differences are the finite sizes of the magnetospheres limited by their physical boundaries, the presence of a strong planetary background magnetic field and spatially very inhomogeneous plasma properties within the magnetospheres. Typical turbulent fluctuations possess amplitudes much smaller than the background field and are characterized by Alfv\'en times, which can be smaller than the non-linear interaction time scales. The magnetospheres of the outer planets are thus interesting laboratories of plasma turbulence. In Jupiter's and Saturn's magnetospheres, turbulence is well established thanks to the in-situ measurements by several spacecraft, in particular by the Galileo and Cassini orbiter. In contrast, the fluctuations in Uranus' and Neptune's magnetospheres are poorly understood due to the lack of sufficient data. Turbulence in the outer planets' magnetospheres have important effects on the systems as a whole. The dissipation of the turbulent fluctuations through wave-particle interaction is a significant heat source, which can explain the large magnetospheric plasma temperatures.