Plasma transport and dynamics in the Saturn and Jupiter magnetospheres: What’s true, what isn’t and what’s been missed

Galileo, Cassini and Juno space missions have provided much data on gas giant magnetospheres. Here we examine the important commonalities of the two systems that also characterise the differences to the plasma environment of the inner planets. Both systems are fast rotators and have internal sources of magnetospheric material deep within the system. The internal sources means there must be a system for transport of material outward. Commonly, marginally stable interchange motions of flux tubes are invoked to provide diffusion on relatively small scales transverse to the field. This no doubt occurs near the source but processes like self-organisation may lead to more ordered motion at larger distances. A large distinction between Jupiter and Saturn systems is that the jovian planetary magnetic field is far from axially symmetric with respect to the planetary rotation axis whereas Saturn’s field is close to axially symmetric. However, despite this, the Saturn system does exhibit variable periodicities in plasma, radio, aurora and the external magnetic field around 10.7 hours. The external magnetic source was a surprise; the ubiquitous Saturn oscillations are still described as “mysterious”. No similar oscillations are recorded at Jupiter. We shall aim to remove some of the mystery and suggest that the dynamical effect of rotation has not been fully appreciated in either system.