A new, general model for radial transport of plasma, angular momentum and energy in the magnetospheres of Jupiter and Saturn

The magnetospheres of giant planets are governed by the interplay of these planets’ fast rotation,
the solar wind and inner plasma sources. In the Saturn and Jupiter magnetospheres, plasma is mainly
produced by the ionization of neutral gas tori at the radial location of active moons: Io at Jupiter
and Enceladus at Saturn. The mechanisms by which these moon-associated plasma sources are re-
distributed throughout these magnetospheres involve both plasma motions and magnetic flux tube
exchanges. These motions are coupled to the rotation of the planets through electric current systems
originating in the equatorial plasma disk and closing into their upper atmosphere and ionosphere.
Models of the net effects of these different mechanisms on the radial transport of plasma are needed
to adequately reproduce the observed populations of electrons and ions in the magnetospheres of giant
planets and to establish the net budgets of exchange of plasma, angular momentum and energy between
moons, magnetospheres and their host planets. Up to now, two different types of transport models
have been developed. The first type (Cowley and Bunce, 2001; Cowley et al., 2005 and following
studies) assumes an infinitely thin plasma disk with null temperature and pressure and derives the
transport of angular momentum in the magnetosphere with due account of magnetosphere-ionosphere-
thermosphere (MIT) coupling. In the second type of model (Bagenal and Delamere, 2011; Ng et al.,
2018), radial diffusion of full flux tubes with finite temperature is calculated throughout the disk,
taking into account hydrodynamical properties of the plasma and turbulent heating in the absence of
MIT coupling.
A self-consistent modelling of radial transport in the magnetosphere of giant planets requires the
unification of the two approaches into a full description of the interactions between the plasma disk
content, the magnetosphere and the ionosphere-thermosphere of the planet. In this communication,
we introduce an approach combining these two types of models to design a more general model. This
new type of model will describe radial transport of plasma, angular momentum and energy in the
Jupiter and Saturn magnetospheres taking into account both diffusive/advective plasma transport
and exchange of angular momentum with the planet’s upper atmosphere. It will be tested against
magnetosphere observations by the Juno mission at Jupiter and the Cassini mission at Saturn.