Global Modeling of the Space Environments of Jupiter and Saturn

At orbital distances of 5 AU and beyond, the low solar wind dynamic pressure and weak interplanetary magnetic field (down by an order of magnitude or more relative to values near Earth) interact with the strong planetary magnetic fields of the rapidly rotating giant planets, Jupiter and Saturn, to create magnetospheres that dwarf Earth’s magnetosphere. At Earth, the global configuration and dynamics of the magnetosphere are controlled primarily by the interaction with the external solar wind. In contrast, at Jupiter and Saturn, although the form of the magnetospheric cavity is still the result of solar wind stresses, many properties of the two magnetospheres are determined largely by internal processes associated with the planets’ rapid rotation and the stresses arising from internal plasma sources associated with their moons (Io in the case of Jupiter, and, Enceladus in the case of Saturn). Coupling between the ionospheres of these rapidly rotating planets and their magnetospheres through electric currents plays a vital role in determining the global configuration and dynamics of the magnetosphere. As for Earth, global magnetohydrodynamic (MHD) models have been extensively applied to the two gas giants to understand the large-scale behavior of the solar wind-magnetosphere-ionosphere interaction, such as the magnetosphere-ionosphere coupling, global plasma convection and current systems. These simulation models provide global context for interpreting and linking measurements obtained in various parts of the coupled system, thereby extending our knowledge of the space environment beyond that available from localized spacecraft observations. In this presentation, we first review recent advances in global MHD modeling of the magnetospheres of Jupiter and Saturn. We then use the BATSRUS global MHD model of Saturn’s magnetosphere as an example to illustrate how localized structures in the ionosphere could impose global effects on the entire magnetosphere. In particular, we discuss model results that offer valuable insight into the physical processes that drive the ubiquitous periodic modulations of particles and fields properties observed in Saturn’s magnetosphere