MHD simulation of magnetospheric interaction of planets and satellites.

Abstract

We used magnetohydrodynamics (MHD) as a unifying approach to global modeling of the magnetospheric interaction of several planetary bodies: the Jovian satellite Io, the Kronian satellite Titan, and the planet Mercury. The equations of ideal MHD are solved numerically using a modern higher-order Godunov-type method. These interactions involve a number of different plasma flow regimes and different types of interactions as determined by the physical properties of the objects. Io and Titan have considerable atmospheres, but no significant internal magnetic field, while Mercury has a modest magnetic moment but lacks an atmosphere. We have used available data from the space missions Galileo, Voyager 1, and Mariner 10 to constrain our numerical models, and for most cases we were able to achieve a good agreement with the measurements. For Io, our model provides an estimate of the total mass-loading rate consistent with the available measurements. We have considered the mass-loading in two different approximations---one assuming a highly conducting path between the satellite and Jovian ionosphere and another one in the absence of such a path. Our comparison with the <italic>in situ</italic> data indicates the existence of a strong electro-magnetic connection between Io and Jupiter, which agrees with the HST observations of lo's footprint in Jovian ionosphere. Depending on the position of Titan along its orbit and on solar wind parameters, Titan may be either in the solar wind or in Kronian magnetosphere; in the latter case, two different regimes of interaction are possible. We have considered these three representative cases for Titan and analyzed in detail the structure of Titan's magnetic wake for the time of Voyager 1 flyby. For Mercury we have obtained a first global picture of the planet's interaction with the solar wind. We have found solar wind conditions at which the direct interaction of the solar wind plasma with Mercury should take place. Finally, we discuss the intrinsic limitations of MHD models and propose several future modifications to our model which will allow us to attain a more precise picture for the plasma environments of planets and satellites.