Idealized Saturn magnetosphere shape and field

Abstract

We construct an idealized three‐dimensional model of Saturn's magnetosphere. The total magnetospheric field is a sum of three contributions; the first two contributions are internal, in the form of a planetary dipole and an equatorial ring current deduced from Voyager observations. We concentrate on the third contribution, resulting from the interaction of the solar wind with the Kronian magnetosphere. From the balance between the solar wind ram pressure and the magnetospheric pressure, we provide simultaneously models of the magnetopause and of the magnetic field due to the surface currents on the magnetopause. The resulting magnetopause has characteristics intermediate between those of analogous Earth and Jupiter magnetospheric models. A natural day‐night asymmetry arises in the total magnetospheric field. Its intensity is tested with Voyager 1 data: the third contribution improves the agreement between data and models in the outer magnetosphere. This work extends the range of a physically reliable model of Saturn's magnetosphere in latitudinal and longitudinal directions from regions where there have been observations to regions where there have not. We discuss several possible applications, particularly some relevant to the future Cassini mission.

The Cassini Magnetic Field Investigation

“…Through much of the Saturnian magnetosphere the dynamics of the system are believed to be controlled by the rotation of the planet (McNutt, 1983), with the planet appearing to enforce corotation through much of the inner regions of the magnetosphere. As material is ionised it is picked up in the corotational flow in the equatorial magnetospheric regions and rotational energy in the form of momentum is transferred from the planet to the equatorial plane.…”

“…Since the magnetised solar wind does not penetrate into the magnetosphere, currents develop on the magnetopause surface, which in turn induce a contribution to the magnetic field. The only model available to date which models the interaction of the solar wind with the Saturnian magnetosphere has been developed by Maurice and Engle (1995). This computes the size and shape of the magnetopause as well as the additional contribution to the total field from the surface currents.…”

Corotation-driven magnetosphere-ionosphere coupling currents in Saturn’s magnetosphere and their relation to the auroras

“…Axisymmetry is broken at large distances, of course, where the effects of the magnetopause and tail currents become important. However, the approximation employed here should generally be sufficient to distances ∼15-20 R S in the equatorial plane (depending, for example, on the dynamic pressure of the solar wind and the degree of extension of the magnetosphere), compared with subsolar magnetopause distances of ∼17-24 R S (Behannon et al, 1983;Maurice and Engel, 1995). As we will find below, radial distances of 15-20 R S in the equatorial plane map to the ionosphere in the co-latitude range ∼13 • -15 • in the Northern Hemisphere and ∼14 • -17 • in the south (with respect to the southern pole).…”

Modeling the Saturnian magnetosphere for the Cassini Mission

“…By superposition principles, B r j ng and Bd ipo i e add to yield the total magnetic field due to the internal magnetospheric sources. This field is displayed in Figure 2 [ Maurice and Engle, 1995]. Figure 2.…”

“…This alignment is unique to Saturn when compared to the Earth and Jupiter, and leads to the near-coincidence of the Saturaian rotational and magnetic planetary coordinate systems. The dipole field of Saturn is displayed in Figure 1 [ Maurice and Engle, 1995].…”