| The existence of a ring current inside Saturn's magnetosphere was first
suggested by Smith et al. (1980) and Ness et al. (1981, 1982), in order to explain
various features in the magnetic field observations from the Pioneer 11 and
Voyager 1 and 2 spacecraft. Connerney et al. (1983) formalized the equatorial
current model, based on previous modelling work of Jupiter's current sheet
and estimated its parameters from the two Voyager data sets. Here, we
investigate the model further, by reconsidering the data from the two Voyager
spacecraft, as well as including the Pioneer 11 flyby data set.
First, we obtain, in closed form, an analytic expression for the magnetic
field produced by the ring current. We then fit the model to the external
field, that is the difference between the observed field and the internal
magnetic field, considering all the available data. In general, through our
global fit we obtain more accurate parameters, compared to previous models.
We point out differences between the model's parameters for the three flybys,
and also investigate possible deviations from the axial and planar symmetries
assumed in the model. We conclude that an accurate modelling of the Saturnian
disk current will require taking into account both of the temporal variations related
to the condition of the magnetosphere, as well as non-axisymmetric
contributions due to local time effects.
Key words. Magnetospheric physics (current systems; planetary
magnetospheres; plasma sheet) |