Abstract
Abstract. 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)
Highlights
First observations of Saturn’s magnetic field were made by the Pioneer 11 spacecraft in 1979. These observations revealed the existence of an internal magnetic field with a surprisingly small dipole tilt (< 1 degree) and with a high degree of axisymmetry (Smith et al, 1980; Acuna and Ness, 1980)
We can conclude that our global least-squares fit, using the more accurate disk model allows, in general, for a significant improvement in our knowledge of the model’s parameters, compared to previous models, which were not optimal in a least-squares sense. It appears that a single current disk model does not fit both the inbound and outbound observations well
We believe that this asymmetry reflects both a dependence on local time and on the state of the magnetospheric cavity, which is not compatible with the assumption of an axisymmetric disk
Summary
First observations of Saturn’s magnetic field were made by the Pioneer 11 spacecraft in 1979. We obtain an analytical expression for the magnetic field produced by the ring current model first proposed by Connerney et al (1981a).
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