Dust-driven and plasma-driven currents in the inner magnetosphere of Saturn

作者：Olson J^*; Brenning N

来源：Physics of Plasmas, 2012, 19(4): 042903.

DOI：10.1063/1.3701995

General equations for dust-driven currents and current systems J(D) in magnetized plasmas are derived and, as a concrete example, applied to the E ring of Saturn at radial distances 3R(S) %26lt; R %26lt; 5R(S). An azimuthal ring current J(D,phi) acts as a current generator and is coupled to two secondary dust-driven current systems down to the ionosphere of Saturn, both rotating with the magnetospheric plasma. One of these closes across the polar cap, and the other over a limited range in latitude. These dust-driven current systems are embedded in three systems of plasma-driven currents J(p): a ring current, a cross-polar-cap current system, and an ion pickup current system. Both the J(D) and the J(p) current systems have been quantitatively assessed from a data set for the E ring of Saturn in which the unknown distribution of small dust is treated by a power law extrapolation from the known distribution of larger dust. From data on the magnetic perturbations during a crossing of the equatorial plane, an approximate constraint on the fraction of the electrons that can be trapped on the dust is derived. For this amount of electron capture, it is demonstrated that all three types of dust-driven currents are, within somewhat more than an order of magnitude, of the same strength as the corresponding types of plasma-driven currents. Considering also that both plasma and dust densities vary with the geyser activity at the south pole of Enceladus, it is concluded that both the dust-driven and the plasma-driven contributions to the current system associated with the E ring need to be retained for a complete description.

• 出版日期2012-4