Charged dust in Saturn's magnetosphere

Abstract

Gravito‐electrodynamic theory of charged dust grains is used to explain a variety of phenomena in those portions of the Saturnian ring system that are known to be dominated by fine (micron and submicron‐sized) dust, and in which collisional forces and Coulomb drag can be neglected. Among the phenomena discussed are the formation and evolution of the rotating near‐radial spokes in the B‐ring, the formation of waves in the F‐ring, the cause of eccentricities of certain isolated ringlets, and the origin and morphology of the broad diffuse E‐ring. Several novel processes predicted by the gravito‐electrodynamic theory, including ‘magneto‐gravitational capture’ of exogenic dust by the magnetosphere, ‘1:1 magneto‐gravitational orbital resonances’ of charged dust with nearby satellites, and ‘gyro‐orbital resonances,’ are used to explain individual observations. The effect of a ring current associated with this charged dust is also evaluated. Finally, the cosmogonic implications of the magneto‐gravitational theory are briefly discussed. While several (although not all) of these processes have been discussed by one or more of the present authors elsewhere, the purpose of this paper is to synthesize all these processes within the framework of gravito‐electrodynamics, and also to show its range of applicability within Saturn's ring system.

Dusty plasma effects in Saturn's magnetosphere

“…The field lines threading the B ring of Saturn arise from much lower latitudes (40°–45°), so the question of how double layers are generated there remains, since it is generally believed that field‐aligned currents are necessary for their formation. Mendis et al [1983] speculated that the answer may perhaps lie in the recognition that the dust ring current (which is due to relative azimuthal motion of the charged ring particulates and the surrounding plasma) is diurnally modulated by Saturn's shadow, as discussed by Ip and Mendis [1983]. The continuity of the current then necessitates field‐aligned currents (which close through the nighttime ionosphere) to flow near the dawn and dusk terminators.…”

“…There are also two different models for the evolution of the spokes to their characteristic wedge shape. In one scenario [ Hill and Mendis , 1982; Mendis et al , 1983] a radial dust streak will eventually evolve into a wedge simply because of the variation of the charge‐to‐mass ratio of the levitated dust particles; those with the lowest specific charge move close to the Kepler speed (and form the slanted edge), while those with the highest specific charge move close to the corotation speed (and form the near‐radial edge).…”

Stability of Halo Orbits

“…Implications for the Cassini mission to Saturn are discussed. PACS numbers: 96.30.Wr, 45.50.Jf, 96.35.Kx With the Cassini spacecraft on route to Saturn to perform detailed in situ measurements of charged dust grains, it is important to understand the nonlinear dynamics of their orbital motion [1][2][3][4][5][6][7]. We report here a complete equilibrium and stability analysis for charged dust grains of arbitrary position and velocity about an axisymmetric planet.…”

Measurement of net electric charge and dipole moment of dust aggregates in a complex plasma

“…The particle electrostatic charge and dipole moment are two of the most important parameters which * Electronic address: Raziyeh˙Yousefi@baylor.edu † Electronic address: Jorge˙Carmona˙Reyes@baylor.edu ‡ Electronic address: Lorin˙Matthews@baylor.edu § Electronic address: Truell˙Hyde@baylor.edu help define the dusty plasma since they determine both the particle interactions with themselves as well as with the plasma particles and existing electromagnetic fields. Grains in a plasma environment often attain charges sufficiently large that they are equally affected by local electrical and gravitational fields [8,9]. One method for calculating the charge of isolated dust grains in a Maxwellian plasma is orbital-motion limited (OML) theory, which has been applied to spherical dust grains [10,11], cylindrical dust particles [12] and less symmetric isolated particles using a non-spherical probe [13].…”