Article Abstract:
Previous models of planetary rings that regarded them as smooth and symmetric have been rendered obsolete by observations of Neptune's rings made by Voyager II in 1989. The Adam's ring, Neptune's most prominent, is characterized by longitudinal clumping along its arc. Such clumps may result from the gravitational perturbations of unseen moons, but it is not understood how these clumps resist keplerian shear and remain stable. Other observations have posed a challenge to modellers as well, but many agree that rings are young, stochastic structures.
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Article Abstract:
Hubbard and colleagues were using an occultation technique when they discovered the ring arcs of Neptune, and two models for arc confinement emerged. Goldreich and colleagues have predicted a beaded ring of regularly spaced clumps, placing constraints on the link between the corotation resonance and the number of beads. Lissauer has shown that perturbations by a moon embedded in the ring, stabilizes arcs 60 degrees away, if another moon is nearby.
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Article Abstract:
A model proposes that Jupiter's ionosphere is the main source of plasma present in its ring. The plasma density is low and it allows ultraviolet radiation from the Sun to photoionize the grains. The particles are positively charged and move toward the planet due to a gradient in the equilibrium charge distribution. The brightness distribution predicted by the model is the same as that observed.
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