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:
Numerical simulations of Saturn's A-, B-, and C-rings were used to estimate the degree of instability prevailing among the particles that make up the rings. Although the simulations showed the C-ring to be stable, instability in the A- and B-rings created gravitational wakes. These wakes were powerful enough in the A-ring to intensify the instability by forcing the particles to accrete into meter-sized boulders. Observations of Saturn's rings support this simulation.
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Article Abstract:
The Voyager images of Jupiter show that its ring is an unstable structure and the orbits of small particles are easily perturbed. Two scientists suggest that the ring is composed of ejecta caused by small submicrometer projectiles bombarding large moonlets. The particles are mostly ionospheric photoelectrons and ions with lifetimes of less than a year, causing the ring's instability.
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