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What causes gaps in Saturnās rings?
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Saturn
Saturn and its spectacular rings, in a natural-color composite of 126 images taken by the Cassini spacecraft on October 6, 2004. The view is directed toward Saturn's southern hemisphere, which is tipped toward the Sun. Shadows cast by the rings are visible against the bluish northern hemisphere, while the planet's shadow is projected on the rings to the left.
Gaps in Saturnās rings are primarily caused by the gravitational influence of moons and orbital resonances.1
- Gravitational Clearing by Moons: Small moons, such as Pan and Daphnis, orbit within specific gaps (like the Encke and Keeler gaps, respectively). These moons clear particles from their immediate vicinity through their gravitational pull.1
- Orbital Resonances: A gap can form when ring particles are in an orbital resonance with a moonāmeaning the orbital periods of the moon and the particles are in a ratio of small whole numbers. In these cases, the moon exerts periodic gravitational "shoves" on the particles. If the resonance is strong enough, these perturbations build up over time, forcing the particles out of that region and clearing a gap.1
For example, the inner edge of the Cassini division is sculpted by a 2:1 resonance with the moon Mimas, where the moon completes one orbit for every two orbits of the ring particles at that location. While many gaps are explained by these mechanisms, the complex structure of the rings remains a subject of ongoing scientific study.1