If one discounts the eccentric shape and corresponding width variations of Uranus's narrow rings, only the Saturn and Neptune ring systems show marked azimuthal variations in ring properties. For the Neptune ring system, the primary azimuthal structure is associated with the ring arcs in the Adams ring. As discussed in Chapter 8, the Adams ring arc structure has changed substantially since the Voyager 2 encounter with Neptune in 1989. Saturn's F ring and, to a lesser extent, the G ring show azimuthal variations indicative of the possible presence of ring parent bodies. Several of the narrow rings and ringlets seem to exhibit clumpiness. The enigmatic radial spokes in the outer half of Saturn's B rings are another example of azimuthal ring structure. They will be discussed again in Section 11.6.
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