Gaps And Noncircular Features In Saturns Rings

In the previous section, we mentioned the narrow gap at the outer edge of the B ring. There is at least one ringlet in that gap. As can be seen from Figure 9.9, the ringlet is eccentric. Multiple partial rings also exist in the Encke gap in the outer A ring, where Saturn's satellite, Pan, was discovered. In some ways, these partial rings have characteristics reminiscent of Neptune's ring arcs or the denser portions of the F ring. It is

Rarified gases in the vicinity of Saturn's rings 123 Table 9.2. Known gaps within Saturn's rings.

Ring region

Notes

C ring

Unnamed

Colombo

Maxwell

Unnamed

Unnamed

74,900 1.241

77,800 1.290

87,500 1.450

88,700 1.470

90,200 1.495

~70 Several features

184 Eccentric ringlet

270 Eccentric ringlet

<10 Opaque ringlet

20 Opaque ringlet

Cassini Division Huygens

117,820 1.953

118,200 1.959

118,300 1.960

118,600 1.966

119,000 1.972

119,900 1.988

285-440 Eccentric ringlet

Unnamed Unnamed Unnamed Unnamed Unnamed

246 Opaque ringlet

38 28 40 42

A ring

Encke Keeler

133,570 2.214 136,530 2.263

325 Several ringlets ~35

possible that narrow eccentric and/or partial rings and small satellites are characteristic of the other clear gaps in Saturn's rings. Again, the Cassini Orbiter holds the key to a number of potential discoveries and better understanding of these gap features.

There are very few clear gaps in Saturn's rings. Already mentioned are the Encke and Keeler gaps in the A ring and the Huygens gap at the inner edge of the Cassini Division. Additionally, the Maxwell gap in the C ring is a major clear gap within the rings of Saturn. Table 9.2 lists the clear gaps known prior to the arrival at Saturn of the Cassini spacecraft. The table has been adapted from table V of Cuzzi et al. [32]. Note that many of these gaps have one or more narrow, often discontinuous ringlets within them. It also seems likely that each gap has one or more moonlets within it that are in part responsible for clearing the gap. Each may additionally have narrow ringlets whose source may well be debris from the embedded moonlet. By analogy with the Encke gap, edge waves, now known to be gravitational wakes of the embedded moonlet Pan, may be present in each of the gaps.

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