of Saturn's A ring (Showalter 1991). The Encke gap is the second largest gap in the main rings (A, B, and C) and is
Six previously unseen
Pan wakes are found interior and exterior to the Encke gap in Saturn's A ring, one in the Voyager roughly 325 km wide. Pan maintains the gap, creates wavy 2 photopolarimeter (PPS) stellar occultation data and five in edges, generates wakes (quasiperiodic radial structure) in the Voyager 1 radio science (RSS) earth occultation data. Pan the ring material near the gap, and probably influences a orbits at the center of the Encke gap and maintains it. Originally noncircular kinky ringlet near the gap's center. No vertical it was hypothesized that a wake would be completely damped or horizontal resonances of known satellites fall near the by the time it reached a longitude of 360Ψ relative to Pan. gap edges to assist Pan in maintaining them. However, five of the six newly detected wakes are at longitudes Cuzzi and Scargle (1985) first suggested the existence of in excess of 360Ψ and are a result of earlier encounters with Pan. The sixth is the first detection of the RSS outer Pan wake. a satellite in the Encke gap from Voyager images, which The new PPS inner wake is at a longitude of 389.8Ψ. The showed wavy gap edges which they hypothesized were new RSS inner wakes are at longitudes of 519.4Ψ Ψ 1.6Ψ and produced by the gravitational effects of a small satellite 879.4Ψ Ψ 1.6Ψ. The RSS outer wakes are at longitudes of orbiting in the gap. Showalter et al. (1986) showed that 200.6Ψ Ψ 1.6Ψ, 560.6Ψ Ψ 1.6Ψ, and 920.6Ψ Ψ 1.6Ψ. Because of the perturbations by this still unseen satellite could also explain time needed for a wake to develop after encountering Pan, the several distinctive gravitational disturbances called wakes higher order wakes (longitude ΟΎ360Ψ) can be more prominent in the ring material beyond the gap. A wake is a radial than their lower order counterparts which are superimposed at the same location. series of slowly varying quasiperiodic maxima and minima The radial dispersion behavior of the Pan wakes are characin the optical depth that remain stationary in a reference terized using a Burg autoregressive power spectral algorithm. frame which corotates with the satellite. The inner wake The wake radial wavelength behavior is compared to a simple leads the satellite in orbital longitude and the outer wake model which ignores collisions and self-gravity. The four wakes trails it. A stationary observer above the rings would see with longitudes below 360Ψ show an average deviation of 0-3% the wakes change in wavelength and amplitude as Pan from the predicted wavelengths, indicative of the strength of moves in its orbit (Showalter et al. 1986, Borderies et al. collective effects. The detection of Pan wakes at longitudes greater than 360Ψ 1989, Stewart 1991).
demonstrates that wakes persist for much longer than originally Showalter et al. (1986) developed and applied a model to hypothesized and may interact with one another. The presence the Voyager 2 photopolarimeter (PPS) stellar occultation and characteristics of these wakes will provide an important data (Esposito et al. 1987) and the Voyager 1 radio science test of kinetic theory models.