DETECTION AND BEHAVIOR OF PAN WAKES IN SATURN A-RING

Six previously unseen Pan wakes are found interior and exterior to the Encke gap in Saturn's A ring, one in the Voyager 2 photopolarimeter ( PPS) stellar occultation data and five in the Voyager 1 radio science (RSS) earth occultation data. Pan orbits at the center of the Encke ga p and maintains it. Originally it was hypothesized that a wake would b e completely damped by the time it reached a longitude of 360 degrees relative to Pan. However, five of the six newly detected wakes are at longitudes in excess of 360 degrees and are a result of earlier encoun ters with Pan. The sixth is the first detection of the RSS outer Pan w ake, The new PPS inner wake is at a longitude of 389.8 degrees. The ne w RSS inner wakes are at longitudes of 519.4 degrees +/- 1.6 degrees a nd 879.4 degrees +/- 1.6 degrees. The RSS outer wakes are at longitude s of 200.6 degrees +/- 1.6 degrees, 560.6 degrees +/- 1.6 degrees, and 920.6 degrees +/- 1.6 degrees. Because of the time needed for a wake to develop after encountering Pan, the higher order wakes (longitude > 360 degrees) can be more prominent than their lower order counterparts which are superimposed at the same location. The radial dispersion be havior of the Pan wakes are characterized using a Burg autoregressive power spectral algorithm. The wake radial wavelength behavior is compa red to a simple model which ignores collisions and self-gravity, The f our wakes with longitudes below 360 degrees show an average deviation of 0-3% from the predicted wavelengths, indicative of the strength of collective effects. The detection of Pan wakes at longitudes greater t han 360 degrees demonstrates that wakes persist for much longer than o riginally hypothesized and may interact with one another, The presence and characteristics of these wakes will provide an important test of kinetic theory models. (C) 1996 Academic Press, Inc.