Saturn ring-plane crossing, May 1995: Pole precession and ring thickness

On 22 May 1995, as the Earth crossed through Saturn's ring-plane, we used the Wide Field Planetary Camera 2 on the Hubble Space Telescope to image Saturn and its rings for 10 hr centered near the predicted time of ring-plane crossing. By performing photometry on the rings, we find that the time of ring-plane crossing is later than the nominal predicted time, suggesting that Saturn's pole is precessing at a rate somewhat slower than is predicted for a rigid body under the influence of torques from the Sun and Saturn's satellites and/or that Saturn's pole position is different from the nominal position. We determine the equivalent thickness of the rings to be 1.4 +/- 0.1 km, and find that the measured value corresponds to the amplitude of perturbations from the Laplace plane warp and satellite-induced bending waves. (C) 1997 Academic Press.