AN ABSOLUTE RADIUS SCALE FOR SATURNS RINGS

Radio and stellar occultation observations of Saturn's rings made by the Voyager spacecraft provide the most precise geometric framework for studies of ring structure and dynamics. Comparisons of published Voyager occultation data, however, reveal systematic discrepancies of almost 10 km in some parts of the rings, limiting those investigations which either require accurate absolute radii, or depend on the comparison of these datasets. We present a revised solution for Saturn's rotation pole (αP = 38.4107 ± 0.0102°, δP = 83.32352 ± 0.00033°, epoch 1950.0), which, while only slightly different from that previously derived by Simpson et al. (1983) removes the remaining systematic discrepancies between the stellar and radio occultation profiles. Our solution yields rms radius residuals of ∼1 km between well-defined features in the diffraction-corrected Voyager 1 radio occultation data and the Voyager 2 Photopolarimeter stellar occultation data, and should have an absolute accuracy of ∼2 km, limited chiefly by uncertainties in the spacecraft trajectories. An examination of spiral density waves in the outer A Ring supports our claim that the revised absolute radii are in error by no more than 2 km. Corrections to previously published radii vary from -2 to -10 km for the radio occultation, and +5 to -6 km for the stellar occultation. Simple polynomial expressions are provided to effect these corrections.