Tiscareno, M.S., Burns, J., Nicholson, P., Hedman, M., Porco, C. (2006). "Sampling Saturn's Rings with Weak Density Waves." American Astronomical Society, DDA meeting #37, #14.06.
The unprecedented clarity of Cassini images of Saturn's rings allows the detection and analysis of a number of previously unobserved density waves, which are raised at inner Lindblad resonances (ILRs) with saturnian satellites. These waves, unlike the strong waves observed by Voyager, generally have strictly linear dispersion, that is, the induced density perturbations are much smaller than the background density. This enables the measurement not only of the rings' background surface density (which we quote at much higher precision than previous authors), but also the growth and damping of a wave's amplitude.We employ a multi-step semi-automated process, based on the continuous wavelet transform, to model weak density waves observed in radial scans of Cassini images. Our results include the following:|
1) In the mid-A Ring (127,000 < r < 133,500 km), the scatter in our background surface density measurements greatly exceeds our error bars, leading us to believe that it reflects real variations. This scatter, between 30 and 50 g/cm2, is in fact somewhat smaller than that given by previous authors, but our error bars are considerably less.
2) In the inner A Ring (r < 127,000 km), by contrast, background surface density falls within a much narrower range, from 31 to 35 g/cm2 for the 7 waves we analyzed.
3) Ring viscosity, which is derived from wave damping and which yields an upper limit on vertical thickness, consistently increases from the Cassini Division outward to the Encke Gap. Meaningful upper limits on the rings' vertical thickness can be quoted in the Cassini Division (3.0 m at r~118,800 km, 4.5 m at r~120,700 km) and the inner A Ring (10 to 15 m for r < 127,000 km).