West, R.A., DiNino, D., Weiss, J., Porco, C. (2009). "Saturn's Photometric and Polarimetric Behavior 2004-2009 from Cassini ISS Images" American Astronomical Society, DPS meeting #41, #22.06.


Abstract
Images of Saturn reveal an optically thin but strongly forward-scattering and highly polarizing haze at high latitudes. This combination of properties was noted for Titan and for Jupiter's polar haze, and like Jupiter, is indicative of aggregate particles formed in the auroral region. Most latitudes do not have a high, thin 'detached' haze, but such a haze is seen over the equator. Infall from the rings might account for this layer, but that is speculative. A wave pattern on the limb at high latitude is seen in one set of eclipse images, probably due to inertia-gravity waves in the high stratosphere. Early in the mission the high northern latitudes contained much less haze than in the south. This is changing although not in a uniform way. Some northern latitudes remain as they were, and some are becoming more 'hazy' as expected from data taken about one seasonal cycle in the past. Polarization patterns are also tied to latitude bands and are not smooth. This suggests that both seasonal and non-seasonal variations contribute to changes we see, on a variety of time scales. Images in some lighting conditions reveal textural features (topography) at the tops of clouds in the upper troposphere. These features are not seen on Jupiter. Small-scale cumulus-type convective clouds are also seen, especially in the northern hemisphere. Some of these correlate well with features seen in VIMS images at longer wavelengths, suggesting that we are seeing down to a few bars pressure, or that the small-scale features extend through multiple scale heights. Albedo and contrasts of many of these features are puzzling. We have also been using these data to examine phase and emission-angle behavior to estimate the planetary bond albedo from near-UV to near-IR. This work was performed in part by the Jet Propulsion Lab, Caltech.