Quantifying Asymmetries in Saturn’s E Ring

Saturn’s E ring is a broad and diffuse ring extending from 180,000 to 482,000 km from the planet’s center. This ring is composed of small water ice particles launched from the moon Enceladus. The brightness of the E ring varies in complex ways with distance from the planet and longitude relative to the Sun. In particular, the sunward side of the ring appears to be persistently brighter than the side of the ring closer to Saturn’s shadow. While the orientation of these patterns indicates that forces such as solar radiation pressure are involved, it is still not clear how these asymmetries are produced and maintained. We investigate these asymmetries using images obtained by Cassini while the spacecraft flew through the planet’s shadow. Understanding the brightness variations in these images is challenging since the ring’s observed brightness depends on both the density of the particles and how light is scattered through the particles in various geometries. We remove the effects of observation geometry by comparing data obtained at the same radius and phase angle, enabling us to map out the variations in the particle density with longitude throughout the ring. We will discuss the features seen in these maps and their implications for the origins of the E ring asymmetries.