  The so-called "Charming Ringlet" (R/2006 S3) is a low-optical-depth, dusty
ringlet located in the Laplace gap in the Cassini Division. This ringlet is
particularly interesting because its radial position varies systematically with
longitude relative to the Sun in such a way that the ringlet's geometric center
appears to be displaced away from Saturn's center in a direction roughly toward
the Sun. In other words, the ringlet is always found at greater distances from
the planet's center at longitudes near the sub-solar longitude than it is at
longitudes near Saturn's shadow. This "heliotropic" behavior indicates that the
dynamics of the particles in this ring are being influenced by solar radiation
pressure. In order to investigate this phenomenon, which has been predicted
theoretically but has never been observed this clearly, we analyze multiple
image sequences of this ringlet obtained by Cassini in order to constrain its
shape and orientation. These data can be fit reasonably well with a model in
which both the eccentricity and the inclination of the ringlet have "forced"
components (that maintain a fixed orientation relative to the Sun) as well as
"free" components (that drift around the planet at steady rates determined by
Saturn's oblateness). While the magnitude of the forced eccentricity is roughly
consistent with theoretical expectations for radiation pressure acting on
10-to-100-micron-wide icy grains, the existence of significant free
eccentricities and inclinations poses a significant challenge for models of
low-optical-depth dusty rings.
