  Saturn's diffuse E ring consists of many tiny (micron and sub-micron) grains
of water ice distributed between the orbits of Mimas and Titan. Various
gravitational and non-gravitational forces perturb these particles' orbits,
causing the ring's local particle density to vary noticeably with distance from
the planet, height above the ring-plane, hour angle and time. Using
remote-sensing data obtained by the Cassini spacecraft in 2005 and 2006, we
investigate the E-ring's three-dimensional structure during a time when the Sun
illuminated the rings from the south at high elevation angles (> 15 degrees).
These observations show that the ring's vertical thickness grows with distance
from Enceladus' orbit and its peak brightness density shifts from south to
north of Saturn's equator plane with increasing distance from the planet. These
data also reveal a localized depletion in particle density near Saturn's
equatorial plane around Enceladus' semi-major axis. Finally, variations are
detected in the radial brightness profile and the vertical thickness of the
ring as a function of longitude relative to the Sun. Possible physical
mechanisms and processes that may be responsible for some of these structures
include solar radiation pressure, variations in the ambient plasma, and
electromagnetic perturbations associated with Saturn's shadow.
