  The Phoebe ring, Saturn's largest and faintest ring, lies far beyond the
planet's well-known main rings. It is primarily sourced by collisions with
Saturn's largest irregular satellite Phoebe, perhaps through stochastic
macroscopic collisions, or through more steady micrometeoroid bombardment. The
ring was discovered with the Spitzer Space Telescope at 24 $\mu$m and has a
normal optical depth of $\sim 2 \times 10^{-8}$ (Verbiscer et al. 2009). We
report the first observations of sunlight scattered off the Phoebe ring using
the Cassini spacecraft's ISS camera at optical wavelengths. We find that
material between $\approx 130-210$ Saturnian radii ($R_S$) from the planet
produces an I/F of $1.7 \pm 0.1 \times 10^{-11}$ per $R_S$ of the line-of-sight
distance through the disk. Combining our measurements with the Spitzer infrared
data, we can place constraints on the ring-particles' light-scattering
properties. Depending on the particles' assumed phase function, the derived
single-scattering albedo can match either photometric models of Phoebe's dark
regolith or brighter sub-surface material excavated by macroscopic impacts on
Phoebe.
