First observations of the Phoebe ring in optical light

Abstract

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.

Accepted for publication in Icarus

References in corpus (1)

• Irregular Satellites of the Planets: Products of Capture in the Early Solar System

Cited by in corpus (5)

• Red material on the large moons of Uranus: Dust from irregular satellites?
• Fundamental limits from chaos on instability time predictions in compact planetary systems
• Cladistical analysis of the Jovian and Saturnian satellite systems
• Radial profiles of the Phoebe ring, a vast debris disk around Saturn
• Direct Imaging of Irregular Satellite Disks in Scattered Light