Cassini Imaging of the Opposition Effect in Saturn's Rings

The cameras onboard the Cassini spacecraft have observed the opposition surge in Saturn's rings on several occasions during the orbital tour. The opposition surge is an abrupt brightening at phase angles very near zero, i.e., close to the direction of exact backscatter. Opposition surges can result from both geometric optics effects ("shadow hiding") and from physical optics phenomena ("coherent backscattering" and the "near-field effect"; see E. V. Petrova et al., Icarus, in press, 2007).

We find that the rings' surge has a narrower angular width and a smaller amplitude in the most optically thick parts of the rings. We will compare the rings' surge with that of other icy and rocky bodies in the Solar System, and will discuss the implications for the nature of the ring particles.