Radio occultations of Saturn ’ s main rings by spacecraft suggest a power law particle size-distribution down to sizes of the order of 1 cm ( ) , ( ) .
The lack of optical depth variations between ultraviolet and near-IR wavelengths indicate a lack of micron-sized particles .
Between these two regimes , the particle-size distribution is largely unknown .
A cutoff where the particle-size distribution turns over must exist , but the position and shape of it is not clear from existing studies .

Using a series of solar occultations performed by the VIMS instrument on-board Cassini in the near-infrared , we are able to measure light forward scattered by particles in the A and C rings .
With a model of diffraction by ring particles , and the previous radio work as a constraint on the slope of the particle size distribution , we estimate the minimum particle size using a truncated power-law size distribution .
The C Ring shows a minimum particle size of 4.1 ^ { +3.8 } _ { -1.3 } mm , with an assumed power law index of q = 3.1 and a maximum particle size of 10 m .

The A Ring signal shows a similar level of scattered flux , but modeling is complicated by the presence of self-gravity wakes , which violate the assumption of a homogeneous ring , and higher optical depths , which require multiple-order scattering .
If q < 3 , our A Ring model requires a minimum particle size below one millimeter ( < 0.34 mm for an assumed q = 2.75 , or 0.56 ^ { +0.35 } _ { -0.16 } mm for a steeper q = 2.9 ) to be consistent with VIMS observations .
These results might seem to contradict previous optical ( ) and infrared ( ) work , which implied that there were few particles in the A Ring smaller than 1 cm .
But , because of the shallow power law , relatively little optical depth ( between 0.03 and 0.16 in extinction , or 0.015 - 0.08 in absorption ) is provided by these particles .