Tiscareno, M., Burns, J.A., Hedman, M.M., Porco, C.C. (2007). "The Population of Propellers in Saturn's A Ring." American Astronomical Society, DPS meeting #39, #10.05.
Saturn's main rings (particularly Ring A) are known to be composed of a distribution of icy particles ranging in size from centimeters to ~10 meters (Zebker et al 1985, Icarus). The first evidence of 'missing-link' particles larger than this size range but smaller than the km-size embedded moons (Pan and Daphnis) was announced by Tiscareno et al (2006, Nature). These intermediate-size moonlets are not directly seen, but rather the propeller-shaped disturbances they create in the ring continuum. Their sizes, subject to some ambiguities in interpretation, are probably ~100 meters.|
Subsequent high-resolution Cassini Imaging data have yielded 148 additional localized features within Ring A, of which 47 are seen to move between two images at the keplerian rate, and of which 66 are resolved as propeller-shaped. Some of these objects have also been noted by Sremcevic et al (2007). These objects are concentrated almost entirely within three narrow (~1000 km) bands in the mid-A Ring; other nearby regions are similarly free of major disturbances but contain no propellers. It is in this same region that self-gravity wakes (Hedman et al 2007, AJ) and the azimuthal brightness asymmetry (Dones et al 1993, Icarus) are at their peaks. It is unclear whether these bands are due to specific events in which a parent body broke up into the current moonlets, or whether a larger initial moonlet population has been sculpted into bands by other ring processes.
We will present further analysis of this population, including their various dimensions and inferred moonlet sizes, and discuss it in context of the overall size distribution of particles in the rings.