Analyzing Bleriot's propeller gaps in Cassini NAC images

Abstract: Among the great discoveries of the Cassini mission are the propeller-shaped structures created by small moonlets embedded in Saturn's dense rings. We analyze images of the sunlit side of Saturn's outer A ring, which show the propeller Bleriot with clearly visible partial propeller gaps. By determining radial brightness profiles at different azimuthal locations, we obtain the evolution of the gap minimum downstream of the moonlet. From the radial separation of the partial propeller gaps we estimate the Hill radius of Bleriot to be about 400m. Further, we fit the analytic solution from Sremcevic et al. (2002) describing the azimuthal evolution of the surface mass density in the propeller gap region to the azimuthal gap evolution obtained from Cassini images. From these fits, we estimate a kinematic shear viscosity in the range of 60 cm$^2$/s to 100 cm$^2$/s in Bleriot's ring region. These values are consistent with the parametrization given by Daisaka et al. (2001) and agree well with values estimated for the Encke gap edge (Tajeddine et al. 2017; Graetz et al. 2018).