  Kilometer-sized moonlets in Saturn's A ring create S-shaped wakes called
"propellers" in surrounding material. The Cassini spacecraft has tracked the
motions of propellers for several years and finds that they deviate from
Keplerian orbits having constant semimajor axes. The inferred orbital migration
is known to switch sign. We show using a statistical test that the time series
of orbital longitudes of the propeller Bl\'eriot is consistent with that of a
time-integrated Gaussian random walk. That is, Bl\'eriot's observed migration
pattern is consistent with being stochastic. We further show, using a
combination of analytic estimates and collisional N-body simulations, that
stochastic migration of the right magnitude to explain the Cassini observations
can be driven by encounters with ring particles 10-20 m in radius. That the
local ring mass is concentrated in decameter-sized particles is supported on
independent grounds by occultation analyses.
