A modified “Type I migration” model for propeller moons in Saturnʹs rings

We propose a mechanism for the observed non-keplerian motion (Tiscareno et al., 2010a) of “propeller” moons embedded in Saturnʹs rings. Our mechanism, in which radial variations in surface density – external to, and unaffected by, the embedded moon – result in an equilibrium semimajor axis for the moon due to “Type I” angular momentum exchange (Crida et al., 2010), provides a good fit to the observations. Future observations should distinguish between our model and others recently proposed.