A modified "Type I migration" model for propeller moons in Saturn's rings

TL;DR

This paper introduces a modified 'Type I migration' model explaining the non-keplerian motion of propeller moons in Saturn's rings, emphasizing radial surface density variations and angular momentum exchange.

Contribution

It presents a new mechanism based on surface density variations that accounts for propeller moon dynamics, fitting observed non-keplerian motions.

Findings

Model fits observed moon motions well

Radial surface density variations are key

Future observations can test the model

Abstract

We propose a mechanism for the observed non-keplerian motion (Tiscareno et al. 2010, ApJL) of "propeller" moons embedded in Saturn's 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, AJ), provides a good fit to the observations. Future observations should distinguish between our model and others recently proposed.