Simulations of Collisional Systems: Implementing Force Model to REBOUND

SALO H.; GIUPPONE C.; MONDINO LLERMANOS A.E.; SCHMIDT J.

Kuusamo

Congreso; Astronomy Day; 2018

Saturn?s dense rings consist of icy particles ranging in size from a few centimeters up to several meters. Furthermore, larger bodies exist in the rings with sizes of tens of meters up to kilometers, evidenced by the ?propeller?-shaped perturbations they induce on the surrounding ring material. The Cassini mission brought data in unprecedented detail monitoring the structure and properties the ring system. The dynamics of an unperturbed planetary ring consisting of macroscopic particles is basically determined by inelastic binary particle collisions and the shearing motion in the gravitational field of the central planet. Furthermore, ring self-gravity and the gravitational interaction with Saturn?s moons, exterior to or embedded in the rings, are important for the dynamics and the formation of structures in the rings. Extensive theoretical studies as well as N-body simulations have been carried out in order to understand the dynamics of planetary rings.REBOUND is an open-source multi-purpose N-body code, which was designed for collisional dynamics such as planetary rings (Rein & Liu, 2012). Its advantages are its high modularity and its full parallelization with MPI, in principle allowing realistic simulations with large number of particles. However, the treatment of impacts is in terms of instantaneous velocity changes (?hard sphere? collisions), which leads to problems if the particles do not separate after the impact. The problem becomes acute if self-gravity or cohesive forces between particles are included. Further difficulties arise for example if gravitational aggregates form. A physically motivated, computationally feasible solution, used in some earlier N-body simulations (Salo, 1995), is to include explicitly the visco-elastic forces affecting the particles in the impact (?soft sphere? collisions).We present our recent advances in implementing the force method into REBOUND code. Our aim is to use this new tool for N-body studies of propeller features in Saturn?s rings, in combination with detailed photometric modeling and comparisons to the publicly available high resolution Cassini imaging. One of our main scientific goals is to understand how propeller dimensions scale with the embedded moonlet size and the dynamical state of the background ring, and thus use them as probes of the properties of unresolved ring particles.