Rings have recently and unexpectedly been discovered around the centaurs Chariklo  and Chiron, and the Kuiper Belt Object Haumea . Because these rings thus far have been discovered in occultation surveys, which require both favorable viewing conditions and a favorable Earth/target/star alignment, these three discoveries may hint that rings are common among Outer Solar System Small Bodies (OSBs). In an effort to understand if such rings could originate from the outward spillage of surface material, we investigate the collisional behavior of icy dust aggregates, both experimentally and numerically. Here, we present the results of Discrete Element Modeling (DEM) simulations that we have developed to compute the viscosity of multi-aggregate systems based on the mechanical properties of individual aggregates.
Our DEM simulations are based on the open-source code EsyS-particle . In a first step, we determined the internal particle properties (ESyS input parameters) that allow to mimic a range of collision and aggregate properties: coefficient of restitution, sticking threshold velocity, and pull-off force. To this purpose we use contact mechanics formalism [4,5] and calibrate our simulations against published experimental data . In a second step, we use the thus characterized simulated particles to determine their granular gas viscosity in a simulated dynamical ring environment. This is performed by determining the radial velocity gradient and shear stress inside the granular system in a shear box that simulates the environment in rings around Chariklo and Haumea. In this way, we link the particle internal mechanical properties to their collisional viscosity behavior in a ring environment.
We present our methodology and results and show how aggregate composition (ice fraction) influences their collisional viscosity in multi-particle systems.
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