Ring particles in the mm to cm range: Coefficients of restitution and viscosity

In this work, we are interested in understanding better how rings can form and evolve around small bodies in the outer Solar System, in particular Centaurs [1,2] and dwarf planets [3]. To this end, we are studying the properties of ring particles experimentally and how they influence the collisional viscosity of numerical multi-particle systems.

We present laboratory work in which we measure the coefficient of restitution of particles and aggregates of particles at speeds of a few 10 cm/s and below. Combining our laboratory microgravity data with published flight data, a picture emerges of coefficients of restitution that are not dependent of the collision speed, unlike concluded from former experiments [4,5]. Instead, the coefficients of restitution show a normal distribution around a mean with a standard deviation significantly increasing towards lower collision speeds.

In order to understand the effects of such coefficients of restitution on the collisional viscosity of multi-particle systems, we set up DEM simulations using the open-source code EsyS-particle [6]. We used contact mechanics formalism [7,8] in order to mimic a range of collision and aggregate properties: coefficient of restitution, sticking threshold velocity, and pull-off force. We then determined the granular gas viscosity of various sets of simulated particles in a dynamical ring environment resembling Chariklo and Haumea’s detected rings. We present how particle properties and speed-constant coefficients of restitution influence ring viscosity and evolution.

[1] Braga-Ribas, Felipe, et al., Nature 508.7494 (2014): 72-75.

[2] Ortiz, J. L., et al., Astronomy & Astrophysics 576 (2015): A18.

[3] Ortiz, J. L., et al., Nature 550.7675 (2017): 219-223.

[4] Bridges, F. G., et al., Nature 309.5966 (1984): 333-335.

[5] Hatzes, A.P., et al., Monthly Notices of the Royal Astronomical Society 231.4 (1988): 1091-1115.

[6] Weatherley, D. K., et al., 2010 IEEE Sixth International Conference on e-Science. IEEE (2010)

[7] Chokshi, A., Tielens, A., and Hollenbach, D., The Astrophysical Journal 407 (1993): 806-819.

[8] Thornton, C., and Ning, Z., Powder technology 99, no. 2 (1998): 154-162.