Granular physics in low‐gravity environments using discrete element method

Granular materials of different sizes are present on the surface of several atmosphereless Solar system bodies. The phenomena related to granular materials have been studied in the framework of the discipline called granular physics, both experimentally and, over the last few decades, by numerical simulations. The discrete element method simulates the mechanical behaviour of a medium formed by a set of particles which interact through their contact points. The difficulty in reproducing vacuum and low‐gravity environments makes numerical simulations the most promising technique in the study of granular media under these conditions. In this work, relevant processes in minor bodies of the Solar system are studied using the discrete element method. Results of simulations of size segregation in low‐gravity environments in the cases of the asteroids Eros and Itokawa are presented. The segregation of particles with different densities was analysed, in particular, the case of comet P/Hartley 2. The surface shaking in these different gravity environments could produce the ejection of particles from the surface at very low relative velocities. The shaking causing the above processes is due to impacts and explosions such as the release of energy by the liberation of internal stresses or the re‐accommodation of material. Simulations of the passage of impact‐induced seismic waves through a granular medium were also performed. We present several applications of the discrete element methods for the study of the physical evolution of agglomerates of rocks under low‐gravity environments.