Collisions between ice-covered silica grains: An atomistic study
ML Nietiadi and Y Rosandi and HM Urbassek, ICARUS, 352, 113996 (2020).
We use molecular dynamics simulation to study collisions of silica grains covered by an ice mantle. Such heterogeneous particles may belong to debris disks of planetary systems below the snow line. For hydroxylated silica spheres, our results of the bouncing velocity obtained for mu m-sized grains extrapolate well to experimental results for gm-sized particles. However, with increasing thickness of the ice mantle, the bouncing velocity strongly increases while the coefficient of restitution is reduced, meaning that the inelastic losses increase. An analysis of the processes occurring during the collision of two core- mantle grains shows that the ice mantle in the collision zone is strongly heated during the collision-induced compression. Temperatures surpass the triple point of water such that the ice may melt and become soft enough to yield sideways during the collision, dissipating collision energy. The ice thus acts both as a 'cushion' to soften the collision dynamics and as a glue to bind the two grains together. As a consequence of the energy dissipation, the bouncing velocity increases with increasing mantle thickness. The consequences of our findings on collisions of larger ice-coated grains are discussed. We conclude that collision-induced heating constitutes an important process in the collision of ice-covered grains, since it changes the collision physics from a 'dry' to a 'wet' contact.
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