Shedding of dust rims in chondrule collisions in the protoplanetary disc

Philipp Umstätter, Nina Gunkelmann, Cornelis P Dullemond, Herbert M Urbassek

Monthly Notices of the Royal Astronomical Society,
Volume 483, Issue 4, 11 March 2019, Pages 4938–4948


“Dust rims covering chondrules may strongly influence their collision dynamics. We use granular-mechanics simulation to analyse in detail such collisions focusing on the bouncing (or sticking) character of the collision. For computational reasons, the simulated chondrules are smaller than in reality, ∼10μm in size. We consider collisions that occur at the same macroscopic parameters (chondrule radius R, collision velocity v⁠, dust rim thickness d, and dust rim filling factor ϕ), but lead to different results; this is caused by the different microscopic grain packing in the dust rim. Bouncing collisions are characterized by a larger loss of dust grains, and are accompanied by a considerably larger energy dissipation caused by the break-up of contacts. A detailed analysis of the energy dissipation processes during the collision reveals that most energy is dissipated in normal motion. Sliding torques help to store some of the translational kinetic energy in rotational energy, while rolling and twisting motions are negligible. Even in peripheral collisions, where only the dust rims overlap, the bouncing velocity is reduced just by a factor of 3 as compared to central collisions. Finally we present a simple model to extend our results to other chondrule parameters. It shows that the bouncing velocity decreases in proportion to the ratio of the dust rim thickness to the chondrule radius. It is concluded that collisions of dressed chondrules in weakly turbulent protoplanetary discs – with expected collision velocities of up to several tens of cms−1 – are in their majority sticking.”