Chondrule formation during planetesimal accretion

We explore the idea that most chondrules formed as a consequence of inefficient pairwise accretion, when molten or partly molten planetesimals ~30-100km diameter, similar in size, collided at velocities comparable to their two-body escape velocity ~100m/s. Although too slow to produce shocks or disrupt targets, these collisions were messy, especially after ~1Ma of dynamical excitation. In SPH simulations we find that the innermost portion of the projectile decelerates into the target, while the rest continues downrange in massive sheets. Unloading from pre-collision hydrostatic pressure P₀~1-100bar into the nebula, the melt achieves equilibrium with the surface energy of chondrule-sized droplets. Cooling is regulated post collision by the expansion of the optically thick sheets. on a timescale of hours-days. Much of the sheet rains back down onto the target to be reprocessed; the rest is dispersed.