Simulation of Pre-planetesimal Collisions with Smoothed Particle Hydrodynamics

In the frame of planet formation by coagulation the growth step from millimetre-sized highly porous dust aggregates to massive kilometre-sized planetesimals is not well constrained. In this regime of pre-planetesimals, collisional growth is endangered by disruptive collisions or mutual rebound and compaction. Both obstacles are addressed in our work. Since laboratory studies of pre-planetesimal collisions are infeasible beyond centimetre-size, we developed a numerical smoothed particle hydrodynamics (SPH) porosity model, which was implemented into the parallel SPH code parasph and calibrated with laboratory benchmark experiments. We summarise the porosity model and a new classification scheme for pre-planetesimal outcome: four-population model. Utilising these tools in parameter studies of two-body collisions, we find that aggregate porosity, size ratio of the collision partners, and compacted shells around the aggregates significantly influence the collision outcome and fragmentation velocity thresholds. We also develop an inhomogeneity damage model and demonstrate that inhomogeneous aggregates, generated e.g. by subsequent collisions, are weaker and more prone to catastrophic disruption.