Collision and tidal interaction between planetesimals

Evolution of two encountering planetesimals in the solar gravitational field is simulated using a 3D smoothed-particle hydrodynamics code in order to obtain the precise coalescence probability including the effects of tidal forces and shock compression on two-body interaction, one of the elementary processes in planetary accumulation. The enlargement factor of the coalescence radius takes its maximum value of 1.7 when the two bodies have uniform density distributions and zero initial relative velocity. The factor decreases with increases in central mass concentration and/or in initial relative velocity. In the cases with initial velocity exceeding 0.5 x their escape velocity, the tidal enhancement of coalescence radius cannot be expected. The amount of escaping mass from the merger after collision is less than a few percent of the total mass in the cases with initial velocities lower than the escape velocity.