Merging Criteria for Planetesimal Collisions

TL;DR

This study investigates the conditions under which planetesimals merge or collide in planet formation, using simulations to determine critical impact velocities based on impact parameters and compositions.

Contribution

It provides new merging criteria for planetesimal collisions derived from detailed SPH simulations, considering various impact parameters and compositions.

Findings

Critical impact velocity decreases with increasing impact angle.

Critical impact velocity is independent of total mass.

Weak dependence of critical velocity on mass ratio.

Abstract

In the standard scenario of planet formation, terrestrial planets, ice giants, and cores of gas giants are formed by the accumulation of planetesimals. However, there are few N-body simulation studies of planetesimal accretion that correctly take into account the merging condition of planetesimals. In order to investigate a realistic accretion process of planetesimals, it is necessary to clarify the merging criteria of planetesimals at collision. We perform numerical collision experiments using smoothed particle hydrodynamics and obtain the merging criteria as a function of planetesimal mass and impact parameters for undifferentiated rocky and icy planetesimals and differentiated icy planetesimals. We vary the total mass of colliding planetesimals, their mass ratios, and the impact angle and obtain the critical impact velocity as the merging criteria distinguishing merging from hit-and-run collision. We find that the critical impact velocity normalized by the two-body surface escape velocity decreases with increasing impact angle. The critical impact velocity does not depend on the total mass, while it has a weak positive dependence on the mass ratio. These results barely depend on the composition and internal structure of the planetesimals.