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Abstract
Collisions are the core agent of planet formation. In this work, we derive an analytic description of the dynamical outcome for any collision between gravitydominated bodies. We conduct highresolution simulations of collisions between planetesimals; the results are used to isolate the effects of different impact parameters on collision outcome. During growth from planetesimals to planets, collision outcomes span multiple regimes: cratering, merging, disruption, supercatastrophic disruption, and hitandrun events. We derive equations (scaling laws) to demarcate the transition between collision regimes and to describe the size and velocity distributions of the postcollision bodies. The scaling laws are used to calculate maps of collision outcomes as a function of mass ratio, impact angle, and impact velocity, and we discuss the implications of the probability of each collision regime during planet formation. Collision outcomes are described in terms of the impact conditions and the catastrophic disruption criteria, Q*RD—the specific energy required to disperse half the total colliding mass. All planet formation and collisional evolution studies have assumed that catastrophic disruption follows pure energy scaling; however, we find that catastrophic disruption follows nearly pure momentum scaling. As a result, Q*RD is strongly dependent on the impact velocity and projectiletotarget mass ratio in addition to the total mass and impact angle. To account for the impact angle, we derive the interacting mass fraction of the projectile; the outcome of a collision is dependent on the kinetic energy of the interacting mass rather than the kinetic energy of the total mass. We also introduce a new material parameter, c*, that defines the catastrophic disruption criteria between equalmass bodies in units of the specific gravitational binding energy. For a diverse range of planetesimal compositions and internal structures, c* has a value of 5 ± 2; whereas for strengthless planets, we find c* = 1.9 ± 0.3. We refer to the catastrophic disruption criteria for equalmass bodies as the principal disruption curve, which is used as the reference value in the calculation of Q*RD for any collision scenario. The analytic collision model presented in this work will significantly improve the physics of collisions in numerical simulations of planet formation and collisional evolution.
Translated title of the contribution  Collisions Between GravityDominated Bodies: 1. Outcome Regimes and Scaling Laws 

Original language  English 
Article number  79 
Journal  Astrophysical Journal 
Volume  745 
Issue number  1 
DOIs  
Publication status  Published  20 Jan 2012 
Keywords
 methods: numerical, planets and satellites: formation
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Projects
 2 Finished

Research in planetary physics, astrophysics and cosmology at Bristol
1/04/12 → 1/04/15
Project: Research
