Fate of the runner in hit-and-run collisions

In similar-sized planetary collisions, a significant part of the impactor often misses the target and continues downrange. We follow the dynamical evolution of "runners" from giant impacts to determine their ultimate fate. Surprisingly, runners re-impact their target planets only about half of the time, for realistic collisional and dynamical scenarios. Otherwise they remain in orbit for tens of millions of years (the limit of our N-body calculations) and longer, or sometimes collide with a different planet than the first one. When the runner does return to collide again with the same arget planet, its impact velocity is mainly constrained by the outcome of the prior collision. Impact angle and orientation, however, are unconstrained by the prior collision.Comment: 24 pages, 14 figures, 4 tables, accepted for publication in Ap

Catastrophic disruptions revisited

We use a smooth particle hydrodynamics method (SPH) to simulate colliding rocky and icy bodies from cm-scale to hundreds of km in diameter, in an effort to define self-consistently the threshold for catastrophic disruption. Unlike previous efforts, this analysis incorporates the combined effects of material strength (using a brittle fragmentation model) and self-gravitation, thereby providing results in the ``strength regime'' and the ``gravity regime'', and in between. In each case, the structural properties of the largest remnant are examined.Comment: To appear in Icaru

Global Scale Impacts

Global scale impacts modify the physical or thermal state of a substantial fraction of a target asteroid. Specific effects include accretion, family formation, reshaping, mixing and layering, shock and frictional heating, fragmentation, material compaction, dilatation, stripping of mantle and crust, and seismic degradation. Deciphering the complicated record of global scale impacts, in asteroids and meteorites, will lead us to understand the original planet-forming process and its resultant populations, and their evolution in time as collisions became faster and fewer. We provide a brief overview of these ideas, and an introduction to models.Comment: A chapter for Asteroids IV, a new volume in the Space Science Series, University of Arizona Press (Patrick Michel, Francesca E. DeMeo, William F. Bottke, Eds.

Impact processes in the Solar System: New understandings through numerical modeling

A collision of two rocky objects circling the sun in space, each roughly the size and mass of a large mountain range, was modeled. A fragmentation hydrocode was developed to perform dynamical computations of collisional outcomes. Explosive framentation and fluid dynamics were used and drawn together into a single application. To model a solid, certain material parameters, such as density, elasticity, rigidity, and energies of melting and vaporization were input. These parameters are well-known for a variety of important materials, such as ice, iron, granite, and basalt. Another important parameter used is the distribution of initial flaws within the material

Collisional Formation and Modeling of Asteroid Families

In the last decade, thanks to the development of sophisticated numerical codes, major breakthroughs have been achieved in our understanding of the formation of asteroid families by catastrophic disruption of large parent bodies. In this review, we describe numerical simulations of asteroid collisions that reproduced the main properties of families, accounting for both the fragmentation of an asteroid at the time of impact and the subsequent gravitational interactions of the generated fragments. The simulations demonstrate that the catastrophic disruption of bodies larger than a few hundred meters in diameter leads to the formation of large aggregates due to gravitational reaccumulation of smaller fragments, which helps explain the presence of large members within asteroid families. Thus, for the first time, numerical simulations successfully reproduced the sizes and ejection velocities of members of representative families. Moreover, the simulations provide constraints on the family dynamical histories and on the possible internal structure of family members and their parent bodies.Comment: Chapter to appear in the (University of Arizona Press) Space Science Series Book: Asteroids I