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 reimpact 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 they sometimes collide with a different planet than the first one. When the runner does return to collide again with the same target 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.