  Collisions are the core agent of planet formation. In this work, we derive an
analytic description of the dynamical outcome for any collision between
gravity-dominated bodies. We conduct high-resolution 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, super-catastrophic disruption, and hit-and-run events. We derive
equations (scaling laws) to demarcate the transition between collision regimes
and to describe the size and velocity distributions of the post-collision
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.
  The analytic collision model presented in this work will significantly
improve the physics of collisions in numerical simulations of planet formation
and collisional evolution. (abstract abridged)
