Small body orbital dynamics in the Solar System : celestial mechanics and impacts

Studying the orbital dynamics of small body populations in the Solar System allows us to understand both their current population and past orbital structure. Planet-crossing populations can also provide impact speeds and probabilities, and when coupled to cratering histories of solid bodies can provide planetary surface ages. The Wide-field Infrared Survey Explorer Near-Earth Object (NEOWISE) detections of the near-Earth object (NEO) orbital distributions (Mainzer et al. 2012) are used to illustrate that a pure-gravity NEO orbital model (Greenstreet et al. 2012) is not rejectable (at >99% confidence). Thus, no non-gravitational physics is required to model the NEO orbital distribution. We discovered in the NEO model numerical integrations the unexpected production of retrograde orbits from main asteroid belt sources, estimating that ~0.1% of the steady-state NEO population is on retrograde orbits. These retrograde near-Earth asteroids (NEAs) may answer two outstanding questions in the literature: the origin of two known MPC NEOs with asteroidal designations on retrograde orbits and the origin of high-strength, high-velocity meteoroids on retrograde orbits. Moving to the outer Solar System, we constructed a Centaur (a_Jupiter < a < a_Neptune) model, supplied from the transneptunian region, to estimate temporary co-orbital capture frequency and duration with the giant planets, finding that at any time 0.4% and 2.8% of the population will be Uranian and Neptunian co-orbitals, respectively. This is in agreement with the known fraction of temporary Uranian and Neptunian co-orbitals, respectively. Thus, the scattering transneptunian population provides a self-consistent external source for the unstable giant-planet co-orbitals. In addition to studying the orbital dynamics of small body populations in the Solar System, impact and cratering rates onto planetary surfaces can be determined. The upcoming New Horizons spacecraft fly-through of the Pluto system in July 2015 will provide humanity's first data for the crater populations on Pluto and its moons. In principle, absolute ages for these surfaces could be determined using the observed surface crater density. However, due to the uncertainty in how the Kuiper belt size distribution extends to small (d<100 km) projectiles, absolute ages are entirely model-dependent and thus fraught with uncertainty.