Short Dynamical Lifetimes and the Importance of Sun-grazing in the Inner Solar System

A. Morbidelli, B. Gladman (Nice Observatory), F. Migliorini (Armagh Observatory), V. Zappala (Turin Observatory), P. Michel (Nice Observatory), A. Cellino (Turin Observatory), Ch. Froeschle (Nice Observatory), H.F. Levison (SWRI, Boulder), M. Bailey (Armagh Observatory), M. Duncan (Queen's University)

To better understand the origin of NEAs and meteorites from the dynamical viewpoint, we have studied by numerical integrations the evolutions of several thousand fictitous particles originally placed in the main resonances of the asteroid belt. We have found that the global picture of their evolution is significantly different in many respects from that usually discussed in the literature. This is due to the fact that the main resonances in the asteroid belt are very efficient in pumping the eccentricities of the resonant bodies to Sun-grazing values. The dynamical timescales are very short: half of the particles `die' in only about 2 Myr, most of them colliding with the Sun. This was first understood a few years ago (Farinella et al, Nature 371, 315), but here we show with the first large scale simulations how this phenomenon dominates the dynamical evolution of most objects on Earth-crossing orbits. This new qualitative picture of how orbits coming out of the asteroid belt evolve requires a complete re-assessment of models of NEA and meteorite production.