The near-earth object population

We examine the dynamics of a sample of 117 near-Earth objects (NEOs) over a time scale of 60 Myr. We find that while 10-20% end their lifetimes by str iking a terrestrial planet (usually Venus or Earth), more than half end the ir lives in a Sun-grazing state, and about 15% are ejected from the Solar S ystem. The median lifetime of our (biased) sample is about 10 Myr. We discu ss the exchange of these objects between the various orbital classes and ob serve the creation of orbits entirely interior to that of Earth. A variety of resonant processes operating in the inner Solar System, while not domina nt in determining the dynamical lifetimes, are crucial for understanding th e orbital distribution. Several dynamical mechanisms exist which are capabl e of significantly increasing orbital eccentricities and inclinations. In p articular, we exhibit important new routes to the Sun-grazing end-state, pr ovided by the nu(5) and nu(2) secular resonances at high eccentricity betwe en a = 1.3 and 1.9 AU. We find no dynamical reason to demand that any signi ficant component of the NEO population must come from a cometary source, al though such a contribution cannot be ruled out by this work. (C) 2000 Acade mic Press.