Secular Resonances: Transport Mechanism to Earth—Crossing Orbits

Abstract

The population of Near—Earth Asteroids (NEAs) is composed of bodies ranging from nearly 40 km to sub—kilometer in diameter with orbits which cross those of the terrestrial planets. Though the identification of their exact birth place is still not determined, many of them have been recognized to originate in the asteroid main belt and two main dynamical mechanisms have been identified as efficient transport mechanisms to the planet—crossing regions: mean motion resonances with Jupiter and secular resonances. Mean motion resonances correspond to commensurabilities between the orbital periods of a small body and Jupiter. We refer to Moons (1997) for a detailed review of the results concerning these resonances. In this paper, we concentrate on secular resonances and we summarize the new results of recent studies (Michel et al., 1996a, b, Michel and Froeschle, 1997, Michel, 1997) which have shown that NEAs can also be transported from their current positions to other zones of the planet—crossing regions not only as a consequence of close approaches to planets but also due to the occurence of secular resonances.