SECULAR RESONANCES AND THE DYNAMICS OF MARS-CROSSING AND NEAR-EARTH ASTEROIDS

We study by numerical integration the secular dynamical behavior of a sample of 32 Mars-crossing and near-Earth asteroids. We divide the pla net-crossing asteroid population into two groups, with semimajor axis a >2 AU and <2 AU. In the former region (a>2 AU), a computer-assisted analytical theory allows us to select 24 objects which are inside or c lose to the main secular resonances. The numerical computation of thei r evolution shows that the global dynamical picture is characterized b y the existence of ''fast tracks'' (strong and rapid changes in the ec centricity due to resonances) and ''slow tracks'' (random walk in semi major axis due to close approaches to the inner planets). The nu(6) se cular resonance appears to be a common and very effective fast-track m echanism. A solar collision is the most probable end-state of bodies o n the fast-track orbits, but hyperbolic ejections following Jupiter en counters are also observed. In the inner region (a<2 AU), no analytica l theory can be applied and we integrate eight orbits of NEAs which ha d shown secular trends in eccentricity and/or inclination in previous (shorter) integrations. Here also evolutions mainly affected by resona nces and by close encounters can be distinguished, although the interp lay of the two kinds of effects appears to be complex. The existence o f secular resonances in this region is pointed out for the first time, but further investigations are needed to understand their locations a nd strengths. (C) 1995 Academic Press, Inc.