THE ORBITAL EVOLUTION OF NEAR-EARTH ASTEROID-3753

Asteroid 3753 (1986 TO) is in a 1:1 mean motion resonance with Earth, on a complex horseshoe-type orbit. Numerical experiments are performed to determine its medium-term stability and the means by which it may have entered its current orbit. Though 3753 moves primarily under the influence of the Sun and Earth, the giant planets (and Jupiter especia lly) play an important role by influencing, through torque-induced pre cession, the position of the asteroid's nodes. Variations in the nodal distance strongly affect the interaction of 3753 with Earth and may c hange or destroy the horseshoe-like behavior currently seen. This prec ession of the nodes provides a mechanism for placing minor planets int o, or removing them from, a variety of horseshoe-type orbits. The chao tic nature of this asteroid's orbit makes predictions difficult on tim escales longer than its Lyapunov time (similar to 150 yr); therefore, ensembles of particles on orbits near that of 3753 are considered. The asteroid has a high probability of passing close to Venus and/or Mars on 10(4) yr timescales, pointing to a dynamical age much shorter than that of the solar system.