Numerous Weak Resonances Drive Asteroids towardTerrestrial Planets Orbits

A systematic exploration of the chaotic structure of the asteroid belt is presented, first taking into account only the perturbations provided by the four giant planets and then including also the effects of the inner planets. We find that both the inner belt (a< 2.5 AU) and the outer part of the main belt (a> 2.8 AU) are mostly chaotic. In the outer part of the belt, chaos is due to the presence of numerous mean-motion resonances with Jupiter and threebody resonances, Jupiter–Saturn–asteroid. In the inner belt, chaos is generated by mean motion resonances with Mars and three-body resonances, Mars–Jupiter–asteroid. Due to the chaoticity of the belt, asteroids tend to slowly migrate in eccentricity. This phenomenon of “chaotic diffusion” allows many bodies in the inner belt to become Mars-crossers. The number of asteroids leaking out from the inner belt is large enough to keep the population of Mars-crossing asteroids in steady state, despite of the short dynamical lifetime of the latter (∼25 Myr). We speculate that chaotic diffusion could have substantially eroded the high-eccentricity part of the asteroid belt, thus providing the impactors responsible for the Late Heavy Bombardment phase of the early Solar System. c © 1999 Academic Press