ORIGIN OF MULTIKILOMETER EARTH-CROSSING AND MARS-CROSSING ASTEROIDS -A QUANTITATIVE SIMULATION

Orbital dynamic simulations show that many asteroids in the main aster oid belt are driven toward Mars-crossing orbits by numerous weak mean motion resonances, which slowly increase the orbital ellipticity of th e asteroids. In addition, half of the Mars-crossing asteroids (MCAs) t ransition to Earth-crossing asteroids (ECAs) in less than 20 million y ears. This scenario quantitatively explains the observed number of lar ge ECAs and MCAs.