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P. Michel (Torino Obs.), F. Migliorini (Torino Obs.), A. Morbidelli (Nice Obs.), V. Zappala (Torino Obs.)
Recent dynamical results have pointed out that the bodies injected by collisions into the main resonances of the asteroid belt could difficultly sustain the observed population of Earth--crossers of large diameter. Another origin for these last bodies could come from the Mars--crosser population. Concerning asteroids larger than 5~~km, Mars--crossers are about 35 times more numerous than Earth--crossers. We have divided the Mars--crossers in different classes based on their orbital distribution and showing different dynamical behaviours. We then have shown with numerical simulations that the asteroids of the dominant class evolve to intersect the Earth's orbit on a median time-scale of about 20 Myr and that the Mars--crosser asteroids can sustain the Earth--crossing population.