on The Population of Mars-Crossers: Classific

times of objects injected into asteroid belt resonances. Science 277, 197–201) have pointed out that the bodies injected by collisions into the main resonances of the asteroid belt could not sustain the ob-served population of Earth-crossers of large diameter. In this paper, we present our numerical exploration of the dynamical evolution of Mars-crosser asteroids initiated by Migliorini et al. (1998. Origin of multikilometer Earth and Mars-crossing asteroids: A quantita-tive simulation. Science 281, 2022–2024.) and improved by comput-ing the evolution over 100 Myr of the orbits of the whole observed sample of this population. Mars-crossers are about 35 times more numerous than Earth-crossers (at least down to 5 km in diame-ter). On the basis of their current orbital elements, we show that this population can be divided in different groups which have well-characterized dynamical behaviors, lifetimes, and end-states. From the dominant group, the asteroids evolve to intersect the Earth’s orbit on a median time scale of about 60 Myr. Then, they can in-terchange between the Earth-crosser state and an evolved solely Mars-crosser one before colliding with the Sun or being ejected out-side Saturn’s orbit. Based on these dynamical results, we show that Mars-crosser asteroids can sustain about half of the multikilome-ter Earth-crossing population, and the expected orbital distribution of Earth-crossers coming from Mars-crossers is computed. Then, from an estimate of the size distribution of the Mars-crosser popu-lation and the spectral analysis of its different groups, we derive ex-pected numbers of Earth-crossers and ratios of different taxonomic types in the Earth-crosser population that are not in disagreement y Died on November 2, 1997, in a mountain accident. This paper is devoted to his memory. with the viability ulation belt. c