Abstract
The size-frequency distributions (SFD) for projectiles which formed craters on terrestrial planets and asteroids Gaspra, Ida, and Mathilde are compared using modern cratering scaling laws. The result shows the relative stability of these distributions during the past 3.7 Gy (Orientale basin and younger formations). The derived projectile size-frequency distribution is compared with the size-frequency distribution of main-belt asteroids. The recent Spacewatch data demonstrate the spectacular similarity of the size distribution of asteroids with diameters larger than 1 km and the population of crater-forming projectiles derived from the cratering data. Consequently one can suppose that the efficiency of the new projectile delivery to planetary crossing orbits does not depend on asteroid size. The migration of large main belt bodies to Mars-crossing orbits or to resonances seems to play an important role in the generation of planet-crossing impactors.
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