How many rubble piles are in the asteroid belt?

We have developed a new Version of the code built by Campo Bagatin et al. ( 1994a, Planet. Space Sci. 42, 1079- 1092; 1994b, ibid., 42, 1099-1107) and Campo Bagatin (1998, Ph.D. thesis, University of Valencia) to model the col lisional evolution of the asteroid size distribution. The new code distingu ishes between "intact," unfractured asteroids that did not undergo catastro phic collisions and asteroids converted by energetic collisions into reaccu mulated bodies, or "rubble piles." The distinction can also be made on a ph ysical ground by assigning different collisional parameters to the two kind s of objects, with the objective of simulating the different responses to e nergetic impacts that rubble piles may have-due to their different structur e-in comparison to unshattered bodies. Rubble-piles abundance when such tar gets are supposed to transfer less kinetic energy to the fragments turns ou t to be generally higher than monolithic asteroids. We have run a number of simulations of the collisional evolution process to assess the size range where reaccumulated bodies should be expected to be abundant in the main asteroid belt. We find that this diameter range goes f rom about 10 to 100 km, but may extend to smaller or larger bodies, dependi ng on the prevailing collisional response parameters, such as the strength of the material the strength scaling law, the fraction of kinetic energy of the impact transferred to the fragments, and the reaccumulation model. Both the size range and the resulting fraction of rubble piles vary widely depending on the input parameters, which reflects the large uncertainties s till present in the modelization of high-velocity impact outcomes. In parti cular, the simulations that take into account the derived "hydrocode" scali ng laws (Davis et at. 1994, Planet. Space Sci. 42, 599-610) show that nearl y 100% of the main belt asteroids larger than a few kilometers should be re accumulated objects, On the other hand, the present code shows that the sca ling law recently proposed by Durda et al. (1998, Icarus 135, 431-440) prod uces almost no rubble pile. This scaling law was pro-posed to match the act ual population of asteroids, which it fails to do if collisional processes are accounted for in a self-consistent way. (C) 2000 Academic Press.