DPS 34th Meeting, October 2002
Session 2. Asteroids I
Oral, Chair(s): R.P. Binzel and H. Scholl, Monday, October 7, 2002, 9:30-11:00am, Ballroom

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[2.04] The Evolution of the Main belt and NEA size Distributions

D. P. O'Brien, R. Greenberg (University of Arizona)

The size distribution of the main belt is governed by collisional evolution as well as by the non-collisional removal of bodies due to the combination of radition forces and resonances. The NEA size distribution is governed in part by the size distribution of the main belt, its primary source, but differs somewhat from it due to the size dependent processes which deliver asteroids from the main belt to near earth space. These two size distributions provide a powerful constraint on any model of asteroid collisional evolution and NEA delivery. Additional constraints are provided by the cratering records on observed asteroids, such as Gaspra and Ida, and by the cosmic ray exposure (CRE) ages of meteorites, which indicate that meter-sized bodies have collisional lifetimes on the order of 10 Myr or more in the main belt. A collisional evolution model for the main belt which incorporates non-collisional removal processes can fit all of these constraints with reasonable parameter choices.

The main parameters in our model are the strength vs. size scaling law and the removal rate of bodies from the main belt as a function of size. With removal rates consistent with the estimates of Bottke et al. (2002) and reasonable strength scaling laws, we are able to match the main belt size distributions observed by either the Sloan Digital Sky Survey or the Spacewatch Survey. The NEA population produced in our model is consistent with the observed NEA population, as determined by Rabinowitz (2000). In addition, lifetimes for meter-sized bodies are consistent with meteorite CRE ages. The inferred population of bodies from 1 m to 1 km is consistent with the cratering records on Gaspra and Ida. Asteroids larger than 10 km have mean collisional lifetimes > 4.5 Byr.

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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.