36th DPS Meeting, 8-12 November 2004
Session 8 Kuiper Belt II: Binaries and Dynamics
Oral, Tuesday, November 9, 2004, 8:30-10:00am, Lewis

## [8.07] The Collisional Evolution of the Trans-Neptunian Object Size Distribution

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

The HST survey of trans-Neptunian objects (TNOs) by Bernstein et al.~[1] detected two distinct populations, classical' and excited', and found a deficit of smaller (\lesssim100 km) TNOs relative to the power law found earlier for larger bodies. Using the analytical model of O'Brien and Greenberg [2] and a numerical collisional evolution model [3] with reasonable strength parameters for icy bodies [4], we find that the TNO populations likely started with shallow initial size distributions, and that bodies \gtrsim10 km in diameter are likely not in a collisional steady state. If the initial size distributions were steeper than the current size distributions, collisional erosion could not remove enough bodies over the age of the solar system to match the observations. The size distribution of TNOs \gtrsim10 km in diameter must therefore be primordial. We also use our numerical model to address the origin of Jupiter-family comets (JFCs). Comparing the classical' and excited' size distributions to the results of numerical simulations of the supply of JFCs, Bernstein et al.~find that most JFCs are ~1 km in diameter and come from the excited' population. An upturn in the size distribution at sizes below their survey limit could increase the size of JFC precursors and possibly allow the classical' population to contribute a significant number of JFCs. Our numerical simulations show that the collisional production of bodies below ~10 km in diameter can create a small upturn in the classical' and excited' size distributions, but it is not able to substantially increase the contribution of JFCs from the `classical' population or increase the size of JFC precursors.

\noindent [1] Bernstein et al., AJ, submitted (AstroPH/0308467 v.3). [2] O'Brien and Greenberg, Icarus 164, 2003. [3] O'Brien and Greenberg, in prep. [4] Benz and Asphaug, Icarus 142, 1999.

Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.