Abstract
One of the oustanding questions about the architecture of the outer solar system is how the trans-Neptunian disk of comets and small planet-scale objects known as the solar system's Edgeworth-Kuiper Belt (EKB) originated and evolved to its present mass and architecture. Applying a time-dependent model of collisonal evolution of the EKB, we find that under a wide range of assumptions, collisional evolution should have depleted the mass of the 30-50 AU zone by >90% early in the history of the solar system, thereby creating a deep scar or gap in the surface mass density across a wide region beyond Neptune, much like what is observed today. Dynamical erosion may have further accelerated the depletion process. Given the fact that Neptune has had far less dynamical influence beyond 50 AU, our results also suggest that unless the solar nebula was truncated near 50 AU, then surface mass density of solids somewhere beyond ~50 AU may increase again, most likely dramatically.