The density of the Kuiper belt and Neptunes very circular orbit, has led scientist to belive that Neptune has shaped the Kuiperbelt. But a new analysis of duoble-asteroids in the Kuiperbelt shows that they originated from their present positions

The existence of extremely wide binaries in the low-inclination component of the Kuiper Belt provides a unique handle on the dynamical history of this population.

Some popular frameworks of the formation of the Kuiper Belt suggest that planetesimals were moved there from lower semi-major axis orbits by scattering encounters with Neptune.This proces would also account for Neptune rather circular orbit, which is an ellipse with an eccentricity of only 29,8 to 30,4AU

A new analysis and computer-modelling of the effects such events would have on binary systems, shows that  the observed amount of wide binaries in the Kuiperbelt, would have been efficiently destroyed by the kinds of scattering events required to create the Kuiper Belt with this mechanism. This indicates that a binary-bearing component of the cold Kuiper Belt was emplaced through a gentler mechanism or was formed in its present prosition

Source: arXiv.org
and read Science Magazine re. Neptunes orbit