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R.L. Allen, G.M. Bernstein (U of Michigan), R. Malhotra (U of Arizona)
The Kuiper Belt is a rapidly evolving field, providing new insights into the formation and evolution of our solar system. However, little is known about the Kuiper Belt beyond 50~AU. Here we present results of a R\approx25 survey, deep enough to detect D\approx200~km sized objects out to 60~AU. Our survey covered a total of 2.4 square degrees and discovered 34 Trans-Neptunian Objects (TNOs), none of which were beyond 53~AU.
Interior to 48~AU, the Kuiper Belt has been extensively depleted over the lifetime of the solar system due to gravitational perturbations from the giant planets. Beyond 50~AU, these perturbations are negligible and the planetesimal density should rise by a factor of 10---100 to primordial levels. Our initial survey work determined that the volume density of TNOs fell beyond 55~AU. Other surveys have also found a lack of TNOs beyond this distance. Several theories have been proposed to explain this observed absence of distant TNOs, with very different implications for the early history of the solar system.
One of these theories suggests the outer Kuiper Belt is in a very cold, primordial dynamical state, visible only as a very thin disk which could have slipped between previous scarce deep survey fields (Hahn, 2000, LPSC~31). The second stage of our survey was designed to test for a thin disk of TNOs in the invariable plane or inclined within a few degrees. No distant TNOs were detected, ruling out all possible cold disk orientations with inclinations to the invariable plane of less than 0.2 degrees. Over 90% of possible cold disk orientations with inclinations less than 1.0 degree, relative to the invariable plane, were also ruled out at the 95% confidence level.
The author(s) of this abstract have provided an email address for comments about the abstract: rhiannon@umich.edu