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R.L. Allen, G.M. Bernstein (U of Mich), R. Malhotra (U of A)
While our knowledge of the Kuiper Belt interior to 50~AU has grown tremendously over the past decade, little is yet known about the region beyond 50~AU. Of over 450 known Kuiper Belt Objects, fewer than 10 KBOs have been dicovered at distances of 50~AU or greater, despite the completion of surveys with sufficient sensitivity to detect 160~km objects at this distance. Several theories have been proposed to explain the absence of these distant KBOs. These theories have distinct predictions for the Kuiper Belt beyond 50~AU, the result of very different assumptions about the early history of the solar system.
One hypothesis is that the region beyond 50~AU is dynamically very cold, forming a very thin disk of objects (Hahn, 2000, LPSC~31). This thin disk could slip between previous, scarce, deep survey fields, which were mainly concentrated on the ecliptic plane. If the distant disk were centered on the invariable plane instead, it could thus far have remained undetected.
We have completed a survey designed to test for such a cold disk in the invariable plane or inclined within a few degrees. No distant KBOs were detected, down to a limit of R=25. The expected population for a thin disk beyond 50~AU was estimated by projecting the classical KBO population observed at 40~AU onto a plane. All possible cold disk orientations with inclinations to the invariable plane of less than 0.2 degrees were ruled out. 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.
This work is supported by NASA Planetary Astronomy grant #NAG5-7860.
The author(s) of this abstract have provided an email address for comments about the abstract: rhiannon@umich.edu