Abstract
We have surveyed for Kuiper Belt objects (KBOs) in six fields of the ecliptic (total sky area 1.5 deg2) to limiting magnitudes between R = 24.9 and R = 25.9. This is deep enough to detect KBOs of diameter ≳160 km at a distance of 65 AU. We detected 24 objects. None of these objects, however, is beyond 53 AU. Our survey places a 95% CL upper limit of Σ < 5 deg-2 on the surface density of KBOs larger than ~160 km beyond 55 AU. This can be compared to the surface density of ~6 deg -2 of ≥160 km KBOs at distances 30-50 AU determined from this survey and previous shallower surveys. The mean volume density of D > 160 km KBOs in the 55-65 AU region is, at greater than 95% confidence, less than the mean density in the 30-50 AU region, and at most two-thirds of the mean density from 40 to 50 AU. Thus, a substantial density increase beyond 50 AU is excluded in this model-independent estimate. A dense primordial disk could be present beyond 50 AU if it contains only smaller objects or is sufficiently thin and inclined to have escaped detection in our six survey fields.
Export citation and abstract BibTeX RIS