  We report the statistical detection (at the >99% confidence level) of a
population of 28th magnitude objects exhibiting proper motions of ~1 arcsecond
per hour at quadrature in deep HST/WFPC2 images. The drift directions imply a
preponderance of objects on prograde orbits concentrated near the ecliptic
plane. We interpret this as the detection of objects which reside in the Kuiper
belt near or beyond the orbit of Neptune, comparable in size to comet 1P/Halley
(radii ~10 km for an albedo of 4%). Our observations imply a population of
~2.5x10^4 objects deg^-2 with V<28.6. This must be viewed as a lower limit
until our search of parameter space is complete. Our observations imply that
there are >2x10^8 objects of this size in the Kuiper belt with inclinations <12
degrees and within ~40 AU of the Sun.
