THE DISCOVERY OF HALLEY-SIZED KUIPER BELT OBJECTS USING THE HUBBLE-SPACE-TELESCOPE

We report the statistical detection (at the >99% confidence level) of a population of 28th magnitude objects exhibiting proper motions of ap proximate to 1 '' hr(-1) at quadrature in deep Hubble Space Telescope (HST)/WFPC2 images. The drift directions imply a preponderance of obje cts on prograde orbits concentrated near the ecliptic plane. We interp ret this as the detection of objects which reside in the Kuiper belt n ear or beyond the orbit of Neptune, comparable in size to comet 1P/Hal ley (radii similar to 10 km for an albedo of 4%). Our observations imp ly a population of similar to 2.5 x 10(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 >2 x 10(8) ob jects of this size in the Kuiper belt with inclinations < 12 degrees a nd within similar to 40 AU of the Sun.