Kuiper belt objects are icy bodies in the outer solar system. They reside in a region past the orbit of Neptune. Pluto and Charon may be the largest examples of these objects. Several of these objects have been discovered during the last few years.
Object 1993 SC (GIF)
This image shows a small part of the discovery frames of 1993 SC, one of the brightest Kuiper-Belt objects so far discovered. It was taken using the 2.5 meter Isaac Newton Telescope on La Palma by Alan Fitzsimmons, Iwan Williams and Donal O'Ceallaigh on September 17, 1994. The two images are separated in time by 4.6 hours, and by comparing them it is clear that one of the objects has moved from upper left of center to a point where its image almost merges with that of a distant galaxy. This motion marks it as being a distant member of our solar system, further away than the planet Neptune.
Subsequent observations over the past year confirm that it is currently 34.0 AU from the sun; however, with a moderate orbital eccentricity of 0.18 it might travel as far as 48 AU. Assuming that Object 1993 SC reflects light much like other primitive asteroids and comets in the out solar system, the diameter is around 300 kilometers (186 miles), or just a quarter the size of Pluto's moon Charon.
Hubble Detection of Comet Nucleus
This pair of images shows one of the candidate Kuiper Belt objects found with Hubble Space Telescope. The object is believed to be an icy comet nucleus several miles across. Each photo is a 5-hour exposure of a piece of sky carefully selected such that it is nearly devoid of background stars and galaxies that could mask the elusive comet.
The left image, taken on August 22, 1994, shows the candidate comet object (inside circle) embedded in the background. The right picture, taken of the same region one hour forty-five minutes later, shows the object has apparently moved in the predicted direction and rate of motion for a Kuiper Belt member. The dotted line on the images is a possible orbit that this Kuiper Belt comet is following. A star (lower right corner) and a galaxy (upper right corner) provide a static background reference. In addition, other objects in the picture have not moved during this time, indicating they are outside our solar system. (Credit: A. Cochran, University of Texas/NASA)
Comet Shoemaker-Levy 9 Impact