Until ten years ago, or so, the solar system seemed to end at Pluto. Since that time, a large number of fairly large objects have been discovered. How large are they? Here is a diagram comparing some of the larger Kuiper objects with the earth and our Moon. All of these object have orbits more or less similar to Pluto's. The existence of these objects was first suggested by the planetary astronomer Gerard Kuiper. His original speculation was based on the orbits of comets in the outer solar system. This outer region has now become known as the Kuiper belt. This diagram shows the location of these objects. What is the outer solar system like? It seems to be filled three letter acronyms. Most recently, I.A.U. has decided on the designation 'pluton' for that class of smaller objects similar to Pluto. However, there is still some confusion about the new terms.
One object, called Sedna, has a very strange elongated orbit. Another of the newly discovered objects has been named Eris, and is actually larger than Pluto as we can see in this diagram. And the most recent object in the news, Haumea, seems to present yet another mystery.
Here is David Jewitt's Kuiper Belt Page.
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Updated December 9, 2010