Wikipedia entries: When astronomers (from the IAU) declared that Pluto was no longer a planet, but had been demoted to a “dwarf planet;” it sounded like the IAU realized no one cared that they existed so they re-wrote the history books to further frustrate elementary teachers all over the earth.
And then it was revealed that since 1992, over one thousand objects in the Kuiper Belt have been documented. In fact, Pluto isn’t even the largest dwarf planet; Eris is 27% (roughly) larger than Pluto and resides even further out than Pluto.
and this is where it all gets interesting:
Beyond the Kuiper Belt astronomers postulate (and can partly prove) that there are at least two other phenomena. The scattered disc, where Eris resides, is thought to be objects that have been scattered by Neptune’s orbit and gravity. Beyond the scattered disc is an even more mysterious and ethereal location, the Oort cloud. Sedna, which lies outside the scattered disc and on the inner reaches of the Oort cloud, has an amazing orbit which seems to be influenced by a large (earth-size or maybe Jupiter-sized) planetoid within the Oort cloud.
Oh, yeah. Then there’s Nemesis, the theoretical star beyond the Oort cloud that is the cause of the comets. Amazing.
p.s. Did you know that many consider Pluto to be a binary system? Yeah, I find that fascinating too. 
