At WWDC last year one of the lunchtime presentations was by Michael Brown, one of the researchers involved here. He was one of the people who proved that Pluto should not be considered a planet and went over the history of the discovery/classification of planet bodies. He also mentioned that they had some evidence of a planet body beyond Pluto due to its gravitational affect of some of the smaller bodies out there even then. Interesting to see this is finally coming to something! He has the appropriate/amusing twitter handle of http://twitter.com/plutokiller