i202 Fall 2010 School of Information, UC Berkeley

Three years ago, scientists published that Pluto would no longer belong to the solar system planets category. In their words, "all small and nearly spherical objects orbiting beyond Neptune, which is now the most distant planet from the sun, will fall under the new tag." 

The reclassification reflects that Pluto is part of a newly recognised and growing number of objects in the solar system.

http://curious.astro.cornell.edu/question.php?number=624