Problem:
When Pluto was discovered it was immediately deemed the ninth planet, because astronomers were looking for a planet, and thought that was what they had found. Over the next half century, as more became known about Pluto, its "oddness" compared to the other planets became apparent. In the mid-1990's many planetologists began to believe that Pluto should not be considered a full-fledged planet, but something lesser. This culminated with the decision by the International Astronomical Union to reclassify Pluto along with a number of other objects in this region of the solar system as "dwarf planets."
What makes something a planet?
What characteristics does Pluto have that would make a planet, or not a planet?
Why was there a need to reconsider Pluto's status?
Explain in a couple of paragraphs.
Remember as always to cite your sources (and you should be using sources).