Is Pluto a planet? New discoveries cloud the issue

For decades, the Solar System has consisted of nine planets, even as scientists debated whether Pluto really belonged. Then the recent discovery of an object larger and farther away than Pluto, an icy rock known as "2003 UB313", really caused some controversy. Should Zena, as it was nicknamed by its discoverer Michael Brown of the California Institute of Technology, become the 10th planet? Should Pluto be demoted? And what exactly is a planet, anyway? Complete story link