UPDATE Is Pluto Really a Planet

from CNN

Nearly 2,500 astronomers from 75 countries gathered in Prague Monday to come up with a universal definition of what qualifies as a planet and possibly decide whether Pluto should keep its planet status. 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 threatened to throw this slice of the cosmos into chaos.

Among the possibilities at the 12-day meeting of the International Astronomical Union in the Czech Republic capital: Subtract Pluto or christen one more planet, and possibly dozens more.


The debate intensified last summer when astronomer Michael Brown of the California Institute of Technology announced the discovery of a celestial object larger than Pluto. Like Pluto, it is a member of the Kuiper Belt, a mysterious disc-shaped zone beyond Neptune containing thousands of comets and planetary objects. Brown nicknamed his find "Xena." The Hubble Space Telescope measured the bright, rocky object officially known as 2003 UB313, at about 70 miles longer than Pluto. At 9 billion miles the sun, it is the farthest known object in the solar system.

The discovery stoked the planet debate that had been simmering since Pluto was spotted in 1930.