Pluto is not a Planet, Astronomers say.

http://news.nationalgeographic.com/news/2006/08/060824-pluto-planet.html

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Pluto has been voted off the island.

The distant icy ball is no longer a true planet, according to a new definition of the term voted on by scientists today.

Whoa! Pluto's dead," said astronomer Mike Brown, of the California Institute of Technology in Pasadena, as he watched a Web cast of the vote. "There are finally, officially, eight planets in the solar system."

In a move sure to generate controversy even as it forces textbooks to be rewritten, Pluto will now be dubbed a "dwarf planet."

But it's no longer part of an exclusive club, since there would be more than 40 of these dwarfs, including the large asteroid Ceres and 2003 UB313, nicknamed Xena—a distant object slightly larger than Pluto discovered by Brown last year.

Researchers voted on the definition at a meeting of the International Astronomical Union in Prague, in the Czech Republic. This group decides on the official names of all celestial bodies.

The tough decision comes after a two-year search for a scientific definition of the word "planet." The term never had an official meaning before.

In the new definition, to qualify as a full-fledged planet, an object orbiting the sun has to be large enough that it has become round due to the force of its own gravity, and it also has to dominate the neighborhood around its orbit.

Pluto would be demoted, because it does not dominate its neighborhood. Charon, its large "moon," is about half the size of Pluto and orbits along with it. All the true planets are far larger than their moons.

The ruling effectively settles a year-long controversy about whether the spherical body announced last year and informally named "Xena" would rise to planetary status. Though somewhat larger than Pluto, the body has been informally known as "Xena" since the formal announcement of its discovery on July 29, 2005 by Brown and his co-discoverers, Chad Trujillo of the Gemini Observatory and David Rabinowitz of Yale University. Xena will now be known as the largest dwarf planet.