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.
An illustration of
Pluto, foreground,
and its satellite
Charon. Two tiny new
moons were discovered
in October 2005.
Participants hope to set scientific criteria for what qualifies as a planet. Should planets be grouped by location, size or another marker? If planets are defined by their size, should they be bigger than Pluto or another arbitrary size? The latter could expand the solar system to 23, 39 or even 53 planets.
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."
An artist's concept of
2003 UB313, an icy body
that lies beyond Neptune
and is bigger than Pluto.
The Hubble Space Telescope measured the bright, rocky object officially known as 2003 UB313, at about 1,490 miles (2,300 kilometers) in diameter, roughly 70 miles (112 kilometers) longer than Pluto. At 9 billion miles (15 kilometers) from the sun, it is the farthest known object in the solar system.
Some argue that if Pluto kept its crown, Xena should be the 10th planet by default -- it is, after all, bigger. Purists maintain that there are only eight traditional planets, and insist Pluto and Xena are poseurs. Jupiter could be labeled a "gas giant planet," while Pluto and Xena could be "ice dwarf planets."
We of course need the "definition" of a planet first !!!
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