Number ten? A new object, bigger and farther than Pluto, is orbiting the Sun. But is it a planet?(new planet )

Publication: Natural History

Publication Date: 01-OCT-05

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COPYRIGHT 2005 Natural History Magazine, Inc.

Pluto--perhaps for reasons having as much to do with Walt Disney's animated dog as with either the Roman god of the underworld or the body's status as the "little guy" of the solar system--seems to be our sentimental favorite among the nine planets. Discovered in 1930 by the American astronomer Clyde W. Tombaugh, Pluto has been an object of curiosity in the three-quarters of a century since then. It is less than 1,500 miles across; in composition it is more like a comet than a gas giant or a terrestrial planet; it has an eccentric elliptical orbit, whose plane is tilted at seventeen degrees from the orbits of the rest of the planets; and it is just one among the uncounted hordes of similar small, icy and rocky bodies in a bagel-shaped region of the solar system known as the Kuiper Belt.

Faced with overwhelming scientific evidence, many of my colleagues have called for...

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