Is there a tenth planet? Astronomers who search the outer reaches of our solar system for undiscovered planets have located many small cometary bodies in the once-theoretical Kuiper Belt. So far, none of the new objects qualifies as a "planet." Such searches face a number of daunting obstacles: At such a great distance - five billion miles or more - even a planet as large as Earth would be almost undetectable and the cold and dark reduce the chance of just "spotting it" to almost zero. Recently, a small but vocal group of astronomers has turned this question back on itself by asking "Is there a ninth planet?" Pluto, these scientists charge, is in fact a giant escapee from the Kuiper Belt, having more in common with an oversized comet than with a planet. The International Astronomical Union, the clearinghouse for the naming and classification of astronomical objects, nevertheless sticks to its guns, and Pluto remains the ninth, and so far the last, of the known planets. (end)