"Astronomers have known for a very long time that Pluto was different," Cesarky added.
So why did Pluto gain planetary status in the first place?
It was discovered in the 1930s "when telescopes weren't very good," explained Don Shapero, director of the Board on Physics and Astronomy at the National Academy of Sciences in Washington, D.C.
Since then, however, telescope quality has developed at a startling pace.
"In this case what ultimately precipitated the change was a better understanding," he said. "As we learn more and understand more, we change how we categorize things, how we name things."
Scientists had been chipping away at Pluto's planetary status for a long time.
In 1978 U.S. Naval Observatory astronomers discovered Pluto's large moon Charon while studying photographic plates of Pluto's position in the sky. The pair form an unusual "double system," since Charon is so large that Pluto and Charon orbit each other, instead of Charon orbiting Pluto.
The scientists also determined that Pluto and Charon's masses were much smaller than previously thought.
In the 1990s astronomers armed with powerful telescopes began finding other objects in the solar system with similar orbits to that of Pluto. This led them to give the area beyond Neptune's orbit its own name: the Kuiper belt, after 20th-century astronomer Gerard Kuiper.
Astronomers say nearly a thousand Kuiper belt objects have been found, several larger than Pluto.
"It appears that Pluto is more a prototype of the Kuiper belt objects," said Geoff Chester, an astronomer and spokesman for the Washington D.C.-based Naval Observatory. (See an interactive model of the solar system.)
Science in Action
The change in Pluto's status also presents a snapshot of the scientific process in action.
"Science should be correctable," said Cornell University astronomer Joe Burns, an expert on small planetary bodies and irregular satellites who attended the IAU vote in Prague.
"If put in the proper light, this really is a shining hour for science."
With so many objects in the solar system with an established orbit around the sun, a clear definition was needed, Chester says.
Otherwise, "How do you distinguish planets from stuff?" he said.
Pluto's new classification could be jarring for schoolkids who have learned otherwise, Shapero, of the National Academy of Sciences, says.
"It's a shocking introduction to the fact that science evolves."
But Pluto's reclassification has also generated interest in astronomy and "catches kids' imagination," added Cecelia Blalock, vice president of the Washington, D.C.-based Young Astronaut Council, a group that promotes science and math education in schools.
"The whole concept of space is changing, and there's a greater appreciation of how much more vast it is than just our solar system," she said.
"These are the concepts that really need to be instilled in children."
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