The International Astronomical Union, dramatically reversing course just a week after floating the idea of reaffirming Pluto's planethood and adding three new planets to Earth's neighborhood, downgraded the ninth rock from the sun in historic new galactic guidelines.
"Pluto is smaller than our moon, not of planetary size," astronomer Sir Patrick Moore told CBS Evening News interim anchor Bob Schieffer. "If we call Pluto a planet, there are others: Xena, Verona, Terran, Ceres — the list is endless. In fact, that makes no sense at all."
The shift will have the world's teachers scrambling to alter lesson plans just as schools open for the fall term.
"It will all take some explanation, but it is really just a reclassification and I can't see that it will cause any problems," said Neil Crumpton, who teaches science at a high school north of London. "Science is an evolving subject and always will be."
Powerful new telescopes, experts said, are changing the way they size up the mysteries of the solar system and beyond. But the scientists at the conference showed a soft side, waving plush toys of the Walt Disney character Pluto the dog — and insisting that Pluto's spirit will live on in the exciting discoveries yet to come.
"The word 'planet' and the idea of planets can be emotional because they're something we learn as children," said Richard Binzel, a professor of planetary science at the Massachusetts Institute of Technology, who helped hammer out the new definition.
"This is really all about science, which is all about getting new facts," he said. "Science has marched on. ... Many more Plutos wait to be discovered."
Pluto, a planet since 1930, got the boot because it didn't meet the new rules, which say a planet not only must orbit the sun and be large enough to assume a nearly round shape, but must "clear the neighborhood around its orbit." That disqualifies Pluto, whose oblong orbit overlaps Neptune's, downsizing the solar system to eight planets from the traditional nine.
Astronomers have labored without a universal definition of a planet since well before the time of Copernicus, who proved that the Earth revolves around the sun, and the experts gathered in Prague burst into applause when the guidelines were passed.
Predictably, Pluto's demotion provoked plenty of wistful nostalgia.
"It's disappointing in a way, and confusing," said Patricia Tombaugh, the 93-year-old widow of Pluto discoverer Clyde Tombaugh.
"I don't know just how you handle it. It kind of sounds like I just lost my job," she said from Las Cruces, N.M. "But I understand science is not something that just sits there. It goes on. Clyde finally said before he died, 'It's there. Whatever it is. It is there."'
The decision by the IAU, the official arbiter of heavenly objects, restricts membership in the elite cosmic club to the eight classical planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.