Prague (Czech Republic): Our solar system would have 12 planets instead of nine under a proposed "Big Bang" expansion by leading astronomers, changing what billions of schoolchildren are taught about their corner of the cosmos.
Much-maligned Pluto would remain a planet – and its largest moon plus two other heavenly bodies would join Earth's neighborhood – under a draft resolution to be formally presented on Wednesday to the International Astronomical Union, the arbiter of what is and is not a planet.
"Yes, Virginia, Pluto is a planet," quipped Richard Binzel, a professor of planetary science at the Massachusetts Institute of Technology.
The proposal could change, however Binzel and the other nearly 2,500 astronomers from 75 nations meeting in Prague to hammer out a universal definition of a planet will hold two brainstorming sessions before they vote on the resolution next week.
But the draft comes from the IAU's executive committee, which only submits recommendations likely to get two-thirds approval from the group.
Besides reaffirming the status of puny Pluto – whose detractors insist should not be a planet at all – the new lineup would include 2003 UB313, the farthest-known object in the solar system and nicknamed Xena; Pluto's largest moon, Charon; and the asteroid Ceres, which was a planet in the 1800s before it was demoted.
The panel also proposed a new category of planets called "plutons," referring to Pluto-like objects that reside in the Kuiper Belt, a mysterious, disc-shaped zone beyond Neptune containing thousands of comets and planetary objects.
Pluto itself and two of the potential newcomers -- Charon and 2003 UB313 -- would be plutons.
Astronomers also were being asked to get rid of the term "minor planets," which long has been used to collectively describe asteroids, comets and other non-planetary objects. Instead, those would become collectively known as "small solar system bodies."
If the resolution is approved, the 12 planets in our solar system listed in order of their proximity to the sun would be Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon, and the provisionally named 2003 UB313.
Its discoverer, Michael Brown of the California Institute of Technology, nicknamed it Xena after the warrior princess of TV fame, but it likely would be rechristened something else later, the panel said.
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Even if the list of planets is officially lengthened when astronomers vote on August 24, it is not likely to stay that way for long: The IAU has a "watchlist" of at least a dozen other potential candidates that could become planets once more is known about their sizes and orbits.
"The solar system is a middle-aged star, and like all middle-aged things, its waistline is expanding," said Jack Horkheimer, director of the Miami Space Transit Planetarium in the United States and host of Public Broadcasting's Stargazer television show.
Opponents of Pluto, which was named a planet in 1930, still might spoil for a fight. Earth's moon is larger; so is 2003 UB313 (Xena), about 70 miles (113 kilometers) wider.
But the IAU said Pluto meets its proposed new definition of a planet: any round object larger than 800 kilometers (nearly 500 miles) in diameter that orbits the sun and has a mass roughly one-12,000th that of Earth.
Moons and asteroids will make the grade if they meet those basic tests.
Roundness is key, experts said, because it indicates an object has enough self-gravity to pull itself into a spherical shape. Yet Earth's moon would not qualify because the two bodies' common center of gravity lies below the surface of the Earth.
"There are as many opinions about Pluto as there are astronomers," Binzel said. "But Pluto has gravity on its side. By the physics of our proposed definition, Pluto makes it by a long shot."
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