Plan boosts solar system to 12 planets

This lineup shows the 12 proposed planets, with a wedge of the sun at far left. Ceres, Pluto, Charon and 2003 UB313 are barely visible. The planets are drawn to scale, but without correct relative distances.

Astronomers propose keeping Pluto in the club — and adding three more

The tally of planets in our solar system would jump instantly to a dozen under a highly controversial new definition proposed by the International Astronomical Union (IAU).

Eventually there would be hundreds as more round objects are found beyond Neptune.

The proposal, which sources tell SPACE.com is gaining broad support, tries to plug a big gap in astronomy textbooks, which have never had a definition for the word "planet." It addresses discoveries of Pluto-sized worlds that have in recent years pitched astronomers into heated debates over terminology.

• The asteroid Ceres, which is round, would be recast as a dwarf planet in the new scheme.

• Pluto would remain a planet and its moon Charon would be reclassified as a planet. Both would be called "plutons," however, to distinguish them from the eight "classical" planets.

• A far-out Pluto-sized object known as 2003 UB313 would also be called a pluton.

That would make Caltech researcher Mike Brown, who found 2003 UB313, formally the discoverer of the 12th planet. But he thinks it's a lousy idea.

"It's flattering to be considered discoverer of the 12th planet," Brown said in a telephone interview. He applauded the committee's efforts but said the overall proposal is "a complete mess." By his count, the definition means there are already 53 known planets in our solar system with countless more to be discovered.

Brown and other another expert said the proposal, to be put forth Wednesday at the IAU General Assembly meeting in Prague, is not logical. For example, Brown said, it does not make sense to consider Ceres and Charon planets and not call our Moon (which is bigger than both) a planet.

IAU members will vote on the proposal Thursday, Aug. 24. Its fate is far from clear.

Q&A on the Proposal / Gallery: The 12 "Planets" / Read the Draft Resolution