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Astronomers May Add Planets to Solar System

Astronomers from around the world are meeting in Prague to reconsider what qualifies as a planet.

Under the new rules, proposed by an International Astronomical Union panel, Pluto would still rank as a planet, despite its small size.

Besides reaffirming the status of puny Pluto -- whose detractors insist it shouldn't be a planet at all -- the new lineup would include 2003 UB313, the farthest-known object in the solar system, nicknamed Xena and discovered by a California scientist; Pluto's largest moon, Charon; and the asteroid Ceres, which was a planet in the 1800s before it got 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.

The proposal has drawn mixed reactions, however. Some say it could open the door to dozens of new planets. But the proposal could change. The 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.

Associated Press contributed to this summary.

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David Kestenbaum is a correspondent for NPR, covering science, energy issues and, most recently, the global economy for NPR's multimedia project Planet Money. David has been a science correspondent for NPR since 1999. He came to journalism the usual way — by getting a Ph.D. in physics first.