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Astronomers Offer New Vision of the Solar System

Astronomers attending an international summit in Prague plan to vote next week on a new classification of Pluto-like objects that will redefine the solar system. Experts discuss the proposed solution to the long-standing debate over whether Pluto is a planet.

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    The classical Solar System that inspired Holst's suite was a simple place: eight large spheres, including Earth, made up the local firmament, but it was soon to change. In 1930, using the latest telescope technology, astronomer Clyde Tombaugh discovered Pluto. It was immediately added to the pantheon of planets.

    But to modern astronomers, Pluto has become a problem. After a decade of debate, the International Astronomical Union today proposed a radical fix.

  • RON EKERS, President, International Astronomical Union:

    The lack of a definition of a planet is becoming increasingly confusing. Now, what's different in this case is this is something, the definition of a planet, which is not only something professional astronomers need, but something that extends beyond astronomy.


    Pluto's not like the other planets. It's on the edge of a swathe of cosmic rubble called the Kuiper Belt, and might just be part of that. And three years ago, a new object named Xena was discovered, bigger than Pluto.

    Today's announcement lays down strict scientific rules defining a planet. The role of gravity is key. It's a bit complicated to explain, so the astronomers reached for the Plasticine.

    RICHARD BINZEL, Massachusetts Institute of Technology: If an object is big enough and massive enough to have enough gravity to pull it into a spherical shape, we have a planet.


    The proposed new rules solve the Pluto problem but also mean an overhaul of nearly 80 years of planetary doctrine. It's farewell to the traditional Solar System, with it's nine planets. Now there's 12 planets in the neighborhood.

    In at number five, the planet formerly just part of the asteroid belt: Ceres.

    Further out is a totally new group: the plutons. They're deemed far too far away from the sun to be classic planets. They're led by Pluto, but the new rules mean that what used to be thought of as Pluto's moon, Charon, becomes a planet of its own. And the third member of the plutons, the newly discovered 2003 UB 313, or Xena for short.