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Pluto dumped by astronomers from list of planets

Astronomers yesterday declared that Pluto is no longer a planet, trimming the solar system to eight and immediately outdating science textbooks around the world. The International Astronomical Union created the first official definition for a planet, and relegated Pluto to a new class of so-called dwarf planets. About 2,500 stargazers at the union's general assembly in Prague have taken up the debate over Pluto's status in recent weeks. The planet's classification has been contested since it was discovered in 1930 by Clyde Tombaugh because it is smaller than the eight other planets -- and smaller than Earth's moon -- and has an elliptical orbit around the sun. „This wasn't done either lightly or capriciously or even meanly to disappoint second-graders,” said Mike Shara, astrophysicist at the American Museum of Natural History in New York. „It was really done on the basis of our increased understanding.” The scientists agreed that in order to be a planet, a celestial body must have an orbit around the sun, must have „sufficient mass for its self-gravity to overcome rigid body forces,” and should „clear the neighborhood around its orbit,” the union said. Pluto's oval-shaped orbit crosses Neptune's path and is inclined about 17 degrees.

Ceres, the largest asteroid in a belt of thousands between Mars and Jupiter, and 2003 UB313, a body about the size of Pluto discovered in January 2005, were also added to the new dwarf class. More dwarf planets „are expected to be announced in the coming months and years,” the union said. „Astronomers will have a new class of objects to study and that's always fun,” said Laura Layton, associate editor of Astronomy magazine. And science textbook writers „are going to be busy.” For some, including the US National Aeronautics and Space Administration, the new classification is just administrative housekeeping. The IAU is responsible for naming newly discovered objects, and bases those names on what type of body it is, said Steve Maran, spokesman for the American Astronomical Society. NASA's New Horizons spacecraft launched in January on a nine-year journey to Pluto, at the time the only of the nine planets that hadn't been included in a space mission. „We will continue pursuing exploration of the most scientifically interesting objects in the solar system, regardless of how they are categorized,” said Paul Hertz, chief scientist for the space mission directorate in an e-mail statement. (Bloomberg)