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Pluto’s status as the ninth planet is safe, for now. Some astronomers have argued that Pluto is an object from the Kuiper Belt, those mysterious icy bodies that orbit the sun beyond Neptune, and should therefore be reclassified. But new infrared images of 18 Kuiper Belt objects taken by NASA’s Spitzer Space Telescope show the objects are much smaller and less massive than had been thought. The information means that astronomers’ models of planet formation may have to be revised, but it also helps to preserve Pluto’s special status as a planet.