Scientists this week discovered what might be the largest object yet seen in the icy outer reaches of the solar system, a finding that may change the way astronomers define a planet, the California Institute of Technology said. The planetlike body, known for now as 2004 DW, is about 4.4 billion miles from Earth in the area called the Kuiper Belt, a region of objects made up of rock and ice orbiting the sun in the frigid darkness beyond Neptune, according to a statement posted on the Pasadena, Calif., university's Web site. It was detected during a sky search Tuesday night. The "planetoid," as researchers described it, is probably a little less than 900 miles across, slightly more than half the size of Pluto and possibly larger than the biggest object recorded in the Kuiper Belt, discovered in June 2002, CalTech said. 2004 DW's orbital tilt, at 20 degrees, is larger than Pluto's. 2004 DW was found by Mike Brown, an associate professor of planetary astronomy, former CalTech professor Chad Trujillo and Yale University Professor David Rabinowitz. They used the 48-inch Samuel Oschin Telescope at CalTech's Palomar Observatory and the recently installed Quest CCD camera. Trujillo wrote on the Web site that these planetoids "really blur the line between planet and asteroid." "They are generally too large to be called asteroids because they approach the size of Pluto, which has been called a planet for more than the last 70 years," he said. About 800 objects have been identified in the Kuiper Belt, most only about 60 miles in diameter, Trujillo said. Astronomers believe there could be about five more objects in the belt between the size of the 1,400-mile Pluto and the 800-mile Charon, that planet's largest moon. "We think we should be able to find five to 10 more of these really big Kuiper Belt objects over the next couple of years, including perhaps a couple of 'super-Plutos,' " wrote Trujillo.