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A planet smaller than Pluto has been discovered in the outlying regions of the solar system. The planet was discovered using the Samuel Oschin Telescope at Palomar Observatory near San Diego, Calif. The discovery was announced by planetary scientist Dr. Mike Brown of the California Institute of Technology in Pasadena, Calif., whose research is partly funded by NASA. The planet is a typical member of the Kuiper belt, but its sheer size in relation to the nine known planets means that it can only be classified as a planet, Brown said. Currently about 97 times further from the sun than the Earth, the planet is the farthest-known object in the solar system, and the third brightest of the Kuiper belt objects. Brown, Trujillo and Rabinowitz first photographed the new planet with the 48-inch Samuel Oschin Telescope on October 31, 2003. However, the object was so far away that its motion was not detected until they re-analyzed the data in January of 2005. Scientists have been studying the planet to better estimate its size and its motions. "It's definitely smaller than Pluto," said Brown, who is a professor of planetary astronomy. Scientists can infer the size of a solar system object by its brightness, just as one can infer the size of a faraway light bulb if one knows its wattage. The reflectance of the planet is not yet known. Scientists can not yet tell how much light from the sun is reflected away, but the amount of light the planet reflects puts a lower limit on its size. “Even though all we know for certain is that Sedna is smaller than 1800 km, we have evidence which suggests that the size might be pretty close to this number” says Brown. " but we're not sure yet of the final size. The size of the planet is limited by observations using NASA's Spitzer Space Telescope, which has already proved its mettle in studying the heat of dim, faint, faraway objects such as the Kuiper-belt bodies. Because Spitzer is unable to detect the new planet, the overall diameter must be less than 1800 kilometres, “ said Brown, “We are virtually certain that the size is larger than the 1250 km size of Quaoar, though this object has shown many unexpected characteristics, so we can't completely rule out a smaller size”. The name for the new planet “Sedna” has been proposed by the discoverers to the International Astronomical Union, and they are awaiting the decision of this body before announcing the name officially.

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