A SURVEY of the sky has spotted what may be the largest object discovered in the solar system since Pluto was found in 1930.
Tentatively called 2004 DW, the object is part of the Kuiper belt 鈥� a collection of icy bodies beyond Neptune. The only objects clearly visible at that distance are Pluto and its moon Charon, as both have icy surfaces that reflect roughly half the incident sunlight. But most Kuiper Belt objects are darker, reflecting only about 9 per cent of sunlight, says Chad Trujillo of the Gemini Observatory, who works on the Caltech sky survey. If that鈥檚 true of 2004 DW, he estimates it is 1650 kilometres in diameter, second only to Pluto at 2320 kilometres.
Since 1992, several hundred Kuiper belt objects more than 100 kilometres across have been spotted. They are thought to be left over from the formation of the solar system. Trujillo and his colleagues discovered the previous record holder, Quaoar, in 2002. At 1250 kilometres across it is slightly smaller than 1270-kilometre-wide Charon.
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The researchers鈥� new find was posted on the website of the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics. They now plan further observations to pin down the object鈥檚 size and orbit.