"10th Planet" Proves Bigger than Pluto

Scientific American
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German astronomers working in Spain have determined that UB313, the tenth planet has a diameter of roughly 3,000 kilometers--roughly 700 kilometers larger than Pluto's.
When astronomers discovered UB313 a little more than a year ago, they had a hunch it might be bigger than Pluto because of its brightness.
But despite several attempts to observe more closely the mysterious object orbiting the sun at a distance of more than 14 billion kilometers, accurate estimates of its size remained elusive. Until now.
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Frank Bertoldi of the University of Bonn in Germany and his colleagues used the IRAM 30-meter telescope in the Sierra Nevada mountains of southern Spain to observe UB313 in the infrared range.
Because visual brightness alone is not an accurate indicator of size--it could result from the body's surface being either actually large or mirrorlike--the researchers made observations in wavelengths longer than those of visible light.
Based on observations made over nine nights in August 2005, the team reports, UB313 appears to have a diameter of between 3,094 and 2,859 kilometers. Even the smallest size in that range would make the candidate planet's diameter more than 500 kilometers larger than Pluto's.
Feb 02, 2006