AFTER all the angst over whether Xena is a planet, the icy world can now lay claim to be one 鈥� at least as much as Pluto, as it鈥檚 bigger.
Controversy has swirled around Xena, aka UB313, ever since its discovery was announced in 2005. It is roughly three times as far from the sun as Pluto. Assuming it was as reflective as Pluto, astronomers used its brightness and distance to estimate that it must be larger.
To calculate Xena鈥檚 size directly, Frank Bertoldi of the University of Bonn, Germany, and his team measured its light at a wavelength of 1.2 millimetres using a telescope array in the Spanish Sierra Nevada. Xena emits this radiation when warmed by the sun, regardless of how reflective its surface is.
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The measurements show Xena is about 3000 kilometres wide, 30 per cent larger than Pluto (Nature, vol 439, p 563). 鈥淧luto is culturally known as a planet, so why not call this a planet too?鈥� says Bertoldi.
