It is a bit bigger than Pluto, an astounding 14.5 billion kilometres from the sun, and the most distant object ever seen in the solar system. Last week's discovery of a "loth planet" should be cause for unreserved celebration - but this Johnny-come-lately is causing as much consternation as joy. That's because astronomers are being forced to re-examine the very definition of a planet, given that there might be more such objects beyond Pluto. The latest announcement came after some astronomical intrigue. Mike Brown of the California Institute of Technology in Pasadena discovered the object - named 2003 UB313 - during a survey of the Kuiper belt, a region beyond Neptune where thousands of icy bodies orbit.
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