Pluto On Brink Of Being 'Just A Rock'

The long-held theory that Pluto is the outermost of the nine planets orbiting the Sun may be on the brink of being vaporised into stardust.

Astronomers have been arguging over the newest discovery in the Solar System, 2003 UB313, and whether it merits being called the Solar System's tenth planet. But during this quest, what they've discovered is something that even they didn't expect - that Pluto is in fact much smaller than the discovered object.

UB313 was found some 15 billion kilometres from Earth and its finding was announced last year by a US team. Pluto's supporters said UB313 was not a planet, but a mere rock. But the latest surprise in the story is that the first detailed measurements, by a German team, show it has a diameter of about 3000km - 1 per cent larger than Pluto.

This is causing lots of discussion and the International Astronomical Union will determine once again what constitutes a planet. This could either mean that the planetary list will expand to include UB313 and possibly many others, or more likely, Pluto will be downgraded to a mere space rock. Now there's something you never thought could happen.

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