!BBC NEWS | Science/Nature | Planets plan boosts tally to 12

The number of planets around the Sun could rise from nine to 12 – with more on the way – if experts approve a radical new vision of our Solar System.

The IAU draft resolution recognises eight “classical” planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune – three “plutons” – Pluto, Charon and UB313 – and the asteroid Ceres.

At just 2,360km (1,467 miles) across, Pluto is significantly smaller than the other planets. But until recently, it was still the biggest known object in the Kuiper Belt. That changed with the discovery of 2003 UB313 by Professor Mike Brown and colleagues at the California Institute of Technology (Caltech). After being measured with the Hubble Space Telescope, it was shown to be some 3,000km (1,864 miles) in diameter, making it larger than the ninth planet. Charon is currently described as a moon of Pluto, but because of its size some experts consider it a twin planet.

Ceres is the largest object in the asteroid belt between Mars and Jupiter, and like a planet is spherical in shape.

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