Pluto was discovered in 1930 by US astronomer Clyde Tombaugh More details

Astronomers are gathering in the Czech capital, Prague, hoping to define exactly what counts as a planet.

The International Astronomical Union hopes to settle the question of Pluto, which was first spotted in 1930.

Experts are divided over whether Pluto - further away and considerably smaller than the eight other planets in our solar system - deserves the title.

The stakes were raised when a bigger planet-type body, known as 2003 UB313, was discovered by a US astronomer.

Professor Mike Brown and colleagues at the California Institute of Technology have discovered several other planetary objects in an area at the edge of the solar system known as the Kuiper Belt.

Now delegates to the Prague conference are being asked to agree on a formal definition of what is a planet for the first time.

One potential outcome of the meeting would be the promotion of 2003 UB313 - nicknamed Xena - into the exclusive club of "official" planets.

But Pluto's status as the ninth planet could also be in danger if the experts decide it no longer makes the grade.

Discovered in 1930, Pluto is just 2,360km (1,467 miles) across, and is vastly different to more familiar planets such as our own Earth, Mars, Jupiter, Saturn or even Neptune, Pluto's nearest neighbour.

But after being measured by the Hubble space telescope, 2003 UB313 was classified larger than Pluto, at some 3,000km (1,864 miles) across its diameter.

About 3,000 astronomers and scientists are meeting in Prague to determine the fate of Pluto and the relevance of millions of schoolbooks and encyclopaedias around the world.

There are suggestions the scientists could decide to include Pluto in a new classification system that marks it out as different to the eight larger planets.

The meeting opens on Monday and is due to last 12 days.