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

The International Astronomical Union (IAU) 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.

Any decision to downgrade Pluto would send shockwaves through the scientific community, instantly outdate textbooks, and change how the basics of the Solar System are taught in schools.

Since the discovery of the ninth planet, astronomers have become aware of a vast population of small, icy bodies resembling Pluto that orbit the Sun beyond Neptune. This has led some astronomers to argue that Pluto belongs amongst these "icy dwarfs" rather than the other planets.

Astronomers could once make allowances for Pluto on account of its size. At just 2,360km (1,467 miles) across, its diameter is six-and-a-half times smaller than Earth's. But until recently, it was still the biggest known Kuiper Belt object.

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.

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

One potential outcome of the meeting would be the promotion of 2003 UB313 - nicknamed Xena, after the TV warrior princess - 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.

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.