Is Pluto a Planet?

3,000 astronomers and scientists (who knew there were that many? They'll never get anything decided on that scale) are meeting in Prague to decide what actually makes a planet.

This has big implications for the ninth planet of the solar system, which has been under dispute since it was discovered in 1930. It's stayed in the planet gang this long because, despite scientists finding numerous asteroids and other bodies similar to Pluto in the Kuiper Belt (an asteroid belt that marks the edge of our solar system), they've all been much smaller, thus avoiding forcing a debate. The recent discovery of an object bigger than Pluto means that either it that gets classed as a planet, or Pluto loses it's status. The other option is to re-classfiy Pluto as a sub-division of the planet group and call it an 'icy dwarf'.

The meeting has some serious implications:

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.

Some observers even believe the new definition of planet could cover other objects smaller than both Pluto and Xena. These include the distant objects Sedna and Quaoar.

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

"It could mean the number of planets leaps to 20 or more, or it drops to eight. But I think most people would prefer not to drop Pluto altogether," Mr Bond told the BBC News website.

It's due to last 12 days, and there's no telling if they'll come to a judgement, or how long that will take to filter out, but hang on to those textbooks showing nine planets, because this may be the last time it's accurate and could be worth a few bob in, oh, a hundred years or so.

Update: It looks like they're favouring increasing the number of planets and introducing a new category of planet called a 'pluton.' Not everyone seems happy about that. Personally, I'd rather have fewer planets rather than sub-categories where any big round rock gets classed as a planet.

Update: It's official, Pluto has been demoted from full planet to dwarf planet. The recently discovered and catchily named 2003 UB313 will join Pluto in that category.