Further to Raul's post below, the IAU have made a surprising decision. Sticking by the rule that "Pluto and anything more or less as big is a Planet", we now have 3 new "astronomer's planets" (my phrase, not theirs) This includes Pluto AND CHARON and "Xena" AND CERES - welcome back, Ceres!

A committee of the International Astronomical Union, which decides such matters, voted unanimously today to add three worlds to our solar system's planetary population. More planets will be added later, astronomers said.

Little Pluto, which had been in peril of losing its place among the planets, keeps its status, but only in a new category of "plutons," distant oddballs wandering outside Neptune in weirdly shaped orbits.

The IAU committee recognized two other plutons - Pluto's smaller companion, Charon, and Xena, an icy body bigger than Pluto that was discovered in 2003.

In addition, Ceres, the biggest asteroid between Mars and Jupiter, will regain the planetary status it enjoyed in the 19th century.

Thus the new roll call of planets, starting closest to the sun, would be: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and Xena. (Xena is officially known as UB313 until the IAU gets around to formally naming it.)

The lineup was recommended unanimously by a seven member Planet Definition Committee created by the IAU after two years of heated controversy. The recommendation must be approved by the 3,000 astronomers attending an IAU conference in Prague, Czech Republic, on August 24.