Pluto no longer a planet!

25th August 2006. After a tumultuous week of clashing over the essence of the cosmos, the International Astronomical Union stripped Pluto of the planetary status it has held since its discovery in 1930. Thursday's decision by the prestigious international group spells out the basic tests that celestial objects will have to meet before they can be considered for admission to the elite cosmic club.

For now, membership will be restricted to the eight "classical" planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Much-maligned Pluto doesn't make the grade under the new rules for a planet: "a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighbourhood around its orbit." Pluto will be reclassified in a new category of "dwarf planets."

The reclassification now has implications for a number of other plutons and small planets, which may have achieved planetary status. A dozen "candidate planets" are already on the IAUs "watchlist". They include Varuna, Quaor and Sedna, all Pluto-like objects residing within a region on the fringe of the solar system known as the "Kuiper Belt".