Pluto has been officially stripped of its status as a planet.
The International Astronomical Union (IAU), made up of over 2,500 astronomers who met in Prague to determine the fate of Pluto, have demoted Pluto to a lower category.
(It has now emerged that whilst over 2,500 astronomers had attended parts of the meeting, only 424 remained on the day of the vote.)
This momentous decision means that textbooks will need to describe the Solar System as containing eight planets.
Pluto, which was discovered in 1930, by Clyde Tombaugh, will now be referred to as a "dwarf planet".
The decision for a strict definition of a planet was deemed necessary after more objects beyond the orbit of Pluto, which rivalled Pluto's size, were discovered. Due to these discoveries, it could have meant textbooks would need to describe as many as fifty or more planets in our Solar System. The IAU voted against this possibility and took the decision to demote Pluto.
The astronomers agreed that for a celestial body to qualify as a planet, it must be in orbit around the Sun, it must be large enough that it takes on a nearly round shape, and, it has cleared its orbit of other objects.
Pluto was automatically disqualified because it's highly elliptical orbit overlaps with that of Neptune. Whereas the other planets all orbit on the ecliptic.
Pluto will now join a new category of dwarf planets.
Pluto is considerably smaller than the other planets, at just 2,360km across, which is even smaller than some moons in the Solar System.
The critical blow for Pluto came with the discovery of an object currently designated "Eris" (see "Sedna, Eris and Buffy" topic page). After being measured by the Hubble Space Telescope, it was shown to be 3,000km in diameter, bigger than Pluto.
Eris will join Pluto in the dwarf category along with Pluto's major moon, Charon, and the largest asteroid, Ceres.
The unmanned US spacecraft, New Horizons, will reach Pluto and the Kuiper Belt in 2015.
Mike Brown, of CalTech (Californian Institute of Technology) who discovered "Eris" and precipitated this debate, will now go down in the history books as the man who killed Pluto.
The former planet, Pluto has suffered more humiliation since it was downgraded from a planet to a "dwarf planet". It has now emerge that Pluto has been given a number, 134340, as is the convention with asteroids and other small bodies. Pluto's three companions, Charon, Nix and Hydra, will be labelled 134340 i, ii and iii.
