A demotion for Pluto
"The match was declared closed at the loss of one planet.' This could well have been the closing statement of anyone doing a running commentary on the proceedings of the 26th General Assembly of the International Astronomical Union (iau). The meeting held at the Czech capital, Prague between August 14 and 25, 2006, saw members voting for a new definition of planets. According to this definition, Pluto will no longer be called a planet: it will be called a dwarf planet instead.
The iau defines a planet as, "A celestial body that is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid forces so that it assumes a hydrostatic equilibrium (nearly round shape), and has cleared the neighbourhood around its orbit.' A dwarf planet has all but one of these properties: it has not cleared the neighbourhood around its orbit. It isn't a satellite as well.
A day before this definition was formulated, astronomers would have said, "The Solar System has nine planets, their 130 satellites and more than 10,000 asteroids or minor bodies