Pluto no longer a Planet

Well it's official ... after 76 years, astronomers have decided to demote Pluto as a fully fledged member of the Planet club.

The International Astronomical Union (IAU) is an official organization, made up of astronomers from around the world, which decides on all things astronomical, such as the names of stars and newly discovered objects. At a meeting in Poland this week, they came up with a more precise definition of what a planet actually is - the previous definition was a bit vague. What they decided was the following ...

A planet is defined as a celestial body that (a) is in orbit around the Sun, (b) has
sufficient mass that its own gravity pulls it into a nearly round shape, and (c) has cleared
the neighbourhood around its orbit of smaller asteroids.

This effectively means that officially, we now have 8 planets in our Solar System, rather than the 9 we have all come to know and love. The new version of the Solar System is shown below.

Today, the IAU also defined a new type of object known as a Dwarf Planet, which will include Pluto, Ceres and the more recently discovered Eris (formerly 2003UB313). These dwarf planets are large enough to be round, but too small to have swept up all the major asteroids occupying the same orbits as them.

All other objects orbiting the Sun, except satellites (i.e. Moons of planets), shall now be referred to collectively as Small Solar-System Bodies.