From 9 to 12

Image: The 12 planets under the newly proposed IAU definition. Planet sizes are shown to scale but their orbital distances are not to scale. Credit: IAU/Martin Kornmesser


According to new definition proposed by the International Astronomical Union (IAU) we now have 12 planets in our solar system.
* The asteroid Ceres, which is round, would be recast as a dwarf planet in the new scheme
* Pluto would remain a planet. It's moon Charon would become planet, and both would be called "plutons"
* A Pluto sized object, 2003 UB313 would also be called a pluton

The discoverer of the 12th planet, Mike Brown, thinks that idea of 12 planets is "lousy". He also says that accourding to the new definition there are already 53 planets in our solar system, and much more to be discovered.

The definition says that all round objects orbiting stars will be called planets.
"A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet."



Image: In proposing a new planet definition, the International Astronomical Union put 12 objects on a watch list of candidates that need further study. They are shown here to scale with Earth. Credit: IAU/Martin Kornmesser