On the way to 12 planets.  



Astronomers are redefining the definition of planet calling it a "pluton". If this redefinition takes place our solar system will have 12 planets instead of nine.

These include the eight classic planets :

  • Mercury

  • Venus

  • Earth

  • Mars

  • Jupiter

  • Saturn

  • Uranus

  • Neptune

  • Pluto

And the three plutons :

  • Ceres - the largest asteroid.

  • Charon

  • The newly discovered 2003 UB313 which has not been officially names but is nicknamed Xena.


Ceres is the largest object in the asteroid belt between Mars and Jupiter and is spherical in shape like a planet.

(Ceres representation by Hubble Telescope)

Charon is currently considered a moon of Pluto but because of its size it is considered to be a twin planet.


If this redefinition takes place in future many more planets could join the sun's family as other plutons are discovered, there are already a dozen candidate planets are already on the waitlist.

Candidates on waitlist are :

  • Varuna

  • Quaor

  • Sedna

These are all Pluto-like objects residing within a region on the fringe of the solar system in the Kuiper Belt.

Plutons differ from classical planets in that :

  • They have orbits round the sun that take longer than 200 years to complete.

  • Their orbits are highly tilted and non circular.

  • This suggests that their origin is different from that of classical planets.

According to the new definition two conditions must be met for an object to be called a planet :

  • First the object must be in orbit around a star, while not itself being a star.

  • Second the most important it must be massive enough for its ow gravity to pull it into a nearly spherical shape.