The 2006 International Astronomical Union (IAU) General Assembly has redefined the definitions of objects in our solar system and created a new classification based on new discoveries.

Planets and other large bodies in our solar system are defined into three categories.
1. A “planet” is a celestial body that (a) is in orbit around the Sun, (b)has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.
2. A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around it orbit, and (d) is not a satellite.
3. All other objects (most asteroids, Trans-Neptunian Objects, comets, and other small bodies) except satellites orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”.

There are now eight planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Dwarf planets now include Pluto (which is now recognized as an important proto-type of a new class of trans-Neptunian objects yet to be categorized further), Ceres, (formerly an asteroid located in the Asteroid Belt), and 2003 UB313 ( a body larger than Pluto located beyond Pluto commonly nicknamed “Xena” but not officially named yet).

A dozen other objects are being watched and considered for identification as “dwarf planets”. The discovery of many large objects beyond the orbit of Pluto created the necessity for a more restrictive definition of a planet. The word “planet” means wanderer, and originally used to describe moving lights in the sky.

The IAU brings together distinguished astronomers from all over the world. Its mission is to promote and safeguard the science of astronomy in all its aspects through international cooperation. It’s the world’s largest professional body for astronomers. It was founded in 1919 and meets every three years.