In August 2006 the IAU (International Astronomical Union) held the XXVIth General Assembly to define 'what is a planet'.
During the Assembly it has been decided that Pluto, Charon, Ceres and 2003/UB313 do not qualify as planets (see elsewhere on this page).

In August 2006 the IAU (International Astronomical Union) held the XXVIth General Assembly to define 'what is a planet'.
This overview shows what has been decided.

Here follows what the IAU decided on August 24, 2006:
The IAU members gathered at the 2006 General Assembly agreed that a "planet" is defined as a celestial body that:

  1. is in orbit around the Sun,
  2. has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
  3. has cleared the neighbourhood around its orbit.

This means that the Solar System consists of eight "planets": Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
The first members of the "dwarf planet" category are Ceres, Pluto and 2003 UB313 (temporary name).
More "dwarf planets" are expected to be announced by the IAU in the coming months and years.
Currently a dozen candidate "dwarf planets" are listed on IAU's "dwarf planet" watchlist, which keeps changing as new objects are found and the physics of the existing candidates becomes better known.

The "dwarf planet" Pluto is recognised as an important proto-type of a new class of trans-Neptunian objects.
The IAU will set up a process to name these objects.