The International Astronomical Union (IAU) has defined a dwarf planet as follows :
- It orbits around the Sun (thereby excluding satellites of other planets);
- It has sufficient mass for its gravitational force to prevail over the cohesive forces and maintain it in hydrostatic equilibrium (in a nearly spherical shape);
- It has not cleared its orbital path;
Adopted on 24 August 2006, this name is justified by the considerable controversy over the classification of certain planets such as Pluto, which are hard to differentiate from the largest asteroids. Today, five bodies are considered to be dwarf planets, (in decreasing order of size) Eris (trans-neptunian), Pluto (former planet), Makemake, Haumea and Ceres (asteroids).
Among the dwarf planets, the IAU has now defined planetoids, which are beyond the orbit of Neptune. For the moment (2011) only Pluto and Eris are considered to be planetoids.