The adopted sons of the Sun: The Dwarf Planets

Unlike planets, dwarf planets lack the gravitational muscle to sweep up or scatter objects near their orbits. They end up orbiting the sun in zones of similar objects such as the asteroid and Kuiper belts. Pluto, Eris and the asteroid Ceres became the first dwarf planets in our solar system, recognized in world-wide astronomy.

On August 24, 2006, the International Astronomical Union voted at the end of its 26th General Assembly to establish definitions for three classes of substellar objects in the Solar System:

Planet - This 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 nearly round shape (due to a hydrostatic equilibrium); and (c) has cleared the neighborhood around its orbit. As now defined, the Solar System has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Dwarf Planet - This is a celestial body that: (a) is in orbit around the Sun; and (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a nearly round shape (due to a hydrostatic equilibrium); but (c) has not cleared the neighborhood around its orbit; and (d) is not a satellite of another planet. As defined, the Solar System has probably has at least one dwarf planet in the Main Asteroid Belt (Ceres), Edgeworth-Kuiper Belt (Pluto and Eris); and Oort Cloud (possibly Sedna). In addition, the "dwarf planet" Pluto is recognized as a prototype of a new class of trans-Neptunian objects.

Earth in comparison with Dwarf Planets

Smaller Solar System Bodies - This category collectively refers to all other celestial bodies orbiting our Sun, Sol (including asteroids, comets, and satellites).

Bibliography:

Sol Company. SolStation.com. 2008. 25 august 2011 <http://www.solstation.com/stars/dwarfpla.htm>.