by Ramona Taylor

Created on: February 15, 2011   Last Updated: September 11, 2011

In ancient times, our Solar System was seen as a fixed configuration of a few planets and the Sun circling the Earth.  With the help of the Hubble Telescope and several deep space probes, man’s ability to study the stars improved and our celestial neighbors were revealed to include comets, asteroids, gas giants and other phenomenon.  With newfound knowledge, scientists were forced to develop new terms to explain extraterrestrial objects, one of the most controversial was the dwarf planet.

What is a Dwarf Planet - The Definition

In 2006, the International Astronomical Union (AIU) developed a new system for classifying new worlds (planets).  In the solar system, bodies are classified by size, mass, composition and orbit types. For planets, Jupiter reigned as the largest with a mass over 300 times that of Earth; however, objects on the smaller end of the spectrum were becoming increasingly harder to class. Objects too large to be called asteroids and too small to be called planets required a name.  The origin of the term was necessary for scientist to classify objects which rivaled the size of Pluto, then-considered the smallest planet in the Solar System.

On February 13, 1930, Clyde Tombaugh of the Lowell Observatory discovered Pluto.  At the time, the former Planet X designee took the scientific world by storm.  Over the next several decades, Pluto remained a mystery. It’s mass was hard to measure and by 1978, Charon, a moon, was discovered orbiting around the planet; however, it was the later discovery of the Kuiper Belt, an asteroid belt beyond Neptune’s orbit, and objects larger than the “ninth planet” that set a debate about whether Pluto should be classified a planet.  In 2006, the AIU formally ruled that Pluto was not a planet, but a dwarf planet.

For a celestial body to be considered a dwarf planet, it must meet basic criteria. The object must orbit the Sun, be spherical in shape (as a result of its own gravity), that it not be a satellite of another planet, and have not cleared the neighborhood of the orbit.

Eris, Ceres, Makemake, and Haumea 

Following the reclassification of Pluto, the AIU has designated four other bodies as dwarf planets within our Solar System.  It is believed that there may be several more of these objects in the Kuiper Belt.

Discovered in 2005 by the Palomar Observatory and impetus for the debate on Pluto’s planetary status, Eris is considered the ninth

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