What are Dwarf Planets

When you hear the term, dwarf planet, you normally think of a planet that is simply smaller than those in our solar system. While this is true, in part, there are other differences. A heavenly body that is more developed than an asteroid, but not as complete as a planet, is known as a dwarf planet. This classification is primarily the reason that in 2006, Pluto was demoted from its traditional planetary status to become one of the first recognized dwarf planets.

The problem arose when Eris, another heavenly body very similar to Pluto was found beyond Neptune. A decision as to what to call Eris would eventually lead to a new term. Instead of including it in our solar system, and declaring it yet another planet, the new classification was established. Unfortunately for Pluto, it fit into the new category, and Pluto, Eris, and the asteroid, Ceres, became the first of the dwarf planets.

Specifically, according to the International Astronomical Union, in order to qualify for a dwarf planet status, the body must orbit the sun, have enough mass to have a nearly round shape, it cannot have cleared the area around its orbit, and it cannot be classified a moon. Technically, a planet orbits the sun, while a dwarf planet may orbit whatever it comes in contact with.

In the history of dwarf planets, Ceres was the first discovered in 1801 by Piazzo, and Pluto was second by Tombaugh in 1930. However, there is every indication that there may be thousands more in the Kuiper belt. The problem with cataloguing all of them is in the fact that in many cases, there is no way to determine if they are indeed round. Sizes of these bodies vary and some are very small. In fact, it is estimated that over 30,000 of them might be able to fit inside the Earth.

The challenge will be to determine which bodies should fall within the dwarf planet status, and which are asteroids. Recognizing that certain objects reside in space doesn’t necessarily give us the ability to determine their shape, however, their age may provide a clue as to their size.

It is predicted that through the years there will be literally tens of thousands of these heavenly bodies that will come under the term dwarf planet.


“Eight Planets.” Web. 15 Feb. 2011. http://web.gps.caltech.edu/~mbrown/dwarfplanets/

Brown, Mike. “Planets: Dwarf Planets.” Solar System Exploration. Web. 15 Feb. 2011. http://solarsystem.nasa.gov/planets/profile.cfm?Object=Dwarf