What are Dwarf Planets

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 largest object in the Solar System.  Unofficially called Xena, Eris is believed to be the farthest object in our planetary system. 

Ceres’ history dates back to the 19th century. Found in 1801, Ceres is the largest body in the asteroid belt which lies between Mars and Jupiter.  First thought to be a planet, Ceres measures about 950 kilometers in diameter. 

Makemake was discovered by the Palomar team as well.  Named for the Rapa Nui God of Creation, this dwarf planet has no satellites, and is second brightest Kuiper Belt object. 

Haumea, named for the Hawaiian goddess of childbirth, was discovered by the Palomar Observatory team in 2004.  Thought to be elliptical in shape, Makemake lies within the Kuiper Belt and is known to have moons orbiting it. 

In a universe full of dark matter, black holes and red giants, scientists must find ways to distinguish new phenomenon.   With technology aiding man’s exploration of his own Solar System, there are certainly more discoveries to be made.  With the reclassification of dwarf planets, the picture of our planetary neighbors becomes clearer and more intriguing. 

For more information about dwarf planets, check out the following websites: