Source: NASA Science Mission Directorate
Published: June 29, 2015

Classic video explaining the history, debate and continuing discussion of the definition of a planet.

What is a planet? The question has been pondered by many since the early Greeks came up with the word "planets." Since then the number of "planets" in our solar system has fluctuated, sometimes numbering as high as 15, before it was determined that some were actually asteroids.

One such celestial object is Pluto, which became the 9th planet in 1930 to much controversy. Then, in 2005, Eris was discovered and hailed as a possible 10th planet. Our technology has progressed to the point where we are able to see farther into space than ever before. In so doing we have discovered a section in our solar system called the Kuiper Belt that has the potential to hold hundreds, if not thousands, of objects similar to Pluto and Eris.

Much like other sciences, such as Biology, where one may discover a new species, classification is a common and needed process which groups like objects for purposes of comparison and further study. The classification of our planets is no exception to this scientific practice, and the astronomical community is currently undergoing a discussion debating the issue of how to classify, or define, a planet.

Using 3D animation, this videowas created to better illustrate the history behind the discussion defining "What is a Planet?" and to outline some of the traits that may be associated with the definition of a planet. So come travel with us as we drive along the "Kuiper Belt highway" at 100 mph to explore the far reaches of our solar system and discover how vast our corner of the galaxy really is.

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