Is Pluto a planet?

Pluto is currently classified as a dwarf planet. Although considered a fully-fledged planet upon its discovery in 1930, further exploration of the solar system, and study of Pluto's characteristics, meant this classification became untenable. The International Astronomical Union came up with its revised categorizations for planets in 2006, effectively 'demoting' Pluto.

As of 2006, the IAU state that a planet must be a body shaped by its own gravity (i.e, spherical) and has also 'cleared the neighborhood' of other objects. Although Pluto may be spherical, it has not cleared other bodies from its orbital path, as it is just one object in the cluster known as the Kuiper Belt. Also acting against Pluto's favor is its elliptical orbit, inclined against the 8 'real' planets.

You might ask why Pluto was ever considered a planet in the first place. In the late 1920s, it was believed a ninth planet, 'Planet X', must exist, to explain the supposed discrepancies in Uranus's orbit not accounted for by the discovery of Neptune in 1840. This led to an intensive search for the ninth planet, whose gravity was pulling upon Uranus.

Upon the discovery of this 'Planet X', subsequently named Pluto, the search ended, as it was believed Pluto would clear up all the questions regarding the behavior of the outer worlds. Soon however, it was clear Pluto was too small to have such an effect on Neptune or Uranus, whose orbital eccentricities were clarified by studying data sent back by the Voyager 2 probe. The discovery of Pluto was more a happy accident, of finding something when the thing astronomers were looking for didn't actually exist!   

To read more about Pluto on Blurtit, check out Should Pluto become a planet again? or What Color Is The Planet Pluto?

And mark the date July 14, 2015 in your diary. Watch this YouTube documentary to find out why: