Demoting Pluto

By | April 26, 2019

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The Sun and Planets of our Solar System Including Pluto. (Photo by: Education Images/UIG via Getty Images)

Since 1930, all of our science textbooks have told us that the Milky Way solar system had nine planets orbiting the Sun. Ask any science-minded kid in a generation or two ago and he or she would tell you that Pluto is the smallest planet and the one furthest from the Sun. An icy, barren, and dark planet, Pluto is tiny compared to its neighbors but had some moons orbiting it. It may not have been as glamorous as Venus, flashy as Saturn, or powerful as Jupiter, but Pluto could command some attention from astronomers. That all changed in 2006 when scientists demoted Pluto from full planet status to that of a newly-established celestial category, dwarf planet. Let’s look at the rise and fall of Pluto. 

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Lowell Observatory in Arizona where Pluto was first observed. Source: (

Discovery of Pluto

As early as the 1840s, there was speculation among astronomers that an undiscovered planet might exist beyond Neptune because it appeared that something was affecting the orbit of Neptune. In 1909, astronomers Percival Lowell and William H. Pickering developed theories and several possible locations for this unknown planet. Using telescopes at the Lowell Observatory in Arizona, founded by Lowell, the two men attempted to locate this planet, which they called Planet X, but to no avail. In 1929, a 23-year old astronomer named Clyde Tombaugh was assigned to review Lowell and Pickering’s research too, once again, pick up the search for the unknown planet.