The vote is in! Pluto should be considered a planet again.
Until 2006, the definition of a planet was "a big ball of rock or gas that orbited our Sun." Schoolchildren were taught that our solar system included nine planets, one of which was Pluto, the Harvard Smithsonian Center for Astrophysics reported.
Pluto's status as a planet was called into question as astronomers started finding objects of the same size orbiting Neptune. The definition of a "planet" became even fuzzier when they discovered hundreds of Jupiter-sized planets orbiting stars in far-off solar systems.
The International Astronomical Union (IAU), which is in charge of making these definitions, discussed the issue in a 2006 meeting. They voted that a "planet" is a celestial body that: orbits the Sun; is round or nearly round; and has "cleared the neighborhood" around its orbit. Pluto was "demoted" from its planet status to "dwarf planet" at this time.
This definition has been hotly debated for a number of reasons. One of the major problems was the definition only applied to planets in our own solar system, leaving it up in the air as to whether or not exoplanets could actually be fit into the revised category.
Now, eight years later, the Harvard-Smithsonian Center for Astrophysics revisited the definition of "planet." They hosted a debate on Sept. 18 that included three leading experts on the subject and allowed the public to vote on their conclusions.
Science historian Dr. Owen Gingerich, who chaired the IAU planet definition committee, argued the historical viewpoint while Gareth Williams, associate director of the Minor Planet Center held the IAU's findings. Gingerich said "a planet is a culturally defined word that changes over time." Dimitar Sasselov, director of the Harvard Origins of Life Initiative, argued the viewpoint of exoplanet scientists, claiming Pluto is "the smallest spherical lump of matter that formed around stars or stellar remnants."
After voting the public ended up siding with Sasselov, which means (as far as the debate goes) Pluto should be classified as a planet.
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