For many of us, when Pluto was declared not a planet by the International Astronomical Union in 2006, it pulled the rug out from underneath us. So many of us learned to remember the planets in our solar system via the following sentence: My very elegant mother just served us nine pizzas. Suddenly in 2006, it became “My very elegant mother just served us nine.” Served us nine? That doesn’t make any sense! How will we ever remember the planets?
However, just as we were beginning to purchase one less styrofoam ball for our dioramas, officials are questioning whether or not it was a smart move to kick Pluto out of The Planet Club.
On September 18th, The Harvard-Smithsonian Center for Astrophysics held a public debate to address the definition of planet. The debate included Dr. Gareth Williams, the associate director of the Minor Planet Center, Dr. Dimitar Sasselov, director of the Harvard Origins of Life Initiative, and Dr. Owen Gingerich, a science historian who previously headed the IAU planet definition committee.
According to the IAU, in order for a celestial body to be considered a planet, it must orbit the Sun, be round and have “cleared the neighborhood” around its orbit. In 2006, Pluto was deemed a “dwarf planet” given that many Pluto-sized objects were found beyond Neptune that weren’t classified as planets. With this discovery and the discovery of exoplanets, the definition of planet has become quite vague.
Despite being on the committee that deemed Pluto a dwarf planet, Gingerich argued that Pluto is indeed a planet and that “a planet is a culturally defined word that changes over time.”
At the end of the debate, the audience voted on the most accurate definition of planet. Dr. Sasselov’s definition was the victor. Sasselov stated that a planet is “the smallest spherical lump of matter that formed around stars or stellar remnants.” By Sasselov’s definition, Pluto definitely qualifies as a planet.
While the conclusion of this debate doesn’t mean Pluto is officially reinstated as a planet, it could influence the IAU to reevaluate their classifications.