Unfortunately, the expression didn't really catch on. And now its basis is being challenged. Members of the Harvard-Smithsonian Center for Astrophysics presented three different viewpoints to the public and the audience could vote on which viewpoint they liked best. The result? Pluto should be called a planet, since "a planet is a culturally defined word."
Eight years later, the Harvard-Smithsonian Center for Astrophysics decided to revisit the question of "what is a planet?" On September 18th, we hosted a debate among three leading experts in planetary science, each of whom presented their case as to what a planet is or isn't. The goal: to find a definition that the eager public audience could agree on! Science historian Dr. Owen Gingerich, who chaired the IAU planet definition committee, presented the historical viewpoint. Dr. Gareth Williams, associate director of the Minor Planet Center, presented the IAU's viewpoint. And Dr. Dimitar Sasselov, director of the Harvard Origins of Life Initiative, presented the exoplanet scientist's viewpoint. Gingerich argued that "a planet is a culturally defined word that changes over time," and that Pluto is a planet. Williams defended the IAU definition, which declares that Pluto is not a planet. And Sasselov defined a planet as "the smallest spherical lump of matter that formed around stars or stellar remnants," which means Pluto is a planet. After these experts made their best case, the audience got to vote on what a planet is or isn't and whether Pluto is in or out. The results are in, with no hanging chads in sight. According to the audience, Sasselov's definition won the day, and Pluto IS a planet.Alas, I have my doubts that a public vote will move the International Astronomical Union (IAU) to reconsider its decision that Pluto not be considered a planet. Their introducing the term "dwarf planet" (which is to be considered distinct from, not a subclass of "planet") doesn't exactly indicate that cultural awareness of linguistic terms is something they care about a lot.