In 2006, the International Astronomical Union came up with its official definition of a planet and poor Pluto was booted off the list. It’s now just a dwarf planet because it doesn’t meet the three fundamental planet requirements. A planet is only a celestial body that is in orbit around the sun, round or nearly round, and has “cleared the neighborhood” around its orbit.
The Harvard-Smithsonian Center for Astrophysics is revisiting this idea and hosted a debate featuring experts in the field. Astrobiology Magazine reported on the event saying:
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.
Of course, if it came down to a popular vote, Pluto would probably be a planet again. Alas, this does nothing to change the official, scientific classification.
See video of the debate after the break.