When the International Astronomical Union came up with an official definition of a planet in 2006, they booted Pluto out of the club and reclassified it as a dwarf planet. But some say the discovery of exoplanets requires that we revisit this definition and give Pluto a second chance.
The current, official definition says that a planet is a celestial body that:
1. is in orbit around the Sun
2. is round or nearly round, and
3. has “cleared the neighborhood” around its orbit.
But this definition only applied to planets in our solar system. What about all those exoplanets orbiting other stars? Are they planets?
But in America, democracy reigns, and last week the Harvard-Smithsonian Center for Astrophysics re-addressed the debate, putting Pluto’s planetary status to a vote once again. A debate preceded the vote, with three planetary experts offering differing points of view.
Dr. Gareth Williams, associate director of the Minor Planet Center in Cambridge, said the icy body does not qualify for planetary status. But Dr. Dimitar Sasselov, director of Harvard’s Origins of Life Initiative, argued otherwise. And Dr. Owen Gingerich, professor emeritus of astronomy at Harvard and a senior astronomer emeritus at the Smithsonian Astrophysical Observatory, argued that defining what a planet is shouldn’t be up to scientists.
“What is a planet is a culturally defined word that has changed over the ages. The IAU was foolhardy to try and define the word planet,” he said.
Bill Nye didn’t participate in the debate, but the self-described “longtime fan of Pluto” told The Huffington Post in an email:
If astronomers want to call Pluto a “planet,” that’s fine with me. If that is the route they choose, I believe they will add the several other objects way out there that have enough gravity to be spherical. … I love Pluto as much as the next guy, but it has a different origin from the traditional planets and orbits in a different plane. It might be exciting to have names for hundreds of new (very old) planets, but I would be fine with 8 “traditionals” and hundreds of “Plutoids.” These objects are out there and have the characteristics they have regardless of what we call them. But I know, people get pretty passionate about it.
After the experts argued their cases, the audience was allowed to vote on what a planet is or isn’t and whether Pluto should be considered a planet. The results were conclusive: Pluto should be a planet once again. The video of the debate is now available online: