Revisiting The Pluto Debate: Should It Be Considered A Planet?

Chuck Bednar for redOrbit.com – Your Universe Online
Pluto may no longer be a planet in the eyes of the International Astronomical Union (IAU), but as a recent debate hosted by the Harvard-Smithsonian Center for Astrophysics (CfA) revealed, not everyone agrees with the official assessment that led to its 2006 demotion.
“What is a planet? For generations of kids the answer was easy. A big ball of rock or gas that orbited our Sun, and there were nine of them in our solar system,” the CfA explained. “But then astronomers started finding more Pluto-sized objects orbiting beyond Neptune. Then they found Jupiter-sized objects circling distant stars, first by the handful and then by the hundreds. Suddenly the answer wasn’t so easy. Were all these newfound things planets?”
The debate led to an August 2006 meeting of IAU scientists in Prague in the Czech Republic, where it was decided to adopt a new definition of the word ‘planet’ that excluded Pluto from the club. Instead, the distant, ice-covered sphere was downgraded to a ‘dwarf planet,’ according to Mason Inman of National Geographic News.
The definition agreed upon by those in attendance at the IAU meeting said that a full-fledged planet had to orbit the sun, had to be large enough to have become round due to the force of its own gravity, and had to dominate the neighborhood around its orbit. It is because of this last factor that Pluto failed to meet the criteria, as it is only about twice the size of its ‘moon’ Charon, while all true planets were found to be far larger than their moons.
The IAU definition “baffled the public and classrooms around the country,” the CfA said. “For one thing, it only applied to planets in our solar system. What about all those exoplanets orbiting other stars? Are they planets? And Pluto was booted from the planet club and called a dwarf planet. Is a dwarf planet a small planet? Not according to the IAU. Even though a dwarf fruit tree is still a small fruit tree, and a dwarf hamster is still a small hamster.”
At the September 18 event, a trio of experts – Dr. Gareth Williams, associate director of the Minor Planet Center in Cambridge; Dr. Dimitar Sasselov, director of Harvard’s Origins of Life Initiative; and Dr. Owen Gingerich, a senior astronomer emeritus at the Smithsonian Astrophysical Observatory – debated what characteristics should actually be used to define what a planet is, said Huffington Post reporter Macrina Cooper-White.

Full length video of the debate and audience voting.
Dr. Gingerich, who chaired the IAU planet definition committee, argued that a planet “is a culturally defined word that changes over time” and that it shouldn’t be up to scientists to establish the criteria. Dr. Williams defended the IAU definition and reiterated that Pluto does not qualify for planetary status, while Dr. Sasselov said that Pluto was a planet because they should be defined as “the smallest spherical lump of matter that formed around stars or stellar remnants,” the Smithsonian said.
After each scientist made his best case, those in attendance were asked to vote on what a planet is or isn’t, and whether or not Pluto should be considered one. They chose Dr. Sasselov’s definition and declared that they believed Pluto should be viewed as a planet. While he did not participate in the debate, Bill Nye contacted Cooper-White to weigh in on the debate, stating that it was “fine with me” if astronomers want to refer to Pluto as a planet.
“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,” he told The Huffington Post in an email. “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,’” Nye added. “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.”
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