The Harvard-Smithsonian Center for Astrophysics hosted a debate surrounding the definition of a planet and whether or not Pluto, which was exiled from planet-status in 2006, should be reinstated as our solar system’s ninth planet.
The International Astronomical Union was placed in charge of developing a universal definition of a planet in 2006 after many objects similar to, and some much larger than, Pluto began surfacing beyond Neptune. They agreed to define a planet as a celestial body that is in orbit around the sun, is round or nearly round and has “cleared the neighborhood” around its orbit. By this definition, it was ruled to disenfranchise Pluto as the ninth planet in our solar system for not meeting the last of the three criteria.
After eight years, the Harvard-Smithsonian Center decided to challenge this definition and hold a public debate in question of the IAU’s stance. This debate featured three separate experts in the field who had three different ways of defining a planet.
Dr. Gareth Williams, associate director of the Minor Planet Center, maintained the definition put into place in 2006. Science historian Dr. Owen Gingerich, who chaired the IAU planet definition committee, argued that the term planet is defined completely by human culture. Dr. Dimitar Sasselov, director of the Harvard Origins of Life Initiative, defined a planet as “the smallest spherical lump of matter that formed around stars or stellar remnants” which would include Pluto.
After the three experts spoke, the Harvard audience sided with Sasselov’s definition and the decision to reinstate Pluto. Dr. Brian Redmond, Wilkes University professor of Environmental and Earth Sciences who teaches Astronomy, disagrees with this decision.
“Definitions can be kind of gray sometimes but, I’m afraid, in the case of Pluto it is just too small,” said Redmond. “There’s just no way it fits into planet class no matter how you want to define planets.”
Redmond hopes that scientists do not adhere to the opinion of the public by reinstating Pluto. He feels the debate only exists because of childhood sentiments surrounding the former ninth planet.
“When we were kids, we were taught there were nine planets,” said Redmond. “People have this sentimental attachment to that. Demoting Pluto leaves us with one less planet. It sounds like you’re losing something. The truth is you aren’t losing anything; it’s just a name.”
No matter which definition of a planet you choose to use or which side of the Pluto debate you may be on, the debate does not seem to be over. The audience of the debate may have agreed to reinstate Pluto’s residency in the Milky Way, but many astronomical experts are sticking with the 2006 decision to evict the formerly ninth planet.
