Back by popular demand: public backs Pluto for planethood

Not long after scientists decided Pluto didn’t fit the definition of a planet, a new public debate has determined that Pluto is a planet once again. According to Science Alert, a group of scientists gathered last week to debate over what a planet actually is. After a popular vote, the congregation decided that Pluto does, indeed, fit the description of a planet — at least for the purposes of our solar system. The debate over Pluto’s fate took place at the Harvard-Smithsonian Center for Astrophysics between three experts. After a debate in front of an audience of scientists, teachers and civilians, the three scientists took a vote on Pluto. Two of them voted that Pluto should be a planet and the other voted against. The initial decision to remove Pluto from the solar system was made in 2006 by the International Astronomical Union (IAU), who determined Pluto was too small to qualify as a planet when compared to the other eight planets in the solar system. Many astronomical objects larger than Pluto have been discovered, like the dwarf planet Eris, that were never considered to be planets. The reasoning was that Pluto shouldn’t count as a planet either if other bigger worlds weren’t earning the classification.

The definition of what a planet is has changed several times in recent history, but the argument put forward by the first scientist in favor of Pluto’s planet-hood had little to do with the official definition. A historian named Owen Gingerich argued that a planet is not determined by astronomical definitions but by human culture. Therefore Pluto must be a planet because humanity decided it was long ago. Dimitar Sasselov’s argument was much more scientific in nature. Sasselov, the director of Harvard’s planetary program, the Origins of Life Initiative, claimed that a planet is defined as the smallest spherical lump of matter that formed around stars or stellar remnants, meaning Pluto is a planet. The scientist who argued against Pluto as a planet was Gareth Williams from the IAU’s Minor Planets Center. He argued that a planet is a spherical body that orbits the Sun and has cleared its path, meaning Pluto can’t be a planet. Last week, at the Harvard-Smithsonian Centre for Astrophysics came the strongest hint yet that the solar system's underdog could be called off the subs bench.

According to the International Astronomical Union, a planet needs to meet the following criteria:

1. It must be in orbit around the Sun.
2. It must have sufficient mass to assume hydrostatic equilibrium (a nearly round shape).
3. It must have "cleared the neighbourhood" around its orbit, meaning it has its orbit all to itself,.

In light of the debate, these could now be up for a rethink.In a public forum made up of teachers, scientists and the public, in Cambridge, Massachusetts, three eminent astronomers debated the topic: "Is Pluto a planet?" Arguing against, the associated director of the International Astronomical Union's Minor Planet Centre, Gareth Williams, said that a planet was defined by having a neighbourhood. "Jupiter has cleared its neighbourhood. Earth has cleared its neighbourhood. Ceres, which is in the main asteroid belt, hasn't. Pluto hasn't," he said. "In my world, Pluto is not a planet."
But Harvard astronomer and historian Owen Gingerich said it was a matter of semantics. Pluto is a planet he argued, and the International Astronomical Union has no business defining the word "planet". It was a remarkable about-face from the academic who was in charge of the International Astronomical Union committee that defined the word "planet" in 2006. "My feeling is that in retrospect, the IAU should not have attempted to define the word 'planet'," he said. "People said, 'This can't go on. We can't have this many planets. We've got to call them something else,' " Professor Gingerich said. "I thought it was really dumb that the IAU took as a category 'dwarf planet' and then said, 'But they're not planets, I was disappointed that it happened that way."
He also revealed that, when Pluto was relegated to sub-planet status in 2006, it was because most of the IAU attendees wanted to get it over and done with so they could go to lunch. Of the International Astronomical Union's nearly 10,000 members, the 424 who voted on the decision then were offered the opportunity to rethink Pluto's demotion, Professor Gingerich said. "They voted not to vote again because they wanted to go to lunch, so that was the end of it." But the crowd's favourite argument came from the director of Harvard's Planets and Life initiative, Dimitar Sasselov. Professor Sasselov argued that a planet should be defined as the smallest spherical lump of matter that formed around stars or stellar remnants. In the end, the audience voted in a landslide - or should that be a 'planetslide'? - to reinstate Pluto. Prominent astronomers said that the result of the debate highlighted how out of touch the International Astronomical Union is. "Every time there is poll it turns out this way," planetary scientist Alan Stern told Time magazine. "The IAU have become largely irrelevant on this."