An Iowa State University professor is at the meeting where the world’s leading astronomers voted to demote the planet Pluto.
Iowa State University physics and astronomy professor Lee Anne Willson voted with the majority to change the definition of what a planet is. That makes Pluto a mere “dwarf-planet.” Willson’s at the International Astronomical Union in Prague and has emailed her faculty colleagues back in Ames, including Steve Kawaler. “The basic shape of the solar system changed today,” Kawaler says.
That means all those posters and mobiles hanging in classrooms and children’s bedrooms that feature nine planets are now obsolete. “Like everyone alive, almost, I’ve lived with nine planets. We’ve had nine planets since 1930,” Kawaler says. “From a scientific point of view it makes a lot of sense and is almost overdue to classify Pluto somewhat differently.”
What makes Pluto basically different from the eight celestial bodies which retain the classification of “planet” is that Pluto has no “measurable” effect on the motions of the major planets whereas things like gravity fields impact the way the eight planets revolve around the sun.
If Pluto had retained its status as a Planet, then the Solar System line-up of planets would have had to expand. “There is one object in particular that’s farther away from the Sun, on average, than Pluto (and) is bigger than Pluto, so if you continue to call Pluto a planet then we would get that guy,” Kawaler says. “But then you can’t not talk about some of the larger objects in the inner Solar System, so you’d have to count that largest asteroid…that’s what? Eleven now, and then…Pluto’s satellite which is almost bigger than Pluto itself, so that’s 12, and so you have this sort of creeping inflation of numbers of planets with the initial definition.”
So, now that Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune are the names of the planets in the Solar System, it means that sentence many of us memorized to remember the order of the planets is antiquated. “It was My Very Educated Mother Just Served…Us Nine Pizzas,” Kawaler says. Kawaler’s quick suggestion for a replacement word to end that sentence is “Nachos.”
Kawaler welcomes the debate about Pluto, and the discussion it’s sparked. “Raising the question of what is a planet is helpful to focus our scientific inquiry but it’s also really useful to sort of re-engaging people into some fundamental questions about where they live in the cosmos,” Kawaler says.