What People Are Getting Wrong This Week: Pluto Is Still a Planet (Sort Of)
The 95th anniversary of the discovery of Pluto, an ice-covered, rocky sphere orbiting about 3.7 billion miles from the Sun, is less than two weeks away. To mark the occasion, the Lowell Observatory in Flagstaff, Arizona, where Pluto was discovered, is hosting its sixth annual I Heart Pluto Festival. But should they do this? Is Pluto even a planet?
According to a recent YouGov poll, 35% of Americans think Pluto is not a planet. In their opinion, the matter is different. But they are all wrong in some sense. To get to the bottom of the status of the planet Pluto, I tracked down planetary scientist Dr. Will Grundy —whom you may recognize from academic papers such as Measuring D/H and 13C/12C Ratios in Methane Ice on Eris and Makemake: Evidence for Internal Activity —and asked him point blank: Is Pluto a Planet or a Scam?
Arguments for the planetarity of Pluto
According to Dr. Grundy, Pluto is a planet. “I use the word planet for this, and most of the planetary science community does,” Grundy said. “Pluto has everything I love about the planet in abundance. It has a satellite system. It has an atmosphere with interesting weather conditions. It has very complex seasonal cycles. There’s all kinds of active geology going on here… it’s got everything you want.”
So Pluto is a planet. Case closed. Well, maybe not completely closed.
Arguments against the planetarity of Pluto
According to the International Astronomical Union , Pluto is not a planet. The IAU shocked the world in 2006 by depriving Pluto of its planetary status.
According to the IAU, to become a planet you must do all of the following:
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In the orbit of the Sun.
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Have enough mass that your own gravity will pull you into a nearly circular shape.
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Clear the area around your orbit of other important objects.
Like my friend Dave, Pluto meets only two of these criteria. The third is too much for Pluto. That’s why the IAU says Pluto can’t sit at the kids’ classroom table with Venus and Saturn; its proper place is with dwarf planets such as Quaoar, Sedna and Orcus.
Why Pluto’s “planet” status is a problem
Pluto’s decline was partly due to our getting better at detecting planets (or “dwarf planets” if you will). In the early 2000s, astronomers identified Haumea, Eris, Makemake and other orbs orbiting our Sun. If the old definition of the word were used, they would all have to be called “planets.” So the IAU struck. “They had a moment of crisis of willpower,” Grundy said. “They got scared because they realized there were going to be a whole bunch of extra planets, and that just panicked them.”
So the cowards at the IAU have come up with guidelines for what makes a planet a planet, apparently based on the traditional planets we all know and love and read about in astrology books. According to many scientists, this was a mistake. “They took a definition from folk culture instead of a scientific definition, and they are ashamed to do it,” Grundy said. “They didn’t want to announce a new planet every year and then expect schoolchildren to have to remember 15 of them, and now, three years later, there are 20, and so on and so forth.”
According to Grundy, the more planets, the better. “Have you ever met a little child who loves dinosaurs and gets offended when he discovers another one?” – Grundy asked.
Is Pluto actually two planets?
How about it blow your mind: Pluto is two planets. Boom! Shots rang out. Pluto’s largest moon, Charon, is almost half the size of Pluto. “I would consider Charon to be large enough to become a planet,” Grundy said. “There’s geology and all sorts of processes going on here. What more could you ask for?
If this sounds like expanding the definition of the word “planet” to mean whatever you want it to mean, that’s how words work. The scientific community talks about planets more than anyone else, and they have no problem using the word in every sense, including in relation to Pluto. “If you listen to a talk on planetary geology, you’ll hear the word used differently than if you go to a talk on the early evolution of the solar system,” Grundy said. “It really just depends on your focus.”
Pluto doesn’t care whether it’s a planet or not.
The question of whether Pluto is a planet or not is not really about the celestial body. It’s about how we label things and how the universe refuses to conform to human taxonomy. It doesn’t matter what we call Pluto, it will still exist and do the same things that Pluto does.
“Textbook authors always seem to be looking for authority. They want a definitive answer because they don’t want to be wrong. But in fact, nature does not work like that. Nature is very messy and messy,” Grundy said. “We used to classify whales as other fish because they lived in the ocean. We don’t do that anymore because we know they are mammals and we know the phylogenetic origins. But why are we more concerned with phylogenetic origins than with location? Thinking develops, and it does not develop for everyone at the same speed and in the same direction.”