Universe Today

A debate today between astronomer Neil deGrasse Tyson and planetary scientist Mark Sykes, moderated by NPR’s Ira Flatow, addressed the issue of Pluto’s planetary status. There was lots of arm-waving and finger-pointing, endless interruptions, disagreements on details big and small, and battling one-liners. The two scientists sat at a table with the moderator between them and Flatow was often obscured by Tyson and Sykes getting in each other’s faces in eye-to-eye confrontation. At one point, Flatow was hit by Tyson’s ebullient arm motions. Yes, it was heated. But it was fun, too. It ended up being not so much a debate between the Pluto-huggers and the Pluto-haters as a disagreement over the lexicon of astronomy and planetary science and, primarily, the definition of a planet. Pluto’s planetary status was definitely not decided here, and the debate concluded with an amicable agree-to-disagree concurrence that the scientific process is an ongoing, evolving practice. But it wasn’t without fireworks.

At the start of the Great Planet Debate, Flatow laid down the ground rules, which included no throwing of perishable items, but that was about the only rule that didn’t get disregarded. Tyson, director of the Hayden Planetarium in New York and host of Nova ScienceNow, and who is in the camp that Pluto is not a planet, began his opening statements with “It’s simple. The word ‘planet’ has lost all scientific value.” He went on, saying “planet” doesn’t tell you much and you have to ask all sorts of questions such as is it big or small, rocky or gaseous, in the habitable zone or not, etc. “If you have to ask twenty questions after I say I’ve discovered a planet, the word has lost its utility.” Tyson said “planet” had utility far back in time when there wasn’t much else we knew about, but we know so much more now. “If we’re going rely on one word and put them all in one pot, what are we doing as scientists and educators? The time has come to discard the useless words and invent a whole new system to respect the level of science we have achieved…We’re in desperate need of a new lexicon to accommodate this knowledge,” he said.

Sykes, director of the Planetary Science Institute, and who believes Pluto should be reinstated as a planet, began, “How we categorize things is part of the science process. It is natural for humans to group things together with common characteristics as a tool to better understand and how they work. This applies to biology and astronomy as well.” He continued that we have discovered planets around other stars and continue to find Kuiper Belt objects that will need to be classified, so classifying objects is not a useless task. The IAU (International Astronomical Union) bit the bullet and decided on a classification, but unfortunately, Sykes said, what they came up with was not very useful.

That was the end of decorum, as Tyson interrupted with, “You wanted a definition. They gave you a definition and now you’re complaining about it!”

“Absolutely,” said Sykes, wanting to continue, but Tyson quickly chimed in, “And let me add…”, where Sykes butted in with “You have to let me start before you add!”

Flatow looked around and said, “I think I’m in a danger zone here.”

Thus began the debate.

Sykes said that any definition has to have a reason, or a purpose. According to the IAU’s definition, planets have to orbit the sun, they have to be round, and they have to have cleared their orbits, among other things. There was immediate confusion with this definition, which Sykes said was a little “goofy.” In order to be a planet, an object has be bigger the farther away it is from the sun, and it ignores the physical characteristics. He believes it’s useful to group things together that are similar and then have subcategories. So, you have planets, under which are terrestrial, gas giants, ice planets, etc.

Tyson said that even for him, the IAU’s definition falls short of taking the total amount of information to task. “If you only want to call round things planets, that puts Pluto in the same class as Jupiter. I happen to like round things. But what other lexicon might be available to group similar things together?”

“That’s why god made subcategories,” said Sykes. “It’s good to have a good general starting point for classifying things.”

Tyson humorously pointed out this debate is big only in the US, which he attributed to Disney’s creation of the lovable, dimwitted cartoon bloodhound named Pluto. School kids, grownups, op-ed writers all say Pluto is their favorite planet. “I am certain that the word ‘plutocracy’ is traceable to what Disney has done, so it’s hard to extricate the sentiment we have for the planet from the dog.”

Sykes said the IAU didn’t expand our perspective on planets, but narrow it. “The planet count went down, and what was the justification of that? The proponents have never given a good explanation of what was motivating that perspective.”

Tyson said numbers aren’t important, but words and definitions are, and we definitely need new ones.

Both scientists gave good arguments for their cause, and since I’m decidedly on the fence with this issue, I found myself leaning towards one option or the other, as each one spoke. Sykes, who wants to see Pluto reinstated as a planet, wants to take what we have and make it better, while Tyson, who thinks Pluto is a comet, wants to start over with new and better words and definitions.

It was an entertaining and educational debate with two well-spoken and intelligent scientists who sometimes weren’t very polite, however. (Sykes said, “When were’ not fighting we get along fine.”) The most important thing, they both agreed though, was that scientists are actually talking about this issue in the public eye and people are interested. But more importantly, the public is seeing the scientific process in action. They said this debate shouldn’t be about making things easy, or worrying about “not confusing the public.” Learning science shouldn’t be rote memorization of lists of objects, but a discussion of how objects are similar and different. “My recommendation to school teachers,” said Tyson “is to get the notion of counting things out of your system and comb the solar system for the richness of objects. Ask about different ways to combine the different objects in our solar system and have a discussion about their different properties.”

The debate will be available online, and we’ll post a link to it here when it is.

Sykes ended with his closing argument: “We both have issues with what happened with the IAU, its part of an ongoing presentation, but the important things is that the public gets to see the debate, and it’s not a battle over what list and what numbers you have, but the debate of the issues. That’s more important whether either of us have convinced you of one perspective. Science in this country is too much memorizing lists promulgated by those in authority. This is helping to expose the messy side of science. This debate is good and positive.”

Tyson ended by saying how charmed he is at the level of public interest in this subject. “How many sciences get to have their issues debated in the op-ed pages and comics?” He said he was happy with the word “planet” until all the data started pouring in from our explorations. “There should be a way to celebrate a new way to think about things. There ought to be a way to capture that” he said.

Obviously, this is not the last word on the subject from either scientist, or either side of the debate.

But that’s a good thing.

For more info on the Great Planet Debate.