Huntsville and Pluto


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Ten years ago today, Pluto was officially reclassified, recognizing that it was less like our solar system’s eight planets than it was like the many, many small bodies populating the region beyond Neptune.

To put that in context, this year’s high-school freshman class has never been taught in school that Pluto was a planet.

If you’ve ever discussed Pluto on an iPhone, it wasn’t a planet when you did.

It’s exciting to think about how much our understanding of our solar system has increased in the last decade. And as a Huntsvillian, I’m proud of my city’s role in the story — “Pluto Killer” Mike Brown is a graduate of Huntsville’s Grissom High School, and Huntsville’s Marshall Space Flight Center managed the program that sent the New Horizons mission to explore Pluto. We had a connection to both correcting a major misconception about Pluto, and to revealing the amazingly spectacular truth.

 

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Pluto and Other Things That Aren’t Planets


Pluto

Pluto: Not a Planet

While the actual data and images coming back from New Horizons have been awesome, it’s been a little frustrating that they’ve come mixed with a heaping helping of posts about how Pluto should totally be a planet again now.

And the bulk of that comes down to “Pluto is interesting, Pluto is awesome, I like Pluto,” ergo Pluto should be a planet. To be sure, Pluto IS interesting. Pluto IS awesome. I DO like Pluto.

But my dog Amos is also interesting, awesome and likable, but I don’t think he should be a planet, ya know?*

Ultimately, taxonomy is relative. Language is subjective, and we can decide how it’s used. If we want the word “literally” to mean “figuratively,” that’s within our power as a literate people. There is no cosmic absolute that determines whether something is a planet or not, it’s just our subjective view of what we want the word planet to mean and how we want to use it.

Scientifically, there’s no reasons we can’t use the term planet to mean “The nine bodies recognized as planets in the year 2000.” In which case, Pluto would officially be a planet. Or even “”The nine bodies recognized as planets in the year 2000, plus David and Rebecca’s dog Amos, who’s pretty awesome and interesting and likable.” In which case, Amos would also totally be a planet.

David and Amos at the Space & Rocket Center

Amos: Also Not a Planet

It comes down to what purpose you think a taxonomy should serve. If you want a system of categorizing celestial objects that’s “merit-based,” “rewarding” bodies that we find more “worthy,” then, sure, there’s no reason you can’t have that sort of classification system, and no reason Pluto can’t be a planet.

But if your goal is to have a taxonomy that promotes better understanding of the solar system (and thus the cosmos), it makes far more sense to use a classification system that groups like things with like things and thus encourages the use of what we learn about one body to help us better understand similar bodies. Calling Amos a planet doesn’t mean he can teach you anything about the other planets. (Trust me on this one; he totally won’t.)

Pluto is utterly unlike any of the other planets in all but the most superficial of senses. Like the other planets, it’s round, as are moons and baseballs. Like the other planets, it orbits the sun, as do asteroids and comets and the S-IVB stage for Apollo 8. (Actually, this one is less true of Pluto, which is substantially affected in its orbit by Charon, than of asteroids and comets and the S-IVB stage for Apollo 8, all of which have a greater claim to planethood under this standard.) Yes, it’s more rare for a body to meet both of these requirements, but it’s not that rare, and there are lots of other things that do that don’t make the “My Very Educated Mother…” list.

Saturn V S-IVB Stage in space

Saturn V S-IVB Stage: Also Also Not a Planet

On the other hand, from what we’ve seen, Pluto is a lot like other Kuiper Belt Objects, tiny objects that populate the far reaches of our solar system. The sad cartoons that depict Pluto as being lonely or sad for being kicked out of the planet club fail to understand or acknowledge that Pluto has far far more celestial cousins than our Earth does.

When we first discovered Pluto, we had not discovered anything else in the solar system like it, so we classified it with the things it was most like. Since then, however, in the Kuiper Belt, we’ve discovered a lot of things that are a lot more like Pluto than the other planets. So we corrected a mistake made in ignorance, and reclassified it with the new discoveries it was most like.

This exact situation happened once before, with Ceres. When Ceres was discovered in 1801, we’d not seen anything else like it. But even though it was small, it was round and orbited the sun, so the most logical classification was to call it a planet. But then we found another body near Ceres. And another, and another. And we realized that Ceres was a lot more like this new type of thing, which we called asteroids, than it was like the other planets.** And when we study Ceres, we study Ceres to learn about asteroids and their place in our solar system.

Ceres

Ceres: Interesting, Crazy Mysterious, But, Yep, Also Also Also Not A Planet

Today, we have a much greater understanding of the asteroid belt, but the same is not true to nearly the same extent of the Kuiper Belt. And right now, Pluto is our best tool for understanding these mysterious worlds; which in some ways have been more alien even than planets orbiting other stars. Pluto has little to teach us about the eight planets, but it has a lot to teach us about the Kuiper Belt. So if scientific understanding is the goal of your taxonomy, you classify Pluto in the latter category rather than the former.

I was inspired to write this post by this article, which hits the nail on the head: It’s not sad that Pluto isn’t a planet. It’s awesome that Pluto is something even more valuable — our Rosetta Stone to distant worlds shrouded in secrecy that remind us how little we still truly know about our universe, and how much wonder still awaits us on our outward odyssey.


*All opinions in this post are purely my own. I make no claim of representing the views of NASA or any other organization on whether Amos (or any other body) is a planet.

**Fair or not, I judge whether someone’s desire for Pluto to be a planet or not is scientific or sentimental based on what they say about Ceres. If you weren’t posting during the Dawn approach that Ceres should be a planet, I assume your interest in Pluto’s planethood is probably based more on your childhood attachment to Pluto than in taxonomy.