Pluto and Other Things That Aren’t Planets


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: 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.

Why I Love My Job

Neil Armstrong


Why I love my job…

The guy in that picture? Forty-six years ago today, he was walking on the moon.

Which, really, is kind of amazing.

On his right shoulder, that man, who walked on the moon, is wearing a red-white-and-blue patch. The symbol of the agency that put him there.

Some days, I get to wear that same symbol and go tell people what that agency is doing today.

Which, really, is kind of amazing.

I don’t, in my line of work, get to do things quite as amazing as that man did. But I do get to do some amazing things. And it is humbling and inspiring in the midst of those things to remember that the same agency that saw fit to send Neil Armstrong to the moon has seen fit to let me blog on its behalf or represent it in another country or share with the public the excitement of a rocket launch or an engine test.

But here’s the really amazing part…

It’s tempting and easy to be overshadowed by that history, by that legacy. It’s easy to go to work one day and listing to Gene Kranz talk about the landing of Apollo 11 or the rescue of Apollo 13 and to feel like our job now is simply to be worthy of what we have inherited.

It’s not.

Our job is to do better.

The NASA I am incredibly incredibly lucky to be a part of is one that is in the midst of undertaking endeavors more ambitious than any it has undertaken before. It is in the midst of beginning a journey monumentally more challenging than the one marking an anniversary this week.

Just as Neil Armstrong will hold a larger place in the history book than Alan Shepard, our job today is to write history that will hold a larger place than his.

That? That’s amazing.

Lackluster Secrets of the Pluto Time Capsule

For nine years now, people all over the world have been looking forward to today. After years silently sailing through the vast void of deep space, the New Horizons spacecraft today finally has its closest encounter with distant Pluto and its moon, giving us an unprecedented look at what has been the greatest mystery of our solar system, a world we’ve known of for the better part of a century, but seen only ever as through a glass darkly.

And, I mean, that’s cool and all.

But me — well, sure, I’ve been looking forward to that part, too — but today is also the day that I got to open my New Horizons time capsule, and unveil the surely equally compelling secrets contained therein.

(Brace now for disappointment.)

Time capsule in a tennis ball case

So back in February 2006, maybe a couple of weeks after New Horizons launched for Pluto, I was attending the Space Exploration Educators Conference in Houston, and attended a workshop about how to get students excited about the mission (and about Pluto, then still a planet), in part via a time capsule activity.

Everyone in the group was given a tennis ball tube and a sheet to use as the basis of the time capsule, and allowed to make their own time capsule during the session so they could have their students do it when they got back to their schools.


And so, there in the class, I worked on the two sheets of the activity, rolled them up into the cylinder, brought it home to Huntsville, and dutifully put it away in a drawer where it has remained untouched ever since. Every once in a while I’ve come across it and wondered what it said (having long since forgotten), but I’ve been good and never opened it again since the session.


(Did I mention you should brace for disappointment?)

Here, then is page one of the two-page contents I wrote back in February 2006:


How’s that for a revealing look at life in 2006? Future historians will no doubt consider this a foundational document for understanding life in the early 21st century.

“Grade: A” So clever, ten-years-ago, David! Don’t ever change! (Spoiler: You totally will. Get ready.)

That said, I still don’t have a favorite color, I still enjoy writing, and I’m trying to do low-carb again. I haven’t worn that shirt in a few years, but I’m pretty sure I know which one I was trying to draw.

So that’s the past.

Now, on to THE FUTURE!!! (Which, er, is actually now the present. But you know what I mean.)


So, yes, the future remained largely unwritten.

I’m guessing I didn’t have time to finish the activity in the session, and was so determined in not touching the capsule again that I forgot I hadn’t finished it. Or, possibly, that’s all the thoughts I had about the future. Either way.

But — “wireless iPod”? What does that even mean? It’s like you had to keep your iPad plugged into anything to use it? Was I wanted one that didn’t involve headphones? Or that, I don’t know, charged or synced without wires?

I’m choosing to believe I accurately predicted how common and important the then-still-a-year-and-a-half-off iPhone would be in today’s society. But who knows?

So there you go — the secrets of the Pluto Time Capsule.

Thankfully, the actual secrets of Pluto have proved much more rewarding. Go check them out now!

Pluto and Charon

Credit: NASA