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Hey, Tumble listeners, it's Lindsay.
And also Marshall.
So before we start today's episode, we have something really exciting to share.
We made a music video.
And by we, I mean Lindsay made it.
I guess I made the song.
So we.
It was a collaboration.
Anyway, we made a music video for one of our most popular tumble songs called There Are Eight Planets in the Solar System.
And it's available on our first album, Tumble Science Songs Volume 1.
But now you can also sing along to the video on our YouTube channel.
It's all about how Pluto got discovered, became a planet, and then got demoted.
Fired.
Fired?
You think there was an awkward meeting where they were like, hey, Pluto.
Hey, Pluto, you're not performing the way that we thought you would.
You got to be bigger.
You got to work on clearing your neighborhood a little better.
Yes, exactly.
You don't exactly have the pull that we look for in a planet.
Ooh, zing.
And that is what the episode you're going to hear today is all about.
We get deeper into the history of Pluto in the secretive way.
It got kicked out of the planet rankings from a scientist who has kind of an ax to grind with the planet Namers.
Yeah, I'm not sure if I'm totally with him, but it's nice to hear him out.
Anyway, we originally made this episode back in 2018.
So has anything changed in the story?
Well, I think if you've looked at a list of the planets recently, you'll know that Pluto is still not a planet, and it's probably safe to say that it's not getting its status back at any point soon.
But as you'll hear in this episode, how we decide things in science is always up for debate.
All right well, let's go ahead and play the episode and stay tuned until the end to hear There Are Eight Planets in the Solar System.
Then check out the music video by clicking the link in the episode description.
Hi, I'm Lindsay.
And I'm Marshall.
Welcome to Tumble, the show where we explore stories of science discovery.
Today, we're weighing in on a scientific controversy of planetary proportions, Pluto.
It's been over a decade since astronomers voted on a new definition of the word planet, kicking Pluto right out of the classroom.
Solar system model.
But not everyone agrees with this planet vote.
We'll find out why some astronomers have never given up fighting for Pluto's planethood.
So before we started making this episode, we took an informal poll on our Patreon page about whether Pluto should be considered a planet or not.
No surprise, Pluto won.
How would you vote?
Think of your answer and your reasons why.
Because in this episode, we're going to present two sides of the planet debate.
At the end, we'll see if your thinking changes.
Usually, we think of scientists as not having strong personal opinions.
Just sort of being objectively detached and saying things like, well, what does the data show?
Right, but there are lots of times when scientists disagree and one might decide to take a stand for what they believe in.
And the debate around Pluto is a prime example.
So if you want to bring Pluto back, guess what?
Pluto never left.
In fact, Pluto brought all his friends with him or her.
That's Kirby Runyon.
He's a planetary geologist, which means he studies the geology of other planets.
It seems like he's pretty obviously in the Pluto is a planet group.
I have a strong opinion, and yes, a lot tied up in what is a planet or not a planet.
Kirby is one of several astronomers who published a scientific paper arguing against the International Astronomers Union, or IAU.
That's the group that decided to call Pluto a dwarf planet, not a real planet.
Ignore the IAU.
Dwarf planets are planets too.
This sounds like a full-on protest slogan.
It is.
Scientists have been divided over Pluto for a long time.
So how did we get to the point where scientists are like chanting slogans?
Well, let's go all the way back to the first stargazers.
The original Greek word for planet, of course, means wandering star.
And that just means that when you look at the night sky, you can see planets like Mercury Venus Jupiter Saturn, and they move relative to the background stars.
So for the Greeks, a planet was just any object in the night sky that moved around faster than the rest of the stars.
Exactly.
But when astronomy got a little bit more advanced, with telescopes and observatories, people started discovering other kinds of celestial bodies in our solar system.
When the first asteroids were discovered in the early 1800s, they were called planets.
Okay, so back then there were like a lot of planets.
Yeah, it was like a planetary explosion.
People didn't have a problem with there being hundreds of planets in the solar system.
Now we know that there are almost 800,000 asteroids in the asteroid belt between Mars and Jupiter.
That is a lot of planets.
It wasn't until between 1953 and 1957 that people started considering asteroids to not be planets.
That's because an astronomer named Gerard Kuiper wrote a scientific paper explaining that asteroids were not like the bigger planets at all.
Their surfaces, their interiors, how they form was just completely different from larger planets.
So it's not just Pluto, like hundreds of space objects formerly known as planets exist.
Well yeah, and it's pretty common for scientists to recategorize things once they learn more about them, whether it's objects in space or species here on Earth.
I mean that makes a lot of sense.
Whenever you learn more about something, you always recategorize it.
I used to think that there was just one kind of shoes, and then I learned that some of them had laces and some had Velcro.
Did you think that when you were a baby?
Well, it took me a little while to figure out the laces thing.
So bringing things back to outer space, it's time to talk about Pluto.
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The American astronomer Clyde Tombaugh discovered Pluto in 1930.
For a long time, astronomers had been looking for a mysterious ninth planet beyond Neptune.
From his observatory in Arizona, Clyde Tombaugh took pictures of the sky each night.
Then he put the photos in a fancy slide machine, clicking back and forth to see if he could spot the differences between the pictures.
It's like the 1930s version of an animated GIF.
And he could see a planet moving across the background stars, and he could then measure how far away it was and how fast it was moving around the sun.
And that planet was Pluto.
Yeah, and not only was it the ninth planet, it turned out to be the first object discovered in a distant belt of space objects beyond Neptune, called the Kuiper Belt.
Ooh, after the guy who demoted the asteroids from being planets.
Can you tell the story is about to come full circle?
Maybe.
So fast forward to 2005, an astronomer named Mike Brown was checking out the Kuiper Belt.
He discovered Eris, a planet-like object that's slightly more massive than Pluto.
The 10th planet.
Eris's size set off what basically amounts to an accounting debate.
To be a planet, it had to get registered with the International Astronomers Union.
That's the organization that holds the official records of all the names of all the objects in the universe.
So they're sort of like space accountants.
Why is that not a sci-fi show?
It would be super exciting.
Captain, I've been going over our balance sheets.
For this 45 minute episode.
We'll be talking about how our escrow account is getting dangerously low.
In reality, every couple years the IAU meets and votes on a bunch of space accountant things that are really boring to most people, even astronomers.
But in 2006, when everyone was confused about what to call Eris, a secret committee decided to vote on the definition of a planet.
Ooh, secret backroom accountant committees.
The intrigue, the fascination.
I'll bet they have awesome spreadsheets.
Yes.
At the end of a very long meeting in Prague, when most astronomers had already gone home, members of the IAU voted on an official definition of a planet that excluded Pluto as well as Eris.
Here's Kirby again.
It was my birthday and I saw the headline in newspapers as I was going out with my family to celebrate at a restaurant and I saw the vote Pluto is no longer a planet and I was like huh.
Pluto and its pal Eris had a new name, dwarf planets.
So what is a dwarf planet?
It's a large object that lives in space and it's round because of its own gravity and it orbits a star like a planet.
But it doesn't, quote unquote, clear the neighborhood of other material in its own orbit.
Uh, okay.
What's that?
It means that there's other space stuff, like whether it's debris asteroids, whatever in the area where the dwarf planet moves.
And that's what's really disqualifying it from being a real planet.
And honestly, I had to think about it for a few years to see where I came down on the issue.
And what really convinced me was the nonsensical claim that dwarf planets are not planets.
I'm like, no, that's just wrong.
And then I realized that I never swore allegiance to the IAU.
I don't have to go with what they say.
So I guess the IAU just really dropped the ball in not getting everyone to swear allegiance to it.
Yeah, it's not really something that they do.
And honestly, Kirby has a problem with authority.
He says that just going along with what people say, as decided by a vote, is really not how science works.
We don't vote on whether gravity is true.
The way that science makes progress is by scientists making discoveries and communicating their results.
Okay, so he's saying that scientists decide on things more by writing and talking?
Sounds like that takes a really long time.
It does.
Controversies or disagreements can take many, many years to resolve in science.
It's really a long process of finding consensus or general agreement between a majority of scientists.
Voting on a scientific concept is really rare, and it's not something even the IAU usually does.
And so, in my opinion, if the International Astronomical Union should do anything, they should rescind their definition of planet and just not replace it.
So he thinks they should just say we take it back?
And then we don't have a definition for what a planet is anymore?
Kirby argues that we don't need a definition by vote.
Getting rid of their definition and not replacing it, would send a message to the general public that hey, it's not based on a vote that we define things.
It's based on how scientists, who are experts in their field, actually use the words in their everyday life.
In other words, Kirby's afraid that regular people like you and me will think that scientific concepts get decided by a vote.
And that's just not true.
I guess that's an important point.
But what's the other side of the story?
Who's defending the vote?
I reached out to Mike Brown, the astronomer who discovered Eris.
He's taking credit for killing Pluto, although he didn't create the new definition or vote on it.
He didn't respond to my emails, and he said on Twitter that he's pretty sick of talking about this.
If I were him, I would be too.
Yeah.
But his position seems to be what's done is done.
He tweeted.
As an educator and a planetary scientist, I would like the public to understand that there are eight dominant bodies going around the sun.
I think the current definition is the best way to make this point.
So it's just, there are eight really big planets and Pluto's not one of them.
Yeah, for him it seems to be more about having a manageable number of planets in the solar system.
So one of the first things we learn about our solar system is the names of all the planets, and we can handle eight.
Yeah, and here's the thing.
If we had a more open definition of the word planet that included Pluto, we would have a lot more planets.
There are probably hundreds of planets in just our own solar system alone, most of which are small dwarf planets like Pluto.
Wait, so we could have hundreds of planets?
We're going to have to come up with a paragraph-length mnemonic device.
That's going to be tough.
Yeah, and our solar system models would be like a total mess.
You'd need like 800 pieces of styrofoam.
Some of them would just be like little specks.
So out beyond Neptune, we'll have a ton of new dwarf planets.
And even moons could fit under an open definition.
So it's really not just about Pluto being a planet, but inviting in a whole new planet squad.
And that's why some astronomers suggest that instead of names, we should learn the types of planets.
Terrestrial planets like Earth and Mars, giant planets like Jupiter and Saturn, and then dwarf planets like Pluto and Eris.
So like maybe there could be a compromise.
Let's see what our listeners think.
Remember our question from the beginning of the episode?
Do you think Pluto should be a planet or not?
Well, now that you've heard the arguments, have you changed your mind?
Think about what you've learned about how scientists have defined planets in the past and their arguments for and against Pluto.
Then talk it over with your family and friends and see if you can find consensus.
Thanks to Kirby Runyon, postdoctoral planetary geomorphologist at Johns Hopkins Applied Physics Laboratory.
I used Dr Mike Brown's book How I Killed Pluto and Why It Had It Coming in my research for this episode.
Special thanks to Dr Joel Green, project scientist at the Space Telescope Science Institute, who helped review this script.
If you want to hear more about the science of planets, visit our blog at sciencepodcastforkidscom.
Slash blog.
For our Patreon members.
We'll have more from our interview with Kirby Runyon on our special ad-free feed.
Sign up now to get access for a pledge of just $1 a month at patreon.com slash tumble podcast.
Get in touch with us at tumblepodcast at gmail.com.
And don't forget to subscribe to Tumble and tell all your friends.
I'm Lindsay Patterson, and I wrote and produced this episode.
And I'm Marshall Escamilla, and I wrote all of the music.
Thanks for listening, and stay tuned for more stories of science discovery.
All right, everybody.
Thanks for listening.
And now the wonderful song written by me.
So everybody loves it.
There are eight planets in the solar system.
Don't get a big head like Pluto.
You know what happened.
Will it get demoted to not be a song?
There are eight planets in the solar system.
There are eight, but there used to be more.
There are eight planets in the solar system.
There are eight, but there were nine before.
About the first six thought they orbit the earth.
Well, we got that wrong, until we met Copernicus.
Well, there are eight planets in the solar system.
There are eight, but there used to be more.
There are eight planets in the solar system.
There are eight, but there were nine before.
By the 20th century, we've discovered all eight And lots and lots of moons besides.
There are eight planets in the solar system.
There are eight, but there used to be more.
There are eight planets in the solar system.
There are eight, but there were nine before.
We discovered something that made us reconsider all that we do.
A distant object more massive than Pluto made people wonder what to do.
So in 2006, the International Astronomical Union meeting, an important decision was made.
Based on the new information, the experts decided that there needed to be a new formal definition of planet.
There are eight planets in the solar system.
There are eight, but there used to be more.
There are eight planets in the solar system.
There are eight, but there were none planets in the solar system.
There are eight, but there used to be more.
There are eight planets in the solar system.
There are eight.
All right, everybody.
Here we are at the end of this wonderful episode about Pluto.
And we all know what that means.
It is time for the birthday shout outs that go to our supporters on Patreon.
But before we get to that, I've got some new patrons I want to give a shout out to.
Those are Rosabelle, Esther and Beth.
Thanks so much, you guys.
And now here are some birthdays.
A happy belated birthday to Ichiro on April 10th.
Keep being curious and happy.
Mommy, Daddy, and Haru love you.
Happy birthday to Seth on May 15th.
Whether you're building epic redstone contraptions in Minecraft or outsmarting us at chess, your curiosity and creativity make the world a more awesome place.
Mom, Dad, and Nathan love you and hope you have an amazing birthday.
Cece, Mom and Dad love you, Peanut, and hope you have a happy birthday on May 16th.
Rosalie, your mama is so proud of you every day and loves you a lot.
And have a happy birthday on May 16th too.
Maximilian in Shanghai, happy birthday on May 18th.
Mom and Dad love you and your curiosity.
A happy birthday on May 20th to the kid who loves science and stuffies, Arthur.
I also like stuffies and science, you know.
A happy May 20th birthday to Paloma.
Mom loves you to infinity.
She is super proud of the scientist you already have become.
To Chloe, have a happy May 20th birthday.
Daddy and mommy love you.
Thomas, you're the best.
Have a happy birthday on May 21st.
A happy May 23rd birthday to Sydney.
Mom and dad love you to another galaxy and back.
Magnolia, your family is in awe of your creative and kind spirit.
It's their greatest joy watching you and your siblings grow and have a happy birthday on May 24th.
Thanks to all of you and to everyone who supports Tumble on Patreon.
We appreciate it a ton.
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If you'd like to get a birthday shout out of your own like these fine folks, just go to patreoncom slash tumble podcast and pledge to support us at the 5 level or higher.
Once again, that is patreon.com slash tumble podcast.
And now here I find myself at the very end of the episode, and I'm pretty sure that nobody is still listening at this point.
But, if you are, I just want to remind you to support us on the Jokathon, too!
Your support there means a lot as well, and we really can do a lot with any money that we raise in this Joke-a-thon this year.
Just go to tumblescience slash joke 2026 and pledge at any level and you yes, you could become an official cheerleader for one of our contestants.
And I want to say, for those of you who are still listening, all I want you to do is just mention that you heard this on the Easter egg on the podcast, and I will reach out to you and give you a special goody, a special, special goody for donating and supporting the Jokathon podcast.
After hearing this,
So just write me a message at tumblepodcasts, at gmailcom, or leave the message when you support us on GiveButter and I will reach out.
You got it?
All right, everybody.
Thanks.
