The Pluto Files

PBS Airdate: March 2, 2010
Go to the companion Web site

NEIL DEGRASSE TYSON (American Museum of Natural History, Hayden Planetarium): In 1930, a farm boy, with a passion for the universe, notices a tiny dot moving across the night sky. He discovers Pluto, four billion miles from the Sun and cloaked in darkness.

Pluto is a mystery. Our best images are nothing more than a blur, and many scientists are arguing over whether it's even a planet.

MARK SYKES (Planetary Science Institute): When we fly our spaceship to Pluto, we'll arrive at a round world.

BRIAN G. MARSDEN (Harvard-Smithsonian Center for Astrophysics): I'm able to use the word "world," if you like, but "planet?"

NEIL DEGRASSE TYSON: The scientific debate over Pluto has even caused a media frenzy.

STEPHEN COLBERT (The Colbert Report/Film Clip from August 17, 2006): I'm sorry, I thought planets might be one of the constants in life.

NEIL DEGRASSE TYSON: Pluto-lovers of America have taken to the streets.

PROTESTORS (News Clip): Pluto forever!

NEIL DEGRASSE TYSON: What is Pluto? A new mission to the far reaches of the solar system promises to answer this question and more.

ALAN STERN (Southwest Research Institute): It's true first-time exploration. Pluto is going to be revealed in all of its glory.

NEIL DEGRASSE TYSON: Join me, Neil deGrasse Tyson, on a journey to explore America's favorite planet...

TOMBAUGH FAMILY MEMBERS (A small group speaking simultaneously): Hi.

NEIL DEGRASSE TYSON: ...and find out why some people are blaming Pluto's problems on me.

SODY (Streator, Illinois Barber): So how do you feel about Pluto, Dr. Tyson?

NEIL DEGRASSE TYSON: These are The Pluto Files, next on NOVA.

For more than 75 years, the great stage of our solar system had a familiar cast of characters, nine players in all. We even memorized their names: Mercury, Venus, Earth and Mars (the rocky planets), Jupiter, Saturn, Uranus and Neptune, (those gas giants), and all the way out at the very edge of the solar system, perhaps the most popular player of all, a lonely little misfit planet: Pluto.

But recently, Pluto lost its starring role, and some folks are blaming that on me. I, Neil deGrasse Tyson, director of the Hayden Planetarium, in New York City, have been accused of being a Pluto-hater. Back in 2000, when my colleagues and I were designing this place, instead of exhibiting Pluto here, with planets like Earth and Mars, or up there, with giants like Jupiter and Saturn, we decided to boldly go where no planetarium had gone before and put Pluto far, far away, all the way downstairs, with a group of newly discovered icy objects in the outer solar system.

If you look hard enough you can find it, right here.

Little did I know how much this decision would change my life. My troubles began with the astute observations of one young visitor...

BOY (Visitor to Hayden Planetarium): I can't find Pluto!

NEIL DEGRASSE TYSON: ...who, just my luck, was overheard by an off-duty journalist from the New York Times. He decides this is a great story, so he calls his Times colleague, science writer Kenneth Chang, and he's shocked.

KENNETH CHANG (The New York Times): Well, I was looking for Pluto, and I couldn't find it. You look everywhere, and you see eight planets, not nine.

NEIL DEGRASSE TYSON: A few days later Chang's story hits the front page, right beneath George W.'s inauguration. The headline reads, "Pluto's Not a Planet? Only in New York."

I received angry emails and a ton of letters, especially from pissed off third-graders.

EMERSON YORK (Dramatized reading of letter from a third grader): Dear Natural History Museum, Pluto is my favorite planet!!!

MADELINE TROST (Dramatized reading): Why can't Pluto be a planet? Please write back, but not in cursive, because I can't read in cursive.

MICHAEL NOVACEK (American Museum of Natural History): I thought, "Oh, my gosh. Kids will probably go to this exhibit and cry because Pluto's no longer a planet."

SOLEDAD O'BRIEN (NBC News Anchor): Could it be the final indignity for the farthest and smallest planet in our solar system?

NEIL DEGRASSE TYSON: Our exhibit had stirred up a media frenzy.

JON STEWART (The Daily Show/Film Clip from January 8, 2009): Pluto was, since 1930, was a planet. He had stature; he had friends. You come along and say "Da, da, da, da, da."

DIANE SAWYER (ABC News Anchor): Neil deGrasse Tyson, you have left a void in the universe, as big as Pluto.

NEIL DEGRASSE TYSON (The Colbert Report/Film Clip from August 17, 2006): I never wanted to kick Pluto out of the solar system. I just wanted to group it with its icy brethren.

STEPHEN COLBERT (The Colbert Report/Film Clip from August 17, 2006): You're saying Pluto should be with its own kind, separate but equal?

NEIL DEGRASSE TYSON (The Colbert Report/Film Clip from August 17, 2006): Yeah, I guess it comes out that way, doesn't it?

STEPHEN COLBERT (The Colbert Report/Film Clip from August 17, 2006): Neil deGrasse Tyson has betrayed us.

BRIAN WILLIAMS(NBC News Anchor): He has thrown his weight around a little too much. He's not the boss of the solar system; he's not the boss of me.

NEIL DEGRASSE TYSON: If Neptune or Mercury had been reclassified, I don't think anyone would cared, but the fact that it happened to Pluto seems to make all the difference.

Pluto has a remarkable grip on the hearts and minds of the American public and the press. Even my colleagues in astrophysics are still arguing over what to do with Pluto, and I don't really know why. But I'm determined to find out.

This is the story of my journey. These are The Pluto Files.

My first stop took me to Cambridge, Massachusetts. A visit to the hallowed halls of Harvard just might help me make sense of this Pluto problem.

Welcome to the Harvard University football field. I brought a few props along with me, much to the surprise of my colleagues.

Astrophysicist, Brian Marsden, doesn't think Pluto is a planet, while planetary scientist Mark Sykes thinks it definitely is. And the esteemed historian of science, Owen Gingerich, is looking for the middle ground.

MARK SYKES: Okay, Neil. What are we doing here?

NEIL DEGRASSE TYSON: We're making a scale model of the solar system, right here on this playing field. So grab one of these. Let's do it.

To evaluate Pluto's planetary status we need to take a closer look at how it compares with the heavy hitters on the solar system team. The planets are millions, even billions of miles apart, so this scale model can't accurately depict their distance from one another, but it can show their relative size.

If this eight-foot balloon represents our Sun, how does Pluto size up against the rest of the team? Let's find out.

Mark, first up, Mercury.

MARK SYKES: Mercury.

NEIL DEGRASSE TYSON: Represented by a bead—in correct size, relative to the Sun—miniscule Mercury may be small, but its diameter is still twice as big as puny Pluto's.

Next up, Venus. Will you have the honor?

Venus, represented by this tiny rubber ball, has a diameter five times as big as Pluto.

MARK SYKES: Earth.

NEIL DEGRASSE TYSON: Earth.

Earth, the big blue marble, is six times as wide as Pluto.

If Earth and Venus were about an inch, Mars would be about a half inch—the sizes of these gumdrops, relative to the Sun. But it still trounces Pluto, three to one.

MARK SYKES: Jupiter, king of the planets.

NEIL DEGRASSE TYSON: King of the planets. You have the honor.

MARK SYKES: There you go.

NEIL DEGRASSE TYSON: The largest planet, King Jupiter, represented by a schoolyard kickball, is a whopping 62 times as wide as pipsqueak Pluto.

Saturn...

MARK SYKES: Saturn.

NEIL DEGRASSE TYSON: ...the size of a bowling ball, relative to the Sun.

Pluto doesn't fare much better against my favorite planet, Saturn, or its next-door neighbor.

MARK SYKES: Uranus.

NEIL DEGRASSE TYSON: Uranus, represented by a bocce ball.

Have you ever played bocce?

MARK SYKES: No, I never played bocce.

NEIL DEGRASSE TYSON: Neither have I.

It would take 22 Plutos in a chain to equal the diameter of one Uranus.

Croquet anyone?

What do you have now?

MARK SYKES: Neptune. Why don't you have the honor?

NEIL DEGRASSE TYSON: Big blue Neptune is 21 times as wide as Pluto.

Last and least...

MARK SYKES: And not least.

NEIL DEGRASSE TYSON: ...we have Pluto, represented by a ball bearing, removed from a roller skate.

MARK SYKES: Sometimes the most valuable things are in the smallest packages.

Excellent.

NEIL DEGRASSE TYSON: Pluto.

Pluto's diameter is just under 1,500 miles. In fact, if it ever decided to visit America, it would stretch only from California to Kansas. No matter how you look at it, Pluto makes a scrawny little planet.

Pluto's really puny, but so is Mercury.

BRIAN MARSDEN: Pluto's a lot punier: one-twentieth the mass of Mercury.

OWEN GINGERICH (Harvard-Smithsonian Center for Astrophysics): That's less than the mass of the moon.

NEIL DEGRASSE TYSON: Touchdown right there.

If we were to keep score of Pluto's oddball traits versus its planet-like characteristics, how would it add up?

Brian thinks Pluto's puny size disqualifies it from the planet team, so he gives one touchdown, and of course the extra point, to Pluto, the oddball.

MARK SYKES: This is ridiculous.

NEIL DEGRASSE TYSON: Mark disagrees. For him, size is less important than shape.

Pluto, like every player on the planet team, is round, and not potato shaped, like nearly all asteroids.

This sequence of images, taken by the Hubble space telescope, shows Pluto as a sphere with a textured surface.

MARK SYKES: When we fly our spaceship to Pluto, we will arrive at a round world that has atmospheres, that has bright and dark areas on the surface. It will look much more like objects we call planets than these little, irregular, inert objects we call asteroids.

NEIL DEGRASSE TYSON: So roundness, you give a full touchdown?

MARK SYKES: Yeah.

OWEN GINGERICH: Two touchdowns.

NEIL DEGRASSE TYSON: But, then again, we all know that Pluto's got this really weird orbit. First of all, it's tipped, the most tipped orbit. What's that worth to you?

BRIAN MARSDEN: Not too much.

NEIL DEGRASSE TYSON: A field goal, not quite a touchdown.

BRIAN MARSDEN: That isn't really the problem. I think the problem was crossing the orbit of Neptune.

NEIL DEGRASSE TYSON: Pluto's orbit isn't just tipped; it's highly elliptical, not nearly circular like other planets', which actually forces Pluto to cross the orbit of another planet. That's bad?

BRIAN MARSDEN: That's really bad.

NEIL DEGRASSE TYSON: Nobody else does that. There you go, touchdown right there, another seven points for the oddball team.

One way you might define a planet is that it ought to have a moon. But, of course, Mercury and Venus don't have moons, and guess what? Tiny little Pluto does. In fact, it has three.

One of those moons, Charon, is so large compared with Pluto that they both orbit a point in space in between them, which might make you wonder which one is the planet.

MARK SYKES: The idea of planets orbiting planets isn't really so foreign. We see many double stars out there, and we see galaxies orbiting galaxies.

OWEN GINGERICH: The solar system is such a complicated place, it's very important to understand that there is this richness out there.

NEIL DEGRASSE TYSON: So, Brian, if we go there and find Pluto has mountains or craters or an atmosphere, it's got world properties that match other objects we're happy to call planets.

BRIAN MARSDEN: I'm able to use the word "world," if you like, but "planet?"

NEIL DEGRASSE TYSON: So then, what is Pluto?

Four billion miles from the Sun, our best images of Pluto and its moons are nothing more than a blur. By analyzing the light reflected from Pluto's surface, planetary scientists think that a day on Pluto might look like this: an icy, frosty, winter's night in the Arctic; the Sun, a tiny pinpoint in a pitch black sky; wispy clouds and fog visible on the horizon; the temperature about 300 degrees below zero.

No spacecraft has yet visited Pluto. Until one does it will remain a mystery.

Both of you are wrong, and no scoreboard today is going to change that.

It was time for me to take a closer look at why an oddball like Pluto was considered a planet in the first place. It's a tale that begins back in 1894, when a New England aristocrat by the name of Percival Lowell built a private observatory, near Flagstaff, Arizona, with one goal in mind: to find life on Mars.

After years of searching in vein, Lowell turned his attention to an unsolved mystery, the hunt for a distant planet whose gravity seemed to be causing disturbances in Neptune's orbit. He called this hypothetical object "Planet X." Lowell spent the rest of his life trying to find it but never did.

After his death, the task was given to the unlikeliest of planet-hunters, a self-educated farm boy who attended a one-room schoolhouse. Clyde Tombaugh's first job in astronomy included cleaning telescopes and sweeping up at the Lowell Observatory. He spent the rest of his time searching for the mysterious Planet X.

Every few nights, he placed a photosensitive glass plate on the telescope, securing it so it would not shift. Then he exposed the plate for two hours to the universe. During that time, the motorized telescope slowly moved to compensate for Earth's rotation.

Several days later, he'd retrace his steps, taking pictures of the same section of the sky he had photographed earlier. Then, using an ingenious device called a "blink comparator," Clyde Tombaugh aligned the two images to carefully examine their differences. The blink comparator enabled him to shift back and forth, searching for the subtlest of changes. Although the human eye is good at spotting differences, finding a dim celestial object, billions of miles away was a daunting task.

After searching for almost a year, a determined Clyde finally found a tiny dot slowly moving across the night's sky.

Can you see it? Here it is.

A month later, the Lowell Observatory proudly announced that a young assistant had fulfilled Percival Lowell's dream. Clyde Tombaugh had finally found Planet X.

The day after the announcement, the news hit the front page of the New York Times. Soon the discovery was heralded worldwide, but the new planet needed a name.

Across the Atlantic, an 11-year-old English schoolgirl would come up with one. On March 14, 1930, Venetia Burney's grandfather, a librarian at Oxford, was reading the morning newspaper and came across the story.

VENETIA BURNEY'S GRANDFATHER (Dramatization): An American has just discovered a new planet. I wonder what they'll call it?

NEIL DEGRASSE TYSON: Venetia had just finished studying the Roman gods and jumped at the opportunity to name it after the god of the underworld.

VENETIA BURNEY (Schoolgirl, Dramatization): They could call it Pluto.

VENETIA BURNEY'S GRANDFATHER: Pluto, perhaps. Yes.

NEIL DEGRASSE TYSON: Her grandfather thought that was a splendid idea. So he wrote a note to the Lowell Observatory.

The director at Lowell liked it, especially because Pluto's official symbol would be the overlapping letters P and L, the initials of the observatory's long-gone founder, the man who started the search for Planet X, Percival Lowell.

For most Americans, the name Pluto didn't exactly conjure up affection. It was associated with a well-known laxative called "Pluto Wate," a popular product that promised "relief from constipation in 30 minutes to two hours." Its slogan: "When Nature won't, Pluto will."

But the name would soon get a makeover, and it would come from a young animator by the name of Walt Disney. Shortly after planet Pluto was discovered, the fledgling Disney Brothers Studio came up with a new character, a playful bloodhound named Pluto the Pup. Walt probably wasn't thinking about constipation when he named Mickey Mouse's new pal, back in 1931.

My journey would lead me south, to a magical place, to meet with a celebrity on a tight schedule.

Pluto, hey, great to see you. Thanks for making time for this. Can we pose for a picture?

Was Walt thinking "planet" when he gave his pup a name?

Maybe Roy Patrick Disney, Walt's great nephew, can help answer this question.

I wonder whether Walt jumped on the opportunity to name this new character after this new cosmic object. Is there any evidence for that in the archives?

ROY P. DISNEY (Walt Disney's Great Nephew): There's no direct evidence. There's a lot of anecdotal evidence. I think its fate; I don't think it's an accident.

NEIL DEGRASSE TYSON: You feel, deep inside, that Walt was thinking planet?

ROY DISNEY: Yes. He was fascinated with space and space exploration. And Walt did four TV shows about space. And all of them made space exploration and science accessible to kids, including myself.

LEONARD MALTIN (Film Critic and Historian): When he did his Man in Space series in 1956 to '57, America wasn't committed to a space program. I know, for a fact, that many people who wound up working at NASA were inspired to do so by watching those television shows. He made learning fun.

NEIL DEGRASSE TYSON: I am certain Pluto, the dog, added some kind of warm and fuzzy feeling for this cosmic object. Cosmic objects don't normally trigger warm and fuzzy feelings.

Pluto, have you ever looked through a telescope before? No? I brought one. Isn't it cool? Now it's daytime, so you can't see much. But let me show you how it works.

What do you think of that? You see something?

You did? Try again.

Whether or not Walt was thinking about the cosmos when he named his dog, doesn't really matter.

Good boy! Good dog!

The seeds were sown for the tiniest of planets to get the kind of attention no other planet had, all because of this loveable pup.

But I shouldn't give credit to the dog alone. Next stop on my journey: Streator Illinois, the hometown of Clyde Tombaugh.

They love him so much, main street is named after him. There's a mural in the center of town that compares his discovery of Pluto with the accomplishments of Copernicus and Galileo. His life is chronicled at the local historical society, where one of his homemade telescopes is on display. There's even a plaque dedicated to him in front of City Hall. Clyde is a local hero. Just about everyone around here can tell you his life story.

SODY (Streator, Illinois Barber): Next victim, I mean, customer, please.

How you doing?

NEIL DEGRASSE TYSON: Doing well. Right now, I'm on a pilgrimage, actually, to try and understand Clyde Tombaugh.

SODY: Clyde Tombaugh; he's from Streator, and he discovered Pluto.

NEIL DEGRASSE TYSON: That's what I heard.

SODY: We're very proud of him, very proud of him, what he did.

NEIL DEGRASSE TYSON: And you learned about him in high school?

TERRI (Streator, Illinois Resident): Elementary school...third grade maybe.

NEIL DEGRASSE TYSON: So that's when most people first learn about the planets. So his name comes up, and you learn he's a local guy.

TERRI: "Streator boy makes good," so to speak. Back in third grade I went, "Wow, that's astounding: from Streator, found Pluto."

NEIL DEGRASSE TYSON: You feel some pride?

TERRI: Oh, you bet. Always had something to point to as far as, "Looka there, that guy discovered Pluto, and he's from our area."

ANOTHER STREATOR, ILLINOIS RESIDENT: Walt Disney named the dog after him.

SODY: So how do you feel about Pluto, Dr. Tyson?

NEIL DEGRASSE TYSON: In the eyes of the town folk of Streator, Illinois, Tombaugh's discovery is not only a part of their history, it's a piece of American history, as well as world history.

It was the ancient Greeks who classified what we call the Moon, the Sun, Mercury, Venus, Mars, Jupiter and Saturn as "planetes," which means the "wanderers" in English. They imagined Earth as a hub around which these planets revolved.

In 1543, the Polish astronomer Nicolas Copernicus published his revolutionary idea that the Sun did not circle Earth, but, instead, Earth and its lone moon circle the Sun, along with the rest of the planets.

By the 17th century, the Italian astronomer Galileo Galilei discovered Jupiter's four largest moons. Meanwhile, Dutchman Christiaan Huygens identified Saturn's rings and discovered Titan, its largest moon. Italian astronomer Giovanni Cassini one-upped him, when he discovered four more.

In the 18th century, Englishman William Herschel discovered Uranus, although he originally called it the Georgian star, after his King, George the III. Can you imagine a planet named George?

The British and French are still fighting over who deserves the credit for predicting the location of Neptune. Some give the honor to John Couch Adams, while others say Urbain Le Verrier deserves it. But there's no doubt that German astronomer Johann Gottfried Galle found it.

The discovery of Pluto finally added an American, Clyde Tombaugh, to this short but esteemed list of planet-hunters.

So the folks in Streator, Illinois, told me that in New Mexico...there are still some Tombaughs there. That's where Clyde moved after discovering Pluto. Clyde's no longer with us, but his 97-year-old widow and both his son and daughter still live there. So I decided I had to check it out.

Wow. That's a lot of Tombaughs.

THE TOMBAUGHS (A small group speaking simultaneously): Hi.

NEIL DEGRASSE TYSON: How many of you are there? Hello, everyone.

ANNETTE TOMBAUGH (Clyde Tombaugh's Daughter): Annette Tombaugh. I'm Clyde's daughter.

NEIL DEGRASSE TYSON: What an honor, my gosh.

ANNETTE TOMBAUGH: This is my brother.

ALDEN TOMBAUGH (Clyde Tombaugh's Son): Neil, Al Tombaugh. I'm Clyde's son.

NEIL DEGRASSE TYSON: Hello.

ANNETTE TOMBAUGH: And this is my mother, Patsy Tombaugh; this is Clyde's wife.

NEIL DEGRASSE TYSON: It is an honor, hello.

PATSY TOMBAUGH (Clyde Tombaugh's Widow): Yes, I've been looking forward to this.

NEIL DEGRASSE TYSON: That could be...I don't know what that means. So tell me about Clyde, as a person.

PATSY TOMBAUGH: He was the oldest of six children, so he was born to help on the farm. But he did not want to be a farmer.

ANNETTE TOMBAUGH: He had not had the opportunity to go to college.

NEIL DEGRASSE TYSON: So, what you're saying is that he discovered Pluto without ever having yet gone to college?

ANNETTE TOMBAUGH: No, he was straight off the farm.

PATSY TOMBAUGH: Lowell Observatory wanted somebody they didn't have to pay very much to do this job. What do you think they pay you for finding a planet?

ANNETTE TOMBAUGH: After discovering Pluto, he got a college scholarship which he would not have otherwise had. And, of course, he was supposed to be the big hero, but he didn't feel like the big hero.

ALDEN TOMBAUGH: Dad was a little embarrassed about the fame; he didn't like the limelight.

NEIL DEGRASSE TYSON: He was humble?

ALDEN TOMBAUGH: Absolutely.

NEIL DEGRASSE TYSON: So what was he just like as a dad? Was he, like, a weird dad, or did you think all dads were like that?

ANNETTE TOMBAUGH: No, I knew he was very different. One of the things...we did have his grinding barrel to make telescopes in the kitchen.

NEIL DEGRASSE TYSON: This is the barrel that grinds glass into the shape of a mirror.

ANNETTE TOMBAUGH: Right; in the kitchen. How mother put up with that I don't know. We had grinding material in our food, and Mother's trying to cook around this situation. Well, finally she made Daddy move out of the kitchen, and he got a shop.

NEIL DEGRASSE TYSON: That, that's good.

You mean to tell me you have some of Clyde's original telescopes here?

Wow, these were his original telescopes.

ALDEN TOMBAUGH: Original telescopes, built by my Dad.

NEIL DEGRASSE TYSON: Very handmade.

ALDEN TOMBAUGH: Built out of old farm machinery, car parts and whatever he could find.

Just push it out.

NEIL DEGRASSE TYSON: I'll help you push.

ALDEN TOMBAUGH: You bet.

NEIL DEGRASSE TYSON: So, Al, I don't recognize any hardware on this at all.

ALDEN TOMBAUGH: The tube itself is probably part of an old grain elevator.

NEIL DEGRASSE TYSON: How about the base?

ALDEN TOMBAUGH: Well, the base is an old cream separator. The axle is off an early model Buick.

NEIL DEGRASSE TYSON: So there's a Buick out there now without an axle.

ALDEN TOMBAUGH: Without an axle. This counterweight was probably a flywheel for an early piece of farm equipment, maybe even steam-powered. We're not sure.

NEIL DEGRASSE TYSON: I see a Coke can. I love this. So, we got the open end of the telescope at the top, and light comes down, reflects off the curved mirror, and light reflects back and comes to an eyepiece under that Coke can.

ALDEN TOMBAUGH: And if we wiggle this Coke can a little bit, like this, there's the eyepiece, ready to go.

NEIL DEGRASSE TYSON: This isn't the only telescope I see back here.

ALDEN TOMBAUGH: No, there's a couple others. Let me pull this one out for you.

NEIL DEGRASSE TYSON: Okay. This is got to be the most homemade-looking telescope I have ever seen. Is this a lawn mower?

ALDEN TOMBAUGH: That is a lawnmower base. This is what the family has called the "grazer gazer." He looked at this and said, "It's got wheels, it's got a handle; we need to put a telescope on that so I can push it around."

NEIL DEGRASSE TYSON: How to make a portable telescope.

ALDEN TOMBAUGH: Absolutely. He built it strictly on a utilitarian base, out of what he had, which was thin plywood and miscellaneous pieces of wood.

NEIL DEGRASSE TYSON: This is insane. This just rotates.

ALDEN TOMBAUGH: Exactly.

NEIL DEGRASSE TYSON: What impresses me is that he didn't care what this thing looked like as long as the image of the universe came out sharp.

ALDEN TOMBAUGH: Right. Aesthetics didn't mean a whole lot.

NEIL DEGRASSE TYSON: On my way out of town, I stopped at a local church where there's a tribute to Clyde Tombaugh, a stained glass window that celebrates his life.

How many scientists have stained glass windows of them? It's more than just a celebration of his discovery, it's a celebration of his life, overcoming obstacles that would keep most people down. To me that's the message here.

After discovering Pluto, Clyde taught astronomy, and he searched for another planet in the far reaches of the solar system. But as hard as he and other astronomers looked—and they looked hard—nobody found anything. Most abandoned the search, assuming there was nothing left to find. But a few simply couldn't accept the prevailing view that the solar system ended with Pluto.

I headed out to California to share a burger with two colleagues who were convinced there was something else out there.

MIKE BROWN (California Institute of Technology): Foods a-comin'.

NEIL DEGRASSE TYSON: Back in the 1980s, David started a search that would put Pluto in a new perspective.

So you start looking in the outer solar system? That's kind of crazy, because everyone knew the solar system ended at Pluto.

DAVID JEWITT (University of California, Los Angeles): Uh, it's a little crazy. But, you know, the flipside is, it didn't seem reasonable; it seemed peculiar that the outer solar system would be this really, really empty place, compared to the inner solar system, which we already knew was full of planets and comets and asteroids and all sorts of stuff.

NEIL DEGRASSE TYSON: Well it's got to end somewhere, why not Pluto?

DAVID JEWITT: Yeah. I mean maybe, but maybe not.

NEIL DEGRASSE TYSON: Despite what felt like impossible odds, David teamed up with Jane Luu—then a graduate student—and they started a search that would take a lot longer then either one of them expected.

JANE LUU (Researcher): Why did it take so long? Um, it was a matter of technology catching up with the problem.

NEIL DEGRASSE TYSON: While it's easy to see distant stars, because they radiate their own light, other celestial bodies are much harder to see. That's because light has to travel all the way from our Sun to the object, reflect off its surface, and then make the long journey back to Earth. By that time it's barely visible.

David and Jane hoped that advances in digital detectors now standard in today's cameras would help them see a whole lot more, that is, if there was anything out there to discover.

In 1992, after searching for five years, they finally found something.

DAVID JEWITT: Here is the set of discovery images for the first object. Obviously, it's the thing with the circle around it. It didn't have a circle around it when we discovered it, but it does now. So you can see this object is drifting from this picture to this one to this one. It's drifting slowly to the left, whereas most of the other objects are fixed stationary bodies in the background.

NEIL DEGRASSE TYSON: When they found several more of these slowly moving objects, David and Jane could finally declare that Pluto is not alone; it's part of region of the solar system never before seen. David named it the Kuiper Belt, after an astronomer who proposed its existence back in the 1950s.

Billions of miles wide, the Kuiper Belt is chock-full of icy objects, in wide orbits around the distant Sun. They're the leftovers from the solar system's formation.

We theorize that more than four billion years ago, our solar system consisted of bits and pieces of debris colliding and sticking together into larger and larger chunks. Eventually these chunks got big enough for gravity to pull them into a nice round shape, forming planets. And as the planets got larger and larger their gravity vacuumed up nearly all the objects in their path, but, in the end, there were still a lot of bits and pieces left over. And they got flung out to the far reaches of the solar system, where they plunged into a deep freeze.

The discovery of this far-out region of the solar system made many of us stop and think, "Is Pluto really a full-blooded planet or just another Kuiper Belt leftover?"

DAVID JEWITT: It didn't make any sense, anymore, to think of it as a planet, because it fits so well with this new population of Kuiper Belt objects.

BRIAN MARSDEN: We all considered Pluto was strange, at that time, but we didn't know how to resolve this.

NEIL DEGRASSE TYSON: And frankly, many of my colleagues weren't ready to mess with America's favorite planet. We all knew Pluto was an icy object, just like everything else in the Kuiper Belt, but it was still the largest one in the neighborhood—that is until my other dinner companion, Mike Brown, came into the picture.

MIKE BROWN: I had just finished my Ph.D., and I was looking for something new to move into. And this seemed like the most obvious thing anyone could start working on. This was an entirely new area of the solar system to go study, so it was very exciting.

NEIL DEGRASSE TYSON: Mike set his sights on doing something really big: finding a Kuiper Belt object larger than Pluto.

MIKE BROWN: I was determined there must still be something out there. I had caught the bug of finding it.

NEIL DEGRASSE TYSON: At the Palomar Observatory, in California, Mike had access to the largest digital camera on Earth. The images were uploaded to Mike's computer where he analyzed them every morning. With technology on his side, the discoveries just kept on coming.

MIKE BROWN: We found Quaoar, which is an object out in the Kuiper Belt that's about half the size of Pluto. The next year we found something about three-quarters the size of Pluto, and the following year we found this thing. And it was so bright and also moving so slowly—moving so slowly, because it was so far away. I looked at it, and I thought, "This can't be right. If it's that bright and moving that slowly, it's the furthest thing we've ever found, and it's the biggest thing we've ever found. It must be quite big, certainly bigger than Pluto, and that's crazy.

NEIL DEGRASSE TYSON: But it wasn't crazy.

MIKE BROWN: On the day that we publicly announced the discovery I had to make a decision. What we were going to call it? Is it a planet? Is it not a planet? Is it the tenth planet? Finally, I had to say, "Okay, it's the tenth planet."

And I will tell you, when everybody kept calling me, congratulating me for discovering the tenth planet, I felt fraudulent the entire day.

NEIL DEGRASSE TYSON: Why?

MIKE BROWN: William Herschel pointed his telescope in the sky and found Uranus. Uranus. Uranus is a major part of the solar system. And he found it. That is a pretty big deal. I discovered a little ice ball out on the fringe, and it just didn't seem like the same magnitude of a discovery. And I had been struggling with this for years. What do you do when you finally find one bigger than Pluto? I did not believe that astronomers had the guts to ever demote Pluto because it's just too publicly painful.

NEIL DEGRASSE TYSON: And if tiny Pluto was a planet shouldn't Mike's discovery be one too?

So he forged ahead, ultimately selecting a clever name for his discovery: Eris, the Greek goddess of discord and strife. Eris instilled jealousy and envy among men, driving them to battle. Mike's choice perfectly captured the destabilizing effect Eris was destined to have on Pluto, although he couldn't have guessed what was about to happen next.

For the past century, the I.A.U., the International Astronomical Union, has been in charge of naming celestial objects, but it couldn't approve the name of Mike's discovery without knowing if it was a Kuiper Belt object or the tenth planet. This posed a problem, because the word "planet" had not been formally defined since ancient Greece. Clearly, our knowledge of the solar system has expanded since then.

So committees were assembled to come up with a new definition, the last of which was headed by my friend from Harvard, Owen Gingerich.

OWEN GINGERICH: So what we proposed was that planets should be round and going around the Sun.

NEIL DEGRASSE TYSON: So, massive enough for gravity to shape them into a nice round form. Under this definition, Pluto would remain a planet; Mike Brown's discovery would be one too. And as new discoveries are made in the outer solar system, the planet count could go up.

OWEN GINGERICH: We realized that doing this would bring scores of planets.

NEIL DEGRASSE TYSON: Into the accounting of the planets in the solar system?

OWEN GINGERICH: That's right.

NEIL DEGRASSE TYSON: But when the definition was proposed, in Prague, at the 2006 I.A.U. conference, many scientists were dead set against it. A rebellion was brewing, and things were getting ugly.

Just to clarify: your original suggestion got overturned within days?

OWEN GINGERICH: Our recommendations were rather pushed to the side, and a new kind of definition came about in the final voting at the union meeting.

NEIL DEGRASSE TYSON: A new definition that included the following line: "A planet must clear the neighborhood around its orbit."

Pluto travels in a crowded neighborhood, littered with thousands of Kuiper Belt objects. It's simply not massive enough to clear them out of the way.

MIKE BROWN: In the definition that the I.A.U. came up with, eight major things which dominate the solar system are planets. They're all big. They go in circular orbits in, in one disk around the sun. And everything else is all in these other crazy orbits, much smaller. Those are not planets. That concept is a rock-solid concept.

NEIL DEGRASSE TYSON: And when this new definition went to a vote of the members present it was a slam dunk.

After 76 years, Pluto was no longer a planet.

STEPHEN COLBERT (The Colbert Report/Film Clip from August 17, 2006): I'm sorry, I thought planets might be one of the constants in life, but scientists just love change more than anything else. Well, I'm sorry, but this isn't change I can believe in.

JON STEWART (The Daily Show/Film Clip from January 8, 2009): ...the whole underpinnings of what we understand as science. Is gravity real or do we just have sticky stuff on our shoes? The whole thing...what are we doing at that point?

MIKE BROWN: I couldn't believe it. I couldn't believe that that was the vote that happened, but when that vote happened, I knew exactly what was going to happen next.

NEWSCASTER (News Clip): Supporters of Pluto are speaking out trying to help it regain planet status.

PROTESTORS (News Clip): Pluto is a planet. Size doesn't matter.

NEIL DEGRASSE TYSON: Pluto-lovers of America did not take the I.A.U. decision lightly. At New Mexico State, where Clyde Tombaugh had taught, students took to the streets.

PROTESTORS (News Clip): Pluto forever!

NEIL DEGRASSE TYSON: The New Mexico legislature declared Pluto was still a planet within state borders...

MUSICIAN (singing): No matter what they say in the chart,

You'll always be a planet in my heart.

NEIL DEGRASSE TYSON: ...and Illinois soon followed, spurred on by efforts led by the concerned citizens of Streator.

So I've got in my hand this legislation, passed by the 96th General Assembly, here in the State of Illinois. No one's got a problem with declaring March 13th "Pluto Day," the anniversary of Clyde Tombaugh announcing the discovery. Who could argue that? It's part of the resolution that says when Pluto passes overhead, overhead of Illinois's night skies, that it be re-established with full planetary status. That's audacious. That's saying, "Forget the scientists, this is Illinois."

SENATOR GARY G. DAHL (Republican, 28^th District, Illinois): This is Streator.

NEIL DEGRASSE TYSON: And don't mess with Streator.

SENATOR GARY G. DAHL: There you go.

NEIL DEGRASSE TYSON: Back at the barbershop, the guys made it clear where they stand.

SODY: I still believe it's a planet. They can't make me think any different.

NEIL DEGRASSE TYSON: But next door, at the Country Cupboard, locals questioned the decision.

SIOBHAN (Streator, Illinois Resident): I was very disappointed.

NEIL DEGRASSE TYSON: Disappointed in the result or how they got the result?

SIOBHAN: Both. You can't change scientific fact or definition with a hand count. You're a scientist, since when do you take a vote on scientific fact?

NEIL DEGRASSE TYSON: But it wasn't just hometown folks who disagreed with the decision. Just a few days after the vote, this petition, signed by hundreds of planetary scientists, hit the Internet. It says, "The undersigned do not accept the I.A.U. definition, and they refuse to use it." Period.

The last stop on my journey would be a visit with a planetary scientist who proudly signed that petition; one of the world's leading experts on Pluto, Alan Stern. He's been mad ever since we opened our new exhibit at the planetarium. And he sure isn't pleased with the I.A.U.

ALAN STERN: You're late. Ready for this?

NEIL DEGRASSE TYSON: Ready as ever.

I can't wait to hear what Alan's got to say about Pluto's demotion.

ALAN STERN: I think the I.A.U. has confused people, because their definition produces such illogical results. What I really like is what I call the Star Trek test. When Kirk and Spock show up orbiting an object, just by looking at the picture of it, they know it's a planet. In an I.A.U. world, Spock would have to come back and say, "Captain, let me survey the entire solar system, determine whatever objects are there. I'll integrate the orbits overnight. I'll get back to you." It's not that hard.

NEIL DEGRASSE TYSON: So you don't even care about whether a zone is cleared or some of these other parameters.

ALAN STERN: No, that's all about location, and location is for realtors not scientists. I don't think it counts at all in terms of what it means to be a planet.

NEIL DEGRASSE TYSON: So, then, what is Pluto?

According to Alan, it's not just a Kuiper Belt object. It's not a lonely oddball either, and it's definitely not demote-able. It's simply a new kind of planet, a dwarf planet, and it turns out there's lots of them.

ALAN STERN: It looked like the solar system consisted of four terrestrial planets, four giant planets and misfit Pluto, but, today, instead, we see a solar system with four terrestrial planets, four freakishly giant planets and a whole cohort of Pluto-like objects, which turn out to be the dominant class of planet in our solar system. These are typically rocky and icy objects. Many have atmospheres; many, possibly most, have moons—all the things we're used to in the planets we're familiar with but in miniature. I think a decent analogue is, if you see a Chihuahua, it's still a dog, because it has the characteristics of the canine species, just in miniature.

NEIL DEGRASSE TYSON: Why then, are these pint-sized planets so much smaller than the rest?

ALAN STERN: The process of planetary formation is a bottom up process. Planets grow from small things to larger and larger things. Dwarf planets were arrested in the mid-stage of planetary growth. They are actually planetary embryos. Pluto and other dwarf planets would have grown much larger, had there been more material around them. Why was there no more material for them? That's a great question, and we don't know the answer to it.

NEIL DEGRASSE TYSON: Many planetary scientists think that dwarf planets were actually born in another region of the solar system, among the gas giants where the food supply was plentiful. But as the gas giants grew larger and larger and migrated to their current positions, the force of their gravity flung the tiny dwarfs outward, to the Kuiper Belt, where they reside today.

While there are thousands of objects in the Kuiper Belt, they're spread millions of miles apart, so far away from each other that the dwarfs no longer come in contact with the material they needed to grow.

ALAN STERN: To study those objects rather than objects that grew to much larger scales will give us a great window into the process of planetary formation.

NASA MISSION CONTROL: Three, two, one. We have ignition and liftoff.

NEIL DEGRASSE TYSON: Alan and his team hope to open that window, when the New Horizons spacecraft, launched in 2006, becomes the first ever to arrive at Pluto: racing at a speed of 37,000 miles an hour; traveling time, nine and a half years; scheduled arrival, 2015.

ALAN STERN: So this is the place. This is mission control for the New Horizons.

NEIL DEGRASSE TYSON: Cool.

ALAN STERN: Yeah, the flight control team is monitoring the data that is coming down, looking at the health of the spacecraft and sending instructions back up, to, basically, choreograph everything that happens on the spacecraft.

NEIL DEGRASSE TYSON: So how long do those instructions take to get there? Like, suppose it says, "Quick, turn left." How long does that take?

ALAN STERN: Well, right now it would take about two hours and 12 minutes for the instruction to get up there, and then, after it's executed, two hours and 12 minutes more to find out that's what happened.

NEIL DEGRASSE TYSON: To complete the roundtrip.

ALAN STERN: That's correct.

NEIL DEGRASSE TYSON: By the time it gets to Pluto...

ALAN STERN: It's going to be nine and a half hours.

NEIL DEGRASSE TYSON: Roundtrip.

ALAN STERN: Yeah.

NEIL DEGRASSE TYSON: So you better know well in advance what you're telling this thing to do.

ALAN STERN: We try and make sure we do that.

NEIL DEGRASSE TYSON: New Horizons has seven scientific instruments, which will study Pluto's atmospheric composition; its surface features; its interior structure; as well as its three moons, Charon, Nix and Hydra.

So, it seems to me that New Horizons, with its experiments, will transform this icy ball out there into a world.

ALAN STERN: It's true first-time exploration. We've never been to a dwarf planet, and I think it will be as revealing as when we first went to Mars and no one expected craters and river valleys.

NEIL DEGRASSE TYSON: All right, so you had enough room for seven scientific instruments, but I heard there's more stuff in there.

ALAN STERN: We've got a few mementos, perhaps the most sentimental and noteworthy are some of Clyde Tombaugh's ashes.

NEIL DEGRASSE TYSON: His ashes.

ALAN STERN: His ashes. It's on its way to the stars.

SIOBHAN'S HUSBAND (Streator, Illinois Resident): The man is on his the way back to the very planet he discovered. And he's due to arrive there in 2015. And that just blows my mind.

And I challenge anyone to put that on their resume.

NEIL DEGRASSE TYSON: Finally, its time to head back home. But my journey isn't quite over. I have one more thing to do, a promise to keep. When I met Annette Tombaugh, she told me that she'd never seen our exhibit and asked if she could see it with me. Of course I agreed.

I was a little nervous about inviting Annette to the Rose Center, because this is kind of where the public awareness of the problems with Pluto began.

ANNETTE TOMBAUGH: I'm excited. I'm really excited about seeing the exhibit. Of course, I am still going to look for Pluto.

NEIL DEGRASSE TYSON: I think what we did here is sensible. So let's hope this works.

Hello. Welcome to New York.

ANNETTE TOMBAUGH: It's good to see you. Oh, my goodness.

NEIL DEGRASSE TYSON: Welcome to the belly of the beast.

I showed Annette where we exhibit the planets. Then I took her downstairs to show her where we put Pluto.

And, so, here we have it.

ANNETTE TOMBAUGH: It's there. I don't see anything wrong with this presentation, at all.

NEIL DEGRASSE TYSON: So, after 10 years, I can rest peacefully at night?

ANNETTE TOMBAUGH: You can rest. I wish it was a little bigger and a little higher.

NEIL DEGRASSE TYSON: So can I offer you my view? Not that you asked. I have a view that's been stereotyped but actually misrepresents my position here. When you look at the richness of this tapestry of information we now have about the solar system, what I would vote for is we recognize the true diversity of stuff that orbits the Sun and invent a new lexicon, commensurate with what our new understanding of the solar system is, because it's no longer just lights moving in the night sky, especially since we've discovered more than 400 planets outside our solar system. Maybe the definition of "planet" should consider the rest of the cosmos, as well.

After all I had seen and learned on my journey, we decided it only seemed right to add to our treatment of Pluto, here at the planetarium. So we attached this plaque. And it says: "Where's Pluto? Some astronomers regard Pluto as a Kuiper Belt object, some call it a planet, and others think of it as both. This confusion arises because a consensus has yet to emerge on the scientific definition of 'planet.'"

So are we ever going to agree?

BRIAN MARSDEN: No, I don't think so.

MARK SYKES: I don't think agreement is necessary.

OWEN GINGERICH: Culture will take its course.

NEIL DEGRASSE TYSON: These two guys are the cantankerous ones.

BRIAN MARSDEN: Me? Cantankerous?

MIKE NOVACEK: Science is an exciting area. It's an area of change. Science is always changing, and you have to go with the flow. And sometimes that means changing names and reclassifying things that are held sacred, like Pluto.

JON STEWART (The Daily Show/Film Clip from January 8, 2009): Tyson has to understand something: we don't care what it really is; we just want to call it Pluto.