how many scientists have stained-glass windows of them? it's more than just a celebration of his discovery. 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 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. food's a-comin'. tyson: mike brown and david jewitt. back in the 1980s, david started a search that would put pluto in a new perspective. tyson: so you start looking in the outer solar system. that's kind of crazy because everyone knew the solar system ended at pluto. uh, it's a little crazy, but, you know, the flip side 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. well, it's got to end somewhere, why not pluto? yeah, i mean maybe, but maybe not. 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 than either one of them expected. luu: why did it take so long? um, it was a matter of technology catching up with the problem. 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. 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 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. 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 a region of the solar system never before seen. david named it the kuiper belt after the astronomer who proposed its existence 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 togetr 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 lots of bits and pieces leftover. 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? 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. marsden: we all considered pluto was strange at that time, but we didn't know how to resolve this. 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. 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 that anyone could start working on. this was an entirely new area of the solar system to go study. so it was very exciting. tyson: mike set his sights on doing something really big, finding a kuiper belt object larger than pluto. brown: i was determined that there still must be something out there. i had caught the bug of finding it. 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. 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. tyson: but it wasn't crazy. 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 on calling me, congratulating me for discovering the tenth planet, i felt fraudulent the entire day. why? 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. like, 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. 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 iau, 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. so what we proposed was that planets should be round and going around the sun. so, massive enough for the gravity to shape them into a nice round form. that's right. tyson: 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. gingerich: we realized that doing this would bring scores of planets. into the accounting of planets in the solar system. that's right.

tyson: but when the definition was proposed in prague at the 2006 iau conference, many scientists were dead set against it. a rebellion was brewing and things were getting ugly. tyson: just to clarify, your original suggestion got overturned within days. 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. 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. brown: in the definition that the iau came up with, eight major things which dominate the solar system

are planets. they're all big. they go in circular orbits in one disk around the sun, and everything else is on these other crazy orbits much smaller; those are not planets. that concept is a rock-solid concept. tyson: and when this new definition went to a vote of the members present, it was a slam-dunk. (trumpet playing taps) after 76 years, pluto was no longer a planet. colbert: 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, that's not change i can believe in. the whole underpinnings of what we understand as science. is gravity real or do we just have sticky stuff on our shoes? i mean, the whole thing. (trumpet continues playing taps) 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. supporters of pluto are speaking out, trying to help it regain planet status. man: ♪ rock on, pluto, you'll always be a planet to me... ♪ tyson: pluto lovers of america did not take the iau decision lightly. at new mexico state, where clyde tombaugh had taught, students took to the streets. go, pluto! pluto forever! tyson: the new mexico legislature declared pluto was still a planet within state borders. man: ♪ no matter what it says on the chart ♪ ♪ you'll always be a planet in my heart... ♪ tyson: and illinois soon followed, spurred on by efforts led by the concerned citizens of streator. man: ♪ rock on, pluto! so i've got in my hand this... legislation passed by the 96th general assembly here in the state of illinois. yes. 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 this part of the resolution that says when pluto passes overhead, (chuckling): 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." yeah, this is streator. and don't mess with streator. and don't mess with us, yeah, there you go. tyson: back at the barbershop, the guys made it clear where they stand. barber: i still believe it's a planet. they can't make me think any different. (laughing) tyson: but next door at the country cupboard, locals questioned the decision. i was very disappointed. disappointed in the result or how they got the result? 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... on scientific fact? 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 iau 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 iau. you're late. ready for this? ready as ever. tyson: i can't wait to hear what alan's got to say

about pluto's demotion. stern: i think that the iau 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 iau 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. so you don't even care about whether a zone is cleared or some of these other parameters. no, that's all about location, and location is for realtors, not scientists. (laughing) i don't think it counts at all in terms of what it means to be a planet. 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.

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 analogy is, when you see a chihuahua, it's still a dog, because it has the characteristics of the canine species, just in miniature. tyson: why, then, are these pint-size planets so much smaller than the rest? the process of planetary formation is a bottoms-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. 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 need to grow. 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.

mission control: three, two, one... we have ignition and lift-off. 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. travel time-- 9 1/2 years. scheduled arrival-- 2015. so this is the place. this is mission control for new horizons. cool. stern: yeah, the flight control team is monitoring the data that's coming down, looking at the health of the spacecraft and sending instructions back up to basically choreograph everything that happens on the spacecraft. so how long do those instructions take to get there? like suppose it says, "quick, turn left!" like, how long does that take? 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 for us to find out that's what happened. to complete the round trip. by the time it gets to pluto...

it's going to be 9 1/2 hours. round trip. yeah. so you better know well in advance what you're telling this thing to do. we try to make sure we do that. 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. 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. all right, so you had enough room for seven scientific instruments, but i heard, like, there's more stuff than that. well, we've got a few mementos. uh-huh. perhaps the most sentimental and noteworthy are some of clyde tombaugh's ashes. his ashes. his ashes-- it's on its way to the stars.

the man is on his way back to the very planet he discovered and he's due to arrive there in 2015... that's great. and that just blows my mind. i'd challenge anybody to put that on their résumé. 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 she had 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. i'm excited. i'm really excited about seeing the exhibit. of course i am still going to look for pluto. i think what we did here is sensible. so let's hope this works. (knocking on glass door) (laughing)

hello. hi! welcome to new york. it's good to see you. oh, my goodness. welcome to the belly of the beast. tyson: 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. it's there. (laughing) okay. i don't see anything wrong with this presentation at all. (kissing) (both laughing) so, after ten years, i can rest peacefully at night. you can rest. i wish it were a little bigger... (both laugh) and a little higher? (laughs) tyson: so can i offer you my view? not that you ask, but i have a view that's been stereotyped but actually misrepresents my position here. when you look at the richness, 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? no, i don't think we are. i don't think agreement is necessary. culture will take its course. these two guys are the cantankerous ones. (all talking at once) 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. tyson has to understand something. we don't care what it really is. we just want to call it pluto. an astounding variety of life-- 9,000 species of birds, 350,000 kinds of beetles, 28,000 types of fish. two million living species and counting. creatures that don't look anything at all like each other are actually deeply connected. how does evolution really work?

"what darwin never knew," next time on nova. major funding for nova is provided by: supporting nova, and promoting public understanding of science. and... and the corporation for public broadcasting and by pbs viewers like you. on nova's "pluto files" web site, what's the best planet in the solar system? listen in as a range of opinionated astronomers argue for their favorites. then vote for your own. find it at pbs.org. captioned by media access group at wgbh access.wgbh.org

this nova program is available on dvd. the companion book, the pluto files, the rise and fall of america's favorite planet, is also available. to order, visit shoppbs.org, or call us at 1-800-play-pbs. available now from shoppbs... is time travel possible? do you exist in another universe? the questions are infinite. the answers start here. "nova: the fabric of the cosmos."

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