Goodbye, Pluto | Translation
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Translated by MC Editorial
[Daniel Alarcón]: This is Radio Ambulante from NPR. I’m Daniel Alarcón.
Song: Nine globes rotate under the sun, and as you count up I live on the third. Nine names you have to learn, so you will know the planetary system.
[Daniel]: What you’re hearing is “The song of the planets,” by Spanish singers Enrique and Ana.
Song: Earth is our planet, and the others are called: Mercury, Venus, Jupiter and Mars, Saturn, Uranus, Neptune and Pluto-to-to-to. Pluto-to-to-to. Pluto-to-to-to.
[Daniel]: The song is from 1982, and I imagine some of our listeners once sang it as a child. Or, if you didn’t get to hear it, you probably did grow up learning what was taught for decades—that the Solar System had nine planets.
We made models, we read about it in schoolbooks, we saw it in documentaries. Always the same image—the nine floating together in the dark. And at the very end, Pluto, the smallest and coldest, the one that is so far from Earth that it needs almost two and a half centuries to go around the Sun.
There were nine, and it didn’t seem like that was going to change. But in 2006, a worldwide discussion broke out about what exactly constituted a planet. And well… not everyone was sure that Pluto qualified.
Among them were two Uruguayan astronomers. They were two researchers who had a lot in common, in addition to a great deal of knowledge about the formation of the Solar System. Both came from families of modest means, both had been student leaders during the dictatorship, and both had to struggle hard to become astronomers.
And that, of course, had formed their character in a certain way.
One is Julio Ángel Fernández.
[Julio Ángel Fernández]: We have a sort of rebelliousness, like not accepting everything that comes from the top down…
[Daniel]: And the other is Gonzalo Tancredi.
[Gonzalo Tancredi]: Do not accept outright what an authority imposes on you. If you disagree, well, fight it!
[Daniel]: The fight, in this case, would be over nothing less than the size of the Solar System.
[Journalist 1]: The Solar System could be reduced to eight members. The one sacrificed: Pluto.
[Journalist 2]: …Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, period.
[Journalist 3]: This will force us to rewrite textbooks and, little by little, change what many of us have learned.
[Daniel]: And Gonzalo and Julio Ángel would become the leaders of a battle that would turn international astronomy upside down.
We’ll be back after a break.
[Daniel]: We’re back with Radio Ambulante. Nicolás Alonso picks up the story.
[Nicolás Alonso]: Pluto was always a different planet in several ways. It was the furthest away, the last to be discovered.
And it was also the only planet that was, so to speak, “American.” In 1930, when amateur astronomer Clyde Tombaugh discovered it from an observatory in Arizona, the news was highly celebrated at the national level, so much so that it is even believed that Walt Disney decided to name Mickey’s friend Pluto for that very reason. It was a source of pride for science in the United States.
[Gonzalo]: It was a way of showing the progress of science, and in particular, of North American astronomy.
[Nicolás]: This is Gonzalo Tancredi, one of the two Uruguayan astronomers we heard at the beginning.
Gonzalo began to study the formation of Pluto and its moon, Charon, for his dissertation in the late eighties. And by then, several astronomers had noticed that Pluto seemed very different from the other planets.
That topic had been suggested to him by his professor, Julio Ángel Fernández, the other protagonist of this story, an expert on comets who had been the third person in Uruguay’s history to graduate with a degree in astronomy.
This is Julio Ángel:
[Julio Ángel]: Pluto always sparked debate about its nature, didn’t it? In other words, once the initial frenzy had passed, articles began to appear saying that it was a somewhat peculiar planet, a little strange, that it was not like the other planets.
[Nicolás]: There was never any discussion about the others. Mercury, Venus, Mars, Jupiter and Saturn were known to the Sumerian civilization five thousand years ago, because they can be seen with the naked eye on a dark night. Uranus and Neptune were discovered with the development of telescopes, in 1781 and 1846. But early in the 20th century, some researchers felt that there might be one more planet, because of some alterations that had been detected in Neptune’s orbit.
They called it “Planet X,” and scientists at the Arizona observatory I mentioned before calculated that it must be huge—six times larger than Earth. These were very wrong measurements and could have led to nothing, but with so much searching they led to the discovery of Pluto.
And its discoverer—a young 24-year-old who had grown up in the country, assembling telescopes out of glass and scrap metal—became a celebrity of American astronomy.
There were no longer eight planets, but nine, and the initial news was that Pluto was the same size or larger than Earth. The New York Times stated on its front page that it might even be larger than Jupiter. But that began to be questioned over the years, with better telescopes, and in the 1970s the truth came out: Pluto was actually tiny, even smaller than our moon, and had a mass only 0.2% that of Earth. If we were able to see it, that was only because its icy surface reflected so much light.
And the fact that it was so small began to raise doubts.
But there were other things, too, like the fact that its moon, Charon, was huge for a satellite—almost half the size of Pluto itself. And Pluto’s orbit was very strange, much more oval and tilted than the other planets’. Its trajectory formed a huge egg-shaped ellipsis, which intersected the orbit of Neptune.
[Gonzalo]: Specific explanations had to be sought for the case of Pluto and Charon. These particular features of the orbit and mass and size made us question its origin.
[Nicolás]: In the early 1990s, several researchers were already doubting whether it was correct to call Pluto a planet… and Gonzalo and Julio Ángel were among them.
But they weren’t just studying Pluto. At the Universidad de la República, in Montevideo, they investigated comets, asteroids, and all kinds of celestial bodies. It was a small college, with one astronomer graduating per year at most, and with little access to large telescopes. But they knew quite a bit about the formation of the Solar System.
And they would soon find themselves in the center of the controversy.
It all started in 1997, when Julio Ángel joined the Committee on the Nomenclature of Small Bodies of the International Astronomical Union. You probably haven’t heard of the IAU, because it is a low-profile institution, but it is something like the FIFA of space. It brings together twelve thousand astronomers from all over the world, who meet every three years to resolve all kinds of issues.
Issues we would never imagine being reviewed and voted on, like exactly how long a second is, for example, thanks to improvements in observations. Or the exact value of a certain unit of measure in astronomy, or the rules for naming the different types of celestial bodies in space.
Julio Ángel was part of that last task. He was a member of the committee charged with approving or rejecting the names of comets and asteroids. The discoverers proposed names, and they had to evaluate them.
[Julio Ángel]: The conflicts were because they could not be political in nature, the names could not be religious in nature. They couldn’t be in bad taste. Sometimes someone suggested the name of their pet, a dog, right? Or there was someone who proposed naming an asteroid Lady Di. That sounded rather cheesy, didn’t it?
[Nicolás]: They went through long lists of names and sometimes got into arguments, but most of the time it was a fairly mechanical task. And that’s how Julio Ángel thought it would always be. But he had been on that committee for just a few months when things started to get weird.
It had to do, of course, with Pluto. And with a discovery in which Julio Ángel had been key. In the early 1980s, while he was living in exile, he provided the first evidence of a huge asteroid belt in the area where Pluto is— hundreds of thousands of pieces of rock and ice that form a disk between us and the rest of the universe. There had been speculations on the idea for a long time, but he demonstrated it theoretically, doing calculations and more calculations on the path of certain comets in the Solar System. And it was not until 1992 that it could be observed for the first time.
It was christened the Kuiper Belt, and its discovery had a huge impact. The Solar System no longer ended with Pluto—there were many, many more objects out there. Some were quite round and icy-surfaced, smaller but similar to Pluto, and some had that same long, tilted orbit.
Several on the committee believed that, rather than a planet, Pluto looked like a large object in that belt. And they felt that it should be demoted.
[Julio Ángel]: Very, very bitter discussions between people who are in favor of changing and others who don’t want to hear about it, so that causes a deep division in the committee.
[Nicolás]: There was a lot of pressure around the issue. There was a group of astronomers, mostly from the United States, who would not hear of it at all. For them, the little king at the end of the Solar System was a planet, period.
It was what schoolbooks had been saying for seven decades, and to degrade it seemed a confusing gesture, an astronomical dishonor and a show of disrespect for the memory of its discoverer, who had died a short time earlier.
It was a subject they came back to over and over again. The committee was supposed to register those new objects of the Kuiper Belt on the long lists of small bodies, like asteroids and comets, and give them a number, because there were not just a few, but thousands, impossible to recall by name.
As the list grew, a proposal came up: Use the number ten thousand and give it to Pluto as a kind of consolation prize. Behind that idea was Brian Mardsten, an influential British astronomer with a certain taste for controversy, who believed that Pluto as a planet was a myth that had to end. And he insisted on numbering it. Julio Ángel agreed.
[Julio Ángel]: Actually, there was a political background to this, because assigning a number to Pluto would mean admitting that it was a small body. Planets do not have numbers.
[Nicolás]: That committee didn’t have the power to demote it officially, but if they gave it a number, it would have a dual status: planet and small body, and the International Astronomical Union would have to decide the matter.
The American Astronomical Society sent an alarmed letter to the committee, asking them not to innovate but to keep Pluto as the ninth planet in the Solar System. The public, they said, was confused.
[Julio Ángel]: Well, so it was decided that there would be no further discussion because this was turning out to be a harsh, divisive subject. The matter would be kept on stand-by.
At least until an object equal to or larger than Pluto was discovered in the area. Which is what happened a few years later…
[Julio Ángel]: Because in 2003, an object was discovered that was almost identical in size to Pluto. That’s where the trouble began, you know?
[Nicolás]: A body found by American astronomer Mike Brown, which would later be named Eris. At first it was thought that it might be 10% larger, although today they are known to be almost the same size. And its mass is much greater. And that, of course, was not good news for Pluto. Here’s Gonzalo again:
[Gonzalo]: That reopened the discussion on the nature of Pluto as a planet in a definitive way.
[Nicolás]: Because then, what was Eris…?
[Gonzalo]: Actually the question was, well, if we take Pluto as a planet, this one would have to be a planet, too.
[Nicolás]: But the issue was deeper, because that doubt regarding Eris and Pluto opened up another question that—incredible as it may seem—had no answer:
[Gonzalo]: It was concluded that we needed to adopt a definition of planet, of the term planet. It is a term that came from ancient times, from the time of the Greeks, but there had never been a precise scientific definition for it.
[Nicolás]: It was the 21st century, and the definition was still the one left by the Greeks thousands of years ago. There had been a lot of study, but what exactly the term planet meant had never been updated. And it’s not like the Greeks were that precise; I mean, they didn’t even have telescopes. In Greek, the word planet means wanderer, and that’s how they defined them: moving objects against a background of fixed stars. And there wasn’t much more to say. Space was so much simpler back then.
But now the International Astronomical Union had to take action on the matter, so they decided to form a special committee, with the mission of defining once and for all what the heck a planet was. To be honest, Jupiter wasn’t very similar to Mercury, nor was Mercury like Earth… but what was the least they had to have in common in order to be considered planets?
So in 2004, a team of 19 planetary scientists, experts on the subject, was convened. They worked a year on it and came up with nothing.
[Gonzalo]: The discussion got quite heated and they could not come to an agreement. There was no proposal. Things were getting intense, precisely because of the consequences of adopting a definition.
[Nicolás]: The clearest consequence was Pluto’s status.
And, as if that were not enough, NASA was about to launch its New Horizons Mission—the first probe to travel to the far reaches of the Solar System to meet Pluto, the only planet never visited before.
[New Horizons archive]: Out here, where the Sun is distant and faint, it’s a place no one has ever seen before. Pluto and its system of moons, the farthest world ever to be explored by humankind.
[Nicolás]: The mission cost 700 million dollars, and was launched from Cape Canaveral on January 19, 2006. It would fly over the last planet in the Solar System, and it was carrying an urn with the ashes of its discoverer. It was a very difficult time to stop seeing Pluto as a planet.
By August 2006, Gonzalo was running a small observatory on the outskirts of Montevideo, and Julio Ángel was dean of the Faculty of Sciences. And at that point in their careers, they already had two asteroids named after them.
They traveled to as many meetings of the International Astronomical Union as they could, although there was never an excess of funds. That year, the IAU General Assembly would be held in Prague, and although the trip was long and expensive, they decided to go.
That August 16, 2006, at the Prague Congress Center, 2,500 astronomers from 75 countries discussed the latest news from the galaxy. Gonzalo and Julio Ángel picked up the Assembly journal. And that’s how they found out.
After so much deliberation, the IAU had a proposal to define what a planet was. Hardly anyone knew, but they had formed a new Planet Definition Committee and had decided to keep it a secret.
There were only seven people on the committee: three from the United States, two from France, one from Japan, and one from England. A mix of astronomers, science historians, and a science communicator.
They had met in Paris two months earlier to discuss what a planet was. The president, an American and a Harvard professor, called it a miracle: After two days of, in his words, a “vigorous debate,” analyzing scientific and cultural aspects, they had reached a total consensus.
What they proposed was that a planet was any body that orbited a star, that was not a satellite and—this was the key point—that had enough gravity to become almost round.
A pretty simple definition. Gonzalo and Julio Ángel were shocked.
[Gonzalo]: It seemed like a definition to make Pluto remain a planet, let’s say.
[Nicolás]: And not just Pluto, because with that definition several more were going to qualify. The usual eight, Pluto, two other celestial bodies, and even Charon, Pluto’s moon, would now also be a planet.
[Gonzalo]: And then there was talk of 12 planets.
[Nicolás]: Pluto and Charon would be something new: a “double planet” system, that is, two planets orbiting each other and the Sun.
But things would not end there, because a dozen more bodies—none of them studied very extensively yet—were now candidates to be new planets. The IAU recommended jointly calling Pluto and all those new, small and distant planets in its area the “Plutos.”
[Julio Ángel]: It seemed very bad to us, from a scientific point of view. Because it was a broad, lax definition. And that seemed to mean there would be tons of planets. If you were going to be broad like that, there could be hundreds.
[Nicolás]: The Assembly would last eight days, and on the seventh, the final vote would be held to define whether or not to approve the definition of the 12 planets. But those votes were almost a formality—Julio Ángel and Gonzalo had never seen the Assembly reject a definition made by a committee.
The proposal was going to be announced that same morning, at a big press conference, and Mike Brown, the discoverer of Eris, one of the new planets, had been told to get a suit pressed and ready to celebrate the announcement.
It seemed almost definite, but they could tell that many of their colleagues were just as surprised as they were. They spoke with astronomers from Italy, the United Kingdom, France. And they weren’t happy.
[Julio Ángel]: There was a spirit of pessimism, as if nothing could be done to change the course of events.
[Nicolás]: They were resigned. But not Gonzalo and Julio Ángel.
[Gonzalo]: That was kind of what we said: No, if we don’t agree, we don’t have to accept it.
[Nicolás]: Julio Ángel, who had played a key role in proving the existence of the asteroid belt where the whole mess had begun, was not going to vote for something he did not believe in. Neither was Gonzalo.
[Gonzalo]: The moment was like a feeling that the spark had to be released; let’s say there was a level of discontent. The idea was to lead and channel that discontent.
[Nicolás]: They wanted to rebel, but they didn’t know whether their colleagues would back them.
[Gonzalo]: The first thing was to say, “Well, we don’t agree, we’ll put together an alternative proposal,” and go out and get support.
[Nicolás]: That was the first thing they needed: to get support, lots of support. And they certainly needed it. What they planned to do was try to knock down a planet.
[Daniel]: We’ll be back after a break.
[Daniel]: We’re back with Radio Ambulante. I’m Daniel Alarcón.
Before the break, we heard how two Uruguayan astronomers, Gonzalo Tancredi and Julio Ángel Fernández, found out that a new definition of a planet was going to be voted on, which would keep Pluto and add three more planets to the Solar System. If approved, eventually there could be hundreds.
It seemed too vague a definition, too unscientific. So they decided to create an alternative proposal and try to convince their colleagues all over the world. The future of the Solar System was at stake.
Nicolás Alonso continues the story.
[Nicolás]: Gonzalo and Julio Ángel needed a reasonable plan. The idea of the 12 planets had the support of the Executive Committee of the IAU, so they were at a clear disadvantage.
[Julio Ángel]: It meant a fight against a very powerful opponent. We had to act quickly so that events would not overtake us.
[Nicolás]: Gonzalo believed that the alternative proposal should not sound so different from the official one. He had learned this as a student leader: A counter-proposal always had to pick up part of the idea it was trying to defeat.
[Gonzalo]: “Let’s try to use several elements from this proposal that is coming up. We are not going to… change everything.” That way we achieved a certain closeness, a better chance of its being accepted while changing the substance.
[Nicolás]: The 12-planet proposal said what we’ve known for centuries—that a planet is a body orbiting a star—but added a geophysical requirement: It had to be large enough and massive enough for its own gravity to make it nearly round. That was the dividing line between a planet and not a planet.
But Julio Ángel and Gonzalo wanted a bigger line. After discussing it with various colleagues, Gonzalo wrote a first draft and reviewed it with Julio Ángel that evening. The idea, which some astronomers had been proposing for years, was to use an evolutionary point of view. And don’t worry, I’m going to explain what they meant by that.
About four and a half billion years ago, a huge ring of dust and gas existed around the Sun. All of that began to come together and collide, forming bodies that grew larger and larger, which in turn gave them more gravity to attract smaller objects and expel others.
OK, but at what point did they start to be Mercury, Venus and Mars—what we call planets? That was the key point, and the rule they added was simple, but decisive: a body would be a planet if it became so massive, if its gravity was strong enough, say, to clear out its entire neighborhood in its orbit around the Sun. Like a giant magnet.
[Gonzalo]: It’s like saying, “I’m the boss in the neighborhood, and I’m the boss by far. The one who rules here by far. I don’t have other chiefs in the same area.”
[Nicolás]: That is to say, unlike Pluto, which was surrounded by thousands of asteroids and therefore had failed to become the dominant object in its zone.
It had failed, ultimately, to be a planet.
They were going to ask their 2,500 colleagues and see how many were on their side.
The next day, with the counter-proposal in hand, it didn’t take them long to get the signatures of astronomers from France, Italy, several Latin American countries, and even some from the United States.
Among those who signed was prominent scientist Daniela Lázzaro, a small-body specialist at the National Observatory in Rio de Janeiro.
[Daniela Lázzaro]: Júlio e Gonzalo chegaram e falaram: “Daniela, a gente acha que a definição é péssima.” Todo mundo concordava que a definição é péssima. “A gente precisa fazer uma contraproposta.”
[Nicolás]: Julio Ángel and Gonzalo told Daniela that the definition seemed terrible to them. That they had to make an alternative proposal. According to Daniela, everyone agreed that the definition was very bad.
But if there was someone who should not make trouble in that assembly, that someone was Daniela. As the representative of Brazil, which was to host the next IAU meeting three years later, she was on a quasi-diplomatic mission. However, when she saw the new definition in the journal, she was offended.
[Daniela]: Como uma pessoa que trabalha na área me senti ofendida porque eu não sabia de nada. Nunca fui consultada. Foi uma imposição, tan passando por cima de mim. Que estou fazendo aqui? É uma ofensa.
[Nicolás]: They never consulted her, even though she was an expert in the field, she says. And it felt like an imposition, as if they had gone right over her. She was a member of several IAU commissions, and she didn’t know anything about it.
[Daniela]: 19 membros cientistas planetários não chegaram a um consenso, por que que sete que não eram todos cientistas planetários chegaria na proposta.
[Nicolás]: It seemed very strange to her that seven chosen ones, not all of them astronomers, would solve what 19 experts on the subject had not been able to agree on in a year.
Several heavyweights in the Solar System felt this way, and there were also some critical voices among the Americans. The most surprising of all was Mike Brown, the discoverer of the celestial body called Eris, which would become one of the new planets according to the commission’s proposal. Despite this, Brown was not in favor. He stated to the press that there were aspects of the official proposal that did not pass—and I quote—the “smell test.” At first, he had felt happy to be the discoverer of a planet, but now the definition seemed meaningless. He himself knew of 43 other bodies in the Solar System that would also become planets. Or more.
But other leading astronomers, such as Alan Stern, the leader of NASA’s New Horizons Mission, believed that the proposal reflected the true complexity of the Solar System, made up of dozens of planets, most of which are more similar to Pluto than to Earth.
And there was no reason to limit them to eight. The prestigious journal Nature said that the definition was going to cause disorder, but that it was coherent in geophysical terms. It voted to accept.
But the opposition did not. I asked Daniela, who immediately became another of its leaders, whether she was afraid of getting into trouble.
[Daniela]: Quando eu vou para a luta, vou pra luta. Não, eu acho que essa era uma luta científica.
[Nicolás]: “When I go for battle, I go for battle,” she said. And she said that hers was a scientific fight, the kind of battle someone like her had to fight.
[Daniela]: Se eu sou obrigada a votar em cima de uma definição, eu quero que a definição seja a mais científica possível. Não é si gosto de Plutão ou não gosto de Plutão. Não é isso.
[Nicolás]: “If I have to vote on a definition, I want the definition to be as scientific as possible,” she says. “It’s not whether I like Pluto or not. It’s not about that.”
The group of rebels numbered about 20 renowned astronomers, and together, they corrected the counter-proposal. They decided to create a new term for Pluto and the other bodies in contention. They would call them “planetoids”—almost planets, but not quite.
And they began to insist to the Executive Committee, the board of 12 members that directed the IAU, to let them share their definition. They had no time to lose, because on the third day there would be a meeting to test support for the official proposal. But the higher-ups did not want to hear about it.
[Julio Ángel]: Saying that no, that it was not a place to discuss alternatives. Nothing is discussed there, nothing is debated, everything is approved.
[Nicolás]: Nor was it common for there to be such a clear disagreement in the view we have of space. And the Executive Committee would probably not want to give that impression. How was it that the world’s leading astronomers could not agree on what was or was not a planet?
[Julio Ángel]: Some might see it from the perspective that scientific issues are not up for debate. They are facts, they are things that all astronomers reach a consensus on, and that is the official opinion.
[Nicolás]: But Julio Ángel thinks that total consensus is a fantasy.
[Julio Ángel]: It is fiction. In fact, why does science move forward? Because certain accepted paradigms fall at some point and are replaced by other paradigms.
[Nicolás]: In the end, they were allowed to submit their counter-proposal, and they stayed up late preparing a presentation. Next morning, there were at least a hundred astronomers in the room—the ones who were the most involved in the discussion because they were members of the Planetary Systems Division.
Gonzalo and Julio Ángel spoke on behalf of the dissidents, and a big debate ensued. Most believed that the official proposal failed to see the Solar System as precisely that—a system, which had principal objects, the planets, and thousands of other bodies that had been by-products of their formation. But others argued that the definition should be simple and applicable to the universe, not just to processes in our Solar System.
Things were not progressing much, but the atmosphere was increasingly volatile, and the members of the Executive Committee seemed concerned. In the end, they decided to hold a vote to measure forces, and out of a hundred, only twenty supported the 12-planet proposal. The rest preferred the counter-proposal.
As Daniela left the auditorium, she walked by two of the seven members of the official committee, who stared at her and said:
[Daniela]: E você ganhou.
[Nicolás]: “You won.”
[Daniela]: “Não ganhei nada. Não estou ganhando nada, não estou aqui pra ganhar. Eu acho que é a melhor definição e ponto final.”
[Nicolás]: “I didn’t win anything,” she replied, “and I’m not here to win anything. I think it is the best definition, period”.
[Daniela]: Mas era uma raiva, uma raiva nos olhos dele.
[Nicolás]: They glared at her. But Daniela was right: they hadn’t won anything yet.
The weekend was a breather for everyone, but on Monday the tension continued to rise. The assembly journal announced that the 12-planet proposal had been defeated, but the ideas of the dissident group appeared only in the online version. And a letter had arrived from the American Astronomical Society calling for support for the official committee.
A new proposal was to be created, but none of the dissident leaders were invited to draft it. And it was like a signal—they needed to start making noise.
[Gonzalo]: The time had come to carry out one more campaign, to make it public and spread massively this discussion that had taken place in a restricted area.
[Nicolás]: Promote the counter-proposal, print copies, talk to the press covering the event. They felt committed.
[Julio Ángel]: You get involved because you have a commitment. If you do science, you do science seriously, and you always aspire to break paradigms. Being lukewarm, not getting involved in any transcendental problem…
[Nicolás]: Then why do science? That time they had to fight, and soon things would get intense in the Prague Congress Center.
It happened on Tuesday morning, at a new meeting with more than 250 astronomers, where the official proposal was submitted again, with some minor changes. Basically, it now distinguished between “classical planets” from Mercury to Neptune, and “dwarf planets”—Pluto and company. Different, but equal; all planets.
And if it was an attempt to add more support, it didn’t work.
[Gonzalo]: Planets are one thing and other things are a different category; we can call it a dwarf planet, we can call it a planetoid, but they are two different categories.
[Nicolás]: There was a line of astronomers waiting to comment: experts in orbits, in extrasolar planets. Some criticized that a maximum mass for planets had not been defined; others doubted that it was possible to know how round a distant planet was or whether it had cleared its orbit.
Several were offended because they had not been consulted, and the IAU President, who wanted the dialogue to focus on the official committee’s proposal, tried to cut off the debate: “We want your opinions, but not now,” he said.
Julio Ángel, who had not been allowed to present dissident ideas, was outraged. Daniela remembers it well:
[Daniela]: Quando o Júlio, do meu lado, começou a gritar: ¡Deixem as pessoas falarem!
[Nicolás]: And he started shouting, “Let people speak!” Andrea Milani, an Italian and a dissident leader as well, asked Daniela to calm him down.
[Daniela]: E aí o Andrea Milani virou para mim. “Daniela, acalma o Júlio. O Júlio vai ter um ataque!”, porque a gente não conhecia o Júlio. Era realmente acalorado naquela situação.
[Nicolás]: He was afraid that he would have a fit. The meeting turned into a shouting match, to the astonishment of the journalists who were there, and in a new tentative vote, the proposal was rejected. The chairman of the official committee told the New York Times—and I quote—that “vocal objectors” had taken “control of the situation.”
[Journalist 1]: The International Astronomical Union is in Prague debating a new definition of planet these days.
[Journalist 2]: They are deciding whether Pluto is no longer considered a planet due to its small proportions; that is, for scientists, it seems that size does matter in the Solar System.
[Nicolás]: That same afternoon, the IAU called Gonzalo and Andrea Milani to negotiate behind closed doors. It was a truce. At the table were the Executive Committee and the authors of the original proposal—about twenty people in all.
[Gonzalo]: The discussion is this: With this new definition, what would Pluto be considered? Would it be a planet or not? There we say, “No, it is not a planet. We are going to use the term dwarf-planet with a hyphen in the middle to indicate that it is a single term. The term dwarf-planet is a noun, not an adjective.”
[Nicolás]: The great discussion on the Solar System was turning into an almost linguistic affair, debating whether dwarf-planet was a noun or a small planet. And it took them two hours to come to terms of peace. In the end, they agreed to distinguish three different types of celestial bodies: planets; dwarf-planets, hyphenated and as a totally different category; and small bodies. And the assembly of 250 astronomers agreed. If that proposal was approved in the final vote, Pluto would no longer be a planet.
That new definition would apply only to our Solar System, and Pluto’s moon Charon would continue to be a moon. The dissidents were happy, but that was short-lived, because the next day, when they reviewed the draft of the proposal, the hyphen had disappeared and an amendment, Resolution 5B, had been added to call the eight usual planets “classical.”
That had to be voted on separately, but the goal was clear: that there would be “classical” and “dwarf” planets, and that they would all be considered planets.
[Gonzalo]: We understood that it was not an amendment, but questioning the essence of the resolution. It was like wanting to put a change out the window, and that changes everything again.
[Nicolás]: They were upset and tired.
[Daniela]: Muita artimanha, coisas por baixo que acabavam cansando a gente, né?
[Nicolás]: A lot of trickery, says Daniela. The IAU told them that they had the right to publish 250 words in the official gazette and 60 seconds to argue, before the final vote, why they were against that amendment. And so the day came.
But that morning, Thursday, August 24, the dissidents would make one more move. They were in a hallway, discussing how to change the confusing “dwarf planet” for something else, like mini-planets or sub-planets… until Julio Ángel came up with a term: “planetinos.” It was something new, it sounded good in several languages, it seemed less than a planet but not that much less; and Gonzalo had an idea:
[Gonzalo]: “Get a printer, print the word planetino on some posters, and have a kind of demonstration, a march inside the assembly, and well, come on, let’s all go together.”
[Nicolás]: All together to the press room. About twenty of the most important astronomers on Earth. It was the March of the Planetinos.
[Gonzalo]: Those were things that one would never think could happen at an IAU assembly. At some point we just may have yelled, “planetino, planetino!”
[Nicolás]: Daniela marched in the middle of the group, with astronomers from Czechia, Serbia, the Netherlands, Norway…
[Daniela]: Aqueles planetinhos. Mas era gente acostumados a lutas estudantis. Então planetinhos era… era uma briga alegre, né?
[Nicolás]: People used to student activism, marching with joy. The room was full of journalists, and the dissidents stated their disagreement. They demanded that “dwarf planet” be changed to “planetino” to avoid further ambiguities. The IAU press officers watched the scene in bewilderment.
Jocelyn Bell, the prestigious astrophysicist from Northern Ireland who would lead the discussion, was not convinced by the last-minute change, but she promised to be very clear about the positions.
And she was willing to write “dwarf planet” in quotation marks, so it would read as a term on its own. It wasn’t what they wanted, but they agreed. The only thing left to do was vote.
[Julio Ángel]: For me it was waiting, waiting with tense expectations. It was a tense day, right? because you didn’t know what was going to happen.
[Nicolás]: At 2:00 in the afternoon, the 424 astronomers who still remained in the assembly met. The rest had already returned to their countries, so these would be the judges of Pluto’s fate.
[Jocelyn Bell]: Last Tuesday. Seems a very long time ago. A very, very long time ago. We have moved a long way since then. To be honest…
[Nicolás]: Jocelyn Bell spoke of the intense debate that had dominated the assembly. Last Tuesday, she said, felt very far away.
The astronomers were preparing to vote. Each one had a ballot—a little yellow card that they would raise in the air to define who was who in the Solar System. In one of the front rows, someone was holding up a picture of Pluto the dog.
A round of questions was opened and, again, the debate began.
[Nicolás]: But, at that point, things were already set. We had to vote.
The first thing was to approve the idea that the Solar System would be divided into planets, dwarf planets and small bodies. And that a planet was a body orbiting the Sun, round, and capable of clearing its neighborhood. Voters were asked to raise their ballots, and that was approved by a large majority.
But still remaining was the vote on Resolution 5B—the one that could change everything, as it proposed that this be the definition for the “classical planets,” from Mercury to Neptune, and that the “dwarfs” were also considered planets. The IAU President asked for a vote in favor. And the English astronomer Mark Bailey, on behalf of the dissidents, argued against.
The matter was so ambiguous, so confusing, that Jocelyn Bell decided to put on a performance so that communicators and journalists would understand.
She explained voting to them as if they were children:
[Bell Archival]: We have planets, the eight that are named. We have dwarf planets in two kinds. Excuse the pun series. And we have small astronomical bodies that are non-spherical.
[Nicolás]: She put a blue globe on the table to represent the eight usual planets; a stuffed Pluto dog, for Pluto; a cereal box representing the dwarf planets; and a lemon for smaller bodies.
[Gonzalo]: And if amendment 5B is adopted—and here she pulls out an umbrella…
[Nicolás]: The umbrella had a sign with the word “Planets”.
[Jocelyn Bell]: What we are doing is creating an umbrella category called planets, under which the planets and the dwarf planets fit.
[Nicolás]: If they accepted this resolution, Pluto and the other dwarfs would be under the umbrella. If they rejected it, they would be out. There was no room for more ambiguities: what every book and every song was going to say, how many little balls were going to be bought by parents for their children’s last-minute homework at school.
It was time. The IAU President asked those in favor of Resolution 5B to raise their votes. The dissidents leaders turned to see how many there were.
89…90…91 yellow ballots up…
[Unknown]: Mr. President, we report 91 votes in favor.
[Nicolás]: Then he asked those who were against to vote. And it was not even necessary to count. Reporters would talk about more than 300 votes, and even Jocelyn Bell stood on stage holding up her yellow ballot. It was exactly 3:33 in the afternoon on Thursday, August 24, 2006, when the Solar System ended up with eight planets.
End of business: goodbye, Pluto.
[Daniela]: Aquele auditório imenso, todas com aquelas papelzinho amarelo. Também não estava conseguindo mudar uma estrutura tão pesada quanto a IAU é muito burocrática.
[Nicolás]: Daniela and her colleagues were proud to have achieved such an important change, considering the weight of all that space bureaucracy. And, mostly, to have fought for something they believed in. It had been a strange, tense, exciting week. The historic Assembly in Prague had come to an end and the news was now appearing in the media.
[Journalist 1]: Agreement has finally been reached on what a planet is, and the big loser has been Pluto, which after 76 years among the greats, has been downgraded.
[Nicolás]: Julio Ángel and Gonzalo were happy, but both told me that they never imagined the commotion that would ensue. The reaction was swift—from a protest in the United States, where demonstrators wore T-shirts reading “Stop Planetary Discrimination,” to interviews with children in astronomy museums. There were even astrologers who claimed it could affect the Scorpio sign.
[Gonzalo]: One of my friends is a senator in my country, so every time I run into him, he says, “Ah, you took away my ruling planet. I don’t know what to do about my astrological sign any more.” Look, Pluto still exists—if you think it influences your life, there it is.
[Nicolás]: Daniela got mail from researchers, people close to her, journalists from everywhere. They talked her about their poor little children who loved Pluto so much.
And in the United States, the controversy continued.
[Journalist]: Well, there seems to be a space controversy growing over the decision to downgrade Pluto…
[Nicolás]: The chairman of the official committee wrote that it was linguistic nonsense for a “dwarf planet” not to be a planet. A popular magazine called the decision ridiculous and its promoters “self-centered malcontents.”
The Air and Space Museum in Washington DC put a black tape on its Pluto panel… but later removed it. There was harsh criticism of the methods of the International Astronomical Union.
[Gonzalo]: For the International Astronomical Union, this was all very traumatic; let’s say, there had never been such a heated discussion, with such media repercussions.
[Nicolás]: A group of astronomers led by Alan Stern, the leading investigator of NASA’s New Horizons Mission, sent a letter demanding a new definition, which was signed by 300 researchers, the vast majority of them Americans. And they denounced that they were not planning to use the approved one.
But the 2009 General Assembly of the IAU in Rio de Janeiro did not take up the issue again. Daniela, who is now vice-president of the Executive Committee, told me that at every Assembly, someone proposes going back to the Pluto issue, but that is not accepted because there is nothing new to discuss. And that is how it will be, until someone makes a finding that casts a fresh view on the debate.
Over time, the outrage over what happened to Pluto became a joke on every more or less scientific television series. From The Big Bang Theory:
[Sheldon]: I liked Pluto, ergo I do not like you.
To Rick & Morty:
[Jerry]: Shut up, Rick. I don’t care what anyone says. If it can be a planet, it can be a planet again. Planet. ¡Planet, planet, planet!
[Nicolás]: The topic inspired songs and memes, and spawned groups of Pluto fans. Data is shared and they dream of recovering its place among the greats.
But although the controversy is now a part of popular culture, there are still astronomers who refuse to accept what the IAU defined in Prague. The NASA website, although it accepts the definition and counts eight planets in our Solar System, presents it as an open debate, which will continue over the years.
[Nicolás]: Although this episode tells the story of the dissidents, I felt is was key to understand the arguments of the other side. So I wrote to Alan Stern, the leader of the New Horizons Mission, which reached Pluto in 2015 and showed that, planet or not, it is a fascinating world, with a heart-shaped glacier and mountains covered in red snow. Each day there lasts 153 hours, and Charon and four smaller moons cross the sky. Imagine what a beauty.
Alan Stern, chosen by TIME magazine as one of the 100 most influential people in the world in 2016, took just 15 minutes to answer my email. And he said that he would be happy to schedule an interview on the subject. When we logged in, we talked about what happened in Prague in 2006.
[Alan]: I think it’s the single worst pedagogical moment for science in our lifetimes, because it’s convinced a lot of people in the public that science is arbitrary.
[Nicolás]: He told me that on a pedagogical level, he considered it the worst moment for science since we have been alive, because it convinced many science could be arbitrary.
According to him, seeing researchers voting made many believe that science is something with which you may or may not agree. It’s similar to what we see today in the discussion on climate change. There is no room for voting in science, he told me.
[Alan]: We don’t vote on scientific matters.
[Nicolás]: Stern, who was part of the first commission, the one with 19 experts who never came up with a proposal, says that he cannot respect a definition voted for by only 4% of the ten thousand IAU members who were in Prague that day. And that it also seems impossible to work with and wrong.
[Alan]: Most planetary scientists just ignore the IAU definition because it’s so unworkable and scientifically flawed.
[Nicolás]: According to him, very few planetary scientists use it. I asked him whether he could explain why it seemed so wrong, and he told me that all celestial bodies—stars, asteroids, galaxies or whatever—should be defined by their characteristics, not by their influence on their surroundings.
It is another way of looking at the matter. His argument is that if one were to move planet Earth, as it is today, into the area of space where Pluto is located, it would not be able to clear out that neighborhood, either.
[Alan]: If anything is a planet, Earth is, no matter where you located it.
[Nicolás]: And that Earth should be considered a planet, wherever it is.
[Alan]: And the definition that Tancredi and the small minority, called dynamicists, like, doesn’t respect that. Instead, it’s really about location and it’s created a horrible snarl.
[Nicolás]: Stern says the definition created a horrible mess, which NASA has never really supported, even though their website does define Pluto as a dwarf planet. He says that he doesn’t have a problem with that term, that he actually likes it, but only as an adjective.
I asked him how many planets he counted in our Solar System.
[Alan]: At least… hundred and twenty.
[Nicolás]: He told me that at least 120. Among them would be our Moon and those of the giant planets. He does not believe that there are reasons to continue limiting them to only eight, other than the pride of the International Astronomical Union.
Raising yellow cards, he repeated to me, will never be science.
[Gonzalo]: Yes, yes, I still have my ballot here, my voting card.
[Nicolás]: Gonzalo still has his little yellow card stuck to a cork in his office in Montevideo. When I interviewed him, he was running from one meeting to another. As the only Latin American at the Planetary Defense Conference of the DART Mission —the first to impact and deflect an asteroid, 11 million kilometers from Earth—, he had monitoring meetings daily.
Gonzalo was the president of the IAU Division of Planetary Systems until 2021. And he believes that the definition that was achieved in 2006 could be made more precise, like everything in science. The term “dwarf planet” still seems a bit confusing to him, and he thinks the idea of when a planet managed to clear out its neighborhood could be further refined today, thanks to newer studies. But he doesn’t think that it is a matter in dispute.
Daniela put it in simple terms: Every time an astronomer publishes a paper on Pluto in one of the important magazines, they must use the number given it by the IAU in the list of small bodies.
[Daniela]: Ganhou o número de 134.340: Plutão. Não é um planeta e ponto final.
[Nicolás]: It got the number 134,340: Pluto. It is not a planet, period.
Gonzalo and Julio Ángel are satisfied at having left their mark on the Solar System, but they insisted that it was not a victory for them, but for the entire dissident group. Which summed up what many other astronomers, over the decades, had discovered about the origin of the Solar System. Even today, every time they give an interview, they end up talking about it. They even talk about what happened in Prague at some schools in Uruguay.
I asked Gonzalo what he would do if the issue were discussed again, if he had to travel to another Assembly, I don’t know where, to fight all over again.
[Gonzalo]: And I don’t… I don’t refuse any discussions. I’m a person who, if I don’t agree with something, I don’t remain silent.
[Nicolás]: Even if Pluto or anyone has to fall.
[Daniel]: As of today, the International Astronomical Union recognizes five dwarf planets in our Solar System: Eris, Ceres, Haumea, Makemake, and Pluto. Although there is one place in the world where, from time to time, there are only four again: the New Mexico House of Representatives passed a resolution in 2007 declaring that, at least for them, Pluto would continue to be a planet… whenever it crosses the skies of that state.
Well, that’s better than nothing.
Nicolás Alonso produced this story. He is a journalist and lives in Santiago de Chile.
This episode was edited by Camila Segura and Daniel Alarcón. Bruno Scelza did the fact-checking. Sound design and music are by Andrés Azpiri.
Our thanks to Uruguayan journalist Leonardo Haberkorn, author of a great article on this story, for helping us understand its context.
And to Ana Pais, our digital editor, who led the interview with Alan Stern.
The rest of the Radio Ambulante team includes Paola Alean, Lisette Arévalo, Pablo Argüelles,g, Aneris Casassus, Diego Corzo, Emilia Erbetta, Camilo Jiménez Santofimio, Rémy Lozano, Selene Mazón, Juan David Naranjo, Melisa Rabanales, Natalia Ramírez, Laura Rojas Aponte, Natalia Sánchez Loayza, Barbara Sawhill, David Trujillo, Ana Tuirán, Elsa Liliana Ulloa and Luis Fernando Vargas.
Carolina Guerrero is the CEO.
Radio Ambulante is a podcast by Radio Ambulante Estudios, produced and mixed on the Hindenburg PRO program.
Radio Ambulante tells the stories of Latin America. I’m Daniel Alarcón. Thanks for listening.