Free The Pluto Files: The Rise and Fall of America's Favorite Planet by Neil deGrasse Tyson

the solar system, there is no question that Pluto got to where it is in exactly the same way as a large fraction of the other trans-Neptunian objects…. So if that’s the question you’re interested in, you absolutely have to classify Pluto as a trans-Neptunian object. Now, this basically means that you should have dual classification.
    But A’Hearn had a surprise up his sleeve. Classifying Pluto as a trans-Neptunian object would place it in the region that produces comets and would subject it to the IAU’s distinctions between comets and asteroids and between comets and minor planets. In other words, if you can see fuzz around an object, it must have an atmosphere, and like icy comets, icy Pluto would have an atmosphere only during perihelion, the few years when its orbit takes it closest to (though still very far from) the Sun’s warmth. So, he concluded, “I think it’s clear we can come out in favor of comet Tombaugh.” The audience loved it.
    Last in line was Levy. Invoking the heroism and devotion of Clyde Tombaugh and the emotional attachment to Pluto felt by children and the cosmic discovery stories recounted to him by his father at the dinner table and the meanness of expert taxonomists who decided that the galumphing brontosaurus of his childhood was actually an apatosaurus and that the beautiful Baltimore oriole was actually a northern oriole, he came down squarely on the side of Pluto’s planethood:
    Science, to me, is not just for scientists. Science, to me, is for everyone; it’s for us. It’s for the children at the Clyde Tombaugh Elementary School. It is for the young people in this audience, who have a better way than we do to look at an object and say, “That’s a planet.” “That’s a brontosaurus.”
    But most important, when we go out under the night sky, and we look up at the stars, we don’t see them as being something incredibly complicated, but instead we see them as something beautiful and simple…. Let’s send a [spacecraft] out to Pluto. If it gets there, and if it clearly takes a picture that shows that there is a dog instead of a planet, then we can have this debate again, and then we can decide that Pluto is not a planet, it is a dog or a brontosaurus. But until then, please, let’s all enjoy the night sky and leave Pluto alone.
    That evening was the first time that we at the Hayden Planetarium—and certainly the people in the audience, or perhaps anybody anywhere—listened to a sustained encounter on the status of Pluto based primarily on the science, but also on culture. And the panelists were divided: one for uncompromising iceballhood, two for dual status, two for planethood. In retrospect, what started as a homework exercise to assist our design of the planet exhibits in the Hall of the Universe was actually a watershed event.
    After the speakers’ opening remarks, I ran a mental applause meter to take the temperature of the room: Who would be perfectly happy to kick Pluto out of the planet club? Weak applause. Who favors planet status? Modest applause plus a scattering of loud whoops. Yet by the end of the evening, everyone from the Hayden Planetarium connected with the Pluto exhibit design had come to believe that Pluto needn’t retain any kind of status at all, except for reasons of nostalgia. And judging by the crowd’s laughter and applause as the debate progressed, a majority of them became convinced as well.
    Monday, May 24, 1999. The night Pluto fell from grace.
     
    The time quickly arrived for us to design the planet exhibits. We didn’t have the power or the authority (or the interest) to declare that the solar system has only eight planets, but that didn’t mean we couldn’t invent innovative ways to treat the subject. That’s when we decided to present the contents of the solar system as families of objects with similar properties, rather than as an enumeration of orbs to be memorized—a trend that was already being seen in textbooks of the