The Pluto Files: The Rise and Fall of America's Favorite Planet

by Neil DeGrasse Tyson

  Who are any of us to argue with the octogenarian discoverer of Pluto?

  Just like Paul Revere, John Henry, Paul Bunyan, Davy Crockett, and other folk heroes, Clyde Tombaugh is memorialized in song. Written in 1996 by New York–based singer-songwriter Christine Lavin, “Planet X” (see Appendix B for complete lyrics) is a hilarious, historical account of Pluto, from before it was discovered through Tombaugh’s modern efforts to protect its planethood:

  It takes 247 earth years

  for Pluto to circle our sun.

  It’s tiny and it’s cold

  but of all heavenly bodies

  it’s Clyde Tombaugh’s favorite one.

  He’s 90 now and works every day

  in Las Cruces, New Mexico

  determined to maintain the planetary status

  of his beloved Pluto.

  Lavin’s 119 lines of text, sung in a kind of folk-rap style, include references to Disney:

  That same year, 1930, Walt Disney

  debuted his own Pluto as well

  but a cartoon dog with the very same name as the CEO of Hell

  was not your normal Disney style

  To disgruntled horoscope readers:

  and Scorpios look up in dismay

  because Pluto rules their sign.

  Is now reading their daily Horoscope

  just a futile waste of time?

  And to an empathetic (de-sainted) St. Christopher:

  St. Christopher is looking down on all this

  and he says, “Pluto, I can relate.

  When I was demoted from sainthood

  I gotta tell you little buddy,

  it didn’t feel real great”

  Lavin was inspired to write the song after reading an article on Pluto by Sal Ruibal in the March 4, 1996, edition of USA Today.

  Clyde Tombaugh died January 17, 1997, just a couple of weeks short of his February 4 birthday, when he would have turned 91. He was a leading force for Pluto, but he was not alone in his support of planethood. Behind him were many whose professional research interests focused on Pluto and who wanted to see a mission sent there. By the 1990s, space probes had flown by, or visited, every planet in the solar system but Pluto. Some groups vying for space missions invented catchy slogans to help sell a flyby of Pluto to Congress, like “the first mission to the last planet.” Phrases such as that imply (1) that the concept of “planet” is strong and real, (2) that Pluto is a planet, and (3) that once you’ve been to Pluto, your reconnaissance of the planets is complete. Such paradigms require, of course, that Pluto be a planet. In addition, there was legitimate, if unspoken, concern that if Pluto were demoted to “ice ball,” or anything less than planet, then funding for a major Pluto mission could be jeopardized. Why? If Pluto was just a ball of ice, astrophysicists could simply study a passing comet and save the American public the money required to travel 4 billion miles to the outer solar system.

  Gerard Kuiper himself voted for demotion of Pluto before anybody else, but for reasons we would deem trivial today. A news story from the science section of Time magazine from February 20, 1956, was prophetically titled “Demoted Planet.”19 The editors begin bluntly—“Astronomers have always felt uncertain about Pluto…”—and go on to list the well-known (oddball) features that distinguish Pluto from the rest of the nine, ending the opening paragraph with, “These deviations suggest that Pluto may not be a real planet.” Then, in the next paragraph, Time reports Kuiper’s additional, but retrospectively lame, argument for demotion:

  Figure 4.4. Cartoonist Tom Briscoe understood Pluto’s needs in times of despair.

  Last week Astronomer Gerard Peter Kuiper (rhymes with piper) of the University of Chicago made another move toward demoting Pluto.

  Recent observations have proved that its period of rotation on its own axis is more than six days. For a planet, says Scientist Kuiper, this is too slow.

  Unknown to Kuiper (and to anybody else) at the time, Venus, Earth’s “sister” planet, takes 243 days to spin once on its axis, which is 18 days longer than it takes Venus to orbit the Sun itself. In other words, the Venus day is longer than the Venus year, yet nobody is rushing to demote Venus. Mercury has a long day too, lasting two-thirds of its year. Such are the risks of classifying an object on the premise that you have isolated its fundamental features for all time.

  After a year of advising the trustees of the American Museum of Natural History on what they might do to reverse the precipitous drop in attendance at its famed Hayden Planetarium, I was appointed acting director. A year after that, in May 1996, museum president Ellen Futter and provost Michael Novacek (a dinosaur paleontologist) formally appointed me as the first occupant of a newly endowed chair, becoming the Hayden Planetarium’s ninth director. From day one, my immediate and biggest task was to serve as project scientist for the creation of the museum’s new $230 million Rose Center for Earth and Space, named for New York real estate magnate and museum trustee Frederick P. Rose and his wife, Sandra P. Rose, the source of its lead gift and the source of the named academic chair that I occupy. This new facility would contain a freshly conceived and outfitted Hayden Planetarium as part of a huge museum wing dedicated to the universe.

  Four principal entities collaborated to shape the look, feel, and content of the Rose Center: (1) the architectural firm Polshek and Partners; (2) the exhibition design firm Ralph Appelbaum and Associates, known to many for their work on the Holocaust Memorial Museum in Washington, D.C.; (3) the science advisory committee, of which I served as chair, consisting of staff scientists hired for just this purpose:

  James Sweitzer, a University of Chicago astrophysicist turned education professional

  Frank Summers, a Princeton cosmologist

  Steven Soter, a planetary scientist who apprenticed at Cornell University

  Charles Liu, a Columbia University expert on galaxy formation and evolution

  as well as selected colleagues drawn from outside the museum with expertise in subfields of astrophysics not represented in the profiles of the local staff; and (4) scientific visualization professionals, led by the astrophysically literate artist Dennis Davidson.

  In the old days, a planetarium visit would target the sky show. The exhibits that lined the feeder corridors were what occupied your idle time while waiting for the show to start. By the late twentieth century, however, astrophysicists had compiled much more than a planetarium show’s worth of information about the universe. So our task was not to face-lift the existing facility, but to invent something entirely new. Besides designing and acquiring state-of-the-art technology to deliver what we now call space shows, we were constructing a unique and arresting architectural facility that would offer ample three-dimensional exhibit spaces suitable for telling cosmic stories on a grand scale.

  The basic architectural design of the Rose Center became a matter of public record in January 1995. It would be a huge, 87-foot-diameter sphere, containing the planetarium space theater within its upper half and another theater in the lower half, featuring a walk through the recreation of the Big Bang. The entire sphere would be supported from its sides, appearing to float above a sprawling Hall of the Universe below it, all strikingly lit within a cubic glass building and visible from the street. We spent the next two years establishing our philosophical approaches to the interplay of design and content before we began three years of total reconstruction in January 1997, during which we turned our attention to the exhibit text and other detailed features of the content. Given how common spheres are in the universe, we knew from the start that the Hayden sphere should serve not only as an enclosure but as an element of exhibitry.

  Figure 4.5. The Frederick Phineas and Sandra Priest Rose Center for Earth and Space, seen at night, containing the Hayden Sphere. This $230 million facility opened to the public on Saturday, February 19, 2000, with solar system exhibits that grouped Pluto with the swarm of icy bodies in the outer solar system known as the Kuiper belt, instead of with the other eight planets of the so
lar system. This decision made a page 1 story in the New York Times and angered schoolchildren across the country.

  To plan content, we first needed to assess the shelf life of various astrophysical subjects. For example, ever since Copernicus, we’ve been convinced that Earth goes around the Sun and not the other way around. That would be content of long shelf life that we can boldly cut into metal displays.

  In the moderate shelf life category, there’s the question of water on Mars. Consensus says that the flowing liquid water that used to be there is currently locked in permafrost, but that notion could get modified by the discoveries of curious rovers on any next NASA mission to the Red Planet. So we display this text and related images with replaceable rear-lit transparencies. Science of possibly brief shelf life would include late-breaking discoveries, any intriguing hypothesis, anything waiting to be verified or trashed by another group of researchers with a different discovery or a more comprehensive theory. For that we simply show videos of research scientists giving their latest ideas. No transparencies. No cut metal. Just swappable video content. Where a given topic landed in these three tiers of information determined the nature of the exhibit treatment it received—which is code for how much money we spent to create the exhibit.

  We hired Steven Soter in November 1997, luring him away from the Smithsonian Air and Space Museum. Soter’s résumé includes collaborating with Carl Sagan and Ann Druyan on the writing of the landmark PBS series Cosmos. Just a few months after his arrival, Steve handed me a February 1998 Atlantic Monthly article on Pluto titled, “When Is a Planet Not a Planet?” written by journalist David H. Friedman. At the top Steve politely penned: “Perhaps we should look into this!” He (correctly) figured that the issues raised in the article might influence the content of our planet exhibits, which were still under design.

  I decided to write an essay of my own on the subject, which became “Pluto’s Honor,” for the February 1999 issue of Natural History magazine,20 timed to coincide with the month that Pluto, in its badly elongated trajectory, recrossed the orbit of Neptune after 20 years, once again becoming the farthest planet in the solar system. My intent was not only to celebrate Pluto’s regaining its far-out status, but also to review the saga and character of Pluto; raise the historical analogy with the asteroid Ceres, which had been labeled a planet when discovered in 1801; and generally address what was simmering in the minds of planetary scientists. At the end of the article, having laid out the various parameters and arguments, I offered a last gasp of sentiment for the little fellow:

  As citizen Tyson, I feel compelled to defend Pluto’s honor. It lives deeply in our twentieth-century culture and consciousness and somehow rounds out the diversity of our family of planets like the troubled sibling of a large family. Nearly every school child thinks of Pluto as an old friend. And there was always something poetic about being number nine.

  But I could not hold back my fundamental conclusions:

  As professor Tyson, however, I must vote—with a heavy heart—for demotion. Pluto was always an enigma to teach. But I’d bet Pluto is happy now. It went from being the runt of the planets to the undisputed King of the Kuiper belt. Pluto is now the “big man” on a celestial campus.

  At the same time, I had no intention of unilaterally imposing my personal perspective on the Rose Center’s presentation of Pluto. That would be professionally irresponsible and would represent an abuse of my authority as project scientist. To do anything unorthodox with our treatment of Pluto would require a consensus of the internal and external science committee. For one thing, planets are not my research area of expertise. I specialize in star formation and galaxy evolution. For another, it’s simply not my role to invent a new classification scheme.

  The article triggered a flow of letters to me and to the magazine, the most memorable of which came under the letterhead “Pluto Planetary Protective Society” and written by its founder and president, Professor Julian Kane, Hofstra University, Long Island, New York. With a clever cue on my “heavy heart” line from the essay, Kane ends his letter with:

  Professor Tyson maintains that with a heavy heart he must vote to demote Pluto. Professor Kane, however, votes with an atrially-fibrillated heart to sustain Planet Pluto while additional factual details are being uncovered.

  Meanwhile, we at the museum were not the only ones grappling with classification schemes of objects in the outer solar system. The International Astronomical Union (IAU) was, too. Founded in 1919 and with a current membership of 10,000, the IAU is the professional society for all the world’s astrophysicists, operating under the mission “to promote and safeguard the science of astronomy in all its aspects through international cooperation.” Among its many duties, the IAU establishes committees and other consensus-building activities to formalize our occasionally confusing nomenclature and lexicon. Their authority derives not from law or dogma but from emergent scientific consensus. Not blind to the Pluto–Kuiper belt ruminations of its membership, they decided to look into what was happening out there. This simple and normal step for them was widely regarded by the media (and by many in the community of astrophysicists) as the IAU raring to demote Pluto. Many in the planetary science community were outraged, fearful that the Plutophiles among them might not fully vet their views.

  Coincidentally, the same month that my article on Pluto appeared in Natural History magazine, IAU general secretary Johannes Andersen issued a candid but clumsy press release denying any rumors that the IAU had endorsed a plan to demote Pluto,21 which is produced here in its entirety:

  THE STATUS OF PLUTO: A CLARIFICATION

  Recent news reports have given much attention to what was believed to be an initiative by the International Astronomical Union (IAU) to change the status of Pluto as the ninth planet in the solar system. Unfortunately, some of these reports have been based on incomplete or misleading information regarding the subject of the discussion and the decision making procedures of the Union.

  The IAU regrets that inaccurate reports appear to have caused widespread public concern, and issues the following corrections and clarifications:

  1: No proposal to change the status of Pluto as the ninth planet in the solar system has been made by any Division, Commission or Working Group of the IAU responsible for solar system science. Accordingly, no such initiative has been considered by the Officers or Executive Committee, who set the policy of the IAU itself.

  2: Lately, a substantial number of smaller objects have been discovered in the outer solar system, beyond Neptune, with orbits and possibly other properties similar to those of Pluto. It has been proposed to assign Pluto a number in a technical catalogue or list of such Trans-Neptunian Objects (TNOs) so that observations and computations concerning these objects can be conveniently collated. This process was explicitly designed to not change Pluto’s status as a planet.

  A Working Group under the IAU Division of Planetary Systems Sciences is conducting a technical debate on a possible numbering system for TNOs.

  Ways to classify planets by physical characteristics are also under consideration. These discussions are continuing and will take some time.

  The Small Bodies Names Committee of the Division has, however, decided against assigning any Minor Planet number to Pluto.

  3: From time to time, the IAU takes decisions and makes recommendations on issues concerning astronomical matters affecting other sciences or the public. Such decisions and recommendations are not enforceable by national or international law, but are accepted because they are rational and effective when applied in practice. It is therefore the policy of the IAU that its recommendations should rest on well-established scientific facts and be backed by a broad consensus in the community concerned. A decision on the status of Pluto that did not conform to this policy would have been ineffective and therefore meaningless. Suggestions that this was about to happen are based on [an] incomplete understanding of the above.

  The mission of the IAU is to promote scientific progres
s in astronomy. An important part of this mission is to provide a forum for debate of scientific issues with an international dimension. This should not be interpreted to imply that the outcome of such discussions may become official IAU policy without due verification that the above criteria are met: The policy and decisions of the IAU are formulated by its responsible bodies after full deliberation in the international scientific community.

  Johannes Andersen

  General Secretary, IAU

  If Anderson’s point was simply to dispel misinformation, the task required many fewer words than what appeared. The release reads as if written by a lawyer instead of scientist. And from its tone and blatantly defensive posture, methinks the gentleman did protest too much, implying self-awareness of a rising storm.

  Given how much money we had spent (and were about to spend) on exhibit design and content, it was incumbent on us not to make hasty decisions about anything astrophysical. We needed to assess, to the best of our abilities, the trends in cosmic discovery, so that long after opening day our exhibits would remain as fresh as possible. So I organized and hosted a panel debate on Pluto’s status, inviting the world’s leading thinkers on the subject to duke it out, on stage, for our benefit and for the benefit of the interested public.

  Eight hundred people descended on the main auditorium (which doubles as an IMAX theater) of the American Museum of Natural History on Monday evening, May 24, 1999, to hear “Pluto’s Last Stand: A Panel of Experts Discuss and Debate the Classification of the Solar System’s Smallest Planet.” You couldn’t get more expert experts than the five scientists who joined me onstage:

  Michael A’Hearn, a comet and asteroid specialist at the University of Maryland in College Park, president of IAU’s Planetary Systems Sciences Division, and chair of IAU’s Committee for Small Body Nomenclature

  David H. Levy, patron saint of amateur astronomers worldwide, discoverer or codiscoverer of dozens of comets and asteroids, and biographer of Clyde Tombaugh