Sunday, January 24, 2010

File Pluto under “K” for “Kuiper Belt”

Posted by Darin Hayton on 01/24 at 02:09 PM

Neil deGrasse Tyson’s book is markedly different from other books on Pluto. It is neither a history of planetary discovery—though Tyson provides a generously illustrated 10-page history of planetary discovery—nor an account of recent discoveries. Instead, The Pluto Files is an opportunity for Tyson to exercise his wit and charm. It is both the shortest and most entertaining of Pluto books, drawing on comics, illustrated letters from school children, and songs. It also offers Tyson another forum to celebrate his own accomplishments and to raise his own profile. Despite his lighthearted tone, Tyson argues for Pluto’s demotion.

Neil deGrasse Tyson’s amusing if unconvincing The Pluto Files

The first three chapters provide the context for the contemporary debates about Pluto’s status. “Pluto in Culture” connects Pluto the planet to Pluto the Disney mutt. By focusing on the connection between Pluto the celestial object and Pluto the cartoon dog, Tyson seems to equate the people who oppose Pluto’s demotion with children. Although there is no evidence for a link between the two, for Tyson it is unnecessary to demonstrate such a link. “What matters is that the seeds were sown for planet Pluto to receive a level of attention from the American public that far exceeds its astrophysical significance in the solar system” (14).1 “Pluto in history” quickly reviews 230 years of planetary discoveries, highlighting the debate about Ceres, first a planet and then an asteroid. In the third chapter, “Pluto in Science,” contains the core of Tyson’s argument: Pluto is less like the other planetary object and more like the Kuiper Belt Objects. Therefore, regardless of our emotional commitments and the unfortunate fact that Pluto is round,2 it doesn’t make sense to group Pluto with the other planets.

This chapter is a great example of how figures—i.e., numbers and relations—cannot tell the whole story. Tyson uses some of the same information that Boyle and others have used—e.g., Pluto’s mass: Tyson—less than 5% that of Mercury; Boyle—Mercury is 25 times more massive—but draws entirely different conclusions. Tyson points out that, by volume, Pluto is mostly ice (ca. 55% by volume). Boyle would surely point out that Pluto is mostly rock (ca. 70% by mass). Pluto has less than 5% the mass of Mercury (Boyle would agree with this figure, but would emphasize Pluto’s volume at ca. 13% that of Mercury). Similar comparisons could be drawn between Tyson’s use of orbital inclination, location, Pluto’s size relative to other celestial debris, etc. The Pluto question cannot be resolved by appealing to data, numbers, and calculations.3

In chapter four Tyson offers some of the background that led to the now infamous Rose Center for Earth and Space’s decision to leave Pluto out of the line-up of planets. In thinking about how best to present the larger objects in our solar system, Tyson was convinced that “planet” was an outdated and pedagogically problematic term. The simple category didn’t meaningfully group the rocky planets, the gas giants, the asteroids, or the larger Kuiper Belt Objects. Thinking about the objects in families, Mercury, Venus, Earth, and Mars form one family, Jupiter, Saturn, Uranus, and Neptune form a second, Pluto and the other icy objects fall into yet another:

“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 day. … Where does Pluto fit? The Kuiper belt. End of story” (74–75).

At 44 pages, this chapter is by far the longest in the book. It is as much a celebration of the Rose Center for Space and Earth as it is an argument about Pluto. Tyson uses the chapter both to distance himself and the center from Pluto’s demotion and, simultaneously and somewhat in tension with that first position, to teak credit for Pluto’s “fall from grace.” He recounts his efforts to organize “Pluto’s Last Stand,” a roundtable discussion held on 24 May 1999. Michael A’Hearn, David Levy, Jane Luu, Brian Marsden, and Alan Stern came together to present their cases for and against Pluto. He credits this discussion with having convinced the audience and the participants that Pluto’s status was entirely based in nostalgia:

Yet by the end of the evening, everyone from the Hayden Planetarium connected with the Pluto exhibit 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.

The brouhaha over the Rose Center’s exhibition that erupted in 2001 following Kenneth Chang’s article NY Times, “Pluto’s not a Planet? Only in New York” suggests that either Tyson was wrong in his impression of that night or the attendees were not a representative sample of the public. One of the more entertaining chapters, “Pluto divides a Nation,” recounts the many letters and email messages Tyson received after the NY Times article appeared.

The last few chapters move rather quickly through the fateful IAU meeting in Prague, the circulation of a petition by planetary scientists objecting to the IAU’s resolution, and the 2008 debate at Johns Hopkins University. Tyson offers little that is new here, except to point to the demographics both of the signatories of the petition and the IAU in general.

Tyson’s real contribution to this literature is to emphasize the relationship between Plutophiles (his term) and U.S. citizens (scientists and non-scientists). He explains the U.S. commitment by referring to Disney’s powerful influence in U.S. culture. He certainly demonstrates how broadly the U.S. population seems to be concerned about Pluto, from comedians, popular music, and school children, to newspaper editorials and state legislatures. Everybody seems to have an opinion about Pluto.

The Pluto Files is an entertaining and readable book. Well worth the hour or so it takes to read, if only for the letters from children and the comics that Tyson reproduces. Conveniently, it has just been released in a paperback edition, perfect for your next coffee break.

Charles Almon’s cartoon about Pluto’s new status (Source: From the NPR Story on Tyson)

1Would planetary scientists oppose Tyson’s assertion, claiming that Pluto merits attention because of its geophysical significance and not its astrophysical significance?
2Tyson put it: “Alas, both Pluto and Charon share an important physical property with the rest of the planets. They’re both round” (38).
3The history of science is ripe with evidence for the insufficiency of data in resolving “scientific” disputes. Beyond the history of science, scholarship in general continues to invoke evidence to support particular claims, the very same evidence that is invoked to challenge those claims. Perhaps evidence is, in the end, unsuitable for deciding contested questions.

Tags: astronomy, clyde tombaugh, kuiper belt objects, museums, neil degrasse tyson, planet, pluto, science writing


Comment posted by laurele on 02/02 at 08:08 PM

Uh, not end of story, not even close. As a Plutophile who attended the Great Planet Debate in August 2008, I can say with certainty that support for Pluto’s planet status is not about the Disney dog. Most who feel strongly in favor of Pluto remaining a planet are people who already have an interest in astronomy and the solar system.

Nor is support for Pluto’s planethood an “American” phenomenon. A look at astronomy blogs and forums online show that Pluto supporters come from all over the world. As someone who runs a Pluto advocacy blog, I have received emails of support from Australia, England, Canada, Malaysia, the Philippines, Egypt, Morocco, New Zealand, Serbia, and many other countries.

File Pluto under both Planet and Kuiper Belt Object, as it is both and should be dually classed. Dwarf planets should be recognized as a third class of planets that are planets because they are spherical, meaning they are large enough to be rounded by their own gravity, but are of the dwarf subcategory because they are not large enough to gravitationally dominate their orbits.

It is important to note that Tyson has distanced himself from the controversial 2006 IAU decision, which he himself admits is flawed. At this point, he even admits that the debate is not over, that it might be too early in the study of planetary scientists for anyone to be defining what a planet is in the first place. This was pretty much his message at the Isaac Asimov Memorial Debate, which he moderated at the American Museum of Natural History on March 10, 2009.

Significantly, only four percent of the IAU voted on Pluto’s demotion, and most are not planetary scientists. Their decision was immediately rejected by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. This debate is far from over.

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