Thursday, January 07, 2010

What’s so Confidential about Pluto?

Posted by Darin Hayton on 01/07 at 10:55 AM

Pluto Confidential is co-written by astronomers on either side of the Pluto debate. Laurence Marschall voted for the IAU’s definition of a planet at the meeting in Prague while Stephen Maran did not attend but would have voted against it. Although the blurb on the back of the book claims that the two authors “conduct their own debate on the pros and cons of the planetary status for our most maligned orbital body,” the book is more a history of astronomy. Two themes recur throughout the book. First, the controversy over Pluto’s status is just the latest in a history of controversies over celestial objects. Second, amateur astronomers are the unsung heros in the efforts to find new celestial objects.

I don’t really understand the title Pluto Confidential

The first two chapters provide much of the general background for the book. They remind us again that of the 9,500 IAU members, only 424 actually voted on the new definition of a planet. The reaction to the vote was swift and hostile. School children were up in arms. State legislatures rejected the IAU’s decision—the city of Madison proclaimed Pluto its ninth planet, New Mexico declared the next 13 March to be Pluto day, the state assembly in California introduced a bill denouncing the decision.1 The authors raise the question of anti-Americanism in this chapter, suggesting that the IAU’s decision was an effort to penalize the U.S. for the Bush administrations foreign policy. They then introduce some of the people who have played and continue to play a role in discussions about Pluto.

Chapter three retells Galileo’s discoveries of Jovian moons and William Herschel’s discovery of Uranus. In 1609 Galileo was a mathematician who, having heard about the new invention, the spyglass, decided to make his own. He hoped to sell them as military tools. However, one night he apparently turned his spyglass toward the heavens and realized the power of this new instrument. “Overnight, Galileo became an astronomer” (38).2 He discovered the Jovian moons, which he dedicated to the Medici. Although he named them the Medicean Stars, his fellow astronomers across Europe did not adopt this name. Instead, they referred to them by Roman numerals. Nearly two centuries later, on 13 March 1781, William Herschel discovered Uranus. Once again, the authors emphasize Herschel’s lack of astronomical training—he was making a living teaching music—and the accidental nature of his discovery—Herschel was looking for double stars when he noticed an unusual object. His observations over the next few nights indicated that the object was moving relative to the fixed star. Once he was convinced that he had discovered a planet, he tried to name it Georgium Sidus after King George IV. As with Galileo’s efforts to honor his patrons, astronomers across Europe again rejected this name, adopting instead Uranus.

The two themes—accidental discovery by amateur astronomers and their difficulty naming objects—recur throughout the book.3 Chapter four catalogs efforts to find a planet between Mars and Jupiter. The Titius-Bode rule seemed to suggest that there should be a planet in the wide space between these two planets. Astronomers found, instead, lots of little asteroids. Then came the naming game:

“there was, as in the past, the issue of a suitable name. Arguably, naming new objects was more difficult than discovering them—at least judging by the experiences of Herschel and Galileo—so Piazzi was quick to assert priority…” (63).

Chapter five provides a straight-forward history of Neptune’s discovery. Astronomers had noticed that Uranus’s orbit was erratic. Using the known planets, they couldn’t accurately predict Uranus’s motion. They concluded that there must be another planet beyond Uranus that was exerting a gravitation pull on it. Urban Le Verrier in France and John C. Adams in England independently calculated the size and position of this planet. Then they had to convince astronomers to look for it. When they finally did, astronomers quickly spotted the planet that we now call Neptune. The authors emphasize on John Adams having been born a tenant farmer and having succeeded against all odds. The main point of this chapter, again, is to show astronomers arguing about objects in the heavens. These arguments didn’t focus just on planets. Astronomers also expended considerable energy arguing about whether or not particular celestial bodies even existed. Chapter six recounts the disputes about Vulcan, the proposed inner-Mercurial object. Flushed with his success calculating Neptune’s position, Le Verrier took up the problem of Mercury’s orbit. Despite considerable observational data to the contrary, Le Verrier and others remained convinced that Vulcan existed. A series of promising claims ultimately turned out to be wrong. By the 1880s astronomers had concluded that Vulcan did not, in fact, exist.

Percival Lowell dedicated his considerable energy and resources to finding the planet the he believed was orbiting beyond Neptune. His efforts to calculate the planet’s size and position failed to find any observational support. However, Lowell, who combined “the mathematical rigor of a professional astronomer with the obsessive zealotry of an amateur” laid the foundation for “the discovery of Pluto in 1930 by a country lad from Kansas named Clyde Tombaugh” (110). We are reminded that Tombaugh was largely self-taught, had built his own telescope, and had taken the chance to write to the Lowell observatory. Tombaugh, apparently, rejected Lowell’s calculations, deciding instead to scan the sky for the planet. Thirteen months after his arrival, the young Kansan located what would become Pluto. Once again, astronomers argued about what to name this new object before settling on a name suggested by 11-year-old Venetia Burney. It is difficult to miss the authors’ argument about the importance of amateurs and serendipity. If Lowell was a quasi-amateur, Tombaugh was the quintessential amateur who discovered the planet largely by accident, the planet that was then named by an even younger amateur.

Chapters eight and nine follow the efforts by astronomers to explore the outer region of the solar system. The first important event was James Christy’s discovery of Pluto’s moon, Charon. At the time Christy was a little-known technician who didn’t have the academic credentials of most astronomers. Despite looking at photographic plates that more respected astronomers had inspected, Christy was able to see something they had missed: images of Pluto seemed to bulge first on one side then on the other. It took him little time to realize that this bulging was caused by Charon’s orbiting around Pluto. By the early 1990s astronomers had identified other objects in the Kuiper Belt. These objects, which seem to share many characteristics with Pluto, raised questions about how to classify objects in the outer reaches of the solar system. When Mike Brown discovered 2003 UB313 (now named Eris) the problem of naming once again became acute. Eris was larger and more massive than Pluto. Should it be named as a planet or as Kuiper Belt object. Deciding that question required determining first whether or not Eris was a planet. This problem, supposedly, forced the IAU to define a planet so that it could name this new object (159–60).

In the final chapter the authors present their opinions about Pluto.4 Marschall agrees with the new definition because he thinks Pluto shares more with other Kuiper Belt objects: Pluto “had already, de facto, lost its unique status in the outer solar system as a result of discoveries of larger objects in orbit beyond Neptune” (184). Further, and perhaps more compellingly, he claims that “Pluto was significantly different in nature and origin from the other eight planets and so similar to like-sized objects in the outer solar system that it deserved to be considered a member of a new class of objects” (184–85). Maran, by contrast, forcefully asserts “Pluto is a planet!” He invokes popular literature and art as well as English-language dictionaries to support his position. He claims that the IAU and authors of astronomy textbooks did not want to expand the number of planets because they didn’t want to have to accommodate these new objects in their tables of planets (187–8). Including more objects would create a “messy problem” that was more easily solved by excluding Pluto.5 In the end, Maran once again assert “Pluto is still the people’s planet and, if anything, more popular as an underdog than ever before” (189). I’m not sure when popularity became an important decision criterion in science, but there you go.

Marschall and Maran offer a readable history of planetary discoveries. Their contribution—that amateur astronomers have played important roles in the development of astronomy and that astronomers argue about their science—will strike some readers as obvious. Beyond this claim, the book offers little that is new. The title and the blurb on the cover suggest that Pluto Confidentail will provide an account of the IAU’s decision that has not been told. Sadly, it fails to live up to that promise.

1Although it is difficult not to see some of this as satirical, the authors present all of this legislation as earnest and binding. For example, the California resolution Bill HR 36 (which can be viewed here) claims that “The mean-spirited International Astronomical Union decided on August 24, 2006, to disrespect Pluto by stripping Pluto of its planetary status and reclassifying it as a lowly dwarf planet” and further that “Pluto, named after the Roman God of the underworld and affectionately sharing the name of California’s most famous animated dog, has a special connection to California history and culture.” Moreover, the “downgrading of Pluto reduces the number of planets available for legislative leaders to hide redistricting legislation and other inconvenient political reform measures” (there are other great statements in this bill. I recommend reading it). Thank goodness the legislature moved to condemn the IAU.
2Their claim here is in tension with much of the literature on Galileo, which claims that he became a natural philosopher, not an astronomer.
3A recent article in Science underscores the role of serendipity in astronomical discoveries: Kenneth R. Lang, “Serendipitous Astronomy” Science 327(1 January 2010): 39–40 (the summary is available here).
4The penultimate chapter offers a brief survey of claims about and discoveries of exoplanets. This chapter serves largely to reinforce the authors’ claim that astronomers have argued about all sorts of celestial objects.
5I am merely summarizing Maran’s position, I am not endorsing it. I have to admit, this argument seems absurd. Not only does the exclusion of Pluto create a problem for textbook authors, who now have to reformat their lists of planets to exclude Pluto (just as they would have to reformat their tables to include more planets), since when did extending the number of objects in a class of present any sort of impediment? Chemists don’t seem concerned about the ever expanding periodic table, which currently includes nearly 120 elements. And school children don’t seem upset by their inability to recite the elements or to spend too much time worrying about mnemonic devices to learn them (though there is a mnemonic for the first nine elements: “Happy HEnry LIkes BEer But Could Not Obtain Food”). Maran hints at the silliness of this argument when he describes how astronomers now maintain lists of asteroids, though only a small number of these are included in textbooks.

Tags: astrology, astronomy, clyde tombaugh, galileo galilei, kuiper belt objects, laurence a. marchall, neptune, percival lowell, planet, pluto, science writing, stephen p. maran, titius-bode rule, uranus, william herschel


Comment posted by laurele on 01/16 at 06:24 PM

It is clear from your discussion that you have already made up your mind in favor of the IAU decision. That is fine, but you should note that from the beginning.

The point in the historical discussion is to show that time and time again, professional astronomers, in spite of often having superior attitudes, have “behaved badly” and put personal rivalries and politics ahead of science. The IAU vote on Pluto fits in perfectly with this history. In contrast, amateur astronomers, who even today are looked down upon by professionals, often accomplish more because their dedication to astronomy is a labor of love and not bound by a need to further their own careers or gain recognition. This contrast is illustrated notably in the fact that during the Prague deliberations, one IAU member actually screamed that if Pluto were counted as a planet, his entire career would be ruined!

Maran’s claim that astronomers who want to keep the number of planets low for convenience is true. Many proponents of the IAU decision have said so themselves, claiming that the term “planet” would no longer be “special” if there were hundreds of them. Why not”? What makes something “special,” anyway. No one objects to there being billions of stars and billions of galaxies. No one tries to limit the number of elements in the Periodic Table. The argument that we cannot have too many planets is blatantly unscientific. The universe is what it is.

In some ways, Pluto is different from the 8 big planets in the solar system, but in other ways, it is similar. It is large enough to be rounded by its own gravity, a state known as hydrostatic equilibrium. It is very likely geologically differentiated into core, mantle, and crust. The majority of Kuiper Belt Objects, with a few exceptions like Eris, which should also be classed as planets, do not share these characteristics.

In fact, Earth could be said to have more in common with Pluto than with Jupiter, as Jupiter has no solid surface and a composition similar to that of the sun while Pluto is 75 percent rock, and a spacecraft could presumably land on its surface.

Many members of the public still do not know the shenanigans that went into the IAU vote, the fact that the IAU violated its own bylaws, that most who voted are not planetary scientists, and the fact that hundreds of professional astronomers immediately rejected the IAU decision. To the extent this book informs people of this, it is a source of vital context to people in helping them make sense of this issue and draw their own conclusions.

A simple resolution to this debate could be found by amending the IAU decision to make dwarf planets a subclass of planets--planets because they are in hydrostatic equilbrium but of the dwarf subcategory because they do not gravitationally dominate their orbits. This would be consistent with the use of the term “dwarf” in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies.

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