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Sunday, December 20, 2009

Govert Shilling: Pluto is Icy Chunk of Space Debris

Posted by Darin Hayton on 12/20 at 10:49 PM

Govert Schilling provides a robust history of the search for new planets that has occupied astronomers since William Herschel discovered Uranus, quite by accident in March 1781. Unlike Wientraub, who surveys the history of how planets were defined (see the review of Weintraub’s book), Schilling seems to know what a planet is and assumes that all rational astronomers will likewise know what a planet is. According to Schilling, Pluto is not a planet. Moreover, reasonable astronomers have raised concerns about Pluto’s status for decades until finally, “in the early 1990s, what had been suspected for many years now proved indisputable—Pluto was only one object in an enormous population of small ice dwarfs in the outer regions of the solar system.” Pluto “now has the second-rate status of a dwarf planet.” Schilling’s conclusion will clearly ruffle the feathers of many Plutophiles while, at the same time, garner the cheers of Plutophobes.



Govert Schilling’s recent effort to demote Pluto to large icy chunk of space debris.

Schilling’s book provides a straight-forward narrative, largely triumphalist and rationalist, celebrating the progress of planetary science in exploring the outer reaches of the solar system. He lays the foundations for his project in the opening 25 or so pages, with the discovery of Uranus and then Neptune. In chapter four Schilling already casts doubt on Pluto’s status by portraying Percival Lowell as a man fascinated by a mysterious Planet X. While he stops short of claiming that Lowell fabricated the orbital deviations he found in Uranus, Schilling certainly draws them into question and portrays Clyde Tombaugh’s discovery of Pluto as largely accidental:

Tombaugh had not taken much notice of Lowell’s calculations. Lowell had first predicted that Planet X would be found in the constellation Libra, but changed his mind a few years later, deciding that the search should focus on Gemini. Tombaugh found this all a little vague, and resolved to search the entire zodiac.

By page 37, Pluto has been discovered and is already in jeopardy: “But it did not take long for doubt to set in. Planet X proved to move in an elongated and highly inclined orbit, and was much smaller than had been expected … [T]he discovery of Planet X so close to the predicted position must have been sheer coincidence.”

The remaining 240 pages detail the discovery of additional small objects around the edges of the solar system, including Pluto’s partner Charon, Nix and Hydra, other ice dwarfs, comets and the Oort Cloud, asteroids, the Kuiper Belt, and other flotsam and jetsam from the early formation of the solar system. The hero in Schilling’s story is technology: as astronomers are able to exploit increasingly powerful technological tools they discover more about the nature of the solar system. Tombaugh’s mechanical blink comparator is replaced by more modern comparators, which are then replaced by CCD digital images and software analysis. Better and larger telescopes are built and continue to be built, telescopes that allow for greater resolution of distant objects. Urbain Le Verrier’s painstaking mathematical analysis is replaced by Robin Canup’s and Hal Levinson’s computer-driven theoretical models that enable astronomers to simulate scenarios at will.

Along the way, a number of people play supporting roles, people whose lives are caricatured in the opening pages of many chapters. Intended to put human faces on the march of science, these exaggerated snapshots detract from Schilling’s argument and suggest that he doesn’t, in fact, think humans play any real role in science:

Robin Canup has difficulty keeping her hands still. On her computer monitor, a cosmic ballet is being played out before her eyes. There is no sound, but you can easily imagine music accompanying the dance. One minute it is subdued and serene, like an ethereal violin, and then it is dynamic and dramatic, with a lot of brass and percussion. Two dancers fall into each other’s arms and a shower of sparks explode into surrounding space. Glowing fragments trace graceful paths across the three-dimensional stage, under the strict choreography of the force of gravity. Some of them merge to form a new ballerina, and the performance ends with an intimate pas de deux. Robin sits transfixed to the screen as the drama unfolds, her shoulders and wrists swaying slightly back and forth in the heavenly breeze, as though her slender body wishes to join the dance.

Directly below this paragraph is a picture of Robin Canup dancing in “Paquita.” Often the details seem contrived, too quotidian to have been remarkable and remembered by the people involved. If these banal minutia (e.g., Mike Brown’s wife saying “That’s nice honey. You won’t forget to pick up some milk on your way home this afternoon now, will you?”) have not been fabricated by Schilling, they have been embellished by the people involved.

Although Schilling gently chastises the people, astronomers and non-astronomers alike, whose emotional attachment to Pluto prevents them from seeing it as just another small icy rock, he has himself an emotional attachment to science’s power to uncover inexorably the truth. Consequently, he is as invested in arguing that Pluto is not a planet as its defenders are committed to saving Pluto. At no point does he seem to ask: Why do we care whether or not Pluto is a planet? Or even: What is a planet and how has the definition varied over time? Such an omission is regrettable, particularly since so much time an energy was devoted to defining a planet preceding and during the IAU 2006 meeting in Prague.

The blurb on the publisher’s website claims that this book reads like a scientific detective story and offers insight into the minds and motivations of the planetary astronomers investigating the outer reaches of the solar system. That claim is rather inflated and a bit misleading. If, however, you are looking for a basic narrative of the recent developments in astronomy that have been enlisted in the debates about Pluto’s planetary status, The Hunt for Planet X will fulfill your needs. If you are looking for something more philosophical, or if you are committed to Pluto as a planet, you will be somewhat disappointed.

Tags: astronomy, clyde tombaugh, govert shilling, historiography, kuiper belt objects, neptune, percival lowell, planet, pluto, uranus

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Comment posted by laurele on 01/04 at 01:41 PM

The argument that those who support Pluto’s planet status do so out of emotion is a straw man. There are strong scientific reasons for keeping Pluto as a planet, specifically, its similarity to the other planets in being rounded by its own gravity, a state known as hydrostatic equilibrium. Objects in hydrostatic equilibrium have geology, are usually differentiated into core, mantle, and crust, and often have weather. Pluto is 75 percent rock.

The IAU decision was made by only four percent of its members in a process that violated the group’s own bylaws. It was immediately rejected by hundreds of professional astronomers in a formal petition led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. The fact that the IAU refused all requests to reopen debate on this issue at the 2009 General Assembly reveals an underlying insecurity with the definition they created and a refusal to take responsibility for the mess they made.

One could easily accuse those who oppose Pluto’s planet status as being motivated by emotion when they argue that “we can’t have too many planets” and the number has to be kept low. Why? Because it’s more convenient for them that way?

Interestingly, readers deserve to know that Schilling has been spending significant amounts of time with Mike Brown, who instead of being proud of having discovered Eris, is obsessed with the idea that he “killed” Pluto to the point that his Twitter username is “Plutokiller.” This man posts pictures of beheaded Disney Pluto toys on the Internet and brags about having Schilling over for dinner. I am a graduate student in astronomy, and when I contacted Schilling to present the other side, he did not even have the decency to respond to my emails. Again, the same refusal to debate, which can only indicate inflexibility and even insecurity with his position.

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