In Defense Of Pluto

An artist's conception of Pluto and its moon Charon. Image credit: NASA.
This column was written by Matthew Yglesias.

News is scarce in late August, so journalists, at a minimum, owe a debt of gratitude to the world's astronomers, who conveniently scheduled their decision to rescind Pluto's planet status for the low point of the yearly news cycle. Others around the world have less reason to be grateful.

Mnemonic devices will have to be altered. Textbooks will need to be rewritten and re-purchased. Educational posters and museum exhibits will need to be changed. And knowledge will become outdated.

Someday, somewhere, a vicious fight is going to break out over a Trivial Pursuit game where the question had one correct answer under the pre-2006 planet scheme but another correct answer in the brave new eight-planet world. And all this will be done for … what exactly?

In essence, for nothing.

In defense of the International Astronomical Union, it appears that a good-faith effort was made to try and find a way to preserve Pluto's planetary status. Unfortunately, it was impossible to devise a reasonably concise rigorous definition of "planet" that would have maintained Pluto's status without adding additional planets, specifically the large asteroid, Ceres; Pluto's largest satellite, Charon; and the trans-Neptunian object 2003 UB313.

This latter object has, in turn, been the subject of a hilariously pointless astronomical controversy. Its discoverer wanted to name it Xena, after the warrior princess. Official names, however, can only be granted by the Committee on Small Bodies Nomenclature of the IAU's Division III, and IAU rules state that trans-Neptunian objects must be named after deities of creation. Xena, being a television character rather than a legitimate mythological figure, was thereby disqualified.

Michael Brown, who discovered the object, formerly argued that this was unfair, since virtually all the Greek and Roman mythological names have already been taken. Thus, "in the past we have named Kuiper Belt objects after Native American, Inuit, and [minor] Roman gods"; the "new proposed name" merely "expands to different traditions."

Perhaps because Inuit found it offensive to see their religious tradition compared to a syndicated television program, Brown has since softened his stance. The current version of his Web site notes that Xena "comes from an internal cod (sic) name that we used before we publicly announced the existence of the planet. Other code names have been 'Santa' (2003 EL61), 'Rudolph' (the moon of 2003 EL61), 'Easterbunny' (2005 FY9) and 'Flying Dutchman' (Sedna), and 'Gabrielle' (the moon of 2003 UB313) ... there is no chance whatsoever that these will become the permanent names of these objects!" (Emphasis his.)

Be all that as it may, Xena was eventually deemed unworthy of planetary status and the IAU adopted a definition of planet that excluded it, Charon and Ceres at the price of likewise excluding Pluto. Henceforth, a planet shall be: "a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit." Pluto, it seems, fails on qualification (c).

Adopting such a definition has accomplished, well, nothing whatsoever for the sake of science. Astronomy, clearly, had been progressing just fine in previous decades without a rigorous definition of "planet." Telescopes, NASA-launched probes, and other instruments were bringing us more and more information about which objects exist in the solar system and about the nature of those objects. The term "planet" meanwhile, had long since ceased to play a substantive role in the science of astronomy.

Before Copernicus, celestial bodies were divided between the planets (the moon, Mercury, the sun, Jupiter, etc.), which moved, and the stars, which didn't. Contemporary astronomy, however, distinguishes among objects according to what they're made of, so that the sun is a star and so forth. The very notion of a planet is, at this point, a piece of folk culture, not an important element of science. And according to cultural tradition, there are nine planets and Pluto is one of them.

There neither was nor is any need for busybody scientists to gin up a rigorous definition and then tell us Pluto doesn't make the cut. It would be akin to gathering a giant conference to decide on a formal distinction between "bugs" and other small, gross animals. If we include worms do we need to include slugs? If we have slugs, then what about snails? And did you know that round worms (nematodes) are no more closely related to segmented worms (annelids) than they are to humans (chordates)? Well, I learned it about a year ago and suffice it say that I still use the word "worm" despite its lack of solid scientific backing. The world is getting on just fine.

Scientists use their Latinate technical terms and ordinary people talk like, well, ordinary people. The resulting arrangement is, like the traditional nine-planet scheme, just fine.

"Planet" could just mean "Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto," and we'd all be better off for it. It's our language, too, dammit, and we shouldn't let scientists prone to squabbling over whether or not Xena is a "real" myth boss us around.
By Matthew Yglesias
Reprinted with permission from The American Prospect, 5 Broad Street, Boston, MA 02109. All rights reserved