Wednesday, December 31, 2008

Dueling Designations

Copyright © 2007 by Joel Marks

Look, up in the sky! It's a planet! No, it's a pluton! No, it's a ... kenning!

On August 24, 2006, the International Astronomical Union voted to demote Pluto from a planet to a dwarf planet. This has not sat well with many in and out of the astronomical community. For one thing, the term “dwarf planet” is bizarre since it is intended to remove Pluto from the ranks of the planets. But if something is a dwarf x, isn’t it still an x? For example, a dwarf star is a kind of star; indeed, our own sun is one.

This means that the term “dwarf planet” is a kenning, a term to which I was led by rhetorician extraordinaire Prof. Kip Wheeler and defined in Wikipedia as “a figure of speech, substituted for the usual name of a person or thing. … compris[ing] two terms, one of which (the 'base word') is made to relate to the other to convey a meaning neither has alone.” Allison Griswold, a former student of mine, suggested the apt example of “starfish,” since a starfish is neither a star nor a fish (and, even more aptly, has the technical name in zoology of “asteroid”!).

Meanwhile there are independent reasons for wanting to retain the planetary status of Pluto. As I argue in a recent article in Think (“A Planet by any Other Name,” winter 2007, pp. 103-106), a periodical of the Royal Institute of Philosophy in Great Britain, it is perfectly legitimate to assign a dual designation to an object of both popular and technical interest. I note that even Brian Marsden, who just stepped down after his long tenure as director of the IAU's Minor Planet Center and who seems quite content to have Pluto added to his erstwhile bailiwick, is “prepared at least to consider a … compromise [that] allows that some planets could be both ‘major’ and ‘minor’ – like music” (personal communication, 8/12/06).

Actually I have no objection to retaining the “dwarf” label for Pluto, for I think there is an analogy that suits the case perfectly. Why not categorize Pluto as a Brown dwarf ... after Mike Brown, the astronomer whose team discovered 2003 UB313, thereby precipitating the current controversy? This seems especially fitting, given that brown (lower-case "b") dwarfs have long held an ambiguous status relative to stars that is analogous to the status large Kuiper Belt Objects like 2003 UB313 hold relative to planets. Nonetheless brown dwarfs are still commonly referred to as stars, albeit “cold, dark” ones, so a Brown dwarf Pluto would still be a planet.

This might even resurrect the planetary status of Mike Brown’s baby, now dubbed Eris. But the name “Eris” presumes the object is not a planet. If it were recognized as a Brown dwarf, and so a kind of planet after all, I would like to suggest it be renamed “Planet X.” This seems triply meet since (1) the name evokes the historical idea of a trans-Neptunian planet, (2) “X” is the Roman numeral for ten, this being then the tenth planet, and (3) it retains the consistency of Roman names for all the planets (except ours!).*

-- January 14, 2007

* Mike Brown subsequently commented that “the name Eris definitely does NOT presume that it is not a planet! We specifically chose a Greek name to fit into the Greek & Roman names (well, ok, mostly Roman, but the Roman version of Eris is Discordia, which just doesn't seem as good a name) of all of the planets” (personal communication, 10/13/08).