Pluton

For a while in August 2006, it seemed that this word would be included in astronomical textbooks as a result of a resolution of the International Astronomical Union (IAU), then meeting in Prague. It was suggested by a seven-member group grandly called the Planet Definition Committee.

The problem for the IAU was that modern observational astronomy has found a number of new bodies in the Solar System, orbiting beyond Pluto in an area called the Kuiper Belt. At least one of these newly noted objects is larger than Pluto itself, requiring astronomers to sort out their terminology.

The most massive bodies are those called simply planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. There are also large numbers of small rocky bodies called collectively the minor planets or asteroids. The committee recommended that in between there should be a new class, to be collectively called plutons. They are massive enough to have been formed into a spherical shape by their own gravity, they orbit the sun so far out that one revolution of the Sun takes at least 200 years, and they have elliptical orbits that are inclined to those of the classical planets, implying that they have a different origin.

Pluto is a typical member of the group and the word was created from its name. Pluto derives from Greek mythology, in which it was a euphemism for the god of the underworld, Hades. Literally, pluto meant “rich one”, in reference to the wealth that came from within the Earth. The planet Pluto was famously named as a result of a suggestion by 11-year-old Miss Venetia Burney, of Oxford. (Walt Disney’s dog, by the way, was named after the planet, not the other way round; popular culture didn’t have the influence it does now, when names like Xena — the warrior princess of the television series — can be seriously considered.)

The news reports on the committee’s recommendation implied it had invented the word. But there are earlier examples: the astronomer Tom Burns used it in the same sense in an article in the Columbus Dispatch in June 1997, as did Frederik Pohl in his SF novel Mining the Oort of 1992; Robert Heinlein created an Earth currency of that name in his novelettes Gulf (1949) and Tunnel in the Sky (1955), though that was based on the element plutonium, itself named after the planet Pluto because it is the next element in the periodic table after Uranium and Neptunium, whose discoverers took their names from the planets.

Pluton is also an established geological term, for a large body of intrusive igneous rock beneath the Earth’s surface; that was created in the 1930s from the adjective plutonic, again taken from the Greek name, that referred to the action of intense heat at great depths upon rocks forming the Earth’s crust. Some astronomers thought having two such different meanings for the word would cause confusion; also the French for Pluto is Pluton, so in that language “there is a pluton on Pluto” would seem redundant.

The debates at the International Astronomical Union meeting rejected not only pluton, making it an official non-word, but also several other neologisms thought up by ingenious astronomers: plutonian object, planetino, plutian, plutoid, plutonoid, plutonid, and plutid. Also dismissed were Tombaugh object and Tombaugh planet, which were put forward in honour of Clyde Tombaugh, who discovered Pluto. The official name for the objects is dwarf planet.

Little Pluto, which had been in peril of losing its place among the planets, keeps its status, but only in a new category of “plutons,” distant oddballs wandering outside Neptune in weirdly shaped orbits.

Daily Telegraph, 16 Aug. 2006

Dozens more plutons could be added after the objects are more thoroughly reviewed by the IAU.

The Seattle Times, 16 Aug. 2006