What Should We Call Pluto?

Abstract

The discovery of 2003 UB313, an object that is larger than and farther away from the sun than Pluto, has reopened the question of what is a planet (“Newfound 'tenth planet' puts Pluto behind the eight ball,” R. A. Kerr, News of the Week, 5 Aug., p. 859). The International Astronomical Union (IAU) has suggested the idea of calling both Pluto and the new object “Trans-Neptunian planets” (TNPs), including planet in the name but with a qualifier. This proposal is worth a try, but it raises some problems. Pluto, UB313, and other similar bodies must be named as asteroids exclusively, not only because they are different from the other eight planets, but because of their similarity in origin, size, composition, and orbital parameters to hundreds of thousands of small rocky objects orbiting the sun at more than 30 AU, in a region called the Edgeworth-Kuiper Belt. If the term “planet” is still included in the name, then we could have hundreds of this new kind of planet in the solar system in the future. If TNPs are a class roughly defined as “large objects that orbit the sun beyond Neptune,” what will be the name of similar small rocky objects that will eventually be discovered orbiting in the outer regions of stellar systems other than ours? ![Figure][1] Image of Pluto taken by the European Space Agency's Faint Object Camera on 21 February 1994, when Pluto was 4.4 billion km from Earth.CREDIT: R. ALBRECHT, ESA/ESO SAPCE TELESCOPE EUROPEAN COORDINATING FACILITY; NASA In planetary science, the tools for examining our cosmic neighborhood continue to be refined and extended, and so we are beginning to appreciate that the richness of our stellar system is much greater than it appeared to earlier explorers and name-givers, demanding revisions of which Pluto is an excellent example. As Confucius said, “The beginning of wisdom is to call things by their right name.” [1]: pending:yes