Astronomers are unable to agree on a definition of "planet," but have called for a conference to--one hopes--resolve their differences.
Some argue that if Pluto kept its crown, Xena should be the 10th planet by default - it is, after all, bigger. Purists maintain that there are only eight traditional planets, and insist Pluto and Xena are poseurs.Consulting a lexicographer won't work. Ambrose Bierce is no help. Samuel Johnson's "erratick or wandering stars" is vague and inaccurate. Even fabled Dictionary.com leaves the door open for planetoids.
"Life would be simpler if we went back to eight planets," said Brian Marsden, director of the astronomical union's Minor Planet Center in Cambridge, Mass.
Still others suggest a compromise that would divide planets into categories based on composition, similar to the way stars and galaxies are classified. Jupiter could be labeled a "gas giant planet," while Pluto and Xena could be "ice dwarf planets."
"Pluto is not worthy of being called just a plain planet," said Alan Boss, an astrophysicist at the Carnegie Institution in Washington, D.C. "But it's perfectly fine as an ice dwarf planet or a historical planet."
(Astrologers, working with only seven planets for the last few centuries, largely have ignored the controversy.)