What is a planet” When is a discovery?

Abstract

The news item above reports on the sighting of a planet outside our solar system, the first time such a discovery has been made. As with many scientific discoveries, however, things are not quite as simple as they seem. The problem with this discovery is that the two groups of astronomers invoked cannot quite agree on who saw what first. Or to put it another way: When is a planet not a planet but a Brown Dwarf and when is a discovery not a discovery but a confirmation? Astronomers from the U.S. Naval Observatory and the University of Arizona are having a little trouble sorting this out.Both groups do agree on the data. A substellar body has been directly and indirectly observed orbiting the intrinsically faint star Van Biesbroeck 8 (VB S) in a constellation of the Milky Way. In fact, both groups agree that the observed substellar body can be called a Brown Dwarf. The definition of a Brown Dwarf, it is agreed, lies somewhere in between the definition of a planet and that of a star. Herein lies the crux: can a Brown Dwarf be called a planet? Richard Harrington, an astronomer with the U.S. Naval Observatory, says that a Brown Dwarf is not a planet. Donald McCarthy, of the University of Arizona, says that it is.