This article at the Sydney Morning Herald details some of the controversy surrounding the classification and definition of “planet,” primarily because of University of California astronomer Gibor Basri’s proposal to the International Astronomical Union to increase the number of planets to 12. “According to Professor Basri’s definition, a planet must orbit a star, not another planet, and it must be round. That means it must be 700 kilometres in diameter, when gravity moulds it into a sphere, or bigger. Smaller objects are potato-shaped.” This proposal would obviously add three more planets to our present system, including the asteroid Ceres, discovered in 1801, and the Kuiper-belt objects of Varuna, discovered in 2000, and Quaoar, discovered just last year. However, many astronomers have already reduced the number of planets to eight, discounting Pluto as a planet, so there is obviously some disagreement on the proposal.
