Double planet arguing that Jupiter is a double star is "not" analogous to arguing Pluto-Charon is a double dwarf planet. The problem is that Jupiter is not even a star, or even a brown dwarf, and due to its low mass it is unable to achieve any form of fusion. Isaac Asimov suggested a distinction between planet–moon and double-planet structures based in part on what he called a "tug-of-war" value, which does not consider their relative sizes. This quantity is simply the ratio of the force exerted on the smaller body by the larger (primary) body to the force exerted on the
Dwarf planet finally precipitated by the discovery of an even more massive object, Eris. The exclusion of dwarf planets from the roster of planets by the IAU has been both praised and criticized; it was said to be the "right decision" by astronomer Mike Brown, who discovered Eris and other new dwarf planets, but has been rejected by Alan Stern, who had coined the term "dwarf planet" in April 1991. As of July 2008 the International Astronomical Union (IAU) recognizes five dwarf planets: in the asteroid belt, and Pluto, , , and in the outer Solar System. Brown criticizes this official recognition: