Natural satellite been directly observed, have been called "moonlets". Small asteroid moons (natural satellites of asteroids), such as Dactyl, have also been called moonlets. The upper limit is also vague. Two orbiting bodies are sometimes described as a double planet rather than primary and satellite. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition of what constitutes a moon. Some authors consider the Pluto–Charon system to be a double (dwarf) planet. The most common dividing line on what is considered a moon rests upon whether the barycentre is below the surface of the larger
IAU definition of planet Pluto would have been the prototype for this class. The term "dwarf planet" would have been available to describe all planets smaller than the eight "classical planets" in orbit around the Sun, though would not have been an official IAU classification. The IAU did not make recommendations in the draft resolution on what separated a planet from a brown dwarf. A vote on the proposal was scheduled for August 24, 2006. Such a definition of the term "planet" could also have led to changes in classification for the trans-Neptunian objects , , Sedna, Orcus, Quaoar, Varuna, , Ixion, and ,