Definition of planet In the original draft proposal, an exception was made for Pluto and its largest satellite, Charon, which possess a barycenter outside the volume of either body. The initial proposal classified Pluto–Charon as a double planet, with the two objects orbiting the Sun in tandem. However, the final draft made clear that, even though they are similar in relative size, only Pluto would currently be classified as a dwarf planet. However, some have suggested that the Moon nonetheless deserves to be called a planet. In 1975, Isaac Asimov noted that the timing of the Moon's orbit is in tandem with the
Eris (dwarf planet) outer belt. Inner-belt objects are expected to be generally more massive than outer-belt objects, and so astronomers expect to discover more large objects like Eris in high-inclination orbits, which planetary searches have traditionally neglected. Because Eris was initially thought to be larger than Pluto, it was described as the "tenth planet" by NASA and in media reports of its discovery. In response to the uncertainty over its status, and because of ongoing debate over whether Pluto should be classified as a planet, the IAU delegated a group of astronomers to develop a sufficiently precise definition of the term "planet" to