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
Definition of planet storms [Titan] shouldn't be put into the same category, whatever you call it. However, he goes on to say that, "For most people, considering round satellites (including our Moon) "planets" violates the idea of what a planet is." Alan Stern has argued that location should not matter and that only geophysical attributes should be taken into account in the definition of a planet, and proposes the term "satellite planet" for a planet-sized satellite. In 2017, Stern, K. D. Runyon et al. proposed a new geophysical definition of planet that defined a planet simply as an object large enough to be