Fictional planets of the Solar System a "tenth planet". Since 1992, a very large number of objects have been found beyond Neptune; all the objects in the following list, however, are purely fictional. Common names for trans-Neptunian planets in fiction include Planet X, after a planet once believed to lie beyond Neptune, and Persephone (or Proserpina), after the wife of Pluto. Rogue planets in fiction usually originate outside the Solar System, but their erratic paths lead them to within detectable range of Earth. In reality, no rogue planet has ever been detected transiting the Solar System. Fictional planets of the Solar System The fictional portrayal of
IAU definition of planet IAU definition of planet The International Astronomical Union (IAU) defined in August 2006 that, in the Solar System, a planet is a celestial body which: Among other things, this definition caused Pluto to no longer be a planet, a change from how it had been widely considered until that point. A non-satellite body fulfilling only the first two of these criteria (such as Pluto) is classified as a "dwarf planet". According to the IAU, "planets and dwarf planets are two distinct classes of objects". A non-satellite body fulfilling only the first criterion is termed a "small Solar System body" (SSSB).