English: A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to planetary geologists is that they may be geologically active bodies, an expectation that was borne out in 2015 by the Dawn mission to Ceres and the New Horizons mission to Pluto.Astronomers are in general agreement that at least the nine largest candidates are dwarf planets: Pluto, Eris, Haumea, Makemake, Gonggong, Quaoar, Sedna, Ceres, and Orcus. Of these nine plus the tenth-largest candidate Salacia, two have been visited by spacecraft (Pluto and Ceres) and seven others have at least one known moon (Eris, Haumea, Makemake, Gonggong, Quaoar, Orcus, and Salacia), which allows their masses and thus an estimate of their densities to be determined. Only one, Sedna, has neither been visited nor has any known moons, making an accurate estimate of mass difficult.There has been some debate as to whether the Pluto–Charon system should be considered a double dwarf planet. The IAU currently says Charon is not considered a dwarf planet but rather a satellite of Pluto, though the idea that Charon might qualify as a dwarf planet may be considered at a later date.