Astronomers are in general agreement that at least the nine largest candidates are dwarf planets – in rough order of size, Pluto, Eris, Haumea, Makemake, Gonggong, Quaoar, Ceres, Orcus, and Sedna. Considering the ten largest candidates adds Salacia. Of these ten, 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. Mass and density in turn can be fit into geophysical models in an attempt to determine the nature of these worlds. Only one, Sedna, has neither been visited nor has any known moons, making an accurate estimate of mass difficult. Some astronomers include many smaller bodies as well, but there is no consensus that these are likely to be dwarf planets.