Natural satellite achieved hydrostatic equilibrium, and Uranus has five. It has been suggested that some satellites may potentially harbour life. Among the identified dwarf planets, Ceres has no known natural satellites. Pluto has the relatively large natural satellite Charon and four smaller natural satellites; Styx, Nix, Kerberos, and Hydra. Haumea has two natural satellites, and Eris and Makemake have one each. The Pluto–Charon system is unusual in that the center of mass lies in open space between the two, a characteristic sometimes associated with a double-planet system. The seven largest natural satellites in the Solar System (those bigger than 2,500 km across)
Eris (dwarf planet) decide the issue. This was announced as the IAU's "Definition of a Planet in the Solar System," adopted on 24 August 2006. At this time, both Eris and Pluto were classified as "dwarf planets," a category distinct from the new definition of "planet." Brown has since stated his approval of this classification. The IAU subsequently added Eris to its Minor Planet Catalogue, designating it "(136199) Eris." Eris has an orbital period of 558 years. Its maximum possible distance from the Sun (aphelion) is 97.65 AU, and its closest (perihelion) is 37.91 AU. It came to perihelion between 1698 and 1699,