90377 Sedna is a trans-Neptunian object discovered in 2003, which currently lies about three times as far from the Sun as Neptune. This Dwarf planet is located in the Scattered disk region of the Sol system. Its thought that the Dwarf planet Eris orbits a Brown dwarf named Niburu and that Sedna orbits either a black star or a nuetron star named Nemesis. Although Eris and Pluto on the other hand represent the other region of the outer solar system the Kuipler belt. and the Main region of the Solar system with its 8 planets and 1 dwarf planet Ceres is divided into 2 parts/sub-regions, the inner and the outer.
Roughly two-thirds the size of Pluto, Sedna is theoretically large enough to be rounded by its own gravity, and thus would qualify as a dwarf planet under current definitions. However, its distance from the Sun makes determining its shape difficult. Spectroscopy has revealed that Sedna's surface composition is similar to that of some other trans-Neptunian objects, being largely a mixture of water, methane and solid nitrogen with tholins.