Sedna

Sedna is a dwarf planet candidate in the outermost reaches of the Solar System, orbiting the Sun far beyond Neptune on one of the most distant and elongated paths known for any body of its size. Discovered in 2003, it is roughly 1,000 kilometers in diameter, and spectroscopic study of its surface shows a mixture of water ice, carbon dioxide, and ethane alongside reddish tholins, a chemical makeup similar to other distant trans-Neptunian objects. It is not expected to hold a substantial atmosphere, and because no moon has been found orbiting it, its mass and density remain unknown.