90377 Sedna.
Sedna is a trans-Neptunian object with the minor-planet number 90377. It was discovered on November 14, 2003, by the astronomers Michael Brown, Chad Trujillo, and David Rabinowitz. As of 2023, Sedna is 84 astronomical units (AU) from the Sun, which is almost three times the distance between Neptune and the Sun. Sedna's orbit is an ellipse and its aphelion is approximately 937 AU (140 billion km). For most of its orbital period, Sedna is farther from the Sun than any known dwarf planet candidate of its size. Sedna is one of the reddest objects in the Solar System. It is mostly composed of water, methane, and nitrogen ices with tholins. It may have formed within the same open cluster where the Sun was born as some astronomers suggest that Sedna is a celestial body captured by the Sun from another star system. Brown considers Sedna to be the most important trans-Neptunian object ever discovered, because its unusual orbit may yield information about the origin and early evolution of the Solar System.
