Sedna is a dwarf planet in the outermost part of the Solar System. Its surface is made up of water, methane, and nitrogen ices with tholins, and is one of the reddest objects in the Solar System. Sedna is one of the largest planetoids without a moon and has a diameter of about 1,000 km. Its orbit is very large and takes it far beyond the closest portion of interplanetary space. Sedna's orbit is highly elongated and takes about 11,400 years to return to its closest approach to the Sun. Some astronomers believe that understanding Sedna's orbit could provide insights about the origin and evolution of the Solar System, and its orbit could have been influenced by nearby stars or captured from another star's planetary system. The clustering of the orbits of Sedna and similar objects is seen as possible evidence for a planet beyond the orbit of Neptune. Sedna was discovered on November 14, 2003 by Michael Brown, Chad Trujillo, and David Rabinowitz. It was observed to move by 4.6 arcseconds over 3.1 hours, indicating that its distance was about 100 AU. Follow-up observations were made using different telescopes, allowing for the accurate determination of its orbit, which showed that Sedna was moving along a distant eccentric orbit, 90.3 AU from the Sun. After initially being called "The Flying Dutchman" because of its slow movement, Sedna was officially named after the goddess Sedna from Inuit mythology. The name was chosen because it was easily pronounceable and because Sedna's location at the bottom of the Arctic Ocean mirrored the object's distance from the Sun. The name caused some controversy among amateur astronomers, but no objections were raised and the name was accepted by the IAU. Sedna does not have an official symbol, but there is a symbol that is sometimes used by astrologers. Sedna has the longest orbital period of any known object in the Solar System, taking around 11,400 years to complete one orbit. Its orbit is very eccentric, ranging from a far distance of 937 AU to a closer distance of 76.2 AU from the Sun. Sedna's rotation period was initially thought to be unusually long, but it is actually around 10 hours, which is typical for a body of its size. Sedna is estimated to have a diameter of approximately 1,000 km and is one of the reddest objects in the Solar System. Its surface is coated with hydrocarbon sludge, giving it a dark red color. It is also composed of tholins, methane ice, water ice, amorphous carbon, nitrogen ices and other compounds. Sedna's deep red color indicates high concentrations of organic material on its surface. It is too cold for methane to evaporate and fall back as snow. The presence of nitrogen suggests the possibility of a tenuous atmosphere for a short time near perihelion.

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