Sedna


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Sedna,

in astronomy, the most distant known large object in the solar system. With a highly eccentric elliptical orbit that ranges from an estimated 76 AU to 937 AU, Sedna also has an extremely long orbital period, estimated at 11,400 years. Although the dwarf planet ErisEris,
in astronomy, the largest known dwarf planet. Eris, whose highly eccentric elliptical orbit ranges from 38 AU to 97 AU and is inclined more than 44°, is the largest known object of the Kuiper belt (see comet), with a diameter (1,445 mi/2,317 km) slightly larger than
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 was later discovered at a more distant location, Sedna's orbit takes it much further from the sun. Its diameter is c.600 mi (1,000 km). Sedna, which appears almost as red as Mars, has a surface that is believed to be covered with tholins (a mix of hydrocarbons, formed from methane and nitrogen by ultraviolet light, which give Sedna its reddish appearance) as well as frozen methane and water.

It is unclear where Sedna was formed, or why its orbit is so elongated. It does not appear to be a Kuiper belt object, because its orbit never gets close to that region of space; some astronomers have suggested Sedna might be an inner Oort cloud object (see cometcomet
[Gr.,=longhaired], a small celestial body consisting mostly of dust and gases that moves in an elongated elliptical or nearly parabolic orbit around the sun or another star. Comets visible from the earth can be seen for periods ranging from a few days to several months.
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). Sedna was discovered on Nov. 14, 2003, by astronomers Mike Brown, Chad Trujillo, and David Rabinowitz, using computer analysis of images taken in a survey of the Kuiper belt. It was named for the Inuit goddess of the ocean because of the cold, remote location its orbit traverses. The term "sednoid" was coined to described bodies found between the Oort cloud and Kuiper belt; a second such planetoid was discovered in 2012.

Sedna

A body orbiting the Sun far out beyond the planet Pluto at a mean distance of 90 AU. Its orbital period has been estimated at about 10 500 years. At the time of its discovery, made in November 2003 by a team led by Mike Brown from the California Institute of Technology, it was thought to be approaching perihelion, a point 76 AU from the Sun. A distinctive feature is its reddish color. Sedna takes its name from the Inuit goddess of the sea. It is believed to be an object made of ice and rock belonging to the inner Oort Cloud. With an estimated diameter of about 1800 km, Sedna is thought to be about halfway in size between Pluto and the Kuiper Belt object Quaoar. The temperature on Sedna is probably lower than 30 K.
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