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{{#invoke:Hatnote|hatnote}} {{#invoke:Infobox|infobox}}

90377 Sedna is a large minor planet in the outer reaches of the Solar System that was, as of 2015, at a distance of about 86 astronomical units (AU) from the Sun, about three times as far as Neptune. 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 nitrogen ices with tholins. Its surface is one of the reddest among Solar System objects. It is most likely a dwarf planet.

For most of its orbit it is even farther from the Sun than at present, with its aphelion estimated at 937 AU<ref name="barycenter"/> (31 times Neptune's distance), making it one of the most distant known objects in the Solar System other than long-period comets.Unknown extension tag "ref"<ref group=lower-alpha name=footnoteF>Small Solar System bodies such as (308933) 2006 SQ372, 2005 VX3, (87269) 2000 OO67, 2002 RN109, 2007 TG422, and several comets (such as the Great Comet of 1577) have larger heliocentric orbits. But only (308933) 2006 SQ372, (87269) 2000 OO67, and 2007 TG422 have a perihelion point further than Jupiter's orbit, so it is debatable whether or not most of these objects are misclassified comets.</ref>

Sedna's exceptionally long and elongated orbit, taking approximately 11,400 years to complete, and distant point of closest approach to the Sun, at 76 AU, have led to much speculation about its origin. The Minor Planet Center currently places Sedna in the scattered disc, a group of objects sent into highly elongated orbits by the gravitational influence of Neptune. However, this classification has been contested, because Sedna never comes close enough to Neptune to have been scattered by it, leading some astronomers to conclude that it is in fact the first known member of the inner Oort cloud. Others speculate that it might have been tugged into its current orbit by a passing star, perhaps one within the Sun's birth cluster (an open cluster), or even that it was captured from another star system. Another hypothesis suggests that its orbit may be evidence for a large planet beyond the orbit of Neptune.

Astronomer Michael Brown, co-discoverer of Sedna and the dwarf planets Eris, Haumea, and Makemake, thinks that it is the most scientifically important trans-Neptunian object found to date, because understanding its unusual orbit is likely to yield valuable information about the origin and early evolution of the Solar System.<ref name="fussman" />


90377 Sedna sections
Intro   History    Orbit and rotation    Physical characteristics    Origin    Population    Classification    Exploration    Notes    References    External links   

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{{#invoke:Hatnote|hatnote}} {{#invoke:Infobox|infobox}}

90377 Sedna is a large minor planet in the outer reaches of the Solar System that was, as of 2015, at a distance of about 86 astronomical units (AU) from the Sun, about three times as far as Neptune. 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 nitrogen ices with tholins. Its surface is one of the reddest among Solar System objects. It is most likely a dwarf planet.

For most of its orbit it is even farther from the Sun than at present, with its aphelion estimated at 937 AU<ref name="barycenter"/> (31 times Neptune's distance), making it one of the most distant known objects in the Solar System other than long-period comets.Unknown extension tag "ref"<ref group=lower-alpha name=footnoteF>Small Solar System bodies such as (308933) 2006 SQ372, 2005 VX3, (87269) 2000 OO67, 2002 RN109, 2007 TG422, and several comets (such as the Great Comet of 1577) have larger heliocentric orbits. But only (308933) 2006 SQ372, (87269) 2000 OO67, and 2007 TG422 have a perihelion point further than Jupiter's orbit, so it is debatable whether or not most of these objects are misclassified comets.</ref>

Sedna's exceptionally long and elongated orbit, taking approximately 11,400 years to complete, and distant point of closest approach to the Sun, at 76 AU, have led to much speculation about its origin. The Minor Planet Center currently places Sedna in the scattered disc, a group of objects sent into highly elongated orbits by the gravitational influence of Neptune. However, this classification has been contested, because Sedna never comes close enough to Neptune to have been scattered by it, leading some astronomers to conclude that it is in fact the first known member of the inner Oort cloud. Others speculate that it might have been tugged into its current orbit by a passing star, perhaps one within the Sun's birth cluster (an open cluster), or even that it was captured from another star system. Another hypothesis suggests that its orbit may be evidence for a large planet beyond the orbit of Neptune.

Astronomer Michael Brown, co-discoverer of Sedna and the dwarf planets Eris, Haumea, and Makemake, thinks that it is the most scientifically important trans-Neptunian object found to date, because understanding its unusual orbit is likely to yield valuable information about the origin and early evolution of the Solar System.<ref name="fussman" />


90377 Sedna sections
Intro   History    Orbit and rotation    Physical characteristics    Origin    Population    Classification    Exploration    Notes    References    External links   

PREVIOUS: IntroNEXT: History
<<>>