Sedna




90377 Sedna is a trans-Neptunian object, discovered by Mike Brown (Caltech), Chad Trujillo (Gemini Observatory) and David L. Rabinowitz (Yale University) on November 14, 2003. Its discovery was the farthest distance at which any natural object in the solar system has ever been observed. Sedna is described as a cold planetoid, perhaps as large as two-thirds the size of Pluto.


General Information

Sedna was discovered during a survey conducted with the Samuel Oschin telescope at Palomar Observatory near San Diego, California (USA) and was observed within days on telescopes from Chile, Spain, and the USA (Arizona, and Hawaii). NASA's orbiting Spitzer Space Telescope was also pointed toward the object, but could not detect it - putting an upper-bound on its diameter at roughly three-quarters that of Pluto.

Because of its cold, distant nature, and because all other planets of the Solar system are named after (Roman and Greek) gods, the scientists who discovered it unofficially named it after Sedna, the Inuit goddess of the sea, who was believed to live in the cold depths of the Arctic Ocean.

Before Sedna was officially named it had provisional designation 2003 VB12. As of September 28, 2004, the International Astronomical Union has officially accepted the name "Sedna".

Orbital Characteristics

Sedna has a highly elliptical orbit, with its aphelion estimated at 942 AU and its perihelion at about 76.1 AU. At its discovery, it was about 90 AU from the Sun, approaching perihelion. This is the furthest from the Sun that any solar system object has been observed, although some objects like long-period comets originally observed at closer distances may currently be further from the Sun than Sedna but are too dim to be observable. For comparison, the average distance of Pluto from the Sun is about 40 AU. Sedna's orbit takes about 11,487 years. It will reach perihelion in 2075 or 2076.

[Update: the Kujper Belt Object 2003 UB313 was detected at 97 AU, and the discovery announced on July 29, 2005. However, its average distance is less than that of Sedna. It is estimated to be 150% the diameter of Pluto.]

When first discovered, Sedna was believed to have an unusually long rotational period (between 20Š50 days). A search was thus made for a natural satellite, the most likely cause for such a long rotation, but investigation by the Hubble Space Telescope in March 2004 observed no such object orbiting the planetoid. New measurements from the MMT telescope suggest a much shorter rotation period, only about 10 hours, rather typical for bodies of its size.

A study done by Hal Levison and Alessandro Morbidelli of the Observatoire de la C™te d'Azur (OCA) in Nice, France suggested that the most likely explanation for Sedna's orbit was that it had been perturbed by a close pass by another star in the first 100 million years or so of the solar system's existence, possibly one of the other stars that formed out of the same collapsing nebula as the Sun. Another, less probable, scenario they proposed that managed to explain Sedna's orbit very well was that Sedna could have formed around a brown dwarf about 20 times less massive than the Sun and was captured by our Solar System when the brown dwarf passed through it.

Another object, 2000 CR105, has an orbit similar to Sedna's but a bit less extreme: perihelion is 45 AU, aphelion is 415 AU, and the orbital period is 3420 years. Its orbit may have resulted from the same processes that produced Sedna's orbit.

Physical Characteristics

Sedna has an estimated diameter of between 1180 and 1800 kilometres (730 to 1470 miles) and at the time of its discovery was the largest object found in the solar system since Pluto was discovered in 1930. The planetoid is so far from the Sun that the temperature never rises above -400 degrees F.

Observations from Chile show that Sedna is one of the reddest objects in the solar system, nearly as red as Mars. Unlike Pluto and Charon, Sedna appears to have very little methane ice or water ice on its surface; Chad Trujillo and his colleagues at the Gemini Observatory in Hawaii suggest that Sedna's dark red color is caused by a hydrocarbon sludge, or tholin, like that found on Pholus . Its surface is homogenous in colour and spectrum; this is probably because Sedna, unlike objects nearer the sun, is rarely impacted by other bodies, which would expose bright patches like that on Asbolus.

Classification

The discoverers have argued that Sedna is actually the first observed body belonging to the Oort cloud, saying that it is too far out to be considered a Kuiper belt object. Because it is a great deal closer to the Sun than was expected for an Oort cloud object, and has an inclination roughly in line with the planets and the Kuiper belt, they describe the planetoid as being an inner Oort cloud object, situated in the disc reaching from the Kuiper belt to the spherical part of the cloud.

However, others believe that its inclination and size qualify it as a Kuiper Belt object. These astronomers suggest that previous assumptions about the outer edge of the Kuiper Belt should be revised outward.Writing in Nature, astronomers Scott J. Kenyon and Benjamin C. Bromley consider Sedna's origin and show that a passing star probably scattered Sedna from the Sun's Kuiper belt into its observed orbit. They estimate the probability that Sedna was captured from the outer disk of the passing star at about 10 percent (Nature 432, 598Š602 (02 December 2004); doi:10.1038/nature03136).

The discovery of Sedna has also resurrected the question of which astronomical objects should be considered planets and which should not. On March 15, 2004, articles in the popular press reported that "the tenth planet has been discovered", and some believe its claim on planethood is comparable to that of Pluto.

Sedna's discoverers (like others) call it a planetoid, but because the two objects are similar in size and composition, a permanent decision to classify Sedna as a planetoid could re-open questions about whether Pluto should also bear that classification. Isaac Asimov suggested the term mesoplanet be used for planetary objects intermediate in size between Mercury and 1 Ceres, which would include both Pluto and Sedna.

See Wikipedia For additional links and information.

"Sedna" spelled backwards is "Andes" which takes us to the Inca Civilization.


Articles in the News


Distant planetoid Sedna gives up more secrets New Scientist - April 2005

The distant planetoid Sedna appears to be covered in a tar-like sludge that gives it a distinctly red hue, a new study reveals. The findings suggests the dark crust was baked-on by the Sun and has been untouched by other objects for millions of years. Astronomers have struggled to explain its extreme orbit, but many believe a star passing by the Sun about 4 billion years ago yanked the planetoid off its original, circular course.

Now, observations by the same team that discovered Sedna suggest the object has since led an uneventful life. Infrared spectra taken with the Gemini Observatory in Hawaii show the surface of the planetoid contains little methane ice, found in significant amounts on Pluto, and little water ice, seen on PlutoÕs moon, Charon.

Chad Trujillo, the team's lead researcher at the Gemini Observatory, says collisions with other objects may have helped expose the icy interiors of Pluto and Charon and believes a lack of collisions might explain Sedna's ice-free surface.He says Sedna, which is probably made up of an equal mixture of ice and rock, may be covered with a metre or so of hydrocarbon sludge. This sludge is produced when the Sun's ultraviolet radiation and charged particles alter the chemical bonds between atoms in the ice.

A similar "space weathering" process occurs on a 200-kilometre-wide object called Pholus, which lies near Saturn and is also very red. Scott Gaudi, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, US, says the new work supports previous theories showing Sedna evolved in a more distant, less crowded environment than Pluto and CharonÕs. "Maybe it was lifted to its higher orbit early on and lived out there for a long time," he says.

But Gaudi recently discovered that, in at least one way, Sedna appears more conventional than previously thought. When Sedna was discovered, astronomers used a 1.3-metre telescope to observe the planetoid's period of rotation, concluding it rotated once every 20 days - an abnormally slow rate which they attributed to the gravitational tugs of a moon.

In March 2004, the mystery deepened when the Hubble Space Telescope failed to detect any moons.

Now, Gaudi and colleagues have taken more than 140 images of Sedna with a 6.5-metre telescope and found that actually Sedna rotates once every 10 hours.


Mythology

In Inuit mythology, Sedna is a sea goddess and master of the animals, especially mammals such as seals, of the ocean. She lives in Adlivun, the Inuit underworld. Sedna is also known as Arnakuagsak or Arnarquagssaq (Greenland) and Nerrivik or Nuliajuk (Alaska). Although Sedna is sometimes thought to predominate throughout the Canadian Arctic she was known by other names by different Inuit groups. One example of this is Arnapkapfaaluk (big bad woman) of the Copper Inuit from the Coronation Gulf area.

According to myth, Sedna was the daughter of the creator-god Anguta and his wife. She is said to have been so huge and hungry that she ate everything in her parents' home, and even gnawed off one of her father's arms as he slept. According to some versions of the myth, she took a dog for her husband. Anguta was so angry that he threw her over the side of his canoe. She clung to its sides, whereupon he chopped her fingers off one by one until she let go. She sank to the underworld, becoming the queen of the monsters of the deep, and her huge fingers became the seals, sea-lions and whales hunted by the Inuit. Anguta was so angry that he threw her over the side of his canoe. She clung to its sides, whereupon he chopped her fingers off one by one until she let go. She sank to the underworld, becoming the queen of the monsters of the deep, and her huge fingers became the seals, sea-lions and whales hunted by the Inuit.

Other tales assert that Sedna was a beautiful and chaste maiden who was innocently lured into marriage by an evil bird spirit. When her father tried to rescue her, the spirit became angry and caused a terrible storm which threatened the very survival of her people. In desperation, Sedna's father threw her into the raging sea. The varying legends each give different rationales for her death at the hands of her father. Sometimes she is the innocent victim, and sometimes she appears to deserve death as punishment for greed or some other evil. But all tales agree that she descended into the depths of the ocean and became the Goddess of Sea Creatures. As such she became a vital deity, eagerly worshipped by hunters who depended on her goodwill to supply food. Sedna is also the adversary on the children's cartoon Inuk which follows the story of a young Inuit boy. Her name was taken also to name a new disputed "tenth" planet, 90377 Sedna, as discovered by Michael Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale University) on November 14, 2003.


Myth 2

There once lived an old widower, Anguta, and his daughter, Sedna, a woman so beautiful that all the Eskimo men sought to live with her. But she found none to her liking and refused all offers. One day, a seabird came to her and promised her a soft life in a warm hut full of bearskins and fish. Sedna flew away with him. The bird had lied. Sedna found her home a stinking nest. She sat, sadly regretting her rejection of the handsome human men. And that was what she told her father, when she listed her complaints when he visited her a year later.

Anguta, "man with something to cut", put his daughter in his kayak to bring her back to the human world. Perhaps he killed the bird husband first, perhaps he just stole the bird's wife, but in either case the vengeance of the bird people followed him. The rising sea threatened the escaping humans with death. On they struggled, until Anguta realized that flight was hopeless.

He shoved Sedna overboard to drown. Desperate for life, she grabbed the kayak with a fierce grip. Her father cut off her fingers. She flung her mutilated arms over the skin boat's sides. Anguta cut them off, shoving his oar into Sedna's eye before she sank into the icy water.

At the bottom of the sea, she lived thereafter as queen of the deep, mistress of death and life, "old food dish," who provided for the people. Her amputated fingers and arms became the fish and marine mammals, and she alone decided how many could be slaughtered for food. She was willing to provide for the people if they accepted her rules: for three days after their death, the souls of her animals would remain with their bodies, watching for violation of Sedna's demands. Then they returned to the goddess, bearing information about the conduct of her people. Should her laws be broken, Sedna's hand would begin to ache, and she would punish humans with sickness, starvation, and storms. Only if a shaman traveled to her country, Adlivun, and assuaged her pains would the sea mammals return to the hunters, which, if the people acted righteously, they did willingly.

In Adlivun in a huge house of stone and whale ribs, Sedna dragged along the ground with one leg bent beneath her. A horrible dog guarded her, said by some to be her husband. Anguta himself lived there too; some versions of the myth say that, hoping the seabirds would think Sedna dead, he allowed her back into the kayak and returned home.

But she hated him thereafter and cursed her dogs to eat his hands and feet; the earth opened and swallowed them. In any case, Anguta served Sedna by grabbing dead human souls with his maimed hand and bringing them home. These dead lived in a region near Sedna's home through which shamans had to pass to reach the goddess. There was also an abyss, in which an ice wheel turned slowly and perpetually; then a caldron full of boiling seals blocked the way; finally, the horrible dog stood before Sedna's door, guarding the knife-thin passageway to her home. Should the shaman pass all these dangers and ease Sedna's aching hands, the goddess permitted him to return, bearing the news that Old Woman had forgiven her people, that the seals would again seek the hunter, that the people would no longer starve.




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