Sedna has a V-band absolute magnitude (H) of about 1.8, and it is estimated to have an albedo of about 0.32, thus giving it a diameter of approximately 1,000 km.[10] At the time of its discovery it was the intrinsically brightest object found in the Solar System since Pluto in 1930. In 2004, the discoverers placed an upper limit of 1,800 km on its diameter,[39] but by 2007 this was revised downward to less than 1,600 km after observation by the Spitzer Space Telescope.[40] In 2012, measurements from the Herschel Space Observatory suggested that Sedna’s diameter was 995 ± 80 km, which would make it smaller than Pluto’s moon Charon.[10] Australian observations of a stellar occultation by Sedna on 13 January 2013 produced similar results on its diameter, giving chord lengths 1025±135 km and 1305±565 km.[11]
Because Sedna has no known moons, determining its mass is currently impossible without sending a space probe. Sedna is currently the largest trans-Neptunian Sun-orbiting object not known to have a satellite.[41] Only a single attempt has been made to find a satellite,[42][43] and it has been suggested that there is a chance of up to 25% that a satellite could have been missed.[44][45]
Observations from the SMARTS telescope show that in visible light Sedna is one of the reddest objects in the Solar System, nearly as red as Mars.[25] Chad Trujillo and his colleagues suggest that Sedna’s dark red colour is caused by a surface coating of hydrocarbon sludge, or tholin, formed from simpler organic compounds after long exposure to ultraviolet radiation.[46] Its surface is homogeneous in colour and spectrum; this may be because Sedna, unlike objects nearer the Sun, is rarely impacted by other bodies, which would expose bright patches of fresh icy material like that on 8405 Asbolus.[46] Sedna and two other very distant objects – 2006 SQ372 and (87269) 2000 OO67 – share their color with outer classical Kuiper belt objects and the centaur 5145 Pholus, suggesting a similar region of origin.
Trujillo and colleagues have placed upper limits in Sedna’s surface composition of 60% for methane ice and 70% for water ice.[46] The presence of methane further supports the existence of tholins on Sedna’s surface, because they are produced by irradiation of methane.[48] Barucci and colleagues compared Sedna’s spectrum with that of Triton and detected weak absorption bands belonging to methane and nitrogen ices. From these observations, they suggested the following model of the surface: 24% Triton-type tholins, 7% amorphous carbon, 10% nitrogen ices, 26% methanol, and 33% methane.[49] The detection of methane and water ices was confirmed in 2006 by the Spitzer Space Telescope mid-infrared photometry.[48] The presence of nitrogen on the surface suggests the possibility that, at least for a short time, Sedna may have a tenuous atmosphere. During a 200-year period near perihelion, the maximum temperature on Sedna should exceed 35.6 K (−237.6 °C), the transition temperature between alpha-phase solid N2 and the beta-phase seen on Triton. At 38 K, the N2 vapor pressure would be 14 microbar (1.4 Pa or 0.000014 atm).[49] Its deep red spectral slope is indicative of high concentrations of organic material on its surface, and its weak methane absorption bands indicate that methane on Sedna’s surface is ancient, rather than freshly deposited. This means that Sedna is too cold for methane to evaporate from its surface and then fall back as snow, which happens on Triton and probably on Pluto.[48]
Models of internal heating via radioactive decay suggest that Sedna might be capable of supporting a subsurface ocean of liquid water.
In their paper announcing the discovery of Sedna, Mike Brown and his colleagues described it as the first observed body belonging to the Oort cloud, the hypothetical cloud of comets thought to exist nearly a light-year from the Sun. They observed that, unlike scattered disc objects such as Eris, Sedna’s perihelion (76 AU) is too distant for it to have been scattered by the gravitational influence of Neptune.[20] 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 described 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.[51][52]
If Sedna formed in its current location, the Sun’s original protoplanetary disc must have extended as far as 75 AU into space.[53] Also, Sedna’s initial orbit must have been approximately circular, otherwise its formation by the accretion of smaller bodies into a whole would not have been possible, because the large relative velocities between planetesimals would have been too disruptive. Therefore, it must have been tugged into its current eccentric orbit by a gravitational interaction with another body.[54] In their initial paper, Brown, Rabinowitz and colleagues suggested three possible candidates for the perturbing body: an unseen planet beyond the Kuiper belt, a single passing star, or one of the young stars embedded with the Sun in the stellar cluster in which it formed.[20]
Mike Brown and his team favored the hypothesis that Sedna was lifted into its current orbit by a star from the Sun’s birth cluster, arguing that Sedna’s aphelion of about 1,000 AU, which is relatively close compared to those of long-period comets, is not distant enough to be affected by passing stars at their current distances from the Sun. They propose that Sedna’s orbit is best explained by the Sun having formed in an open cluster of several stars that gradually disassociated over time.[20][55][56] That hypothesis has also been advanced by both Alessandro Morbidelli and Scott Jay Kenyon.[57][58] Computer simulations by Julio A. Fernandez and Adrian Brunini suggest that multiple close passes by young stars in such a cluster would pull many objects into Sedna-like orbits.[20] A study by Morbidelli and Levison suggested that the most likely explanation for Sedna’s orbit was that it had been perturbed by a close (approximately 800 AU) pass by another star in the first 100 million years or so of the Solar System’s existence.
The trans-Neptunian planet hypothesis has been advanced in several forms by a number of astronomers, including Rodney Gomes and Patryk Lykawka. One scenario involves perturbations of Sedna’s orbit by a hypothetical planetary-sized body in the Hills cloud. Recent simulations show that Sedna’s orbital traits could be explained by perturbations by a Neptune-mass object at 2,000 AU (or less), a Jupiter-mass (MJ) object at 5,000 AU, or even an Earth-mass object at 1,000 AU.[56][60] Computer simulations by Patryk Lykawka have suggested that Sedna’s orbit may have been caused by a body roughly the size of Earth, ejected outward by Neptune early in the Solar System’s formation and currently in an elongated orbit between 80 and 170 AU from the Sun.[61] Mike Brown’s various sky surveys have not detected any Earth-sized objects out to a distance of about 100 AU. It is possible that such an object may have been scattered out of the Solar System after the formation of the inner Oort cloud.[62]
Caltech researchers Konstantin Batygin and Mike Brown have hypothesised the existence of a giant planet in the outer Solar System, nicknamed Planet Nine. The planet would be about 10 times as massive as Earth. It would have a highly eccentric orbit, and its average distance from the Sun would be about 20 times that of Neptune (which orbits at an average distance of 30.1 astronomical units (4.50×109 km)). Its orbital period would be 10,000 to 20,000 years. The planet’s existence was hypothesised using mathematical modeling and computer simulations, but it has not been observed directly. It may explain the orbits of a group of objects that includes Sedna.
It has been suggested that Sedna’s orbit is the result of influence by a large binary companion to the Sun, thousands of AU distant. One such hypothetical companion is Nemesis, a dim companion to the Sun that has been proposed to be responsible for the supposed periodicity of mass extinctions on Earth from cometary impacts, the lunar impact record, and the common orbital elements of a number of long-period comets.[60][64] No direct evidence of Nemesis has been found, and many lines of evidence (such as crater counts) have thrown its existence into doubt.[65][66] John J. Matese and Daniel P. Whitmire, longtime proponents of the possibility of a wide binary companion to the Sun, have suggested that an object of 5 MJ lying at roughly 7,850 AU from the Sun could produce a body in Sedna’s orbit.[67]
Morbidelli and Kenyon have also suggested that Sedna did not originate in the Solar System, but was captured by the Sun from a passing extrasolar planetary system, specifically that of a brown dwarf about 1/20th the mass of the Sun (M☉)[57][58][68] or a main-sequence star 80 percent more massive than our Sun, which, owing to its larger mass, may now be a white dwarf. In either case, the stellar encounter had likely occurred early after the Sun’s formation, about less than 100 million years after the Sun had formed.[57][69][70] Stellar encounters during this time would have minimal effect on the Oort cloud’s final mass and population since the Sun had excess material for replenishing the Oort cloud population.
Sedna’s highly elliptical orbit means that the probability of its detection was roughly 1 in 80, which suggests that, unless its discovery was a fluke, another 40–120 Sedna-sized objects would exist within the same region.[20][38] Another object, 2000 CR105, has a similar but less extreme orbit: it has a perihelion of 44.3 AU, an aphelion of 394 AU, and an orbital period of 3,240 years. It may have been affected by the same processes as Sedna.[57]
Each of the proposed mechanisms for Sedna’s extreme orbit would leave a distinct mark on the structure and dynamics of any wider population. If a trans-Neptunian planet was responsible, all such objects would share roughly the same perihelion (about 80 AU). If Sedna were captured from another planetary system that rotated in the same direction as the Solar System, then all of its population would have orbits on relatively low inclinations and have semi-major axes ranging from 100 to 500 AU. If it rotated in the opposite direction, then two populations would form, one with low and one with high inclinations. The perturbations from passing stars would produce a wide variety of perihelia and inclinations, each dependent on the number and angle of such encounters.[62]
Acquiring a larger sample of such objects would help in determining which scenario is most likely.[71] “I call Sedna a fossil record of the earliest Solar System”, said Brown in 2006. “Eventually, when other fossil records are found, Sedna will help tell us how the Sun formed and the number of stars that were close to the Sun when it formed.”[18] A 2007–2008 survey by Brown, Rabinowitz and Megan Schwamb attempted to locate another member of Sedna’s hypothetical population. Although the survey was sensitive to movement out to 1,000 AU and discovered the likely dwarf planet Gonggong, it detected no new sednoid.[71] Subsequent simulations incorporating the new data suggested about 40 Sedna-sized objects probably exist in this region, with the brightest being about Eris’s magnitude (−1.0).
The Minor Planet Center, which officially catalogs the objects in the Solar System, classifies Sedna as a scattered object.[76] This grouping is heavily questioned, and many astronomers have suggested that it, together with a few other objects (e.g. 2000 CR105), be placed in a new category of distant objects named extended scattered disc objects (E-SDO),[77] detached objects,[78] distant detached objects (DDO),[60] or scattered-extended in the formal classification by the Deep Ecliptic Survey.[79]
The discovery of Sedna resurrected the question of which astronomical objects should be considered planets and which should not. On 15 March 2004, articles on Sedna in the popular press reported that a tenth planet had been discovered. This question was answered under the International Astronomical Union definition of a planet, adopted on 24 August 2006, which mandated that a planet must have cleared the neighborhood around its orbit. Sedna has a Stern–Levison parameter estimated to be much less than 1,[d] and therefore cannot be considered to have cleared the neighborhood, even though no other objects have yet been discovered in its vicinity. To be a dwarf planet, Sedna must be in hydrostatic equilibrium. It is bright enough, and therefore large enough, that this is expected to be the case,[81] and several astronomers have called it one.
Sedna will come to perihelion around July 2076.[9][b] This close approach to the Sun provides an opportunity for study that will not occur again for 12,000 years. Although Sedna is listed on NASA’s Solar System exploration website,[87] NASA is not known to be considering any type of mission at this time.[88] It was calculated that a flyby mission to Sedna could take 24.48 years using a Jupiter gravity assist, based on launch dates of 6 May 2033 or 23 June 2046. Sedna would be 77.27 or 76.43 AU from the Sun when the spacecraft arrived near the end of 2057 or 2070, respectively.[89]
In May 2018, astrophysicist Ethan Siegel publicly advocated for a space probe mission to study Sedna as it approaches perihelion. Siegel characterized Sedna as an attractive target due to its status as a possible inner Oort cloud object. Because of Sedna’s long orbital period, “we will not get the opportunity to study it this close to the Sun for many millennia again.”[90] Such a mission could be facilitated by Dual-Stage 4-Grid ion thrusters that might cut cruise times considerably if powered, for example, by a fusion reactor.
More than one version of the Sedna legend exists. Some legends have her as the daughter of a goddess named Isarrataitsoq, while others only mention her father.[3]
In one legend Sedna is a giant, the daughter of the creator-god Anguta, with a great hunger that causes her to attack her parents. Angered, Anguta takes her out to sea and throws her over the side of his kayak. As she clings to the sides, he chops off her fingers and she sinks to the underworld, becoming the ruler of the monsters of the deep. Her huge fingers become the seals, walruses, and whales hunted by the Inuit.[4]
In another version of the legend, she is dissatisfied with men found for her by her father and so marries a dog. Her father is so angry at this that he throws her into the sea and, when she tries to climb back into the boat, he cuts off her fingers. Her fingers become the first seals and she becomes a mighty sea goddess.[2] When she is angered, the shaman travels to wash and comb her hair for her, after which she is placated and releases the animals to the hunters.[5] In other versions, she’s unable to comb her hair because she lacks fingers, so a shaman must brush it for her.[6]
In the Netsilik region, the story states that Nuliayuk was a mistreated orphan. One day the people tried to get rid of her by attempting to drown her by chopping off her fingertips. But the fingertips would transform into seals and walruses..[7] Eventually, Nuliayuk marries a sculpin and lives in the sea controlling all sea mammals.
Other versions of the legend depict Sedna as a beautiful maiden who rejects marriage proposals from the hunters of her village. When an unknown hunter appears, Sedna’s father agrees to give her to him as wife in return for fish. Sedna’s father gives Sedna a sleeping potion and gives her to the hunter who takes her to a large nest on a cliff, revealing his true form: a great bird-spirit (variously described as a raven, a fulmar or a Kokksaut/petrel-spirit). She wakes surrounded by birds. Her father attempts to rescue her, but the bird-spirit becomes angry, causing a great storm. In desperation, Sedna’s father throws her into the raging sea. Attempting to cling to the kayak, her hands freeze and her fingers fall off becoming the creatures of the sea. She falls to the bottom of the sea and grows a fishtail.
Sedna is kidnapped or deceived by a different bird creature in yet another version. Her father then leaves in his kayak to rescue her from the floating ice-island where she is imprisoned while the bird creature is away. The creature, enraged by her disappearance, calls to a spirit of the sea to help him. The sea spirit locates the kayak with the two humans aboard and creates huge waves to kill them. Her father throws Sedna overboard in the hope that this will appease the angry god. Sedna clings to the kayak but her father grabs a little ax and chops three of her fingers off before striking her on the head. The three fingers each become a different species of seal. The stroke to her head sends Sedna to the ocean floor where she resides, commanding the animals of the sea..[8]
In one Baffin Island tradition, Sedna was in a kayak with her family when a storm started. Her parents thought she was to blame for the storm and threw her into the sea. She clung to the kayak, but her father cut her fingers off: first the tips, then the second knuckle, then the last knuckle. Her disembodied fingers turned into sea creatures. Sedna gained control over the animals. If humans angered her, she could stop the animals from coming to their hunting sites, thus causing famine.[9]
The varying legends each give different rationales for Sedna’s death. Yet, in each version, her father takes her to sea in his kayak, chopping off her fingers.[10] In each version she sinks to the bottom of the sea, worshiped by hunters who depend on her goodwill to supply food. She is generally considered a vengeful goddess, and hunters must placate and pray to her to release the sea animals from the ocean depths for their hunt.[11] At Killiniq, people threw worn-out harpoon-heads, broken knives, and morsels of meat and bone into the sea as offerings.
Sedna was first manufactured by Snaed Manufacturing Company (later Deans, Logan & Co. Ltd.), of 16 Commercial Court, Belfast, and went on sale in 1897.[1] In 1898 the company had secured 10 outlets, which had grown to 100 in 1899.[2]
It has been suggested the brand name was chosen as “Andes” (source of the coca extract) spelled backwards,[3] but it may be significant that both “Sedna” and “Snaed” are anagrams of “Deans”. Alex Deans was a principal of the company, and uncle of George Deans (1875–1938), head of Charles Moore and Co.‘s Perth, Western Australia, emporium.[4]
The company was in the hands of a liquidator in 1932.
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Sedna was from 1908 imported into Australia and marketed by the Seppelts wine company.[6] The trade ran both ways – Deans and Logan marketed Australian wines in Britain.[4]
In New Zealand it was classed as a “tonic” and only sold in chemist’s shops,[7] while in Australia it was classed as an alcoholic beverage and legally sold only in licensed premises. In 1920 two Rundle Street, Adelaide businesses were fined for selling the product: Foy & Gibson (a major department store), and Birks Chemists.[8] Chemists in country areas were convicted of sale of Sedna and Maltox (a similar product made by Bickford’s), evidence being produced by police “sting operations“.[9]
Outrageous behaviour by persons who became inebriated on the tonic has been ascribed to the cocaine and caffeine content of Sedna.[10] After 1923[11] advertisements no longer mentioned coca and beef in advertisements for the product, kola remaining an essential ingredient.
At some stage Sedna sold in Australia was locally produced by the Seppeltsfield company, and it is likely but by no means certain that Seppelts purchased rights to the brand name from Deans & Logan’s liquidators c. 1932. Later bottles are clearly marked “PRODUCE OF AUSTRALIA”, and the product has been identified by wine writer Philip White as based on Grenache port from the Para vineyard.[3] It was sold in 750ml bottles and had an alcoholic content 33% proof. It has been reported as containing 15 grains per fluid ounce (around 30g/litre) of kola nut powder,[12] perhaps 60 mg/100 ml of caffeine. (Red Bull contains 32 mg/100 ml).
Marketing of Sedna in Australia ceased some time after 1950. Early postcards advertising the product appear to be quite collectible and are advertised for sale at prices between $50 and $100.[13] It has no connection to the wine made in the Napa Valley AVA or the vodka made in Newfoundland.
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