90377 Sedna

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90377 Sedna
Sedna, highlighted by the green circle
Discovery[1]
Discovered byM. Brown,
C. Trujillo,
D. Rabinowitz
Discovery dateNovember 14, 2003
Designations
Designation
90377 Sedna
Pronunciation/ˈsɛdnə/ SED-nə
Named after
Sedna
2003 VB12
Trans-Neptunian object
detached object[2]
Orbital characteristics[2]
Epoch September 26, 1990 (JD 2 448 160.5)
Aphelion1.459×1014 m (975.56 AU)
Perihelion1.139 3×1013 m (76.156 AU)
7.866 8×1013 m (525.86 AU)
Eccentricity0.855
around 4,404,480 d (12,059.06 a)
1.04 km/s
357.457°
Inclination11.934°
144.514°
311.123°
Physical characteristics
Dimensions1,200–1,600 km[3]
<1,600 km[4]
Mass8.3×1020–7.0×1021 kg[5]
(0.05–0.42 Eris)
Mean density
2.0? g/cm³
0.33–0.50 m/s²
0.62–0.95 km/s
0.42 d (10 h) 1
Albedo0.16–0.30[3]
Temperature~12 K (see note w here)
Spectral type
(red) B-V=1.24; V-R=0.78[6]
21.1[7]
20.4 (Perihelic)[8]
1.56[9]

90377 Sedna is a trans-Neptunian object and likely dwarf planet discovered by Michael Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale University) on November 14, 2003. It is currently 88 AU from the Sun,[7] about three times as distant as Neptune. For most of its orbit Sedna is farther from the Sun than any other known dwarf planet candidate. Eris, the largest known dwarf planet, is currently farther from the Sun than Sedna, though it is near its aphelion, or maximum distance from the Sun, while Sedna is nearing its perihelion, or minimum distance.

Sedna's exceptionally long and elongated orbit, taking roughly 12,000 years to complete, and distant perihelion (76 AU) have led to much speculation as to 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, Sedna never comes close enough to Neptune to be affected by its gravity, leading some astronomers to conclude that it is in fact the first known member of the inner Oort cloud. Mike Brown claims that Sedna is the most scientifically important new object yet discovered in the regions beyond Neptune, as understanding its peculiar orbit is likely to yield valuable information about the origin and early evolution of the Solar System.[10]

Discovery and naming

Sedna (provisionally designated 2003 VB12) was discovered during a survey conducted with the Samuel Oschin telescope at Palomar Observatory near San Diego, California (USA) using Yale's 160 megapixel Palomar Quest camera and was observed within days on telescopes from Chile, Spain, and the USA (Arizona, and Hawaii). NASA's orbiting Spitzer Space Telescope was later pointed toward the object, putting an upper-bound on its diameter at roughly three-quarters that of Pluto (less than 1,600 km).[4]

Due to the object's undoubtedly frigid surface temperatures, the team named it after Sedna, the Inuit goddess of the sea, who was believed to live in the cold depths of the Arctic Ocean. Brown also suggested to the IAU that any future objects discovered in Sedna's orbit should also be named from Inuit mythologies.[11] The team's decision to name the object "Sedna" was made public before it had been submitted to the International Astronomical Union's Minor Planet Center for official consideration. Brian Marsden, the head of the Minor Planet Center, complained that such an action was a violation of protocol, and that some members of the IAU might vote against it.[12] The name was, however, officially adopted later that year.

Orbit and rotation

Sedna has a highly elliptical orbit, with its aphelion estimated at 975 AU and its perihelion at about 76.16 AU. At its discovery it was approaching perihelion and about 89.6 AU from the Sun. At the time of its discovery it was the most distant object in the Solar System yet observed; although the orbits of some objects—like long-period comets—extend farther than that of Sedna, they are basically too dim to be observed except near perihelion. Eris was later detected at 97 AU.

Panels showing the location of Sedna in relation to other astronomical objects.

Sedna's precise orbital period is not yet known, but it is calculated at between 10,500 and 12,000 years for a single orbit around the Sun. It should reach perihelion in late 2075[2][13] to mid 2076.[8] Sedna will overtake Eris as the farthest now-known spheroid orbiting the Sun in 2114.[8]

When first discovered, Sedna was believed to have an unusually long rotational period (20 to 50 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.[14]

Physical characteristics

Artist's impression of 90377 Sedna.

Sedna has an absolute magnitude (H) of 1.6,[9] and it is estimated to have an albedo of 0.16 to 0.30,[3] thus giving it a diameter between 1,200 and 1,600 km.[3] At the time of its discovery it was the largest object found in the Solar System since the discovery of Pluto in 1930. It is now generally believed to be the fifth largest known trans-Neptunian object after Eris, Pluto, Makemake, and Haumea.[3][15] In 2004, the discoverers placed an upper limit of 1,800 kilometers on its diameter,[16] but by 2007 it was revised downward to being less than 1,600 km after observations from the Spitzer Space Telescope.[4]

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 colour is caused by a hydrocarbon sludge, or tholin, like that found on 5145 Pholus.[17] 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 like that on 8405 Asbolus.[18]

In 2005, astronomers compared Sedna's spectrum with that of Triton, and suggested the following common model of the surface: 24% Triton-type tholins, 7% amorphous carbon, 26% methanol ice with 33% methane.[19]

Although Sedna's 200-year perihelion period may allow its surface temperature to rise above the 35.6 K (−237.4°C or −395.3°F) boundary required for nitrogen to shift from solid to gas,[19] its deep red spectrum, indicative of high concentrations of organic material, and weak methane absorption bands suggest that, unlike similar large objects like Triton or Pluto, Sedna never forms an atmosphere.[20]

Amateur astronomers using advanced software and long exposures have been able to detect Sedna.[21]

Origin

EarthMoonCharonCharonNixNixKerberosKerberosStyxStyxHydraHydraPlutoPlutoDysnomiaDysnomiaErisErisNamakaNamakaHi'iakaHi'iakaHaumeaHaumeaMakemakeMakemakeMK2MK2XiangliuXiangliuGonggongGonggongWeywotWeywotQuaoarQuaoarSednaSednaVanthVanthOrcusOrcusActaeaActaeaSalaciaSalacia2002 MS42002 MS4File:10 Largest Trans-Neptunian objects (TNOS).png
Artistic comparison of Pluto, Eris, Makemake, Haumea, Gonggong (2007 OR10), Sedna, Quaoar, Orcus, 2002 MS4, and Salacia.

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, saying that, unlike scattered disc objects such as Eris, its perhihelion (78 AU) is too distant for it to have been scattered by the gravitational influence of Neptune.[22] 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.[23][24]

If Sedna formed in its current location, its orbit must originally have been circular; otherwise accretion (the coalescence of smaller bodies into a larger one) would not have been possible because the large relative velocities between planetesimals would have been too disruptive, and so it must have been tugged out of its original orbit into its current eccentricity.[25] Brown, Rabinowitz et al. suggested three possible gravitational causes for Sedna's orbit: 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.[22] These remain the most widely accepted hypotheses among astronomers today.

The passing star hypothesis has been advanced by both Alessandro Morbidelli and Scott J. Kenyon.[26][27] A study by Morbidelli and Hal Levison suggested that the most likely explanation for Sedna's orbit was that it had been perturbed by a close (~800 AU) 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.[26][28]

Brown and his team considered the possibility that Sedna's orbit resulted from the Sun's formation in an open cluster which gradually disassociated over time[29] to be the most likely of the three proposed scenarios.[22] 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.[22]

The trans-Neptunian planet hypothesis has been advanced in several forms by a number of astronomers, including Gomes and Patryk Lakawka. One scenario involves perturbations of Sedna's orbit by a hypothetical planetary-sized body in the inner Oort cloud. Recent simulations show that Sedna's orbital characteristics could be explained by perturbations by a Neptune-mass object at 2000 AU (or less), a Jupiter-mass at 5000 AU, or even an Earth-mass object at 1000 AU.[30][29] Computer simulations by Patryk Lakawka 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.[31] It has also been proposed that Sedna's orbit is the result of influence by and in resonance with Nemesis, a theorized dim companion to the Sun which has been proposed to be responsible for the 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.[30][32]

Morbidelli and Kenyon have even suggested that Sedna may not have originated in our Solar System at all, but instead was captured by the Sun from a passing star, specifically a brown dwarf about 20 times less massive than the Sun.[26]

Population

Sedna's extremely elliptical orbit meant that the probability of its detection was roughly one in 60, suggesting that, unless its discovery was a fluke, another 40–160 Sedna-sized objects should exist within its region.[33] Another object, 2000 CR105, has an orbit similar to Sedna's but a bit less extreme: perihelion is 44.3 AU, aphelion is 394 AU, and the orbital period is 3240 years. Its orbit may have resulted from the same processes that produced Sedna's orbit.[26] The structure and dynamics of this region may reveal clues as to the origin of Sedna-like objects. 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 1000 AU and discovered the large and distant object 2007 OR10, it detected no new bodies in Sedna-like orbits.[34] Subsequent simulations incorporating the new data suggested that a total of ~40 Sedna-sized objects probably exist in this region.[34]

Classification

The Minor Planet Center, which officially catalogs the objects in the Solar System, classifies Sedna as a scattered object.[35] However, 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 (E-SDO),[36] detached objects,[37] distant detached objects (DDO)[30] or scattered-extended in the formal classification by the Deep Ecliptic Survey.[38]

The last classification, introduces a formal distinction between scattered-near objects (which could be scattered by Neptune) such as Eris from scattered-extended objects like Sedna. The distinction is made formally, using the orbital elements (see Tisserand's parameter).

The discovery of Sedna 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 a tenth planet had been discovered. This question was answered under the new International Astronomical Union definition of a planet, adopted on August 24, 2006. It is unknown whether or not Sedna is in hydrostatic equilibrium. If, as currently suspected,[39] it is, then it would qualify as a dwarf planet. Sedna has a Stern–Levison parameter estimated at between 8×10−5 and 6×10−3 times that of Pluto,[40] and therefore cannot be considered to have cleared the neighborhood of its orbit, even though no other objects have yet been discovered in its vicinity.

Exploration

Sedna's perihelion will be reached within this century, after which it will move back out and farther away from the Sun again for another estimated 12 thousand years. Though an exploration target within the Solar System,[41] NASA is not considering any type of mission at this time.

See also

References

  1. ^ "Discovery Circumstances: Numbered Minor Planets (90001)-(95000)". IAU: Minor Planet Center. Retrieved 2008-07-23.
  2. ^ a b c Buie, Marc W. (2007-08-13). "Orbit Fit and Astrometric record for 90377". Deep Ecliptic Survey. Retrieved 2006-01-17.
  3. ^ a b c d e Brown, Michael E. "The largest Kuiper belt objects" (PDF). CalTech. Retrieved 2008-09-19.
  4. ^ a b c Stansberry, John (2007). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope". University of Arizona, Lowell Observatory, California Institute of Technology, NASA Ames Research Center, Southwest Research Institute, Cornell University. Retrieved 2008-07-27. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help) Cite error: The named reference "spitzer" was defined multiple times with different content (see the help page).
  5. ^ Radius of 590 km and density of 0.97 = 8.3×1020 kg mass. Radius of 900 km and density of 2.3 = 7.0×1021 kg mass
  6. ^ Tegler, Stephen C. (2006-01-26). "Kuiper Belt Object Magnitudes and Surface Colors". Retrieved 2006-11-05.
  7. ^ a b "AstDys (90377) Sedna Ephemerides". Department of Mathematics, University of Pisa, Italy. Retrieved 2009-03-16.
  8. ^ a b c "Horizons Output for Sedna 2076/2114". Retrieved 2007-11-19. Horizons
  9. ^ a b "JPL Small-Body Database Browser: 90377 Sedna (2003 VB12)". 2007-11-08 last obs. Retrieved 2008-06-11. {{cite web}}: Check date values in: |date= (help)
  10. ^ Cal Fussman (2006). "The Man Who Finds Planets". discover magazine. Retrieved 2010-05-22.
  11. ^ Mike Brown. "Mike Brown: Sedna". Caltech. Retrieved 2010-05-22.
  12. ^ Duncan Walker (2004). "How do planets get their names?". BBC News. Retrieved 2010-05-22.
  13. ^ Lowell DES Perihelion Epoch = 2000.0 + (2479283.2278 − 2451545.0)/365.25 = 2075.9431 = (2076-1-1 - 20.7768 days) = 2075-12-11 (Julian Date Converter)
  14. ^ Gaudi, B. Scott (2005). "On the Rotation Period of (90377) Sedna". Astrophys.J. 629: L49–L52. doi:10.1086/444355. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  15. ^ D. L. Rabinowitz (2006). "Photometric Observations Constraining the Size, Shape, and Albedo of 2003 EL61, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt". The Astrophysical Journal. 639 (2): 1238–1251. doi:10.1086/499575. {{cite journal}}: |format= requires |url= (help); External link in |format= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  16. ^ W. M. Grundy, K. S. Noll, D. C. Stephens. "Diverse Albedos of Small Trans-Neptunian Objects". Lowell Observatory, Space Telescope Science Institute. Retrieved 2007-03-26.{{cite web}}: CS1 maint: multiple names: authors list (link)
  17. ^ McKee, Maggie (2005). "Distant planetoid Sedna gives up more secrets". NewScientist.com news service. Retrieved 2005-03-05.
  18. ^ Alexander, Amir (2005). "Sedna: Mysterious Planetoid Slowly Yielding Up Its Secrets". The Planetary Society. Retrieved 2006-09-15. {{cite web}}: Unknown parameter |month= ignored (help)
  19. ^ a b Barucci, M. A. (2005). "Is Sedna another Triton?". Astronomy & Astrophysics. 439: L1–L4. doi:10.1051/0004-6361:200500144. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  20. ^ J. P. Emery, C. M. Dalle Ore, D. P. Cruikshank; et al. (2007). "Ices on 90377 Sedna: Conformation and compositional constraints". Astronomy and Astrophysics. 406: 395–398. Retrieved 2010-06-14. {{cite journal}}: Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)
  21. ^ RickJ. "1.5 hour exposure of Sedna (apmag 21) and UGC 2712 (apmag 17)". Bad Astronomy and Universe Today Forum. Retrieved 2009-08-01.
  22. ^ a b c d Mike Brown, David Rabinowitz, Chad Trujillo (2004). "Discovery of a Candidate Inner Oort Cloud Planetoid" (PDF). Astrophysical Journal. Retrieved 2010-07-16. {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: multiple names: authors list (link)
  23. ^ Jewitt, David, Morbidelli, Alessandro, & Rauer, Heike. (2007). Trans-Neptunian Objects and Comets: Saas-Fee Advanced Course 35. Swiss Society for Astrophysics and Astronomy. Berlin: Springer. ISBN 3540719571.
  24. ^ Lykawka, Patryk Sofia & Mukai, Tadashi. (2007). Dynamical classification of trans-neptunian objects: Probing their origin, evolution, and interrelation. Icarus Volume 189, Issue 1, July , Pages 213–232. doi:10.1016/j.icarus.2007.01.001.
  25. ^ Scott S. Sheppard (2005). "Small Bodies in the Outer Solar System" (PDF). Frank N. Bash Symposium. The University of Texas at Austin. Retrieved 2008-03-25. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  26. ^ a b c d Morbidelli, Alessandro (2004). "Scenarios for the Origin of the Orbits of the Trans-Neptunian Objects 2000 CR105 and 2003 VB12 (Sedna)". The Astronomical Journal. 128: 2564–2576. doi:10.1086/424617. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help) (Original Preprint)
  27. ^ Kenyon, Scott J. (2004). "Stellar encounters as the origin of distant Solar System objects in highly eccentric orbits". Nature. 432 (7017): 598–602. doi:10.1038/nature03136. PMID 15577903. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  28. ^ "The Challenge of Sedna". Harvard-Smithsonian Center for Astrophysics. Retrieved 2009-03-26.
  29. ^ a b "Transneptunian Object 90377 Sedna (formerly known as 2003 UB313)". The Planetary Society. Retrieved 2010-01-03.
  30. ^ a b c Gomes, Rodney S. (2006). "A distant planetary-mass solar companion may have produced distant detached objects". Icarus. 184: 589–601. doi:10.1016/j.icarus.2006.05.026. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help) Cite error: The named reference "Gomez 2006" was defined multiple times with different content (see the help page).
  31. ^ P. S. Lykawka and T. Mukai (2008). "An Outer Planet Beyond Pluto and the Origin of the Trans-Neptunian Belt Architecture". Astronomical Journal. 135: 1161. doi:10.1088/0004-6256/135/4/1161. arXiv:0712.2198.
  32. ^ Staff. "Evidence Mounts For Companion Star To Our Sun." SpaceDaily, April 25, 2006. Accessed November 27, 2009.
  33. ^ M. A. Barucci; et al., eds. (2008). "The Solar System Beyond Neptune". University of Arizona Press: 335. {{cite journal}}: Cite has empty unknown parameter: |1= (help); Cite journal requires |journal= (help); Explicit use of et al. in: |editor= (help); line feed character in |publisher= at position 22 (help)
  34. ^ a b Megan E. Schwamb ,Michael E. Brown, and David L. Rabinowitz (2009). "A Search for Distant Solar System Bodies in the Region of Sedna" (PDF). letters. Astrophysical Journal. Retrieved 2010-07-16. {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: multiple names: authors list (link)
  35. ^ IAU: Minor Planet Center (2008-07-02). "List Of Centaurs and Scattered-Disk Objects". Central Bureau for Astronomical Telegrams, Harvard-Smithsonian Center for Astrophysics. Retrieved 2008-07-02.
  36. ^ Evidence for an Extended Scattered Disk?
  37. ^ Jewitt, D., A. Delsanti, The Solar System Beyond The Planets in Solar System Update : Topical and Timely Reviews in Solar System Sciences , Springer-Praxis Ed., ISBN 3-540-26056-0 (2006) Preprint of the article (pdf)
  38. ^ Elliot, J. L., S. D. Kern, K. B. Clancy, A. A. S. Gulbis, R. L. Millis, M. W. Buie, L. H. Wasserman, E. I. Chiang, A. B. Jordan, D. E. Trilling, and K. J. Meech The Deep Ecliptic Survey: A Search for Kuiper Belt Objects and Centaurs. II. Dynamical Classification, the Kuiper Belt Plane, and the Core Population. The Astronomical Journal, 129 (2006), pp. preprint.
  39. ^ Brown, Michael E. "The Dwarf Planets". California Institute of Technology, Department of Geological Sciences. Retrieved 2008-02-16.
  40. ^ Stern–Levison parameter (using unlikely highest estimated mass) = ((7×1021) / (5.9736×1024))^2 / 12,059 yr = 1.14×10−10
    (Sedna 1.14×10−10) / (Pluto 1.95×10−8) = 5.8×10−3
  41. ^ "Solar System Exploration: Multimedia: Gallery". NASA. Retrieved 2010-01-03.

Bibliography

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