90377 Sedna

90377 Sedna
An image of Sedna seen through an Earth-based telescope: it is a faint point of light.
Discovery image of Sedna (identified by the yellow arrow)
Discovery[1]
Discovered by Michael E. Brown,
C. Trujillo,
D. Rabinowitz
Discovery date November 14, 2003
Designations
MPC designation 90377 Sedna
Pronunciation /ˈsɛdnə/ SED-nə
Named after Sedna
Alternate name(s) 2003 VB12
Minor planet
category		 Trans-Neptunian object
detached object[2]
Epoch 2010-Jul-23 (JD 2455400.5)
Aphelion 1.437 × 1014 m
(960.78 AU)
Perihelion 1.142 3 × 1013 m
(76.361 AU)
Semi-major axis 7.757 6×1013 m
(518.57 AU)
Eccentricity 0.8527
Orbital period around 4,313,319 d
(11,809 yr)
Average orbital speed 1.04 km/s
Mean anomaly 358.01°
Inclination 11.927°
Longitude of ascending node 144.26°
Argument of perihelion 311.02°
Physical characteristics
Dimensions 1,200–1,600 km[4]
<1,600 km[5]
Mass 1.8–4.3 x 1021 kg[a]
Mean density 2.0? g/cm³[a]
Equatorial surface gravity 0.33–0.50 m/s²
Escape velocity 0.62–0.95 km/s
Sidereal rotation
period		 0.42 d (10 h)[6][3]
Albedo 0.16–0.30[4]
Temperature ~12 K (see note w here)
Spectral type (red) B-V=1.24; V-R=0.78[7]
Apparent magnitude 21.1[8]
20.5 (Perihelic)[9]
Absolute magnitude (H) 1.58[3]

90377 Sedna is a trans-Neptunian object, discovered in 2003, which currently lies about three times as far from the Sun as Neptune. However, its farthest orbital distance from the Sun is estimated to be 960 astronomical units (AU), and thus it is, for the majority of its orbit, the most distant known object in the Solar System after long-period comets.[b]

Roughly two-thirds the size of Pluto, Sedna is hypothetically large enough to be rounded by its own gravity, and thus would qualify as a dwarf planet under current definitions. However, its distance from the Sun makes determining its shape difficult. Spectroscopy has revealed that Sedna's surface composition is very similar to that of other trans-Neptunian objects, being largely a mixture of various ices, including water, methane and nitrogen. Its surface is one of the reddest in the Solar System.

Sedna's exceptionally long and elongated orbit, taking approximately 12,000 years to complete, and distant point of closest approach to the Sun, at 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, this classification has been contested, as 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, 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 Mike Brown, who co-discovered Sedna, claims it is the most scientifically important trans-Neptunian object found to date, as understanding its peculiar orbit is likely to yield valuable information about the origin and early evolution of the Solar System.[10]

Contents

Discovery and naming

Sedna (provisionally designated 2003 VB12) was discovered by Mike Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale University) as part of a survey begun in 2001 with the Samuel Oschin telescope at Palomar Observatory near San Diego, California using Yale's 160 megapixel Palomar Quest camera. On November 14, 2003, an object was observed to move by 4.6 arcseconds over 3.1 hours relative to stars, which indicated that its distance was about 100 AU. Follow-up observations in November–December 2003 with the SMARTS telescope at the Cerro Tololo Inter-American Observatory in Chile as well as with the Tenagra IV telescope at the W. M. Keck Observatory in Hawaii revealed that the object was moving along a distant highly eccentric orbit. Later the object was identified on older precovery images made by the Samuel Oschin telescope as well on images from Near Earth Asteroid Tracking consortium. These previous positions expanded its known orbital arc and allowed a more precise calculation of its orbit.[11]

"Our newly discovered object is the coldest most distant place known in the Solar System," said Mike Brown on his website, "so we feel it is appropriate to name it in honour of Sedna, the Inuit goddess of the sea, who is thought to live at the bottom of the frigid Arctic Ocean."[12] Brown also suggested to the International Astronomical Union's (IAU) Minor Planet Center that any future objects discovered in Sedna's orbital region should also be named from Inuit mythologies.[12] The team made the name "Sedna" public before the object had been officially numbered.[13] 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.[14] However, no objection was raised as to the name itself, and no competing names were suggested. The IAU's Committee on Small Body Nomenclature formally accepted the name in September 2004,[15] and also considered that, in similar cases of extraordinary interest, it might in future allow names to be announced before they were officially numbered.[13]

Orbit and rotation

Barring comets, Sedna has the longest orbital period of any known object in the Solar System, calculated at between 11,800 and 12,100 years.[2] This represents a best-fit solution, as Sedna has only been observed over a brief part of its orbital arc. Its orbit is extremely elliptical, with an aphelion estimated at 960 AU and a perihelion at about 76 AU. At its discovery it was approaching perihelion at 89.6 AU[16] from the Sun, and was the most distant object in the Solar System yet observed. Eris was later detected by the same survey at 97 AU. Although the orbits of some long-period comets extend farther than that of Sedna, they are too dim to be discovered except when approaching perihelion in the inner Solar System. Even as Sedna nears its perihelion in late 2075[c] to mid 2076,[9] the Sun would appear merely as a bright star in its sky: with an angular diameter too small to resolve as a disc, it would be only 100 times brighter than a full Moon on Earth.[17]

When first discovered, Sedna was believed to have an unusually long rotational period (20 to 50 days).[17] It was initially speculated that Sedna's rotation was slowed by the gravitational pull of a large binary companion, similar to Pluto's moon Charon.[12] A search for such a satellite by the Hubble Space Telescope in March 2004 observed no such object orbiting the planetoid.[18][e] Subsequent measurements from the MMT telescope suggest a much shorter rotation period, only about 10 hours, rather typical for bodies of its size.[19]

Physical characteristics

Sedna, a red, icy globe, is barely lit by a distant Sun
Artist's impression of 90377 Sedna

Sedna has an absolute magnitude (H) of 1.6,[3] and it is estimated to have an albedo of 0.16 to 0.30,[4] thus giving it a diameter between 1,200 and 1,600 km.[4] At the time of its discovery it was the largest object found in the Solar System since the discovery of Pluto in 1930. Mike Brown and colleagues now believe it to be the fifth largest known trans-Neptunian object after Eris, Pluto, Makemake, and Haumea.[4][20] In 2004, the discoverers placed an upper limit of 1,800 kilometers on its diameter,[21] but by 2007 it was revised downward to being less than 1,600 km after observation by the Spitzer Space Telescope.[5] As Sedna has no known moons, determining its mass is very difficult. However, if the above estimates for its diameter are coupled with Pluto's density of 2.0 g/cm3, the resultant estimated mass range is 1.8–4.3 x 1021 kg.[a]

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.[12] Chad Trujillo and his colleagues suggest that Sedna's dark red colour is caused by a hydrocarbon sludge, or tholin, like that found on 5145 Pholus.[22] 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.[22] Sedna and two other very distant objects ((87269) 2000 OO67 and 2006 SQ372) share their colour with outer classical Kuiper belt objects, possibly suggesting a similar region of origin.[23]

Trujillo and colleagues have placed upper limits of 60% for methane ice in Sedna's surface composition and 70% for water ice.[22] The presence of methane further supports the existence of tholins on Sedna's surface, as they are produced by the action of irradiation on methane.[24] 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, 26% methanol and 33% methane.[25] The detection of methane and water ices was confirmed in 2006 by Spitzer Space Telescope mid-infrared photometry.[24] The presence of nitrogen on the surface suggests the possibility that, at least for a short time, Sedna may possess an atmosphere. A 200-year period exists around its perihelion during which Sedna's surface temperature may rise above the 35.6 K (−237.4°C) minimum required for nitrogen to shift from solid to gas.[25] However, 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 fallen. This means that Sedna is too cold for methane to evaporate from its surface and then fall back as snow, as happens on Triton and probably on Pluto.[24]

Origin

The orbit of Sedna lies well beyond these objects, and extends many times their distances from the Sun
The orbit of Sedna (red) set against the orbits of Jupiter (orange), Saturn (yellow), Uranus (green), Neptune (blue), and Pluto (purple)

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 believed 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.[11] 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.[26][27]

If Sedna formed in its current location, the Sun's original protoplanetary disc must have extended as far as 11 billion km into space.[28] Sedna's initial orbit must 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. Therefore, it must have been tugged out of its original orbit into its current eccentricity.[29] In their initial paper, Brown, Rabinowitz and colleagues 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.[11]

Mike Brown and his team favoured 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 1000 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's having formed in an open cluster of several stars that gradually disassociated over time.[30][11][31] That hypothesis has also been advanced by both Alessandro Morbidelli and Scott J. Kenyon.[32][33] 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.[11] 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 (approximately 800 AU) pass by another star in the first 100 million years or so of the Solar System's existence.[32][34]

The Earth Dysnomia Eris Charon Pluto Makemake Haumea Sedna Orcus Quaoar
Comparison of Eris, Pluto, Makemake, Haumea, Sedna, Orcus, 2007 OR10, Quaoar, and Earth (all to scale)

The trans-Neptunian planet hypothesis has been advanced in several forms by a number of astronomers, including Gomes and Patryk Lykawka. 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.[35][31] 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.[36] Mike Brown's various sky surveys have not detected any Earth-sized objects out to a distance of about 100 AU. However, it is possible that such an object may have been scattered out of the Solar System after the formation of the inner Oort cloud.[37]

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 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.[35][38] 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 five times the mass of Jupiter lying at roughly 7850 AU from the Sun could produce a body in Sedna's orbit.[39]

Morbidelli and Kenyon have suggested that Sedna may not have originated in our Solar System, but was captured by the Sun from a passing star, specifically a brown dwarf about 20 times less massive than the Sun.[32][33]

Population

the Sun appears merely as a point of light, distended by dust. The surface of Sedna is red ice, dimly glimmering in the noontime sunlight
Artist's conception of the Sun, as seen from Sedna

Sedna's highly 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.[4] Another object, 2000 CR105, has an orbit similar to Sedna's but less extreme: perihelion is 44.3 AU, aphelion is 394 AU, and the orbital period is 3240 years; it may have been affected by the same processes as Sedna.[32]

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 (~80 AU). If Sedna were captured from another star system that rotated in the same direction as the Solar System, then Sedna's population would all possess relatively low inclinations and range from 100–500 AU. If it rotated in the opposite direction, then two populations would form, one with low inclinations and one with high. The gravity of other stars would produce a wide range of perihelia and inclinations, each dependent on the number and angle of such encounters.[37]

Gaining a larger sample of such objects therefore could help in determining which scenario is most likely.[40] "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."[10] 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 dwarf planet candidate 2007 OR10, it detected no new bodies in Sedna-like orbits.[40] Subsequent simulations incorporating the new data suggested that a total of about 40 Sedna-sized objects probably exist in this region.[40]

Classification

The Minor Planet Center, which officially catalogs the objects in the Solar System, classifies Sedna as a scattered object.[41] 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 objects (E-SDO),[42] detached objects,[43] distant detached objects (DDO)[35] or scattered-extended in the formal classification by the Deep Ecliptic Survey.[44]

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, 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. It is unknown whether or not Sedna is in hydrostatic equilibrium. If it is, as is currently suspected,[45] then it would qualify as a dwarf planet, though the IAU's 2008 decree that only those TNOs with an absolute magnitude brighter than +1 be allowed into the category would appear to exclude Sedna for the time being.[46]

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 ~12,000 years. Though an exploration target within the Solar System,[47] NASA is not considering any type of mission at this time.

Notes

References

  1. ↑ "Discovery Circumstances: Numbered Minor Planets (90001)–(95000)". IAU: Minor Planet Center. http://www.cfa.harvard.edu/iau/lists/NumberedMPs090001.html. Retrieved 2008-07-23. 
  2. ↑ 2.0 2.1 Marc W. Buie (2009-11-22). "Orbit Fit and Astrometric record for 90377". Deep Ecliptic Survey. http://www.boulder.swri.edu/~buie/kbo/astrom/90377.html. Retrieved 2006-01-17. 
  3. ↑ 3.0 3.1 3.2 3.3 "JPL Small-Body Database Browser: 90377 Sedna (2003 VB12)". 2010-01-05 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Sedna. Retrieved 2008-06-11. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 Michael E. Brown. "The largest Kuiper belt objects". In M. Antonietta Barucci, Hermann Boehnhardt, Dale P. Cruikshank (pdf). The Solar System Beyond Neptune. University of Arizona press. pp. 335–345. ISBN 0816527555. http://www.gps.caltech.edu/~mbrown/papers/ps/kbochap.pdf. 
  5. ↑ 5.0 5.1 John Stansberry, Will Grundy, Mike Brown, Dale Cruikshank, John Spencer, David Trilling, Jean-Luc Margot (2008). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope". In M. Antonietta Barucci, Hermann Boehnhardt, Dale P. Cruikshank (pdf). The Solar System Beyond Neptune. University of Arizona press. pp. 161–179. arXiv:astro-ph/0702538v2. ISBN 0816527555. http://www.lpi.usra.edu/books/ssbn2008/7017.pdf. 
  6. ↑ "Case of Sedna's Missing Moon Solved". Harvard-Smithsonian Center for Astrophysics. 2005-04-05. http://www.cfa.harvard.edu/news/2005/pr200510.html. Retrieved 2005-04-07. 
  7. ↑ Stephen C. Tegler (2006-01-26). "Kuiper Belt Object Magnitudes and Surface Colors". Northern Arizona University. http://www.physics.nau.edu/~tegler/research/survey.htm. Retrieved 2006-11-05. 
  8. ↑ 8.0 8.1 "AstDys (90377) Sedna Ephemerides". Department of Mathematics, University of Pisa, Italy. http://hamilton.dm.unipi.it/astdys/index.php?pc=1.1.3.0&n=Sedna. Retrieved 2009-03-16. 
  9. ↑ 9.0 9.1 9.2 JPL Horizons On-Line Ephemeris System (2010-07-18). "Horizons Output for Sedna 2076/2114". http://home.comcast.net/~kpheider/Sedna2076.txt. Retrieved 2010-07-18.  Horizons
  10. ↑ 10.0 10.1 Cal Fussman (2006). "The Man Who Finds Planets". Discover. http://discovermagazine.com/2006/may/cover. Retrieved 2010-05-22. 
  11. ↑ 11.0 11.1 11.2 11.3 11.4 Mike Brown, David Rabinowitz, Chad Trujillo (2004). "Discovery of a Candidate Inner Oort Cloud Planetoid". Astrophysical Journal 617 (1): 645–649. doi:10.1086/422095. arXiv:astro-ph/0404456. http://adsabs.harvard.edu/abs/2004ApJ...617..645B. 
  12. ↑ 12.0 12.1 12.2 12.3 Mike Brown. "Sedna". CalTech. http://www.gps.caltech.edu/~mbrown/sedna/. Retrieved 2010-07-20. 
  13. ↑ 13.0 13.1 "MPEC 2004-S73 : Editorial Notice". IAU Minor Planet Center. 2004. http://www.cfa.harvard.edu/mpec/K04/K04S73.html. Retrieved 2010-07-18. 
  14. ↑ Duncan Walker (2004-03-16). "How do planets get their names?". BBC News. http://news.bbc.co.uk/1/hi/magazine/3515658.stm. Retrieved 2010-05-22. 
  15. ↑ "MPC 52733". Minor Planet Center. 2004. http://www.minorplanetcenter.org/iau/ECS/MPCArchive/2004/MPC_20040928.pdf. 
  16. ↑ "AstDys (90377) Sedna Ephemerides 2003-11-14". Department of Mathematics, University of Pisa, Italy. http://hamilton.dm.unipi.it/astdys/index.php?pc=1.1.3.1&n=90377&oc=500&y0=2003&m0=11&d0=14&h0=0&mi0=0&y1=2003&m1=11&d1=15&h1=0&mi1=0&ti=1.0&tiu=days. Retrieved 2008-05-05. 
  17. ↑ 17.0 17.1 "Hubble Observes Planetoid Sedna, Mystery Deepens". Hubblesite STScI-2004-14. 2004. http://hubblesite.org/newscenter/archive/releases/2004/14/image/e. Retrieved 2010-07-21. 
  18. ↑ "Hubble Observes Planetoid Sedna, Mystery Deepens". HubbleSite. 2004. http://hubblesite.org/newscenter/archive/releases/2004/14/. Retrieved 2010-08-30. 
  19. ↑ B. Scott Gaudi; Krzysztof Z. Stanek, Joel D. Hartman, Matthew J. Holman, Brian A. McLeod (CfA) (2005). "On the Rotation Period of (90377) Sedna". The Astrophysical Journal 629 (1): L49–L52. doi:10.1086/444355. arXiv:astro-ph/0503673. http://adsabs.harvard.edu/abs/2005ApJ...629L..49G. 
  20. ↑ David L. Rabinowitz, K. M. Barkume, Michael E. Brown, et al. (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. arXiv:astro-ph/0509401. http://adsabs.harvard.edu/abs/2006ApJ...639.1238R. 
  21. ↑ W. M. Grundy, K. S. Noll, D. C. Stephens. "Diverse Albedos of Small Trans-Neptunian Objects". Icarus 176: 184–191. doi:10.1016/j.icarus.2005.01.007. arXiv:astro-ph/0502229. http://adsabs.harvard.edu/abs/2005Icar..176..184G. 
  22. ↑ 22.0 22.1 22.2 Chadwick A. Trujillo, Michael E. Brown, David L. Rabinowitz, Thomas R. Geballe (2005). "Near Infrared Surface Properties of the Two Intrinsically Brightest Minor Planets (90377) Sedna and (90482) Orcus". The Astrophysical Journal 627 (2): 1057–1065. doi:10.1086/430337. arXiv:astro-ph/0504280. http://adsabs.harvard.edu/abs/2005ApJ...627.1057T. 
  23. ↑ Sheppard, Scott S. (2010). "The colors of extreme outer Solar System objects". The Astronomical Journal 139 (4): 1394–1405. doi:10.1088/0004-6256/139/4/1394. arXiv:1001.3674. http://adsabs.harvard.edu/abs/2010AJ....139.1394S. 
  24. ↑ 24.0 24.1 24.2 J. P. Emery, C. M. Dalle Ore, D. P. Cruikshank et al. (2007). "Ices on 90377 Sedna: Conformation and compositional constraints" (pdf). Astronomy and Astrophysics 406 (1): 395–398. doi:10.1051/0004-6361:20067021. http://giraffe.phy.nau.edu/~trilling/sedna.pdf. 
  25. ↑ 25.0 25.1 M. A. Barucci, D. P. Cruikshank, E. Dotto, et al. (2005). "Is Sedna another Triton?". Astronomy & Astrophysics 439 (2): L1–L4. doi:10.1051/0004-6361:200500144. http://adsabs.harvard.edu/abs/2005A%26A...439L...1B. 
  26. ↑ David Jewitt, Alessandro Morbidelli, Heike Rauer (2007). Trans-Neptunian Objects and Comets: Saas-Fee Advanced Course 35. Swiss Society for Astrophysics and Astronomy. Berlin: Springer. p. 86. arXiv:astro-ph/0512256v1. ISBN 3540719571. 
  27. ↑ Lykawka, Patryk Sofia; Mukai, Tadashi (2007). "Dynamical classification of trans-neptunian objects: Probing their origin, evolution, and interrelation". Icarus 189 (1): 213–232. doi:10.1016/j.icarus.2007.01.001. http://adsabs.harvard.edu/abs/2007Icar..189..213L. 
  28. ↑ S. Alan Stern (2005). Regarding the accretion of 2003 VB12 (Sedna) and like bodies in distant heliocentric orbits. 129. Astronomical Journal. pp. 526-529. http://iopscience.iop.org/1538-3881/129/1/526. Retrieved 2010-08-05. 
  29. ↑ Scott S. Sheppard, D. Jewitt (2005). "Small Bodies in the Outer Solar System" (PDF). Frank N. Bash Symposium. The University of Texas at Austin. http://www.dtm.ciw.edu/users/sheppard/pub/Sheppard06smallbodies.pdf. Retrieved 2008-03-25. 
  30. ↑ Mike Brown (2004). "Sedna and the birth of the solar system". Bulletin of the American Astronomical Society (American Astronomical Society Meeting 205) 36 (127.04): 1553. http://adsabs.harvard.edu/abs/2004AAS...20512704B. Retrieved 2010-08-05. 
  31. ↑ 31.0 31.1 "Transneptunian Object 90377 Sedna (formerly known as 2003 VB12)". The Planetary Society. http://www.planetary.org/explore/topics/our_solar_system/trans_neptunian_objects/sedna.html. Retrieved 2010-01-03. 
  32. ↑ 32.0 32.1 32.2 32.3 Alessandro Morbidelli, Harold F. Levison (2004). "Scenarios for the Origin of the Orbits of the Trans-Neptunian Objects 2000 CR105 and 2003 VB12 (Sedna)". The Astronomical Journal 128 (5): 2564–2576. doi:10.1086/424617. arXiv:astro-ph/0403358. http://adsabs.harvard.edu/abs/2004AJ....128.2564M. 
  33. ↑ 33.0 33.1 Scott J.Kenyon, Benjamin C. Bromley (2 December 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. http://arxiv.org/abs/astro-ph?papernum=0412030. 
  34. ↑ "The Challenge of Sedna". Harvard-Smithsonian Center for Astrophysics. http://www.cfa.harvard.edu/~kenyon/pf/sedna/. Retrieved 2009-03-26. 
  35. ↑ 35.0 35.1 35.2 Rodney S. Gomes, John J. Matese, and Jack J. Lissauer (2006). "A distant planetary-mass solar companion may have produced distant detached objects". Icarus 184 (2): 589–601. doi:10.1016/j.icarus.2006.05.026. http://adsabs.harvard.edu/abs/2006Icar..184..589G. 
  36. ↑ P. S. Lykawka and T. Mukai (2008). "An Outer Planet Beyond Pluto and the Origin of the Trans-Neptunian Belt Architecture". Astronomical Journal 135 (4): 1161. doi:10.1088/0004-6256/135/4/1161. arXiv:0712.2198. http://arxiv.org/pdf/0712.2198. 
  37. ↑ 37.0 37.1 Megan Schwamb (2007). Searching for Sedna's Sisters: Exploring the inner Oort cloud. Cal Tech. http://www.astro.caltech.edu/~george/option/candex07/schwamb_report.pdf. Retrieved 2010-08-06. 
  38. ↑ Staff (April 25, 2006). "Evidence Mounts For Companion Star To Our Sun". SpaceDaily. http://www.spacedaily.com/reports/Evidence_Mounts_For_Companion_Star_To_Our_Sun.html. Retrieved November 27, 2009. 
  39. ↑ John J. Matese, Daniel P. Whitmire and Jack J. Lissauer (2006). "A Widebinary Solar Companion as a Possible Origin of Sedna-like Objects". Earth, Moon, and Planets 97 (3-4): 459-470. doi:10.1007/s11038-006-9078-6. http://www.springerlink.com/content/87v1p11t23832736/. Retrieved 2010-08-17. 
  40. ↑ 40.0 40.1 40.2 Megan E. Schwamb, Michael E. Brown, and David L. Rabinowitz (2009). "A Search for Distant Solar System Bodies in the Region of Sedna". The Astrophysical Journal Letters 694: L45–L48. doi:10.1088/0004-637X/694/1/L45. arXiv:0901.4173. http://adsabs.harvard.edu/abs/2009ApJ...694L..45S. 
  41. ↑ IAU: Minor Planet Center (2008-07-02). "List of Centaurs and Scattered-Disk Objects". Central Bureau for Astronomical Telegrams, Harvard-Smithsonian Center for Astrophysics. http://www.minorplanetcenter.org/iau/lists/Centaurs.html. Retrieved 2008-07-02. 
  42. ↑ Brett Gladman (2001). "Evidence for an Extended Scattered Disk?". Observatoire de la Cote d'Azur. http://www.obs-nice.fr/gladman/cr105.html. Retrieved 2010-07-22. 
  43. ↑ David Jewitt, A. Delsanti (2006). "The Solar System Beyond The Planets". Solar System Update : Topical and Timely Reviews in Solar System Sciences. Springer-Praxis Ed.. ISBN 3-540-26056-0. http://www.springerlink.com/content/w87u54604t288341/. 
  44. ↑ J. L. Elliot, S. D. Kern, K. B. Clancy et al. (2006). "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 (2). doi:10.1086/427395. http://adsabs.harvard.edu/abs/2005AJ....129.1117E. 
  45. ↑ Michael E. Brown. "The Dwarf Planets". California Institute of Technology, Department of Geological Sciences. http://web.gps.caltech.edu/~mbrown/dwarfplanets/. Retrieved 2008-02-16. 
  46. ↑ "Plutoid chosen as name for Solar System objects like Pluto". International Astronomical Union (News Release—IAU0804). 2008-06-11, Paris. http://www.iau.org/public_press/news/release/iau0804. Retrieved 2008-06-11. 
  47. ↑ "Solar System Exploration: Multimedia: Gallery". NASA. http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=1504. Retrieved 2010-01-03. 
  48. ↑ S. Alan Stern and Harold F. Levison (2002). "Regarding the criteria for planethood and proposed planetary classification schemes" (PDF). Highlights of Astronomy 12: 205–213, as presented at the XXIVth General Assembly of the IAU–2000 [Manchester, UK, 7 August-18 August 2000]. http://www.boulder.swri.edu/~hal/PDF/planet_def.pdf. 

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