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20000 Varuna

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This article is about 20000 Varuna, a minor planet. For other uses of the word, see Varuna (disambiguation)
20000 Varuna
Artist's conception of Varuna
Discovery
Discovered byR. McMillan (Spacewatch)
Discovery date28 November 2000
Designations
Designation
20000 Varuna
Pronunciation/ˈværənə/ VARR-ə-nə [1]
Named after
Varuna
2000 WR106
TNO (cubewano)[2]
Scat-Ext[3]
AdjectivesVarunian
Orbital characteristics
Epoch 14 July 2004 (JD 2453200.5)
Aphelion6 781.985 Gm (45.335 AU)
Perihelion6 120.810 Gm (40.915 AU)
6 451.398 Gm (43.129 AU)
Eccentricity0.051
103 440.6 d (283.20 a)
4.53 km/s
89.673°
Inclination17.2°
97.296°
271.631°
Physical characteristics
Dimensions800 km (avg of thermals)[4]
500 ± 100 km (Spitzer adopted)[5]
(scalene ellipsoid)?[6][7]
Mass≈3.7×1020? kg[6][8]
Mean density
0.992 g/cm³[6]
0.15 m/s²
0.39 km/s
0.132 16 d (3.17 h)
Albedo0.037–0.26[4]
Temperature≈43–41 K
Spectral type
(moderately red) B-V=0.93 V-R=0.64[9]
19.9 (opposition)[10]
3.7[11]

20000 Varuna is a large classical Kuiper Belt object (KBO) and a potential dwarf planet. It previously had the provisional designation 2000 WR106 and has been precovered in plates dating back to 1953.

Name

Varuna is named after the Hindu deity, Varuṇa. Varuṇa was one of the most important deities of the ancient Indians, and he presided over the waters of the heaven and of the ocean and as the guardian of immortality.[12] Due to his association with the waters and the ocean, he is often identified with Greek Poseidon and Roman Neptune. Varuna received the minor planet number 20000 because it was the largest cubewano found so far, and was believed to be as large as Ceres.[13]

Size

Size estimates for Varuna:
Year Diameter (km) Notes
2001 900[14] Jewitt
2002 1060[15] Lellouch
2005 936[16] Grundy
2005 >621[5] Spitzer 2-Band
2007 502[5] Spitzer 1-Band

The size of the large KBOs can be determined by simultaneous observations of thermal emission and reflected sunlight. Unfortunately, thermal measures, intrinsically weak for distant objects, are further hampered by the absorption of the Earth atmosphere as only the weak ‘tail’ of the emissions is accessible to Earth-based observations. In addition, the estimates are model-dependent with the unknown parameters (e.g. pole orientation and thermal inertia) to be assumed. Consequently, the estimates of the albedo vary resulting in sometimes substantial differences in the inferred size.

Estimates for the size of Varuna have varied from 500 to 1060 km.[4] The two most recent estimates from Spitzer are closer to the 500 kilometres (310 mi) range and inconsistent with the 2005 estimate of a size of 936 +238
−324 km,[16] based on earlier results (900 +129
−145)[14] and (1060 +180
−-220).[15] This inconsistency of the Spitzer results with the earlier (sub-millimetre) observations was recently addressed by the original authors (Stansberry et al.); given a number of difficulties in Varuna case, the authors are inclined to favor the sub-millimetre results (Jewitt, Lellouch) for this object over those from Spitzer.[17]

Varuna was predicted to occult a magnitude 14.7 star in Gemini on December 7, 2008.[18] This type of event in principle is of the type that might have allowed at least a lower limit to be placed on Varuna's size. If multiple observers at different locations record the event, several chords across Varuna might have been measured, which would have allowed the precise size to be measured.[19] Predictions suggested the event was visible only from South America and southern Africa.[20] The collaboration of observers did not report a conclusive observation of the event,[21] but they have also not yet released their peer-reviewed data summary.

Orbit

Orbits of Varuna (blue) and Pluto (red).

Varuna is classified as a classical trans-Neptunian object and follows a near-circular orbit with a semi-major axis of ≈43 AU, similar to that of Quaoar but more inclined. Its orbital period is similar to Quaoar at 283 Earth years. The graph shows the polar view (top; Varuna’s orbit in blue, Pluto’s in red, Neptune in grey). The spheres illustrate the current (April 2006) positions, relative sizes and colours. The perihelia (q), aphelia (Q) and the dates of passage are also marked. Interestingly, the orbits of Varuna and Pluto have similar inclination and are similarly oriented (the nodes of both orbits are quite close).

At 43 AU and on a near-circular orbit, unlike Pluto which is in 2:3 orbital resonance with Neptune, Varuna is free from any significant perturbation from Neptune. The ecliptic view illustrates the comparison of Varuna's near-circular orbit with that of Pluto (highly eccentric, e=0.25), both similarly inclined.

Physical characteristics

Varuna has a rotational period of approximately 3.17 hours (or 6.34 hours, depending on whether the light curve is single or double-peaked). Given the rapid rotation, rare for objects so large, Varuna is thought to be an elongated spheroid (ratio of axis 2:3), with a mean density around 1g/cm³ (roughly the density of water).[7] Examination of Varuna's light curve has found that the best-fit model for Varuna is a triaxial ellipsoid with the axes a,b,c in relations: b/a = 0.63 − 0.80, c/a = 0.45 − 0.52 and a bulk density of 0.992 g/cm³.[6] Since the discovery of Varuna, another, even larger, rapidly rotating (3.9 h) object Haumea has been discovered, also thought to have an elongated shape.[22]

The surface of Varuna is moderately red (similar to Quaoar) and small amounts of water ice have been detected on its surface.[23]

References

  1. ^ Merriam Webster's Collegiate Dictionary. From the Sanskrit वरुण [ʋəˈrʊɳə]
  2. ^ "MPEC 2009-P26 : DISTANT MINOR PLANETS (2009 AUG. 17.0 TT)". IAU Minor Planet Center. 2009-08-07. Retrieved 2009-09-16.
  3. ^ Marc W. Buie (2007-01-12). "Orbit Fit and Astrometric record for 20000". SwRI (Space Science Department). Retrieved 2008-09-19.
  4. ^ a b c Stansberry (2008). "TNO/Centaur diameters and albedos". Retrieved 2006-11-08.
  5. ^ a b c John Stansberry, Will Grundy, Mike Brown, Dale Cruikshank, John Spencer, David Trilling, Jean-Luc Margot (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 2007-12-01.{{cite web}}: CS1 maint: multiple names: authors list (link)
  6. ^ a b c d Lightcurves Lacerda P., Jewitt D. Dentisities Of Solar System Objects From Their Rotational Lightcurves", accepted to AJ Dec. 2006 Preprint
  7. ^ a b Jewitt D, Sheppard S (2002). "Physical Properties Of Trans-Neptunian Object (20000) Varuna". Astronomical Journal. 123 (April): 2110–2120. doi:10.1086/339557. Preprint on arXiv.
  8. ^ Calculated using Lacerda and Jewitt (2007) diameter of 900 km and density of 0.992 g/cm³.
  9. ^ "TNO and Centaur Colors". Retrieved 2006-11-08.
  10. ^ "HORIZONS Web-Interface". JPL Solar System Dynamics. Retrieved 2008-07-02. {{cite web}}: External link in |publisher= (help)
  11. ^ "JPL Small-Body Database Browser: 20000 Varuna (2000 WR106)". 2007-11-17 last obs. Retrieved 2008-07-02. {{cite web}}: Check date values in: |date= (help)
  12. ^ MW Sanskrit-English dictionary
  13. ^ "M.P.C. 41805" (PDF). The Minor Planet Circulars/Minor Planets and Comets. 2001-01-09. Retrieved 2010-07-04.
  14. ^ a b Jewitt D, Aussel H, Evans A (2001). "The size and albedo of the Kuiper-belt object (20000) Varuna". Nature. 411 (6836): 446–7. doi:10.1038/35078008. PMID 11373669.{{cite journal}}: CS1 maint: multiple names: authors list (link) PMID 11373669. Reprint on the Author's site.
  15. ^ a b E. Lellouch, R. Moreno, J. L. Ortiz, G. Paubert, A. Doressoundiram and N. Peixinho (2002). "Coordinated thermal and optical observations of Trans-Neptunian object (20 000)Varuna from Sierra Nevada". Astronomy & Astrophysics. 391: 1133–1139. doi:10.1051/0004-6361:20020903.{{cite journal}}: CS1 maint: multiple names: authors list (link) Preprint on arXiv.
  16. ^ a b Grundy, W. M.; Noll, K. S.; Stephens, D. C. (2005). "Diverse albedos of small trans-neptunian objects". Icarus,. 176: 184–191. doi:10.1016/j.icarus.2005.01.007.{{cite journal}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link) Preprint on arXiv.
  17. ^ J. Stansberry, W. Grundy, M. Brown, D. Cruikshank, J. Spencer, D.Trilling, J-L. Margot (2008). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from the Spitzer Space Telescope". In The Solar System Beyond Neptune, ISBN 978-0-8165-2755-7. {{cite journal}}: Italic or bold markup not allowed in: |journal= (help)CS1 maint: multiple names: authors list (link)
  18. ^ "20000 VARUNA : Important observation, Dec 7 at 2 hrs UT". mpml · A list for asteroid and comet researchers. Retrieved 2008-12-01.
  19. ^ Lakdawalla, Emily. "Attention: South American and southern African observers needed for observations of a stellar occultation by Varuna". Planetary Society blog. Retrieved 2008-12-01.
  20. ^ "Varuna: information for observers". Retrieved 2008-12-01.
  21. ^ "Varuna: information for observers". Retrieved 2009-01-13.
  22. ^ D. L. Rabinowitz, K. M. Barkume, M. E. Brown, H. G. Roe, M. Schwartz, S. W. Tourtellotte, C. A. Trujillo (2005), Photometric Observations Constraining the Size, Shape, and Albedo of 2003 EL61, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt, The Astrophysical Journal (2006), 639, Issue 2, pp. 1238-1251 Preprint on arXiv
  23. ^ Licandro J, Oliva E, Di Martino M (2001). "NICS-TNG infrared spectroscopy of trans-neptunian objects 2000 EB173 and 2000 WR106". Astronomy & Astrophysics. 373 (July): 29–32L. doi:10.1051/0004-6361:20010758.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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