Artist's conception of Varuna as a scalene ellipsoid
|Discovered by||R. McMillan (Spacewatch)|
|Discovery date||28 November 2000|
|MPC designation||20000 Varuna|
|Alternative names||2000 WR106|
|Minor planet category||TNO (cubewano)
|Epoch 23 July 2010 (JD 2455400.5)|
|Aphelion||45.313 AU (6778.797 Gm)|
|Perihelion||40.494 AU (6057.848 Gm)|
|Semi-major axis||42.904 AU (6418.322 Gm)|
|Orbital period||281.03 a (102646.1 d)|
|Average orbital speed||4.53 km/s|
|Longitude of ascending node||97.303°|
|Argument of perihelion||266.736°|
|Mass||≈ 3.7×1020? kg|
|Mean density||0.992 g/cm3|
|Equatorial surface gravity||0.15 m/s2|
|Escape velocity||0.39 km/s|
|Sidereal rotation period||6.34 h|
|Temperature||≈ 43–41 K|
|Spectral type||(moderately red) B-V=0.93 V-R=0.64|
|Apparent magnitude||19.9 (opposition)|
|Absolute magnitude (H)||3.7|
Varuna is named after a Hindu deity. Varuna 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 was the guardian of immortality. 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.
The size of the large Kuiper belt objects 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's 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. 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, based on earlier results (900+129
−145) and (1060+180
−220). 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.
Varuna was predicted to occult a magnitude 14.7 star in Gemini on December 7, 2008. 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 had recorded the event, several chords across Varuna might have been measured, which would have allowed the precise size to be measured. Predictions suggested the event was visible only from South America and southern Africa. The collaboration of observers did not report a conclusive observation of the event.
A 28-second occultation of an 11.1 magnitude star by Varuna was observed from Camalau, Paraiba, Brazil, on the night of February 19, 2010. Results of the 2010 occultation as seen from São Luís with a duration of 52.5 seconds corresponds with a chord of 1003 km. But Quixadá 255 km away had a negative result suggesting a significantly elongated shape is required for Varuna. Since the occultation occurred near Varuna's maximum brightness, the occultation was observing the maximum apparent surface area for an ellipsoidal shape.
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.
Varuna has a rotational period of approximately 6.34 hours. It has a double-peaked light curve. 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 1 g/cm3 (roughly the density of water). 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. Since the discovery of Varuna, Haumea, another, even larger, rapidly rotating (3.9 h) object, has been discovered and is also thought to have an elongated shape. The surface of Varuna is moderately red (similar to Quaoar) and small amounts of water ice have been detected on its surface.
- "MPEC 2009-P26 :Distant Minor Planets (2009 AUG. 17.0 TT)". IAU Minor Planet Center. 7 August 2009. Retrieved 2009-09-16.
- M. W. Buie (12 January 2007). "Orbit Fit and Astrometric record for 20000". SwRI (Space Science Department). Retrieved 2008-09-19.
- Merriam Webster's Collegiate Dictionary. From the Sanskrit वरुण [ʋəˈrʊɳə]
- "JPL Small-Body Database Browser: 20000 Varuna (2000 WR106)". 2010-02-09 last obs. Retrieved 2011-01-02.
- W. R. Johnston (2008). "TNO/Centaur diameters and albedos". Retrieved 2006-11-08.
- J. Stansberry et al. (2007). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope". arXiv:astro-ph/0702538 [astro-ph].
- Bruno Sicardy. "The 2010, February 19 stellar occultation by Varuna". 42nd DPS Meeting. Retrieved 2010-11-12.
- P. Lacerda, D. Jewitt (2006). "Densities Of Solar System Objects From Their Rotational Lightcurve". arXiv:astro-ph/0612237 [astro-ph].
- D. Jewitt, S. Sheppard (2002). "Physical Properties Of Trans-Neptunian Object (20000) Varuna". Astronomical Journal 123 (4): 2110–2120. arXiv:astro-ph/0201082. Bibcode:2002AJ....123.2110J. doi:10.1086/339557.
- Calculated using Lacerda and Jewitt (2007) diameter of 900 km and density of 0.992 g/cm3.
- "TNO and Centaur Colors". Archived from the original on 2006-09-08. Retrieved 2006-11-08.
- "HORIZONS Web-Interface". JPL Solar System Dynamics. Retrieved 2008-07-02.
- MW Sanskrit–English dictionary
- "M.P.C. 41805". The Minor Planet Circulars/Minor Planets and Comets. 9 January 2001. Retrieved 2010-07-04.
- D. Jewitt, H. Aussel, A. Evans (2001). "The size and albedo of the Kuiper-belt object (20000) Varuna". Nature 411 (6836): 446–7. doi:10.1038/35078008. PMID 11373669. Archived from the original on 29 April 2006. Retrieved 23 April 2006.
- E. Lellouch et al. (2002). "Coordinated thermal and optical observations of Trans-Neptunian object (20 000)Varuna from Sierra Nevada". Astronomy & Astrophysics 391 (3): 1133–1139. arXiv:astro-ph/0206486. Bibcode:2002A&A...391.1133L. doi:10.1051/0004-6361:20020903.
- W. M. Grundy, K. S. Noll, D. C. Stephens (2005). "Diverse albedos of small trans-neptunian objects". Icarus (journal) 176 (1): 184–191. arXiv:astro-ph/0502229. Bibcode:2005Icar..176..184G. doi:10.1016/j.icarus.2005.01.007.
- J. Stansberry et al. (2008). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from the Spitzer Space Telescope". The Solar System Beyond Neptune. ISBN 978-0-8165-2755-7.
- "20000 VARUNA : Important observation, Dec 7 at 2 hrs UT.". Minor Planet Mailing List. Retrieved 2008-12-01.
- E. Lakdawalla (1 December 2008). "Attention: South American and southern African observers needed for observations of a stellar occultation by Varuna". Planetary Society. Retrieved 1 December 2008.
- "Varuna: information for observers". Retrieved 2008-12-01.
- "RELATÓRIO FINAL OCULTAÇÃO DA ESTRELA UCAC2 41014042 PELO ASTEROIDE VARUNA". Retrieved 2010-09-18. (Portuguese)
- D. L. Rabinowitz et al. (2006). "Photometric Observations Constraining the Size, Shape, and Albedo of 2003 EL61, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt". Astrophysical Journal 639 (2): 1238–1251. arXiv:astro-ph/0509401. Bibcode:2006ApJ...639.1238R. doi:10.1086/499575.
- J. Licandro, E. Oliva, M. di Martino (2001). "NICS-TNG infrared spectroscopy of trans-neptunian objects 2000 EB173 and 2000 WR106". Astronomy & Astrophysics 373 (3): 29–32L. arXiv:astro-ph/0105434. Bibcode:2001A&A...373L..29L. doi:10.1051/0004-6361:20010758.
- Michael E. Brown (Sep 23, 2011). "How many dwarf planets are there in the outer solar system? (updates daily)". California Institute of Technology. Retrieved 2011-09-23.
- Tancredi, G.; Favre, S. (2008). "Which are the dwarfs in the solar system?". Asteroids, Comets, Meteors. Retrieved 2011-09-23.
- Tancredi, G. (2010). "Physical and dynamical characteristics of icy "dwarf planets" (plutoids)". Icy Bodies of the Solar System: Proceedings IAU Symposium No. 263, 2009. Retrieved 17 January 2012.
- "Size and Albedo of Kuiper Belt Object (20000) Varuna". David Jewitt's Home Page. Retrieved 23 January 2010.
- Orbital simulation from JPL (Java) / Ephemeris