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20000 Varuna (pronounced /ˈværənə/ VARR-ə-nə,[9] from Sanskrit वरुण [vəˈrʊɳə]) 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.
[edit] NameVaruna is named after the Hindu deity Varuṇa. Varuṇa was one of the most important deities of the ancient Indo-Aryans, and he presided over the waters of the heaven and of the ocean and as the guardian of immortality.[10] Due to his association with the waters and the ocean, he is often identified with Greek Poseidon and Roman Neptune. [edit] Size  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.[2] The two most recent estimates are closer to the 500km range. The 2005 estimate of a size of 936 +238−324 km,[11] based on earlier results (900 +129−145)[12] and (1060 +180−-220),[13] may be too high. Varuna is predicted to occult a magnitude 14.7 star in Gemini on December 7th, 2008.[14] This event will allow 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 will be measured, and this will allow the exact size to be measured.[15] Current predictions[16] suggest the event will be visible only from South America and southern Africa. [edit] Orbit
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. [edit] Physical characteristicsVaruna 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).[4] 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.[3] 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.[17] The surface of Varuna is moderately red (similar to Quaoar) and small amounts of water ice have been detected on its surface.[18] [edit] References
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