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20000 Varuna
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20000 Varuna ( VARR-?-n?, from Sanskrit ???? ) is a large classical Kuiper Belt object (KBO) and a potential dwarf planet. It previously had the provisional designation and has been precovered in plates dating back to 1953.
na is named after the Hindu deity . 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.
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Encyclopedia
20000 Varuna ( VARR-?-n?, from Sanskrit ???? ) is a large classical Kuiper Belt object (KBO) and a potential dwarf planet. It previously had the provisional designation and has been precovered in plates dating back to 1953.
Name
Varuna is named after the Hindu deity . 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. Due to his association with the waters and the ocean, he is often identified with Greek Poseidon and Roman Neptune.
Size
Image:EightTNOs.png|thumb|250px|left|Varuna compared to Eris, Pluto, Makemake, Haumea, Sedna, Orcus, Quaoar, and Earth.
- Earth
rect 646 1714 2142 1994 The Earth
- Eris and Dysnomia
circle 226 412 16 Dysnomia
circle 350 626 197 (136199) Eris
- Pluto and Charon
circle 1252 684 86 Charon
circle 1038 632 188 (134340) Pluto
- Makemake
circle 1786 614 142 (136472) Makemake
- Haumea
circle 2438 616 155 (136108) Haumea
- Sedna
circle 342 1305 137 (90377) Sedna
- Orcus
circle 1088 1305 114 (90482) Orcus
- Quaoar
circle 1784 1305 97 (50000) Quaoar
- Varuna
circle 2420 1305 58 (20000) Varuna
- link to image (under all other links)
rect 0 0 2749 1994
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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. The two most recent estimates are closer to the 500km range. The 2005 estimate of a size of 936 km, based on earlier results (900 )
and (1060 ), may be too high.
Varuna was predicted to occult a magnitude 14.7 star in Gemini on December 7th, 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 record 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, but they have also not yet released their peer-reviewed data summary.
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 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, ’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). 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, another, even larger, rapidly rotating (3.9 h) object has been discovered, also thought to have an elongated shape.
The surface of Varuna is moderately red (similar to ) and small amounts of water ice have been detected on its surface.
External links
Site updated Reretrived on 2006-07-10
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