20000 Varuna
Artist's impression of Varuna
|
|
| Discovery | |
|---|---|
| Discovered by | R. McMillan (Spacewatch) |
| Discovery date | 28 November 2000 |
| Designations | |
| MPC designation | 20000 Varuna |
| Pronunciation | /ˈværənə/ VARR-ə-nə |
|
Named after
|
Varuna |
| 2000 WR106 | |
|
TNO (cubewano) Scat-Ext |
|
| Adjectives | Varunian |
| Orbital characteristics | |
| Epoch 13 January 2016 (JD 2457400.5) | |
| Uncertainty parameter 3 | |
| Observation arc | 22351 days (61.19 yr) |
| Aphelion | 45.299 AU (6.7766 Tm) |
| Perihelion | 40.947 AU (6.1256 Tm) |
| 43.123 AU (6.4511 Tm) | |
| Eccentricity | 0.050464 |
| 283.19 yr (103435 d) | |
|
Average orbital speed
|
4.53 km/s |
| 105.119° | |
| 0° 0m 12.53s / day | |
| Inclination | 17.165° |
| 97.290° | |
| 270.890° | |
| Earth MOID | 39.9904 AU (5.98248 Tm) |
| Jupiter MOID | 36.2032 AU (5.41592 Tm) |
| Jupiter Tisserand parameter | 5.615 |
| Physical characteristics | |
| Dimensions |
668+154 −86 km |
|
Mean radius
|
450 ± 70 km |
| Mass | ≈ 3.7×1020 kg |
|
Mean density
|
0.992 g/cm3 |
|
Equatorial surface gravity
|
0.22 m/s2 |
|
Equatorial escape velocity
|
0.38 km/s |
| 6.3436 h (0.26432 d) | |
|
Sidereal rotation period
|
6.3418 h |
|
0.127+0.040 −0.042 |
|
| Temperature | ≈ 43–41 K |
| (moderately red) B−V=0.93 V−R=0.64 |
|
| 19.9 (opposition) | |
| 3.760±0.035, 3.7 | |
20000 Varuna is a large classical Kuiper belt object. It is probably a dwarf planet. It rotates rapidly and hence its shape is probably very elongated.
Varuna was discovered on 28 November 2000 by Robert McMillan of Spacewatch. It was given the provisional designation 2000 WR106 and has been precovered in plates dating back to 1954.
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 Earth's atmosphere, because 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 diameter of Varuna have varied from 500 to 1,060 km. Multi-band thermal measurements from the Herschel Space Observatory in 2013 yielded a diameter of 668+154
−86 km.
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