Portia (moon)
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Discovery
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| Discovered by | Stephen P. Synnott / Voyager 2 |
| Discovery date | January 3, 1986 |
| Semi-major axis | 66,097.265 ± 0.050 km[1] |
| Eccentricity | 0.00005 ± 0.00008[1] |
| Orbital period | 0.5131959201 ± 0.0000000093 d[1] |
| Inclination | 0.05908 ± 0.039° (to Uranus' equator)[1] |
| Satellite of | Uranus |
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Physical characteristics
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| Dimensions | 156 × 126 × 126 km[2] |
| Mean radius | 70 ± 4 km[2] |
| Surface area | ~57,000 km²[3] |
| Volume | ~1,300,000 km³[3] |
| Mass | ~1.7×1018 kg[3] |
| Mean density | ~1.3 g/cm³ (assumed) |
| Equatorial surface gravity | ~0.023 m/s2[3] |
| Escape velocity | ~0.058 km/s km/s[3] |
| Rotation period | synchronous[2] |
| Axial tilt | zero[2] |
| Albedo | 0.08 ± 0.01 [4] |
| Temperature | ~64 K |
Portia (por'-shə, IPA: /ˈpɔrʃə/) is an inner satellite of Uranus. It was discovered from the images taken by Voyager 2 on 1986-01-03, and was given the temporary designation S/1986 U 1.[5] The moon is named after Portia, the heroine of William Shakespeare's play The Merchant of Venice. It is also designated Uranus XII.[6]
Portia is the second-largest inner satellite of Uranus after Puck. The Portian orbit, which lies inside Uranus' synchronous orbital radius, is slowly decaying due to tidal deceleration. The moon will one day either break up into a planetary ring or hit Uranus.
It heads a group of satellites called Portia Group, which includes Bianca, Cressida, Desdemona, Juliet, Rosalind, Cupid, Belinda and Perdita.[4] These satellites have similar orbits and photometric properties.[4]
Little is known about Portia beyond its size of about 140 km,[2] orbit,[1] and geometric albedo of about 0.08.[4]
In the Voyager 2 images, Portia appears as an elongated object whose major axis points towards Uranus. The ratio of axises of the Portia's prolate spheroid is 0.8 ± 0.1.[2] Its surface is grey in color.[2] Observations with Hubble Space Telescope and large terrestrial telescopes found water ice absorption features in the spectrum of Portia.[4][7]
[edit] References
- ^ a b c d e Jacobson, R.A. (1998). "The Orbits of the Inner Uranian Satellites From Hubble Space Telescope and Voyager2 Observations". The Astronomical Journal 115: 1195-1199. doi:.
- ^ a b c d e f g Karkoschka, Erich (2001). "Voyager's Eleventh Discovery of a Satellite of Uranus and Photometry and the First Size Measurements of Nine Satellites". Icarus 151: 69–77. doi:.
- ^ a b c d e Calculated on the basis of other parameters
- ^ a b c d e Karkoschka, Erich (2001). "Comprehensive Photometry of the Rings and 16 Satellites of Uranus with the Hubble Space Telescope". Icarus 151: 51–68. doi:.
- ^ Smith, B. A. (January 16 1986). IAU Circular No. 4164. Retrieved on 2006-08-06.
- ^ Planet and Satellite Names and Discoverers. Gazetteer of Planetary Nomenclature. USGS Astrogeology (July 21 2006). Retrieved on 2006-08-06.
- ^ Dumas, Christophe (2003). "Hubble Space Telescope NICMOS Multiband Photometry of Proteus and Puck". Astronomical Journal 126: 1080–1085. doi:.
[edit] External links
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