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|Discovered by||Stephen P. Synnott / Voyager 2|
|Discovery time||January 3, 1986|
|Longest distance from the center of its orbital path
|66,097.265 ± 0.050 km|
|How egg-shaped its orbit is
|0.00005 ± 0.00008|
|How long it takes to complete an orbit||0.5131959201 ± 0.0000000093 d|
|Angle above the reference plane
|0.05908 ± 0.039° (to Uranus' equator)|
|What it orbits||Uranus|
|Size and Other Qualities|
|Measures||156 × 126 × 126 km|
|Average distance from its center to its surface||70 ± 4 km|
|Area of its surface||~57,000 km²|
|Volume inside it||~1,300,000 km³|
|Average density||~1.3 g/cm³ (assumed)|
|Gravity at its surface||~0.023 m/s2|
|Slowest speed able to escape into space
|~0.058 km/s km/s|
|How long it takes to turn around one time||synchronous|
|Angle at which it turns
(in relation to its orbit)
|How much light it reflects||0.08 ± 0.01 |
|Avg. surface temp.||~64 K|
Portia is a closer moon to Uranus. It was found from the images taken by Voyager 2 on 1986-01-03, and was given the designation S/1986 U 1. The moon is named after Portia, the heroine of William Shakespeare's play The Merchant of Venice. It is also designated Uranus XII.
Portia is the second biggest closer moon of Uranus after Puck. The Portian orbit, which lies inside Uranus' synchronous orbital radius, is slowly shrinking due to tidal deceleration. The moon will one day either break up into a planetary ring or hit Uranus.
It heads a group of moons called Portia Group, which includes Bianca, Cressida, Desdemona, Juliet, Rosalind, Cupid, Belinda and Perdita. These moons have similar orbits and photometric properties.
In the Voyager 2 images, Portia appears as a stretched object whose major axis points towards Uranus. The ratio of axises of the Portia's prolate spheroid is 0.8 ± 0.1. Its surface is grey in color. Observations with Hubble Space Telescope and large terrestrial telescopes found water ice absorption features in the spectrum of Portia.
- Jacobson, R.A. (1998). "The Orbits of the Inner Uranian Satellites From Hubble Space Telescope and Voyager2 Observations". The Astronomical Journal 115: 1195-1199. . http://adsabs.harvard.edu/abs/1998AJ....115.1195J.
- 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. . http://adsabs.harvard.edu/abs/2001Icar..151...69K.
- Calculated on the basis of other parameters
- Karkoschka, Erich (2001). "Comprehensive Photometry of the Rings and 16 Satellites of Uranus with the Hubble Space Telescope". Icarus 151: 51–68. . http://adsabs.harvard.edu/abs/2001Icar..151...51K.
- Smith, B. A. (January 16 1986). "IAU Circular No. 4164". http://cfa-www.harvard.edu/iauc/04100/04164.html#Item1. Retrieved 2006-08-06.
- "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology. July 21 2006. http://planetarynames.wr.usgs.gov/append7.html. Retrieved 2006-08-06.
- Dumas, Christophe (2003). "Hubble Space Telescope NICMOS Multiband Photometry of Proteus and Puck". Astronomical Journal 126: 1080–1085. . http://adsabs.harvard.edu/abs/2003AJ....126.1080D.