|Discovered by||Stephen P. Synnott / Voyager 2|
|Discovery date||January 3, 1986|
|Semi-major axis||66,097.265 ± 0.050 km1|
|Eccentricity||0.00005 ± 0.000081|
|Orbital period||0.5131959201 ± 0.0000000093 d1|
|Inclination||0.05908 ± 0.039° (to Uranus' equator)1|
|Dimensions||156 × 126 × 126 km2|
|Mean radius||67.6 ± 4 km234|
|Surface area||~57,000 km²a|
|Mean density||~1.3 g/cm³ (assumed)3|
|Equatorial surface gravity||~0.023 m/s2a|
|Escape velocity||~0.058 km/sa|
Portia (// POR-shə) is an inner satellite of Uranus. It was discovered from the images taken by Voyager 2 on 3 January 1986, and was given the temporary designation S/1986 U 1.6 The moon is named after Portia, the heroine of William Shakespeare's play The Merchant of Venice. It is also designated Uranus XII.7
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 the Portia Group, which includes Bianca, Cressida, Desdemona, Juliet, Rosalind, Cupid, Belinda and Perdita.5 These satellites have similar orbits and photometric properties.5
In the Voyager 2 images, Portia appears as an elongated object whose major axis points towards Uranus. The ratio of axes 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.58
- Calculated on the basis of other parameters.
- Jacobson, R. A. (1998). "The Orbits of the Inner Uranian Satellites From Hubble Space Telescope and Voyager 2 Observations". The Astronomical Journal 115 (3): 1195–1199. Bibcode:1998AJ....115.1195J. doi:10.1086/300263.
- Karkoschka, Erich (2001). "Voyager's Eleventh Discovery of a Satellite of Uranus and Photometry and the First Size Measurements of Nine Satellites". Icarus 151 (1): 69–77. Bibcode:2001Icar..151...69K. doi:10.1006/icar.2001.6597.
- "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. Retrieved 2008-12-12.
- Williams, Dr. David R. (2007-11-23). "Uranian Satellite Fact Sheet". NASA (National Space Science Data Center). Retrieved 2008-12-12.
- Karkoschka, Erich (2001). "Comprehensive Photometry of the Rings and 16 Satellites of Uranus with the Hubble Space Telescope". Icarus 151 (1): 51–68. Bibcode:2001Icar..151...51K. doi:10.1006/icar.2001.6596.
- Smith, B. A. (January 16, 1986). "Satellites of Uranus". IAU Circular 4164. Retrieved 29 October 2011.
- "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology. July 21, 2006. Retrieved 2006-08-06.
- Dumas, Christophe; Smith, Bradford A.; Terrile, Richard J. (2003). "Hubble Space Telescope NICMOS Multiband Photometry of Proteus and Puck". The Astronomical Journal 126 (2): 1080–1085. Bibcode:2003AJ....126.1080D. doi:10.1086/375909.