Portia (moon)


Discovered byStephen P. Synnott / Voyager 2
Discovery dateJanuary 3, 1986
Uranus XII
AdjectivesPortian /ˈpɔːrʃən/[1]
Orbital characteristics
66,097.265 ± 0.050 km[2]
Eccentricity0.00005 ± 0.00008[2]
0.5131959201 ± 0.0000000093 d[2]
9.37 km/s[a]
Inclination0.05908 ± 0.039° (to Uranus' equator)[2]
Satellite ofUranus
Groupring shepherd
Physical characteristics
Dimensions156 × 126 × 126 km[3]
Mean radius
67.6 ± 4 km[3][4][5]
~57,000 km²[a]
Volume~1,300,000 km³[a]
Mass~1.7×1018 kg[a]
Mean density
~1.3 g/cm³ (assumed)[4]
~0.023 m/s2[a]
~0.058 km/s[a]
Temperature~64 K

Portia 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.[7] The moon is named after Portia, the heroine of William Shakespeare's play The Merchant of Venice. It is also designated Uranus XII.[8]

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.[6] These satellites have similar orbits and photometric properties.[6]

Little is known about Portia beyond its size of about 140 km in diameter,[3] orbit,[2] and geometric albedo of about 0.08.[6]

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.[3] Its surface is grey in color.[3] Observations with Hubble Space Telescope and large terrestrial telescopes found water ice absorption features in the spectrum of Portia.[6][9]


See also


Explanatory notes

  1. ^ a b c d e f Calculated on the basis of other parameters.


  1. ^ a b "Portia". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  2. ^ a b c d e 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.
  3. ^ 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 (1): 69–77. Bibcode:2001Icar..151...69K. doi:10.1006/icar.2001.6597.
  4. ^ a b c "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. Retrieved 2008-12-12.
  5. ^ a b Williams, Dr. David R. (2007-11-23). "Uranian Satellite Fact Sheet". NASA (National Space Science Data Center). Retrieved 2008-12-12.
  6. ^ 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 (1): 51–68. Bibcode:2001Icar..151...51K. doi:10.1006/icar.2001.6596.
  7. ^ Smith, B. A. (January 16, 1986). "Satellites of Uranus". IAU Circular. 4164. Retrieved 29 October 2011.
  8. ^ "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology. July 21, 2006. Retrieved 2006-08-06.
  9. ^ 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.

External links

  • Portia Profile by NASA's Solar System Exploration
  • Uranus' Known Satellites (by Scott S. Sheppard)