Portia (moon)

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Discovered byStephen P. Synnott / Voyager 2
Discovery dateJanuary 3, 1986
Orbital characteristics
66,097.265 ± 0.050 km[1]
Eccentricity0.00005 ± 0.00008[1]
0.5131959201 ± 0.0000000093 d[1]
Inclination0.05908 ± 0.039° (to Uranus' equator)[1]
Satellite ofUranus
Physical characteristics
Dimensions156 × 126 × 126 km[2]
Mean radius
70 ± 4 km[2]
~57,000 km²[3]
Volume~1,300,000 km³[3]
Mass~1.7×1018 kg[3]
Mean density
~1.3 g/cm³ (assumed)
~0.023 m/s2[3]
~0.058 km/s km/s[3]
Albedo0.08 ± 0.01 [4]
Temperature~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.[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 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.[4] These moons 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 a stretched 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]

References[change | change source]

  1. 1.0 1.1 1.2 1.3 1.4 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:10.1086/300263.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 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:10.1006/icar.2001.6597.
  3. 3.0 3.1 3.2 3.3 3.4 Calculated on the basis of other parameters
  4. 4.0 4.1 4.2 4.3 4.4 Karkoschka, Erich (2001). "Comprehensive Photometry of the Rings and 16 Satellites of Uranus with the Hubble Space Telescope". Icarus. 151: 51–68. doi:10.1006/icar.2001.6596.
  5. Smith, B. A. (January 16 1986). "IAU Circular No. 4164". Retrieved 2006-08-06. {{cite web}}: Check date values in: |date= (help)
  6. "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology. July 21 2006. Retrieved 2006-08-06. {{cite web}}: Check date values in: |date= (help)
  7. Dumas, Christophe (2003). "Hubble Space Telescope NICMOS Multiband Photometry of Proteus and Puck". Astronomical Journal. 126: 1080–1085. doi:10.1086/375909. {{cite journal}}: Unknown parameter |coaurhors= ignored (help)

Other websites[change | change source]