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Portia (moon)

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Portia
Discovery
Discovered byStephen P. Synnott / Voyager 2
Discovery dateJanuary 3, 1986
Designations
Designation
Uranus XII
Pronunciation/ˈpɔːrʃə/[1]
AdjectivesPortian /ˈpɔːrʃən/[1]
Orbital characteristics[2]
66,097.265 ± 0.050 km
Eccentricity0.00005 ± 0.00008
0.5131959201 ± 0.0000000093 d
9.37 km/s[a]
Inclination0.05908 ± 0.039° (to Uranus' equator)
Satellite ofUranus
Groupring shepherd
Physical characteristics
Dimensions156 × 126 × 126 km[3][note 1]
~58 000 km2[a]
Volume1296800±14.8% km3[4]
Mass(1.1671±0.1730)×1018 kg[4]
Mean density
≥0.57 g/cm3[4]
~0.90 g/cm3 (assumed)
~0.013–0.02 m/s2[a]
~0.045–0.05 km/s[a]
synchronous[3]
zero[3]
Albedo
Temperature~64 K[a]
  1. ^ Only two dimensions are known; the third dimension has been assumed to equal the smaller known dimension.

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.[8] The moon is named after Portia, the heroine of William Shakespeare's play The Merchant of Venice. It is also designated Uranus XII.[9]

Portia is the second-largest inner satellite of Uranus after Puck. The Portian orbit, which lies inside Uranus's 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.[citation needed]

It is the namesake of 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]

Little is known about Portia beyond its dimensions of about 156 × 126 km,[3] orbit,[2] and geometric albedo of about 0.08.[5]

In Voyager 2 imagery, 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.[5][10] Observations with James Webb Space Telescope have also found evidence for water ice or hydrated minerals on Portia's surface, and have also confirmed that Portia group members Juliet, Belinda, and Cressida have roughly similar spectra to Portia.[11]

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  • Portia seen on January 23, 1986.
    Portia seen on January 23, 1986.

See also

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Notes

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

References

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  1. ^ a b "Portia". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  2. ^ a b 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 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 French, Richard G.; Hedman, Matthew M.; Nicholson, Philip D.; Longaretti, Pierre-Yves; McGhee-French, Colleen A. (2024-03-15). "The Uranus system from occultation observations (1977–2006): Rings, pole direction, gravity field, and masses of Cressida, Cordelia, and Ophelia". Icarus. 411: 115957. arXiv:2401.04634. Bibcode:2024Icar..41115957F. doi:10.1016/j.icarus.2024.115957. ISSN 0019-1035.
  5. ^ 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.
  6. ^ "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. Retrieved 2008-12-12.
  7. ^ Williams, Dr. David R. (2007-11-23). "Uranian Satellite Fact Sheet". NASA (National Space Science Data Center). Retrieved 2008-12-12.
  8. ^ Smith, B. A. (January 16, 1986). "Satellites of Uranus". IAU Circular. 4164. Retrieved 29 October 2011.
  9. ^ "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology. July 21, 2006. Retrieved 2006-08-06.
  10. ^ 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.
  11. ^ Belyakov, Matthew; Davis, M. Ryleigh; Milby, Zachariah; Wong, Ian; Brown, Michael E. (2024-05-01). "JWST Spectrophotometry of the Small Satellites of Uranus and Neptune". The Planetary Science Journal. 5 (5): 119. arXiv:2404.06660. Bibcode:2024PSJ.....5..119B. doi:10.3847/PSJ/ad3d55. ISSN 2632-3338.
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