Portia (moon)

Infobox Planet
name = Portia


bgcolour = #ffc0c0
discovery = yes
discoverer = Stephen P. Synnott / "Voyager 2"
discovered = January 3, 1986
semimajor = 66,097.265 ± 0.050 kmcite journal|last=Jacobson|first=R.A.|title=The Orbits of the Inner Uranian Satellites From Hubble Space Telescope and Voyager2 Observations|journal=The Astronomical Journal|url=http://adsabs.harvard.edu/abs/1998AJ....115.1195J|year=1998|volume=115|pages=1195–1199|doi=10.1086/300263]
eccentricity = 0.00005 ± 0.00008
period = 0.5131959201 ± 0.0000000093 d
inclination = 0.05908 ± 0.039° (to Uranus' equator)
satellite_of = Uranus
physical_characteristics = yes
dimensions = 156 × 126 × 126 kmcite journal|last=Karkoschka|first=Erich|authorlink=Erich Karkoschka|title=Voyager's Eleventh Discovery of a Satellite of Uranus and Photometry and the First Size Measurements of Nine Satellites|journal=Icarus|volume=151|pages=69–77|year=2001| doi=10.1006/icar.2001.6597|url=http://adsabs.harvard.edu/abs/2001Icar..151...69K]
mean_radius = 70 ± 4 km
surface_area = ~57,000 km²Calculated on the basis of other parameters]
volume = ~1,300,000 km³
mass = ~1.7e|18 kg
density = ~1.3 g/cm³ (assumed)
surface_grav = ~0.023 m/s²
escape_velocity = ~0.058 km/s km/s
rotation = synchronous
axial_tilt = zero
albedo = 0.08 ± 0.01 cite journal|last=Karkoschka|first=Erich|authorlink=Erich Karkoschka|title=Comprehensive Photometry of the Rings and 16 Satellites of Uranus with the Hubble Space Telescope|journal=Icarus|volume=151|pages=51–68|year=2001| doi=10.1006/icar.2001.6596|url=http://adsabs.harvard.edu/abs/2001Icar..151...51K]
single_temperature = ~64 K

Portia "(por'-shə," IPAEng|ˈpɔrʃə) is an inner satellite of Uranus. It was discovered from the images taken by "Voyager 2" on 1986-01-03, and was given the temporary designation S/1986 U 1. [cite web|last=Smith|first=B. A.|title=IAU Circular No. 4164|date=January 16 1986|url=http://cfa-www.harvard.edu/iauc/04100/04164.html#Item1|accessdate=2006-08-06] The moon is named after Portia, the heroine of William Shakespeare's play "The Merchant of Venice". It is also designated Uranus XII.cite web|title=Planet and Satellite Names and Discoverers|work=Gazetteer of Planetary Nomenclature|publisher=USGS Astrogeology|date=July 21 2006|url=http://planetarynames.wr.usgs.gov/append7.html|accessdate=2006-08-06]

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 Portia Group, which includes Bianca, Cressida, Desdemona, Juliet, Rosalind, Cupid, Belinda and Perdita. These satellites have similar orbits and photometric properties.

Little is known about Portia beyond its size of about 140 km, orbit, and geometric albedo of about 0.08.

In the Voyager 2 images, Portia appears as an elongated 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.cite journal|last=Dumas|first=Christophe|coaurhors=Smith, Bradford A.; and Terrile, Richard J.|title=Hubble Space Telescope NICMOS Multiband Photometry of Proteus and Puck|journal=Astronomical Journal|year=2003|volume=126|pages=1080–1085|doi=10.1086/375909|url=http://adsabs.harvard.edu/abs/2003AJ....126.1080D]

References

External links

* [http://solarsystem.nasa.gov/planets/profile.cfm?Object=Ura_Portia Portia Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]