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Portia (moon) - Wikipedia

From Wikipedia, the free encyclopedia

Portia
Discovery

Discovered by	Stephen P. Synnott / Voyager 2
Discovery date	January 3, 1986
Designations
Designation	Uranus XII
Pronunciation	/ˈpɔːrʃə/^[1]
Adjectives	Portian /ˈpɔːrʃən/^[1]
Orbital characteristics^[2]
Semi-major axis	66,097.265 ± 0.050 km
Eccentricity	0.00005 ± 0.00008
Orbital period (sidereal)	0.5131959201 ± 0.0000000093 d
Average orbital speed	9.37 km/s^[a]
Inclination	0.05908 ± 0.039° (to Uranus' equator)
Satellite of	Uranus
Group	ring shepherd
Physical characteristics
Dimensions	156 × 126 × 126 km^[3]^{[note 1]}
Surface area	~58 000 km²^[a]
Volume	1296800±14.8% km³^[4]
Mass	(1.1671±0.1730)×10¹⁸ kg^[4]
Mean density	≥0.57 g/cm³^[4] ~0.90 g/cm³ (assumed)
Surface gravity	~0.013–0.02 m/s²^[a]
Escape velocity	~0.045–0.05 km/s^[a]
Synodic rotation period	synchronous^[3]
Axial tilt	zero^[3]
Albedo	0.08 ± 0.01 ^[5] 0.07^[6]^[7]
Temperature	~64 K^[a]
^ 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]

Gallery

Portia seen on January 23, 1986.

Notes

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

References

^ ^a ^b "Portia". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ ^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.
^ ^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.
^ ^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.
^ ^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.
^ "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.
^ 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.
^ 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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Uranus

Outline

Geography

Major moons

Astronomy

Discovery	William Herschel Gerard Kuiper James L. Elliot William Lassell
General	Uranus-crossing minor planets
Co-orbitals	Trojans 2011 QF₉₉ 2014 YX₄₉ 83982 Crantor (472651) 2015 DB216

Exploration

Past	Voyager 2 (1986 flyby)
Future	Tianwen-4 (2029, flyby 2045)
Proposals	MUSE OCEANUS ODINUS Uranus Orbiter and Probe Uranus Pathfinder

Fiction

Moons of Uranus

Listed in approximately increasing distance from Uranus

Inner

Major (spheroid)

Miranda
Ariel
Umbriel
Titania
Oberon

Outer (irregular)

Prograde	Margaret
Retrograde	Francisco Caliban Stephano S/2023 U 1 Trinculo Sycorax Prospero Setebos Ferdinand

Geological features

v t e Natural satellites of the Solar System
Planetary satellites of	Earth Mars Jupiter Saturn Uranus Neptune
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Minor-planet moons	Near-Earth Florence Didymos Dimorphos Moshup Squannit 1994 CC 2001 SN₂₆₃ Main belt Kalliope Linus Euphrosyne Daphne Peneius Eugenia Petit-Prince Sylvia Romulus Remus Minerva Aegis Gorgoneion Camilla Elektra Kleopatra Alexhelios Cleoselene Ida Dactyl Roxane Olympias Pulcova Balam Dinkinesh (Selam) Jupiter trojans Patroclus Menoetius Hektor Skamandrios Eurybates Queta TNOs Lempo Hiisi Paha 2002 UX₂₅ Sila–Nunam Salacia Actaea Varda Ilmarë Gǃkúnǁʼhòmdímà Gǃòʼé ǃHú 2013 FY₂₇
Ranked by size	Ganymede largest: 5268 km / 0.413 Earths Titan Callisto Io Moon Europa Triton Titania Rhea Oberon Iapetus Charon Umbriel Ariel Dione Tethys Dysnomia Enceladus Miranda Vanth Proteus Mimas Ilmarë Nereid Hiʻiaka Actaea Hyperion Phoebe ...
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