Cressida (moon)

Cressida
	Enhanced Voyager 2 image of Cressida
Discovery
Discovered by	Stephen P. Synnott / Voyager 2
Discovery date	January 9, 1986
Designations
Designation	Uranus IX
Pronunciation	/ˈkrɛsədə/
Named after	Χρησίδα
Adjectives	Cressidian /krɛˈsɪdiən/
Orbital characteristics
Semi-major axis	61,766.730 ± 0.046 km
Eccentricity	0.00036 ± 0.00011
Orbital period (sidereal)	0.463569601 ± 0.000000013 d
Inclination	0.006 ± 0.040° (to Uranus' equator)
Satellite of	Uranus
Physical characteristics
Dimensions	92 × 74 × 74 km
Surface area	~20000 km2
Volume	263800±38.0% km3
Mass	(1.839±0.212)×1017 kg
Mean density	0.70+0.44; −0.21 g/cm3
Surface gravity	~0.006–0.009 m/s2
Escape velocity	~0.023–0.026 km/s
Synodic rotation period	synchronous
Axial tilt	zero
Albedo	0.08±0.005; 0.07
Temperature	~65 K
	^ Only two dimensions are known; the third dimension has been assumed to equal the smaller known dimension. ;

There is also an asteroid called 548 Kressida.

Cressida /ˈkrɛsədə/ is an inner satellite of Uranus. It was discovered from the images taken by Voyager 2 on 9 January 1986, and was given the temporary designation S/1986 U 3.^[8] It was named after Cressida, the Trojan daughter of Calchas, a tragic heroine who appears in William Shakespeare's play Troilus and Cressida (as well as in tales by Geoffrey Chaucer and others). It is also designated Uranus IX.^[9]

Cressida belongs to the Portia group of satellites, which includes Bianca, Desdemona, Juliet, Portia, Rosalind, Cupid, Belinda and Perdita.^[6] These satellites have similar orbits and photometric properties.^[6] Other than its orbit,^[3] size of 92 × 74 km^[4] and geometric albedo of 0.08,^[6] virtually nothing is known about it.

In the Voyager 2 images Cressida appears as an elongated object, its major axis pointing towards Uranus. The ratio of axes of Cressida's prolate spheroid is 0.8 ± 0.3.^[4] Its surface is grey in color.^[4]

Cressida orbits close to a 3:2 resonance with the η ring, one of the rings of Uranus. Perturbations of the ring's shape provide a way to measure the mass of Cressida, which in 2024 was found to be (1.839±0.212)×10¹⁷ kg.^[5] Cressida is one of the few small satellites of Uranus for which the mass has been directly measured.^[10]^[5]

Cressida may collide with Desdemona within the next 100 million years.^[11]

Notes

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

References

^ Benjamin Smith (1903). The Century Dictionary and Cyclopedia.
^ Kellog (1995). Boccaccio's and Chaucer's Cressida.
^ ^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. S2CID 118616209.
^ ^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 ^d ^e 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. doi:10.1016/j.icarus.2024.115957. ISSN 0019-1035.
^ ^a ^b ^c ^d 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.
^ Williams, Dr. David R. (23 November 2007). "Uranian Satellite Fact Sheet". NASA (National Space Science Data Center). Retrieved 12 December 2008.
^ 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 6 August 2006.
^ Chancia, Robert. A.; Hedman, Matthew M.; French, Richard G. (28 August 2017). "Weighing Uranus' moon Cressida with the η ring". The Astronomical Journal. 154 (4): 153. arXiv:1708.07566. Bibcode:2017AJ....154..153C. doi:10.3847/1538-3881/aa880e. S2CID 54827255.
^ Duncan, Martin J.; Lissauer, Jack J. (1997). "Orbital Stability of the Uranian Satellite System". Icarus. 125 (1): 1–12. Bibcode:1997Icar..125....1D. doi:10.1006/icar.1996.5568.