Astronomy:Cressida (moon)

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Short description: Moon of Uranus
There is also an asteroid called 548 Kressida.
Cressida
Cressida enhanced Southern skies-2.png
Enhanced Voyager 2 image of Cressida
Discovery
Discovered byStephen P. Synnott / Voyager 2
Discovery dateJanuary 9, 1986
Designations
Designation
Uranus IX
Pronunciation/ˈkrɛsədə/[1]
Named afterΧρησίδα
AdjectivesCressidian /krɛˈsɪdiən/[2]
Orbital characteristics
Mean orbit radius61,766.730 ± 0.046 km[3]
Eccentricity0.00036 ± 0.00011[3]
Orbital period0.463569601 ± 0.000000013 d[3]
Inclination0.006 ± 0.040° (to Uranus' equator)[3]
Satellite ofUranus
Physical characteristics
Dimensions92 × 74 × 74 km[4]
Mean radius39.8 ± 2 km[4][5][6]
Surface area~20,000 km2[lower-alpha 1]
Volume~260,000 km3[lower-alpha 1]
Mass2.5±0.4×1017 kg[7]
Mean density0.86±0.16 g/cm3[7]
~0.013 m/s2[lower-alpha 1]
~0.034 km/s[lower-alpha 1]
Rotation periodsynchronous[4]
Axial tiltzero[4]
Albedo
Physics~64 K[lower-alpha 1]


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.[9] 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.[10]

Cressida belongs to the Portia group of satellites, which includes Bianca, Desdemona, Juliet, Portia, Rosalind, Cupid, Belinda and Perdita.[8] These satellites have similar orbits and photometric properties.[8] Other than its orbit,[3] radius of 41 km[4] and geometric albedo of 0.08,[8] 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 was found to be 2.5±0.4×1017 kg. Cressida is the only small satellite of Uranus for which the mass has been directly measured.[7]

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

See also

References

Explanatory notes

  1. 1.0 1.1 1.2 1.3 1.4 Calculated on the basis of other parameters.

Citations

  1. Benjamin Smith (1903) The Century Dictionary and Cyclopedia
  2. Kellog (1995) Boccaccio's and Chaucer's Cressida
  3. 3.0 3.1 3.2 3.3 3.4 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. doi:10.1086/300263. Bibcode1998AJ....115.1195J. 
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 Karkoschka, Erich (2001). "Voyager's Eleventh Discovery of a Satellite of Uranus and Photometry and the First Size Measurements of Nine Satellites". Icarus 151 (1): 69–77. doi:10.1006/icar.2001.6597. Bibcode2001Icar..151...69K. 
  5. 5.0 5.1 "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 24 October 2008. http://ssd.jpl.nasa.gov/?sat_phys_par. 
  6. 6.0 6.1 Williams, Dr. David R. (23 November 2007). "Uranian Satellite Fact Sheet". NASA (National Space Science Data Center). http://nssdc.gsfc.nasa.gov/planetary/factsheet/uraniansatfact.html. 
  7. 7.0 7.1 7.2 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. doi:10.3847/1538-3881/aa880e. Bibcode2017AJ....154..153C. 
  8. 8.0 8.1 8.2 8.3 Karkoschka, Erich (2001). "Comprehensive Photometry of the Rings and 16 Satellites of Uranus with the Hubble Space Telescope". Icarus 151 (1): 51–68. doi:10.1006/icar.2001.6596. Bibcode2001Icar..151...51K. 
  9. Smith, B. A. (January 16, 1986). "Satellites of Uranus". IAU Circular 4164. http://www.cbat.eps.harvard.edu/iauc/04100/04164.html#Item1. Retrieved 29 October 2011. 
  10. "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology. July 21, 2006. http://planetarynames.wr.usgs.gov/Page/Planets. 
  11. Duncan, Martin J.; Lissauer, Jack J. (1997). "Orbital Stability of the Uranian Satellite System". Icarus 125 (1): 1–12. doi:10.1006/icar.1996.5568. Bibcode1997Icar..125....1D. 

External links