Cressida (moon)


There is also an asteroid called 548 Kressida.
Cressida enhanced Southern skies-2.png
Enhanced Voyager 2 image of Cressida
Discovered byStephen P. Synnott / Voyager 2
Discovery dateJanuary 9, 1986
Uranus IX
Named after
AdjectivesCressidian /krɛˈsɪdiən/[2]
Orbital characteristics
Mean orbit radius
61,766.730 ± 0.046 km[3]
Eccentricity0.00036 ± 0.00011[3]
0.463569601 ± 0.000000013 d[3]
Inclination0.006 ± 0.040° (to Uranus' equator)[3]
Satellite ofUranus
Physical characteristics
Dimensions92 × 74 × 74 km[4]
Mean radius
39.8 ± 2 km[4][5][6]
~20,000 km²[a]
Volume~260,000 km³[a]
Mass2.5±0.4×1017 kg[7]
Mean density
0.86±0.16 g/cm³[7]
~0.013 m/s2[a]
~0.034 km/s[a]
Temperature~64 K[a]

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


Explanatory notes

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


  1. ^ Benjamin Smith (1903) The Century Dictionary and Cyclopedia
  2. ^ Kellog (1995) Boccaccio's and Chaucer's Cressida
  3. ^ a b c d e 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.
  4. ^ a b c d e f g 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.
  5. ^ a b "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 24 October 2008. Retrieved 12 December 2008.
  6. ^ a b Williams, Dr. David R. (23 November 2007). "Uranian Satellite Fact Sheet". NASA (National Space Science Data Center). Retrieved 12 December 2008.
  7. ^ a b c 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.
  8. ^ 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.
  9. ^ Smith, B. A. (January 16, 1986). "Satellites of Uranus". IAU Circular. 4164. Retrieved 29 October 2011.
  10. ^ "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology. July 21, 2006. Retrieved 6 August 2006.
  11. ^ 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.

External links

  • Cressida Profile by NASA's Solar System Exploration
  • Uranus' Known Satellites (by Scott S. Sheppard)