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. Bibcode: 1998AJ....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. Bibcode: 2001Icar..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. Bibcode: 2017AJ....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. Bibcode: 2001Icar..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. Bibcode: 1997Icar..125....1D. 

External links



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