Cressida (moon)

Cressida /ˈkrɛsɪdə/ 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]

There is also an asteroid called 548 Kressida.
Cressida
Voyager 2 image of Cressida
Discovery
Discovered byStephen P. Synnott / Voyager 2
Discovery dateJanuary 9, 1986
Designations
Designation
Uranus IX
Pronunciation/ˈkrɛsɪdə/[1]
Named after
Χρησίδα
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[lower-alpha 1]
Volume~260,000 km³[lower-alpha 1]
Mass2.5±0.4×1017 kg[7]
Mean density
0.86±0.16 g/cm³[7]
~0.013 m/s2[lower-alpha 1]
~0.034 km/s[lower-alpha 1]
synchronous[4]
zero[4]
Albedo
Temperature~64 K[lower-alpha 1]

    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. 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. 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. 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. "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 24 October 2008. Retrieved 12 December 2008.
    6. Williams, Dr. David R. (23 November 2007). "Uranian Satellite Fact Sheet". NASA (National Space Science Data Center). Retrieved 12 December 2008.
    7. 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. 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.
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