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Moon of Uranus From Wikipedia, the free encyclopedia
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]
Discovery | |
---|---|
Discovered by | Stephen P. Synnott / Voyager 2 |
Discovery date | January 9, 1986 |
Designations | |
Designation | Uranus IX |
Pronunciation | /ˈkrɛsədə/[1] |
Named after | Χρησίδα |
Adjectives | Cressidian /krɛˈsɪdiən/[2] |
Orbital characteristics[3] | |
61,766.730 ± 0.046 km | |
Eccentricity | 0.00036 ± 0.00011 |
0.463569601 ± 0.000000013 d | |
Inclination | 0.006 ± 0.040° (to Uranus' equator) |
Satellite of | Uranus |
Physical characteristics | |
Dimensions | 92 × 74 × 74 km[4][note 1] |
~20000 km2[lower-alpha 1] | |
Volume | 263800±38.0% km3[5] |
Mass | (1.839±0.212)×1017 kg[5] |
Mean density | 0.70+0.44 −0.21 g/cm3[5] |
~0.006–0.009 m/s2[lower-alpha 1] | |
~0.023–0.026 km/s[lower-alpha 1] | |
synchronous[4] | |
zero[4] | |
Albedo | 0.08±0.005[6] 0.07[7] |
Temperature | ~65 K[lower-alpha 1] |
|
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 Voyager 2 imagery Cressida appears as an elongated object, with 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]
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