Moon Cressida
Cressida /ˈkrɛsədə/ is an inner satellite of Uranus.
- There is also an asteroid called 548 Kressida.
It was discovered from the images taken by Voyager 2 on 9 January 1986, and was given the temporary designation S/1986 U 3. 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.
 Enhanced Voyager 2 image of Cressida | |
| Discovery | |
|---|---|
| Discovered by | Stephen P. Synnott / Voyager 2 |
| Discovery date | January 9, 1986 |
| Designations | |
Designation | Uranus IX |
| Pronunciation | /ˈkrɛsədə/ |
Named after | Χρησίδα |
| Adjectives | Cressidian /krɛˈsɪdiən/ |
| Orbital characteristics | |
| 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 |
| ~20000 km2 | |
| Volume | 263800±38.0% km3 |
| Mass | (1.839±0.212)×1017 kg |
Mean density | 0.70+0.44 −0.21 g/cm3 |
| ~0.006–0.009 m/s2 | |
| ~0.023–0.026 km/s | |
| synchronous | |
| zero | |
| Albedo | 0.08±0.005 0.07 |
| Temperature | ~65 K |
Cressida belongs to the Portia group of satellites, which includes Bianca, Desdemona, Juliet, Portia, Rosalind, Cupid, Belinda and Perdita. These satellites have similar orbits and photometric properties. Other than its orbit, size of 92 × 74 km and geometric albedo of 0.08, 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. Its surface is grey in color.
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. Cressida is one of the few small satellites of Uranus for which the mass has been directly measured.
Cressida may collide with Desdemona within the next 100 million years.
See also
Notes
References
External links
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