Moon Calypso

It was discovered in 1980, from ground-based observations, by Dan Pascu, P. Kenneth Seidelmann, William A. Baum, and Douglas G. Currie, and was provisionally designated S/1980 S 25 (the 25th satellite of Saturn discovered in 1980). Several other apparitions of it were recorded in the following months: S/1980 S 29, S/1980 S 30, S/1980 S 32, and S/1981 S 2. In 1983 it was officially named after Calypso of Greek mythology. It is also designated Saturn XIV or Tethys C.

Calypso

Calypso image from Cassini (February 13, 2010)
Discovery
Discovered by	Dan Pascu P. Kenneth Seidelmann William A. Baum Douglas G. Currie
Discovery date	March 13, 1980
Designations
Designation	Saturn XIV
Pronunciation	/kəˈlɪpsoʊ/
Named after	Καλυψώ Kalypsō
Alternative names	Tethys C S/1980 S 25
Adjectives	Calypsoan /kælɪpˈsoʊ.ən/, Calypsonian /kælɪpˈsoʊniən/
Orbital characteristics
Semi-major axis	295000 km
Eccentricity	0.001
Orbital period (sidereal)	1.887803 d
Inclination	1.56° (to Saturn's equator)
Satellite of	Saturn
Group	L5 Tethys trojan
Physical characteristics
Dimensions	29.4 × 18.6 × 12.8 km (± 0.6 × 1.8 × 0.6 km): 2
Mean diameter	19.0±0.8 km: 2
Volume	3591 km3
Mass	≈ 2×1015 kg (assumed; unmeasured)
Mean density	≈ 0.5 g/cm3 (assumed; unmeasured): 3
Surface gravity	≈ 0.0009–0.0013 m/s2: 3
Escape velocity	≈ 0.004 km/s at longest axis to ≈ 0.006 km/s at poles
Synodic rotation period	synchronous
Axial tilt	zero
Albedo	1.34±0.10 (geometric)

Calypso is co-orbital with the moon Tethys, and resides in Tethys' trailing Lagrangian point (L₅), 60 degrees behind Tethys. This relationship was first identified by Seidelmann et al. in 1981. The moon Telesto resides in the other (leading) Lagrangian point of Tethys, 60 degrees in the other direction from Tethys. Calypso and Telesto have been termed "Tethys trojans", by analogy to the trojan asteroids, and are half of the four presently known trojan moons.

Like many other small Saturnian moons and small asteroids, Calypso is irregularly shaped, has overlapping large craters, and appears to also have loose surface material capable of smoothing the craters' appearance. Its surface is one of the most reflective (at visual wavelengths) in the Solar System, with a visual geometric albedo of 1.34. This very high albedo is the result of the sandblasting of particles from Saturn's E-ring, a faint ring composed of small, water-ice particles generated by Enceladus' south polar geysers.

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  Another February 13, 2010 image showing flow-like albedo features
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  Cassini image from September 23, 2005
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  Calypso as seen by Voyager 2 (August 1981)

• List of natural satellites