Telesto (moon)

Telesto /təˈlɛstoʊ/ is a moon of Saturn. It was discovered by Smith, Reitsema, Larson and Fountain in 1980 from ground-based observations, and was provisionally designated S/1980 S 13.^[4] In the following months, several other apparitions were observed: S/1980 S 24,^[5] S/1980 S 33,^[6] and S/1981 S 1.^[7]

Telesto

Telesto as seen by the Cassini probe on 11 October 2005
Discovery
Discovered by	Bradford A. Smith Harold Reitsema Stephen M. Larson John W. Fountain
Discovery date	April 8, 1980
Designations
Designation	Saturn XIII
Pronunciation	/təˈlɛstoʊ/
Named after	Τελεστώ Telestō
Alternative names	Tethys B S/1980 S 13
Adjectives	Telestoan /tɛləˈstoʊ.ən/ or Telestoian /tɛləˈstoʊ.iən/
Orbital characteristics
Semi-major axis	295000 km[1]
Eccentricity	0.001[1]
Orbital period (sidereal)	1.887802 d[1]
Inclination	1.19° (to Saturn's equator)
Satellite of	Saturn
Group	L4 Tethys trojan
Physical characteristics
Dimensions	33.2 × 23.4 × 19.2 km (± 0.6 × 0.6 × 0.4 km)[2]: 2
Mean diameter	24.6±0.6 km[2]: 2
Volume	7795 km3[a]
Mass	≈ 4×1015 kg (assumed; unmeasured)[b]
Mean density	≈ 0.5 g/cm3 (assumed; unmeasured)[2]: 3
Surface gravity	≈ 0.0011–0.0014 m/s2[2]: 3
Escape velocity	≈ 0.006 km/s at longest axis to ≈ 0.007 km/s at poles
Axial tilt	zero
Apparent magnitude	18.7[3]

In 1983 it was officially named after Telesto of Greek mythology.^[c] It is also designated as Saturn XIII or Tethys B.

Telesto is co-orbital with Tethys, residing in Tethys's leading Lagrangian point (L₄). This relationship was first identified by Seidelmann et al. in 1981.^[8] Another moon, Calypso, resides in the other (trailing) Lagrangian point of Tethys, 60 degrees in the other direction from Tethys. The Saturnian system has two additional trojan moons. It eclipsed Tethys in 2024.^{[citation needed]}

Exploration

The Cassini probe performed a distant flyby of Telesto on October 11, 2005. The resulting images show that its surface is surprisingly smooth, devoid of small impact craters.

Notes

1. Calculated from Telesto's volume-equivalent sphere radius of 12.3±0.3 km given by Thomas et al. (2020)^[2]: 2
2. Calculated by multiplying Telesto's volume with its assumed density of 500 kg/m³.
3. Transactions of the International Astronomical Union, Vol. XVIIIA, 1982 (confirms Janus, names Epimetheus, Telesto, Calypso) (mentioned in IAUC 3872)