Telesto (moon)

Telesto
Telesto, recorded by Cassini in October 2005
Provisional or systematic name	S / 1980 S 13
Central body	Saturn
Properties of the orbit
Major semi-axis	294,619 km
Periapsis	294,560 km
Apoapsis	294,678 km
eccentricity	0.0002
Orbit inclination	1.190 °
Orbital time	1,887802 d
Mean orbital velocity	11.36 km / s
Physical Properties
Albedo	0.994
Apparent brightness	18.7 mag
Medium diameter	24.8 ± 0.8 (32.6 × 23.6 × 20.0) km
Dimensions	4.0464 · 10 15 kg
surface	1,932 km 2
Medium density	0.5 g / cm 3
Sidereal rotation	1.887802 days
Axis inclination	0 °
Acceleration of gravity on the surface	≈ 0.0033 m / s 2
Escape speed	≈ 9.0 m / s
discovery
Explorer	Bradford A. Smith Harold Reitsema, Stephen M. Larson, John W. Fountain
Date of discovery	April 8, 1980
Remarks	Largest albedo of all moons in the solar system
Size comparison of Tethys and its Trojan moons Telesto (left) and Calypso (right)

Telesto (also Saturn XIII ) is the sixteenth and one of the smaller of the 82 known moons of the planet Saturn and one of two Trojan moons of Tethys . It has the brightest of all known surfaces in the solar system, which even exceeds the reflectivity of freshly fallen snow.

Discovery and naming

Telesto was discovered on April 8, 1980 by astronomers Bradford A. Smith , Harold James Reitsema , Stephen M. Larson, and John W. Fountain through terrestrial telescope observations ; the moon Telesto was initially given the provisional designation S / 1980 S 13.

In October 1980, the Voyager 1 space probe took pictures while flying past Saturn, on which Telesto can be seen as a tiny point, from which it was possible to deduce a very small size.

In 1983 the moon of Saturn was officially named after Telesto , a daughter of Oceanus and Tethys from Greek mythology . The name means "success" in translation. Telesto is sometimes referred to as "Tethys B".

Track properties

Orbit

Telesto orbits Saturn on a prograde , almost perfectly circular orbit at an average distance of 294,619 km (approx. 4,888 Saturn radii) from its center , i.e. about 234,351 km above its cloud ceiling. The orbit eccentricity is 0.0002, the orbit is 1.19 ° inclined to the equator of Saturn , so it lies almost in the equatorial plane of the planet. Due to the very low eccentricity, the distance to Saturn only varies by about 118 km.

The orbit of the next inner moon Enceladus is on average about 56,671 km from Telesto's orbit, the distance of the orbits of the next outer moon Dione and the orbits of its Trojan moons Helene and Polydeuces is on average about 82,777 km.

Telesto orbits Saturn in 1 day, 21 hours, 18 minutes and 26.1 seconds. Telesto needs 12 hours and around 25.3 minutes longer than its inner neighbor Enceladus for one orbit.

Telesto's orbit is deep in Saturn's magnetosphere , so the plasma that rotates with the planet will hit the next hemisphere. It is also hit by energetic particles ( electrons and ions ).

Lagrange points L ₁ to L ₅

Railway resonances

Telesto's orbit is co-ordinate with the orbits of the much larger, dominant Tethys and the slightly smaller Calypso . These so-called Tethys Trojan moons , Telesto and Calypso, run in Tethys' Lagrange points L ₄ and L ₅ , each at an angular distance of 60 ° in front of and behind this moon, on the same orbit around the planet (1: 1 orbital resonance ) . Telesto runs through the leading Lagrangian point L ₄ and therefore leads the orbit. Tethys follows 60 ° behind, Calypso Saturn orbits another 60 ° behind in the following Lagrangian point L ₅ .

Tethys and her two Trojan moons orbit Saturn within the E-Ring , so the surfaces of the moons are in constant bombardment by micrometeorites .

rotation

The rotation time is the same as the orbital time and Telesto shows, like the earth's moon and all the large satellites of the gas giants , a synchronous rotation , which also takes place within 1 day, 21 hours, 18 minutes and 26.1 seconds, so Telesto always shows with the same hemisphere to Saturn. The axis of rotation is inclined by 0 ° with respect to the orbit, so it is exactly perpendicular to the plane of rotation.

Physical Properties

Telesto towards the leading hemisphere from 36,000 km away (Cassini, 2009)

size

Telesto is irregularly shaped, with a mean diameter of 15 miles. The exact dimensions are 32.6 × 23.6 × 20.0 km, which gives the moon the shape of a three-axis ellipsoid . The long axis is aligned with Saturn, the middle axis is between the leading and following hemispheres and the shortest axis is between the poles . In its shape, but not in its dimensions, it resembles the Pandora that runs further within . Telesto is the seventeenth largest moon of Saturn.

In terms of size, Telesto is roughly comparable to the larger Martian moon Phobos .

The total area of ​​Telesto is around 1,932 km², which roughly corresponds to the area of ​​the island state of Mauritius or the Swiss canton of St. Gallen .

internal structure

The density is very low at 0.5 g / cm ³ , which indicates that Telesto is mainly composed of water ice . The low density also indicates that it may belong to the so-called rubble piles , which have cavities inside due to the comparatively weak gravity.

Telesto: false color representation from IR, Vis and UV images from a distance of 20,000 km (Cassini, 2005)

Telesto (dark point above the ring) from a great distance with Saturn's main rings and the moons Titan (large), Dione (medium) and Prometheus (point on the lower edge of the ring) (Cassini, 2005)

surface

The Trabant has a very bright surface (currently the brightest known surface in the solar system ) with an albedo of 0.994, i. That is, 99.4% of the incident sunlight is reflected . Some of the meteorite impact craters are clearly visible. In general, however, the surface is very gentle with few traces of older craters, suggesting a thick layer of fine-grained ice regolith , possibly resulting from constant bombardment by the E-Ring particles.

Overall, the surface does not show a uniform color. The origin of the color differences is not yet understood, but they may come from subtle differences in the surface composition or from a different size of the particles of the regolith mantle.

exploration

Seen from the earth, the Saturn companion with an apparent brightness of 18.7 ^m (which is one 13,200,000th of the central planet) is a faint object.

Telesto has been visited by three space probes so far , namely by the flyby probes Voyager 1 on November 12, 1980 and Voyager 2 on August 25, 1981 and finally Cassini-Huygens , which has been orbiting Saturn since July 1, 2004. Cassini's next flyby occurred on October 11, 2005, when the Telesto probe passed at a distance of 11,429 km.

Web links

• IAUC 3466: Satellites of Saturn April 10, 1980 (discovery)
• IAUC 3872: Satellites of Jupiter and Saturn September 30, 1983 (designation)
• Current Cassini recordings from Telesto picture gallery (English)

Individual evidence

1. ↑ Paul Rincon: Saturn overtakes Jupiter as planet with most moons. BBC , October 7, 2019, accessed March 20, 2020 . 

further inside	Saturn moons	further outside
Tethys	Semi- major axis  (km) Telesto 294.700	Calypso