Telesto (moon)

Bradford A. Smith, Harold Reitsema, Stephen M. Larson, John W. Fountain

Telesto ( Saturn XIII) is the sixteenth and one of the smaller of the 62 known moons of the planet Saturn, as well as 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.

• 3.1 size
• 3.2 Internal structure
• 3.3 Surface

Discovery and designation

Telesto was discovered on April 8, 1980 by the astronomer Bradford A. Smith, Harold James Reitsema, Stephen M. Larson and John W. Fountain on the basis of ground-based telescopic observations; the moon Telesto first received the provisional designation S/1980 S 13

The space probe Voyager 1 took 1980 pictures on the flyby of Saturn, on which Telesto is recognizable as pinhead- sized dot, from which it could be concluded on a very small size already.

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

Web properties

Orbit

Telesto orbits Saturn on a prograde, nearly perfectly circular orbit at an average distance of 294,619 kilometers (about 4,888 Saturn radii ) from the center (or the center of gravity ), or about 234,351 km on whose cloud tops. The orbital eccentricity is 0.0002, the orbit is inclined 1.19 ° relative to the equator of Saturn, that is nearly in the equatorial plane of the planet. Due to the very low eccentricity, the web varies in distance to Saturn at about 118 km.

The orbit of the next inner moon Enceladus is on average about 56,671 km away from the orbit of Telesto, the removal of the tracks of the next outer moon Dione and its Trojan moons Helene and Polydeuces is an average of about 82,777 km.

Telesto orbits Saturn in 1 day, 21 hours, 18 minutes and 26.1 seconds. This is about 2 hours and 50.9 minutes longer than the orbital period of Jupiter's moon Io. Telesto required for one revolution about 12 hours, and 25.3 minutes longer than the inner adjacent Enceladus.

The orbit of Telesto lies deep in the magnetosphere of Saturn, so that the plasma co-rotates with the planet that meets the following hemisphere. It is thus also hit by energetic particles (electrons and ions).

Train resonances

The orbit of Telesto is co-orbital with the orbits of the much larger, dominant Tethys as well as the slightly smaller Calypso. These so-called Tethys Trojan moons, Telesto and Calypso, run in Tethys ' Lagrange points L4 and L5, respectively at an angular distance of 60 ° in front and behind the moon, on the same orbit around the planet ( 1:1 orbital resonance ). Telesto running it through the leading Lagrange point L4, and therefore leads to the orbit. 60 ° behind follows Tethys, another 60 ° behind Calypso orbits Saturn in the following Lagrangian point L5.

Tethys and its two Trojan moons orbit Saturn within the E ring, so that the surfaces of the moons are in a constant bombardment by micrometeorites.

Rotation

The rotation period is equal to the orbital period and Telesto has with how the Earth's moon and all the major satellites of the gas giants, in a synchronous rotation, which therefore also takes place within 1 day 21 hours, 18 minutes and 26.1 seconds, so always shows with the same hemisphere to Saturn. The axis of rotation is inclined 0 ° to the orbit, so is therefore precisely perpendicular to the plane of rotation.

Physical Properties

Size

Telesto is irregularly shaped, with a mean diameter of 24.8 km. The exact dimensions are 32.6 × 23.6 × 20.0 km, which gives the moon the shape of a triaxial ellipsoid. The longitudinal axis is aligned with Saturn, the central axis is between leading and following hemisphere and the shortest axis between the poles. In its form, but not in its dimensions, it resembles the more inward current Pandora. Telesto is the siebzehntgrößte Saturn moon.

From the size Telesto is to be compared for instance with the larger Martian moon Phobos.

The total area of ​​1932 km ² Telesto is about, this is roughly equivalent to the area of ​​the island nation of Mauritius. It is also comparable with the area of the Swiss canton of St. Gallen.

Internal construction

The density is 0.5 g/cm3 with very low, indicating that Telesto is composed mainly of water ice. The low density indicates that it may be one of the so-called Rubble Piles, which, due to the relatively weak gravitational inside cavities.

Surface

The Trabant has an extremely bright surface (currently the brightest known surface in the solar system ) with an albedo of 0.994, ie, 99.4 % of the incident sunlight is reflected. Clearly visible are several impact craters from meteorites. Generally, however, the surface is very smooth and has few traces of older craters, indicating a thick layer of fine-grained ice - regolith, possibly resulting from the continuous bombardment by the particles of the E- ring.

Overall, the surface does not have a uniform color. The origin of the color differences is not yet understood, but it may originate from subtle differences in the surface composition or of a different size of the particles of Regolithmantels.

Research

From the Earth as seen from Saturn companion with an apparent brightness of 18.7 m ( 1:13200000 of the central planet is ), a light faint object.

Telesto was attended by three previous spacecraft, notably by the flyby probes Voyager 1 on 12 November 1980 and Voyager 2 on 25 August 1981 and finally Cassini -Huygens, the orbiting Saturn since July 1, 2004. The next flyby of Cassini took place on 11 October 2005, when the spacecraft Telesto happened at a distance of 11,429 km.