Calypso (moon)
| Calypso | |
|---|---|
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| Calypso, received on 13 February 2010 by the NASA -Raumsonde Cassini | |
| Provisional or systematic name | S / 1980 S 25 |
| Central body | Saturn |
| Properties of the orbit | |
| Major semi-axis | 294,619 km |
| Periapsis | 294,472 km |
| Apoapsis | 294,766 km |
| eccentricity | 0.0005 |
| Orbit inclination | 1.56 ° |
| Orbital time | 1,887802 d |
| Mean orbital velocity | 11.36 km / s |
| Physical Properties | |
| Albedo | 0.70 |
| Apparent brightness | 18.7 mag |
| Medium diameter | 21.4 ± 1.4 (30.2 × 23.0 × 14.0) km |
| Dimensions | 2.5477 · 10 15 kg |
| surface | 1,439 km 2 |
| Medium density | 0.5 g / cm 3 |
| Sidereal rotation | 1.887802 days |
| Axis inclination | 0 ° |
| Acceleration of gravity on the surface | ≈ 0.0027 m / s 2 |
| Escape speed | ≈ 7.1 m / s |
| Surface temperature | −198 ° C (75) K |
| discovery | |
| Explorer |
Dan Pascu, |
| Date of discovery | August 13, 1980 |
| Remarks | Simply bound rotation |
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| Size comparison of Tethys and its Trojan moons Telesto (left) and Calypso (right) | |
Calypso (or Saturn XIV ) is the seventeenth and one of the smaller of the 82 known moons of the planet Saturn, as well as one of two Trojan moons of Tethys .
Discovery and naming
Calypso was discovered on August 13, 1980 by the astronomers Dan Pascu , P. Kenneth Seidelmann , William A. Baum and Douglas G. Currie on the basis of terrestrial telescope observations ; the moon was initially given the provisional designation S / 1980 S 25 . In the following months, Calypso was given the additional designations S / 1980 S 29 , S / 1980 S 30 , S / 1980 S 32 , and S / 1981 S 2 , which all turned out to be the same object.
In 1983 she was officially named after Calypso , a nymph from Greek mythology who held the hero Odysseus on her island Ogygia for seven years . Odysseus was released again on the orders of Zeus , transmitted by the messenger of the gods Hermes . Reluctantly, she provides him with tools to build a raft, and later with travel food. Calypso is said to be a daughter of the titan Atlas .
In the translation, the name means "hiding place", "hidden".
Track properties
Orbit
Calypso 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 (or the center of gravity ), i.e. approx. 234,351 km above its cloud ceiling. The orbit eccentricity is 0.0005, the orbit is inclined 1.56 ° to the equator of Saturn , so it is almost in the equatorial plane of the planet. Due to the very low eccentricity, the orbit varies by about 295 km in the distance to Saturn.
The orbits of the nearest inner moon Enceladus are on average about 56,671 km from the orbit of Calypso, the distances of the orbits of the next outer moons Dione and their Trojan moons Helene and Polydeuces are on average about 82,777 km.
Calypso orbits Saturn in 1 day, 21 hours, 18 minutes and 26.1 seconds. Calypso needs 12 hours and about 25.3 minutes longer than its inner neighbor Enceladus for one orbit.
Calypso'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 ).
Railway resonances
The orbit of Calypso is co-ordinate with the orbits of the much larger, dominant Tethys and the slightly larger Telesto . These so-called Tethys Trojan moons , Telesto and Calypso, run in Tethys' Lagrange points L 4 and L 5 , each at an angle of 60 ° in front of and behind this moon, on the same orbit around the planet (1: 1 - Railway resonance ). Calypso runs through the following Lagrangian point L 5 and therefore forms the bottom of the divided orbit.
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 Calypso 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, i.e. always shows 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
size
Calypso is irregularly shaped, with a mean diameter of 13.4 miles. The exact dimensions are 30.2 × 23.0 × 14.0 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 . Calypso is Saturn's nineteenth largest moon.
In terms of size, Calypso can be compared to the larger Martian moon Phobos .
The total area of Telesto is around 1,439 km², which is roughly in the middle of the areas of the Swiss cantons of Lucerne and Aargau .
internal structure
The density is very low at 0.5 g / cm 3 , which indicates that Calypso is mainly composed of water ice . The low density indicates that it may belong to the so-called rubble piles , which have cavities inside due to the comparatively weak gravity.
surface
The Trabant has a very light surface with an albedo of 0.70, i.e. That is, 70% 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 that may have resulted from constant bombardment by the E-Ring particles.
exploration
Seen from the earth, the Saturn companion with an apparent brightness of 18.7 m (which is 1: 15900000 of the central planet) is a faint object.
So far, Calypso has been visited by three space probes : namely by the flyby probes Voyager 1 on November 12, 1980 and Voyager 2 on August 25, 1981 and Cassini , which orbited Saturn since July 1, 2004. The last flyby by Cassini occurred on February 13, 2010 at a distance of 23,000 km.
Web links
- IAUC 3496: Satellites of Saturn July 31, 1980 (discovery)
- IAUC 3872: Satellites of Jupiter and Saturn September 30, 1983 (designation)
media
Individual evidence
- ↑ Paul Rincon: Saturn overtakes Jupiter as planet with most moons. BBC , October 7, 2019, accessed March 20, 2020 .
| further inside | Saturn moons | further outside |
| Telesto |
Semi- major axis (km) Calypso 294.700 |
Dione |