William Herschel

Enceladus ( Saturn II) is the fourteenth and sixth largest of the 62 known moons of the planet Saturn. He shows kryovulkanische activities that generate their very high fountains of water ice in the southern hemisphere, a thin atmosphere. These fountains probably feed the E-ring of Saturn. In the area of ​​volcanic activity and liquid water is assumed, so that Enceladus is one of the possible places in the solar system with favorable conditions for the emergence of life.

  • 3.1 size
  • 3.2 Internal structure
  • 3.3 Surface
  • 4.1 Volcanic activity in the southpole
  • 4.2 Methods for life on Enceladus

Discovery and designation

Enceladus was discovered on 28 August 1789 by the British astronomer William Herschel.

Enceladus is the sixth discovered Saturn's moon and the 12th discovered moon in the solar system. He was the second- innermost of the seven previously known large moons of Saturn by the International Astronomical Union ( IAU) designated by the Roman numbering II Through his time at the second closest to Saturn orbit.

The moon was named after the giant Enceladus ( Latin form: Enceladus ) from Greek mythology.

The name " Enceladus " and seven other moons of Saturn was suggested by William Herschel's son, the astronomer John Herschel, in a 1847 publication published ( Results of Astronomical Observations made ​​at the Cape of Good Hope). They should be named after siblings of the Titans Cronus, corresponding to the Roman Saturn.

Web properties


Enceladus orbits Saturn on a prograde, nearly perfectly circular orbit at an average distance of 237,948 km (about 3.948 Saturn radii ) from the center (or the center of gravity ), or about 177,680 km on whose cloud tops. The orbital eccentricity is 0.0047, the orbit is inclined 0.019 degrees from the equator of Saturn, that is nearly in the equatorial plane of the planet. Due to the low eccentricity of the track varies in distance to Saturn by about 2236 km.

The orbits of the next inner moon Pallene is removed an average of about 25,668 km from the orbit of Enceladus, the distances of the orbits of the moons Tethys and their next outer Trojan moons Telesto and Calypso are on average about 56,671 km.

Enceladus orbits Saturn in 1 day, 8 hours, 53 minutes and 6.82 seconds. This is about 1 hour and 2.3 minutes less than the orbital period of Uranus moon Miranda. Enceladus required for a round 5 hours, and about 12.7 minutes longer than the neighboring inner Pallene.

Train resonances

Enceladus is in gravitational interaction with its neighborhood. He is currently in a 2:1 orbital resonance with Dione, as well as close to a 3:2 resonance with Mimas. In addition, Enceladus runs almost in a 4:3 orbital resonance with the next outer moon Tethys. It also bothers his immediately inner neighbors Pallene by its gravitational pull, causing deviations in the path of the order of about 4 km.


The E- ring, sometimes called " Enceladus Ring ", is the outermost of the regular Saturn rings. It is compared to the other rings of the planet extremely broad; it is a very diffuse disk of microscopic ice or dust particles ( with silicates, carbon dioxide and ammonia), which stretches from about the orbit of Mimas to the railway of Rhea, though some observations suggest that it is even up to the titanium -Bahn continues, which means a width 340000-1040000 km. Various mathematical calculations show that such a ring is unstable and has a lifespan of between 10,000 and one million years ago, so he must be constantly fed with new material. The orbit of Enceladus is located within the ring, at its narrowest, but also present the densest place. For this reason, it is believed that the main source of Enceladus ring particles. This theory was supported by the flybys by Cassini. There are two different mechanisms that can feed the Ring: The first and perhaps most important source is the cryovolcanic regions at the South Pole, which eject material, the majority of which indeed falls back to the surface, but by Enceladus ' low escape velocity of 866 km / h particles can escape and go into orbit around Saturn. The second mechanism is the bombardment of micrometeorites, the strike on the moon's surface, releasing dust particles. The latter process is not unique to Enceladus, it affects all the moons that orbit Saturn within the E ring.


The rotation period is equal to the orbital period and Enceladus has with how the Earth's moon and all the major satellites of the gas giant, synchronous rotation, which therefore also takes place within 1 day 8 hours, 53 minutes and 6.82 seconds, so always shows with the same hemisphere to Saturn. The axis of rotation is inclined 0 ° to the orbit, so is therefore perpendicular to the plane of rotation.

Physical Properties


Enceladus is approximately spherical, with an average diameter of 504.2 km. The exact dimensions are 513.2 × 502.8 × 496.6 km. The deviation of about 3 % is due to the tidal forces of Saturn, which gives the moon the shape of an ellipsoid. The longitudinal axis is aligned with Saturn, the central axis is between leading and following hemisphere and the shortest axis between the poles. Enceladus is the sixth- largest moon of Saturn and is ranked in the solar system in the 17th place in all the planet 's moons and the 82nd place out of all hitherto known body at all (as of November 2011).

From the size Enceladus is best compared with the second largest main belt asteroids Vesta and the fifth largest Uranus moon Miranda.

The total area of ​​Enceladus is about 798,650 km ², this is roughly equivalent to the area of ​​Mozambique or Pakistan. The surface can also be compared with that of France and the United Kingdom (excluding overseas territories).

Internal construction

Enceladus is probably composed mostly of water ice. 1.61 g/cm3, it has the third highest density of all Saturn's large moons ( only surpassed by Phoebe and Titan, whose density is increased by gravitational compression). Inside therefore larger amounts of dense material must be present, such as siliceous rock; It is accordingly a differentiated body.


Enceladus is exceptionally bright because it is a large area covered with pure water ice, which reflects 99% of the incident sunlight. This is the highest albedo of a celestial body in the solar system, which even exceeds the reflectivity of freshly fallen snow. Due to the high reflection of sunlight prevail on Enceladus most temperatures below -200 ° C or below 70 Kelvin.

On its surface different terrains could be identified. In addition to craters flat plains as well as pronounced fractures and dislocations are visible. A part of its surface appears to be relatively young, with an estimated age of 100 million years ago. This suggests that Enceladus is geologically active. The cause is obvious Kryovulkanismus ( Kältevulkanismus ), in which water escapes from the interior of the moon and spreads over the surface. Enceladus is the smallest known body in the solar system, which has a geological activity of this kind.

Exploration by the Cassini probe

The Cassini spacecraft examined the moon with several close encounters flights from March 2005. The probe discovered a magnetic field and a thin water vapor atmosphere. Since gravity of Enceladus is too weak to hold the gases a long time, this indicates a permanent source on the moon itself. The gases originate either from the surface or from the interior of the moon. It was suspected that they could be ejected by volcanoes, geysers and other activities. Enceladus is thus, in addition to the Titan, the second moon of Saturn, has an atmosphere. However, the Enceladusatmosphäre seems to be limited to the geologically active south polar region, revealed as more data from the Cassini mission.

Volcanic activity in the southpole

Surprisingly, located at the south pole of this moon a local heating zone, the more heat the surface there by about 20 to 25 K, as would be expected. The energy source for the volcanic processes is unknown. It will be discussed different models. Enceladus is much too small to allow radioactive decay would lead to a significant warming in the interior of the moon. It orbits Saturn in a 2:1 resonance with the moon Dione (like the moons Io and Europa Jupiter ), which tidal forces are effective, cause friction in the lunar interior and thus warming. However, this mechanism is not sufficient to generate enough heat for the liquefaction of water ice. The overall rate of heating, which results from the sum of the possible radioactive decay in the interior as well as the maximum tidal forces only is about one tenth of the observed heat energy. In the interior of Enceladus chemical substances might be present, the lower the melting point of ice. It is discussed the presence of ammonia, which could cause this. Waite et al. published 2009, new data from Cassini, in which ammonia could be detected for the first time.

In the geologically active region, the surface is traversed by parallel, hundreds of kilometers long strip, consisting of up to 300 meters deep crevices in which crystalline ice penetrates to the surface. The environment is reminiscent in appearance to a temporarily froze viscous mass. Possibly moving under the surface the ice in convective and triggers a kryovulkanische column activity. The process is reminiscent in its effects to the plate tectonics of the earth or to similar activities on Jupiter 's moon Europa. The discharge volume of the tiger stripes varies cyclically. The weakest appear the geysers when Enceladus is on the saturn next point of its orbit, and then steadily increase in their activity, the further the moon from his planet. The discharge rate is at saturnfernsten point finally saturn next three to four times as high as on. An explanatory model is that with greater proximity to Saturn and the resulting stronger gravitational load, the tiger stripes are squeezing literally, thereby reduce the discharge ports and so less material can escape.

This region seems obvious the source of very fine E- ring of Saturn and the thin atmosphere around Enceladus to be. Since the ring material can not last longer than a few thousand years on its orbit, provides the geological activity of the moon for a steady supply.

On 14 July 2005 were countless chunks of ice from the Cassini spacecraft, which flew over the moon in only 175 km distance observed in the size of a detached house, whose origins are not entirely clear. As these chunks are in the aforementioned stripe pattern is most likely a connection to the cryovolcanic activities of the south polar region.

Possibilities for life on Enceladus

On 9 March 2006, NASA announced that recordings from Cassini have liquid water suspect in the south polar region of Enceladus. It could be in chambers that may be only a few meters and then would break like a geyser to the surface from below the surface. The geyser fountains in the south polar region were observed up to an altitude of 500 kilometers. Part of the ice particles fall back to the surface and causes particularly large reflectance of Enceladus. From most of the escaped into space particles, a portion reaches the surface of Saturn's other moons, therefore, are also Mimas, Tethys, Dione and Rhea - the satellites in the field of E- ring - compared to other moons unusually bright

On 12 March 2008 Cassini Enceladus has happened at a distance of only 23 kilometers. This was the smallest distance flyby of a spacecraft in space history. Here, Cassini flew by freshly ejected particles. Two instruments were at this time in operation: The Cosmic Dust Analyzer and the Ion and Neutral Mass Spectrometer. The measurement results showed a much higher density of volatile gases such as water vapor, carbon dioxide and carbon monoxide to be accepted. But even organic materials that have already been detected by a spectroscopic analysis of an occultation, were about 20 times more often than expected. The particle density was so high that a measurable torque working through them to the probe. An unexpected surprise was the chemical composition of the ejected particles which is similar to a comet. In contrast to a comet Enceladus but is heated from the inside.

Thus Enceladus has heat, water and organic chemicals, some of the essential building blocks for the development of life.

Electrical connection with Saturn

Enceladus is connected along Saturn's magnetic field lines by an electric current with Saturn. Where the electrons hit the atmosphere of Saturn, created in the polar regions in the UV light shining spots.