Satellites of Saturn

The main physical parameters of Saturn ssatellites are given in Table 4.2. 

Considering the relative masses of Saturn s moons we have to state that 96% of the mass of them is concentrated in Titan, thus this satellite dominates the system. The six medium-sized spheroidal moons constitute 4%, and all small moons together just 0.01%. As of 2006 sixty satellites of Saturn have been confirmed. 

Moon Diameter km Mass kg Orbital radius km Orbital period d 

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Diacetylene (HC=C—C=CH) has been identified as a component of the hydrocarbon rich atmospheres of Uranus Neptune and Pluto It is also present m the atmospheres of Titan and Triton satellites of Saturn and Neptune respectively... 

In a parallel set of discoveries, a reflectance band in the visible, similar to that for solid 02, was seen at low latitudes on Ganymede. In addition, a UV feature associated with O3 was seen on Ganymede and on the icy satellites of Saturn. Coupled with these observations was the much earlier discovery of a band indicative of SO2 in ice at Europa and Callisto and the recent discovery of CO2 trapped in the icy surfaces. The SO2 was initially assumed to be due to sulfur ions originating at lo implanted into the ice at Europa, " but the SO2 is also a radiation decomposition product like the O2, as discussed below. " The CO2 source is probably internal as carbon ions have not yet been seen in the plasma. 

Cmikshank D. P. (1980) Near-infrared studies of the satellites of Saturn and Uranus. Icarus 41, 246-258. 

Fink U., Larson H. P., Gautier T. N., and Treffers R. R. (1976) Infrared-spectra of satellites of Saturn—identification of water ice on lapetus, Rhea, Dione, and Tethys. Astrophys. J. 207, L63-L67. 

Titan, the largest satellite of Saturn, is one of tlie smallest known bodies with an atmosphere. The Voyager observation provided information on Titan s atmosphere, and the origin and evolution of the Titan s atmosphere have been discussed from many aspects. Titan can be used to simulate planetary-scale chemical activity and surface-atmosphere interactions in tlie absence of tlie influence... 

Saturn is the second-largest planet in the solar system, after Jupiter. Its equatorial radius is 37,448 miles (60,268 km), about nine times that of Earth, and its mass is 568.46 x 1024 kg, about 95 times that of Earth. As of early 2007, scientists had found 56 satellites of Saturn, the largest of which is Titan, with a radius of 8,448 feet (2,575 km, about 50 percent larger than that of Earth s Moon), and a mass of 1,345.5 x IO20 kg (about twice that of the Moon). Saturn s density is 0.687 g/cm3, less than that of water. This fact means that (if one could find a body of water large enough) Saturn would float on water. It is the only planet with a density less than that of water. 

Cassini, Giovanni Domenico (1625-1712) Italian-bom French astronomer, who was professor of astronomy at Bologna. In 1669 he moved to Paris to run the new observatory there, becoming a French citizen inl673. He is best known tor his discovery (1675) of the gap that divides Saturn s ring system into two parts, now called the Cassini division. He also discovered four new satellites of Saturn. 

Titan, the largest satellite of Saturn, is surrounded by a substantial atmosphere and therefore one expects a correspondingly significant ionosphere. To date the only opportunity for a radio occultation measurement of an ionosphere occurred when Voyager 1 was occulted by Titan. The initial analysis of that data could only provide upper limits of 3 X 10 cm and 5x10 cm on the peak electron densities at the evening and morning terminators. 

Water ice has now been observed on Europa, Ganymede (Pilcher et al. 1972 Fink et al. 1973), the rings of Saturn (Pilcher et al. 1970 Kuiper et al. 1970), and four satellites of Saturn (Fink et al. 1976 Morrison et al. 1976), It is feasible to extend such observations to a number of other satellites at resolution adequate to identify the dominant surface constituents. A probable identification of methane ice on Pluto has been made on this basis ( lorrison 1976b). 

Sagan and Chyba (1997) [287] proposed that the early Earth had an organic haze layer in its atmosphere. Such a layer can be found in the atmosphere of Titan, the largest satellite of Saturn and is produced by methane photolysis in the presence of nitrogen. An organic haze layer would preferentially absorb ultraviolet light, thereby allowing ammonia and methane to persist in the atmosphere. 

The famous rings of Saturn extend from 6630 km to 120700 km above its surface. The rings are extremely thin, only 20 m and consist mainly of ice 93% is water ice, 7% is amorphous carbon. The sizes of the ring particles range from micrometers to several m. The gaps observed in the rings are caused by resonances with nearby satellites of Saturn. 

This satellite of Saturn is also designated as Saturn IV. Its semi major axis is 377 396 km, the orbital period is 2.73 d. The mean radius is 561 km and its mean density is 1.47 g/cm. Because of this relatively low density, this satellite must be mainly composed of water, about 45% seems to be silicate rocks which are mainly concentrated in its interior. Like Rhea its trailing and leading hemisphere are dissimilar. On its surface, wisps were found (see Fig. 4.12) which were identified by the fiyby of the Cassini probe in December 2004 as bright ice cliffs created by tectonics. 

If a habitable zone is restricted to the presence of liquid water, then we must also include the interiors of giant planets and the ice covered Galilean Moons of Jupiter, or the icy satellites of Saturn and maybe even other places. Therefore, the search for life must not be restricted to the study of circumstellar habitable zones. But it seems that life requires much more than just liquid water. 

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