Thursday, May 10, 2012

Moons of Saturn


Artist's concepts of the Saturnian ring–moon system
A spherical yellow-brownish body (Saturn) can be seen on the left. It is viewed at an oblique angle of to its equatorial plane. Around Saturn there are rings and small ring moons. Further to the right large round moons are shown in order of their distance.
Saturn, its rings and major icy moons—from Mimas to Rhea
In the foreground there are six round fully illuminated bodies and some small irregular objects. A large half-illuminated body is shown in the background with circular cloud bands around the partially darkened north pole visible.
Images of several moons of Saturn. From left to right: Mimas, Enceladus, Tethys, Dione, Rhea; Titan in the background; Iapetus (top) and irregularly shaped Hyperion (bottom). Some small moons are also shown. All to scale.
The moons of Saturn are numerous and diverse, ranging from tiny moonlets less than 1 kilometre across, to the enormous Titan, which is larger than the planet Mercury. Saturn has 62 moons with confirmed orbits, fifty-three of which have names, and only thirteen of which have diameters larger than 50 kilometres.[1][2][3] Saturn has seven moons that are large enough to be ellipsoidal due to having planetary mass, as well as dense rings with complex orbital motions of their own. Particularly notable among Saturn's moons are Titan, the second largest moon in the Solar System, with a nitrogen-rich Earth-like atmosphere and a landscape including hydrocarbon lakes and dry river networks, and Enceladus, which emits jets of gas and dust and may harbor liquid water under its south pole region.
Twenty-four of Saturn's moons are regular satellites; they have prograde orbits not greatly inclined to Saturn's equatorial plane. They include the seven major satellites, four small moons which exist in a Trojan orbit with larger moons, two mutually co-orbital moons and two moons which act as shepherds of Saturn's F Ring. Two other known regular satellites orbit within gaps in Saturn's rings. The relatively large Hyperion is locked in a resonance with Titan. The remaining regular moons orbit near the outer edge of the A Ring, within G Ring and between the major moons Mimas and Enceladus. The regular satellites are traditionally named after Titans and Titanesses or other figures associated with the mythological Saturn.
The remaining thirty-eight, all small except one, are irregular satellites, whose orbits are much farther from Saturn, have high inclinations, and are mixed between prograde and retrograde. These moons are probably captured minor planets, or debris from the breakup of such bodies after they were captured, creating collisional families. The irregular satellites have been classified by their orbital characteristics into the Inuit, Norse, and Gallic groups, and their names are chosen from the corresponding mythologies. The largest of the irregular moons is Phoebe, the ninth moon of Saturn, and was discovered at the end of the 19th century.

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