Gas Giants, Page 27: [Previous Page] [First Page] [Class Home Page] Textbook pages 202 - 227

Saturn's Moons

Beyond it's incredible ring system, Saturn has 18 named moons (below) and a large number of other small `candidate' moons which intermix among complex ring system. Click on the figure below to get a full view of all of Saturn's moon.


Titan is the fifteenth of Saturn's known satellites and the largest. Discovered in 1655 by Dutch physicist and astronomer, Christiaan Huygens. The orangy haze seen in the picture above is due to Titan's thick atmosphere, and we have no direct images of the surface.

Diameter = 5150 km (about 1/2 Earth)
Mass = 10²³ kg (about 1/50th Earth)
Density = 1.9 x Water (Earth is 5.5 x Water)
Sun Distance = 9 AU (9 x Earth-Sun distance)

Titan is in synchronous rotation with Saturn (tied to its 16 day orbital period around Saturn). It was thought Titan was the largest moon. But Titan's atmosphere is so thick, its now known that its solid surface is slightly smaller than Ganymede's (a moon of Jupiter's). However, Titan's surface is just les than Mercury's, but is larger and more massive than Pluto. It can, for all practical purposes, be considered a planet!

Titan's low density
Earth has a dense iron rich core, giving it its high density. Even the Moon has a significantly higher density, 3 x water, and is made mostly of silicate rock (little iron). Titan's low density suggests it contains a lot of frozen water, methane, carbon dioxide and ammonia. Water ices are common and ubiquitous all over the outer solar system, in Jupiter, on the icy rings of Saturn and are the predominant ice found in Comets.

Saturn's remaining moons
The remaining moons show heavy cratering, though Enceladus appears to show evidence of more recent geological activity, having a relatively crater-free region on its surface. All of the moons, including Titan, are tidally locked to Saturn. See ground based image here.

Interactions between Rings and Moons
There are complex tidal resonances between some of Saturn's moons and the ring system: some of the moons, the so-called "shepherding satellites" (i.e. Atlas, Prometheus and Pandora) are clearly important in keeping the rings in place. Shepherd satellites or moons move just inside or outside of a ring system, and confine the narrow rings through their gravitational effect. Moons can also clear out sections of the rings: Mimas seems to be responsible for the paucity of material in the Cassini division; Pan is located inside yet another gap (Encke Division). The whole system is very complex and as yet poorly understood. A diagram of the ring and moon system is shown HERE.