My favourite! Largely because it involves my favourite moon in the Solar system: Titan.
Like Jupiter, Saturn also spins extremely fast, making a rotation in only 10.2 Earth hours, and it revolves around the sun in 29.5 Earth years. It’s density is only 0.69 g/cm3, meaning that if you could find a swimming pool large enough and drop Saturn in, it would float. Also like Jupiter, its atmosphere is made up mostly of hydrogen with some helium and other elements, but unlike Jupiter a haze of NH3 clouds obscures its belts and zones.
The internal structure of Saturn is similar to that of Jupiter, but its zone of liquid metallic hydrogen is proportionately smaller, so its magnetic field is considerably weaker.The small core of ice and silicates represents only a tiny portion of Saturn, but is still 17 times larger than Earth.
Like with Jupiter, the lack of a rocky surface makes this planet rather uninteresting from a geological perspective (though it makes up for this by being awesome in other areas), so I won’t put too much into it, but focus on the satellites instead.
The ring system is massive in diameter, but extremely thin, and is well organized into many consistent, separate rings, some of which are kept in place by small “shepherd” moons.
There are three theories of how the rings formed: 1. gravitational disruption of a satellite tore a small satellite to pieces when it got too close to the planet; 2. Fragmentation of moons when impacted by bolides or by each other created debris, and fragmentation has been ongoing to replenish the rings; 3. accretionary remnants never formed into a satellite but stuck around as rings because of the gravitational influence of other already formed satellites. Considering the complexity of this ring system, any one or combination of these may have been the cause.
Titan has a density of 1.9 g/cm3, and is the only moon in our solar system with an appreciable atmosphere, which is made mostly of nitrogen with some hydrocarbons.
It actually has a hydrocarbon cycle not unlike the water cycle on Earth, with oceans, lakes, rivers, ice, rain, and snow, all made of hydrocarbons like methane.
It also has strong wind that erodes the surface and produces dunes around the equator. The presence of hydrocarbons makes Titan another point of interest in the search for life beyond our planet.
Phoebe orbits Saturn in the opposite direction to the other Moons, and is orbiting at an angle, suggesting it was captured by Saturn’s gravitational field and did not originate there. It is spherical in shape, which is unusual because bodies this small don’t generally have a strong enough gravitational force to pull themselves into this shape. It is of rocky silicate composition, rather than icy like most of the other moons out here.
Pronounced en-sell-a-dus, this one is a ball of ice with a young surface, likely resurfaced frequently by slush ice from its interior. There is active eruption on this planet’s surface, but instead of erupting hot lava and ash, it erupts H2O vapour and ice particles in cold geysers from subsurface, pressurized liquid H2O chambers. Water is able to stay liquid in spite of the freezing temperatures because it is mixed with ammonia, which lowers the melting point. It is also kept slightly warmer than it otherwise would be because of tidal friction caused by a nearby moon, Dione. Like with Jupiter, Dione orbits Saturn exactly once for every two orbits of Enceladus, keeping the tidal flexing regular and allowing the moon’s interior to heat up.
It is much denser than other satellites around Saturn, implying a higher silicate and lesser volatile content. It has some cratered terrain, as would be expected, as well as smoother terrain, suggesting that some resurfacing has taken place, most likely from eruptions of water and frost from fractures in the icy surface some time after the cratering took place.