Interior - Internal Heating - Saturn reradiates three times as much energy as it absorbs; therefore, there must be an internal heat source.

It is believed that this extra heat is produced as the result of what is called “helium rain”.

At Saturn’s internal temperature, liquid helium will not dissolve in liquid hydrogen.

Instead it forms droplets which fall through Saturn’s interior and depletes the helium in the upper levels.

As the helium rain sinks toward the center, gravity compresses it and heats it. This produces the excess internal heat.

Internal Structure - Saturn has a rocky core that is larger than Jupiter’s. The amount of metallic hydrogen is smaller than Jupiter.

The core pressure is around 1/10 the core pressure of Jupiter (about the same as Earth).

The magnetic field strength of Saturn is about 1/20 of Jupiter’s. This is still 1000 times Earth’s.

Saturn’s magnetic field is not inclined to its rotation axis. (Earth’s and Jupiter’s are)

Saturn’s magnetic field envelops its ring system and the innermost 16 moons.

Saturn’s largest moon,Titan, is sometimes inside, sometimes outside the magnetic field depending on the strength of the solar wind.

Saturn and its moons produce no plasma torus.

Ring system - All the Jovian planets have ring systems. Saturn’s is the brightest and most extensive.

The rings are composed of a great number of small particles, primarily of water ice, all independently orbiting.

The size of the particles ranges from fractions of a mm to ten’s of meters. The average size is that of a large snowball.

The rings are very thin, only ten’s of meters thick in some places. Collisions with other particles keep the particles in circular orbits.

Why do the Jovian planets have rings? Moons too close to the planet are torn apart by tidal gravitational forces (the same forces that produce Io’s internal heat).

The pieces of the destroyed moon spread out to form the rings.

For a given planet and a given moon, the critical distance, inside of which the moon will be destroyed is called the Tidal Stability Limit, or the Roche Limit.

The material that forms the rings might be a destroyed moon or material from the formation of Saturn that never came together to form a moon.

Voyager found that rather than 3 main bands of rings there are actually tens of thousands of narrow ringlets.

The smaller gaps between the rings are not actually empty but have a low density of particles. The fine structure of the system varies over time.

The true gaps are probably swept clean by moonlets, but only one moonlet has been found. The other gaps are caused by resonances with the innermost major moon, Mimas.

Other moons that cause resonance gaps are Atlas, Janus, and Epimetheus.

There is a very thin, “braid-looking”, F-ring influenced by two small moons called shepherd satellites (Prometheus, Pandora).

Prometheus

Pandora

Voyager revealed more rings than had ever been seen before, both nearer the planet and further away than the original known rings.

One other strange feature discovered by Voyager was a series of dark spokes on the B-ring. These moved during one orbital period then disappeared.

These spokes were actually shadows of dust above the ring. The dust was held in place by electrostatic forces in the ring plane.

Saturn’s rings are probably relatively new (50,000,000 years old). There is too much dynamics for them to be stable for billions of years.