Lecture 32 - Saturn's Rings and Moons

What are the 4 models for the age and origin of Saturn's rings?

1. The rings are an ancient feature (~4.5 Ga) resulting from destruction of a planet or moon that entered the Roche Limit around Saturn. 2. The rings are an ancient feature composed of material left over from the original disk of material that surrounded Saturn during accretion. 3. The rings are an ancient feature resulting from partial or complete disruption (destruction) of one of Saturn's moons due to a giant impact. 4. The rings are a young (less than a few 100 million years) feature resulting from partial or complete disruption (destruction) of one of Saturn's moons due to a giant impact.

What should Saturn's moons be made of? What if the moons were disintegrated?

Saturn's moons, like Jupiter's moons, should be made of a mixture of rock and ice. If a moon disintegrated, we should see both the rocky and icy components preserved in the ring material.

What kind of structure does Titan have? What moon is this similar to? What makes Titan fascinating?

Titan is thought to have a differentiated structure much like what we saw for Ganymede, with a silicate core surrounded by icy layers and possibly a liquid water layer sandwiched in between. However, what makes Titan fascinating to scientists isn't it's internal structure but its atmosphere.

Titan has what kind of atmosphere? Hazy or clear? Why?

Titan's atmosphere is "hazy" or opaque, due to the presence of organic compounds that form through reactions involving methane and nitrogen. These organic compounds slowly rain down to the surface.

True or false? What we learned from Jupiter we can apply to Saturn as well.

True!

What is an important clue to the origin of Saturn's rings?

An important clue to the origin of Saturn's rings is their composition-they are almost pure water ice (93%), with most of the remaining material some form of carbon (7%).

Why does Io have such a thin atmosphere? How does plasma torus happen? What is plasma torus? How much material is removed form Io every second? What process causes this? How hot does it get in the torus?

Because of Io's volcanism, the moon has a very thin atmosphere composed mostly of sulfur and sodium compounds. These components are ionized by radiation from Jupiter, and swept up in Jupiter's magnetic field. The result is a plasma torus composed of charged particles that flows between Io and Jupiter. Basically, these two worlds are bound by an electric current of several million amps.

What would make the moons consistent with the composition of the icy rings? What would complete disruption result in?

If the moon had differentiated into a rocky core and icy mantle, and if the impact ejected material from the mantle portion into the ring (similar to formation of our own moon), then this would be consistent with the icy composition of the rings. Complete disruption, however, would result in rocky material present in the rings, which we don't see.

Are the rings as old as the solar system? Why or why not?

If the rings were as old as the solar system, they should have accumulated a lot of chondritic "soot", which would make them much darker. Some scientists (not all) therefore feel that the rings may be the result of a relatively recent (last few 100 million years) catastrophic impact on one of Saturn's icy moons.

What did the Miler-Urey experiment show?

In 1952, the Miller-Urey experiment showed that amino acids could be produced from a N2-CH4 atmosphere. The surface of Titan is a natural experiment conducted on a grand scale

What does the composition suggest about the ratio of ice to rock in Saturn's moons relative to Jupiter's moons?

It's much colder where Saturn's moons are and formed.

What is the recipe for pre-life? What was the result?

Recipe for (pre-)life: 1) Mix water, methane, and nitrogen. 2) Add energy (electrical spark, UV radiation, etc.) 3) Wait. Result? Lots of amino acids, nucleic acids, and other essential building blocks needed to make proteins and DNA or RNA.

What are Saturn's rings composed of? What does their composition give us clues to? How big are the main rings? Are they thick or thin?

Saturn's rings are composed of countless small icy particles, ranging in size from ~1 meter to < 1 micrometer. The main rings range from 7,000 up to 80,000 km above Saturn's equator. They are incredibly thin-in many areas no more than ~10 meters thick. The rings are composed mostly of water ice (~93%). This may provide a clue to how they formed.

Are Saturn's rings clean? Is the solar system clean?

Saturn's rings are very "clean". However, the solar system is a dirty place, with lots of dark chondritic material floating about.

What does deformation cause?

Stresses to be exerted

What is the Roche Limit? What happens to moons that wander into this limit?

The Roche Limit is the distance from a celestial body (e.g., a planet) within which a smaller object held together by gravity will be torn apart by the tidal forces exerted by the larger body. Any moon that wanders within this limit will be destroyed.

Why does Mimas attest to the fact that the solar system is a violent place? What does this have to do with the rings of Saturn?

The giant impact basin seen on Saturn's moon Mimas attests to the fact that the solar system was and is a violent place. Such impacts may periodically replenish Saturn's rings with icy material. Rings may have formed and been destroyed several times over the history of the solar system.

Why are the moons mixtures of rock and ice?

The moons are mixtures of rock and ice because that is what was present in the disks surrounding Jupiter and Saturn during their formation. If the rings are leftover disk material, where is the rocky component?

What does the surface of Titan contain?

The surface of Titan contains the products of a Miller-Urey experiment that has been going on for 4.5 Ga. We now know that the surface of Titan has "lakes" of ethane.

Titian's atmosphere is composed of? Which element is mysterious and why?

Titan has a dense atmosphere composed mostly of N2 (~95%) and CH4 (~5%) in the troposphere. The presence of large quantities of methane in Titan's atmosphere is a mystery, because methane should be quickly converted into other compounds by exposure to solar radiation.

Titan is the _____ largest moon in the solar system Titian is Saturn's ________ moon Titan has a ____ density indicating that it is composed of: _____ and_____ Titan has an atmosphere composed of: _______ and _______

Titan is the second largest planetary moon in the solar system (after Ganymede). It is by far the largest moon of Saturn, with a diameter of 5150 km and a mass nearly twice that of our own moon. It's low density (1.89 g/cm3) indicates it is composed of ~50:50 mixture of rock and ice. Titan has a dense atmosphere composed of nitrogen and methane.

Why is Titan's atmosphere so fascinating?

Why is Titan's atmosphere so fascinating? It may help us to determine how the "primordial soup" of amino acids and other organic components necessary to create life were formed in the early solar system.