Saturn Module 12 . . . by Kari Hetcher, Scott Hughes and Mary Hodges

Reading (some of these chapters you also read for Jupiter):

  • Chapter 14 Interiors of the Giant Planets by William B. Hubbard
  • Chapter 15 Atmospheres of the Giant Planets by Andrew P.Ingersoll
  • Chapter 16 Planetary Rings by Joseph A. Burns
  • Chapter 20, Titan, by Tobias Owen
  • Chapter 22, Midsize Icy Satellites, by William B. McKinnon
  • saturn
    Like rings around Saturn
    the furies of her life encircle her.
    Not knowing she is the planet,
    She gives them power…
    When the time is right, she will know
    The galaxy is more than Saturn-
    She is not held by imaginary bonds.

    (Adapted from Bonnie Michael)


    Saturn

    Saturn is the second largest object in our solar system, but similar to Jupiter, has a surprisingly low density due to its gaseous nature. It is the most oblate planet we have seen because of the rapid rate of rotation and its fluid state. Its chemical composition resembles Jupiter’s, at about 75% Hydrogen, 25% Helium, with trace quantities of water, methane, ammonia, and rock. The internal structure of Saturn consists of a gas outer layer with traces of  ice, a middle layer of liquid metal hydrogen, and, possibly, a rocky core.

    Review Saturn's properties, rings, moons, and history of exploration by visiting the Nine Planets website.

    Atmosphere

    The light-colored blotchs near the equator in these pictures of Saturn are huge storms in Saturn's atmosphere. Saturn’s atmosphere has bands of colored clouds near the equator similar to those on Jupiter, but they are moving 4 times faster. The velocity of the winds in this region can be 15 miles per minute or 900 m.p.h.

    The bands become wider near the equator, and are usually light yellow and white colors, made up of hydrogen and ammonia ice crystals. Some storms can be seen on Saturn as brighter spots, and are probably caused by the rapid rotation of the planet. At the top of the cloud layer of this huge planet, one day is only ten hours long! This speed results in shearing among the different cloud bands, which can form massive storm systems.

    Orbital and Physical characteristics of the planet Saturn

    Mean Distance from the Sun relative to Earth (earth=1) 9.54
    Diameter at the Equator

    120,660 km

    Mass relative to Earth 95
    Volume relative to Earth 760
    Density 0.69 g/cm3
    Gravity at the Surface relative to Earth 1.16
    Period of Revolution 29.5 years
    Period of Rotation 10.2 hours
    Axis Inclination 29°
    Known Satellites 17

    Saturns Ring System

    The most obvious feature of Saturn is the beautiful ring system that surrounds the planet. The outer edge of the rings are sharply defined, but the inner edge grades gently in toward the planet. The rings are made up of billions of particles ranging in size from less than a micron to a kilometer in diameter. The particles are probably water ice or rocky bits coated with water ice. The particles are subjected to a variety of forces. This means that there must be some mechanism to perpetuate the addition of material to the ring system. Study the chart below about Saturn's ring structure to get an idea of the complexity of the rings.

    Spokes are an aspect of the rings of Saturn not discovered until recently, when advanced pictures of the ring structure were seen. The spokes within the rings are faint, dark areas perpendicular to the rings that seem to grow and shrink. Little is known about the spokes, but they may be charged particles that float above the actual ring plain. The spokes rotate at the same speed as the magnetic field of Saturn, so they are thought to be associated with the planet's electromagnetic forces in some way. In the animated image above you can see the spokes.

    Adrastea and Metis, two of Saturn’s co-orbital moons, may at times collide and send particles into the ring system. Another possibility is that the ions of the solar winds occasionally hit the surfaces of the moons and eject the regolith, sending particles into the rings. The rings are said to be kept in place by the motions of the "shepherd satellites" near Saturn. See the NASA/JPL page on rings:http://ringmaster.arc.nasa.gov/saturn/saturn.html

    http://pds-rings.seti.org/saturn/cassini/

    Shepherd Moons

    Why are these moons called shepherd satellites?

    What do they really do for the ring systems?

     

    Shepherding moons are satellites that orbit along side a ring. Due to gravitational effects from the shepherding moon, the edges of the rings are kept sharp and distinct. If the shepherding moon was not present, then the ring material would have a tendency to spread out. If two satellites are orbiting on both sides of the ring, then ring will be constrained on both sides into a narrow band.

    click image for larger image

    The Moons of Saturn

    Saturn has 30 named satellites plus one discovered in 2003. Of those moons for which rotation rates are known, all but Phoebe and Hyperion rotate synchronously. The three pairs Mimas-Tethys, Enceladus-Dione and Titan-Hyperion interact gravitationally in such a way as to maintain stable relationships between their orbits. The period of Mimas' orbit is exactly half that of Tethys, they are thus said to be in a 1:2 resonance. Enceladus-Dione are also 1:2, and Titan-Hyperion are in a 3:4 resonance. Study these moons and their attributes using the Nine Planets website:

    Much recent information about Saturn, the rings and moons (especially Titan!) has been obtained recently during the Cassini-Huygens Mission controlled by JPL.


    Task for Saturn Module:

    Answer the following questions and email them to your instructor.

    1. Compare Jupiter and Saturn with regard to density, size, and distance from the sun. Explain why these planets have the chemical compositions that they do.

    2. What is the role of the "shepherd satellites" in the ring system of Saturn?

    3. What is the Roche limit and how does it impact which planets will have rings? How did these differences come about?

    4. Write a simple weather report for Saturn including the area within the white spot [pretend there is one at the present].

    5. Saturn radiates 2.8 times as much heat as it receives from the sun. What is the likely cause?


    Other WEB SITES to learn more about Saturn:

    http://www.nineplanets.org/

    http://www.seds.org/nineplanets/nineplanets/saturn.html

    http://www.solarviews.com/eng/saturn.htm

    http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-saturn.html

    http://www.the-planet-saturn.com/

    http://saturn.jpl.nasa.gov/index.cfm

    http://solarsystem.nasa.gov/planets/index.cfm

    http://www.jpl.nasa.gov/solar_system/


    Glossary

    Did you email your assignments?

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