Universe Cycle - Solar System (3)
Post Lab 

  • Investigating the gas giants.
  • Comparing Jupiter, Saturn, Neptune, and Uranus.
  • gas giants
  • kelvin
  • magnetic field
  • rotation
  • worksheets

Students look at magnetic fields of gas giants.




Our knowledge of the gas giant planets comes from two sources, ground based telescopes and spacecraft. Because of their great distance from Earth and the interference of the Earthís atmosphere, telescopes are of limited use in gathering scientific information about these planets. The most detailed information about the gas giants has come from 1) the Voyager 1 and 2 spacecraft, which visited these planets, starting in 1979, and from the Galileo probe which orbited around Jupiter. Scientists are really just beginning to learn about these planets. They have only a general understanding of their composition, structure, magnetic properties, and other characteristics.

The atmospheres of the four gas giant planets are composed largely of hydrogen and helium. The upper atmospheres of both Jupiter and Saturn are mostly hydrogen; scientists hypothesize that much of this material has sunk into the interiors of the two planets. The upper atmospheres of Uranus and Neptune seem to have somewhat larger fractions of helium.

The colors of the gas giant planets are due to gasses in their upper atmospheres. The visible surface clouds of Jupiter and Saturn are mainly ammonia ice. Trace impurities give these clouds their coloration, such as the reddish tints of Jupiter's Great Red Spot. Methane is 10 times as abundant in the atmospheres of Uranus and Neptune as the atmospheres of Jupiter and Saturn. The abundance of methane makes Uranus and Neptune both appear blue to human eyes. Methane absorbs red and orange light in their atmospheres.


On each of the gas giant planets, the atmospheres are organized into zones that run parallel to the equator. These zones range from prominent on Jupiter and to almost indistinguishable on Uranus. These zones are controlled by a stable pattern of planetary winds. On Jupiter wind speeds vary with latitude and shift from easterly to westerly many times between the equator and the pole. Storm activity, in the form of swirling oval patches, can be seen on Jupiter, Saturn, and Neptune but not on Uranus.

The temperatures of the upper atmosphere of the gas giants are quite hot. For Jupiter the temperatures are in excess of 1000EK, 600-800°K for Saturn, and 750-800°K for Uranus and Neptune. The minimum temperature for Jupiter is 110°K, for Saturn is 80°K, Uranus is 52°K  and Neptune is 50°K.


All four of the gas giants have magnetic fields. Scientists explain how the fields are generated using the dynamo theory. Essentially, each of the gas giants has a core which is partially liquid metallic hydrogen. As this material circulates, it generates electrical energy, which creates the magnetic field. The magnetic fields are dipolar; they have well defined north and south magnetic poles. Magnetic forces travel from the negative to the positive pole. On the studentís diagram below, the magnetic field is shown as imaginary lines of force.  The magnetic poles of the gas giant planets correspond only poorly with the their rotational axes. The reasons for this, especially the wide divergence seen in Uranus, are not clear.

  1. Use the worksheets to compare the gas giant planets with Earth. You may wish to review their relative sizes, distances from the Sun, rotational speeds, and other features.
  2. Compare the magnetic fields of each of the planets using the diagram. The dashed line shows the planetís rotational axis, the solid straight lines show the equator of each planet, and the curved solid lines show the directions of the magnetic field. In particular, note that magnetic fields of Uranus and Neptune are vastly different from the Earth's because they are greatly offset from the rotational axis.
  3. Stress to students that scientists do not know all there is about these gas giants. Future information will help us to understand these giants. Remember these worksheets are for students to compare and contrast, not to memorize.

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