Objectives
After viewing the video and participating in one or more of the Hands-On Activities, students
will be able to:
• describe key characteristics of the gas giant planets (e.g. no solid surfaces, internal
heat sources, rings, and more)
• recognize a giant planet's large moons as places where dynamic change is possible
• understand that heat energy can be created through gravitational interactions and tidal
friction, as well as by a star's light
• appreciate that planetary astronomers can be surprised by new observations
Program Description
"Gas Giants" uses images from the Pioneer, Voyager and Galileo missions, and explanations from
NASA astronomers, to introduce the most important characteristics that differentiate Jupiter,
Saturn, Uranus and Neptune from the terrestrial planets.
• "Flying by the Gas Giants" (3:47) presents large size (in comparison to Earth), lack of a
solid surface (all clouds and gases in motion-though possibly with solid cores) and internal heat
sources (in contrast to external heating by the Sun), as some of the most important features. The
chemistry of Saturn, Jupiter and Uranus, and the icy composition of the rings of the former, are
also introduced. (For Neptune's composition, see online, PLANETS.)
• "The Jupiter System" (5:32) uses recent findings from the Galileo mission to explore the
4 large moons and their interactions with their parent planet in greater detail. Findings from
Galileo's probe, which entered Jupiter's clouds, show great variation in water vapor and humidity
in various places on the planet. We see that the moons of the Jupiter-known as the Galilean
satellites after the Italian astronomer who first saw them-are active and interesting places in
themselves. Jupiter's tremendous gravity-the result of its great size-produces tidal fluxes in
the rocks and solid matter of the moons, resulting in heating via friction. Io (some astronomers
prefer to pronounce this "ee-oh" and some "eye-oh") has more than 300 volcanoes, some of which
erupt lava almost one mile above the surface. Io was the first volcanically-active body, other
than Earth, to be discovered in the solar system, and remains the most active.
• "Discovery Machines" (2:35) looks forward to what we might see when the Cassini spacecraft
arrives at Saturn in-if all goes well-2004, and begins close study of its giant moon, Titan.
Voyager sent back images indicating a thick, hydrocarbon atmosphere. Recent ground and Hubble
Space Telescope observations show evidence of continents and possible oceans on its surface.
Torrence Johnson (Galileo project scientist and a member of the Voyager imaging team) says that Jupiter's Great Red Spot-a storm that has persisted for at least 300 years-is like a hurricane on Earth. He states that lightning on Jupiter is thought to be triggered by similar processes to those here on Earth. Heidi Hammel, formerly of MIT and now at the Space Science Institute, in Boulder, CO, uses the disappearance of a "Great Dark Spot", seen by Voyager on Neptune, to argue that some large features on the gas giants are changeable over the short term. She explains that the weather systems we see on the gas giant planets may help us understand weather on Earth, where continents of dry land amid water oceans make weather much more complicated to study. Claudia Alexander (like Johnson, a member of the Galileo imaging team) explains that as Galileo returned in subsequent orbits for closer and closer observations of Jupiter's second moon, Europa, mission scientists were surprised to see more and more details hinting at fractured ice floes on top of what might be an ocean of liquid water. Johnson and Alexander argue that the discovery that Ganymede has a magnetic field indicates that it too has an interior in motion. This was the first time any moon in the solar system was found to have such a magnetic field.
