The Jupiter Mission

Activity 3C: The Energy Equation


To predict which of Jupiter's moons will be the "brightest" in infrared wavelengths.

Ask students to imagine a black pan and a white pan outside in the sunlight on a hot day. Which one would look brighter? Which one would be warmest to the touch?

Explain that the brightest object would show up better in a photograph, (i.e. in visible light) but that an infrared detector would see the darker object as warmer, and therefore brighter at infrared wavelengths. (Activity 1C, p19)

Materials activity 3C bound into a Mission Logbook

Procedure Distribute the Activity sheet. Encourage students that they should be able to interpret the data provided on the sheet about Jupiter's moons to predict which one will be the brightest. Allow groups to work together to make their prediction. Have each group make a presentation, stating their middle thinking as well as their conclusions. Write predictions on the chalkboard and note they'll be able to check them when live data comes in during the KAO flight. They will probably hear the astronomers answer several questions about the moons during the videos, and find out how other students made their predictions.

The energy which an object receives from the sun is either reflected back off an object as visible light or absorbed and re-emitted at longer wavelengths such as infrared. For this reason, brighter visible light objects are often fainter at infrared wavelengths.

Interdisciplinary Connection

Jupiter has been called a "still-born star". If the planet had been 80 times as massive, it would have created a temperature and pressure great enough for the planet to generate its own energy--and become in effect, a star. Astronomers think they've seen other such objects, called "brown dwarfs", elsewhere in space. Then our solar system would have been a double star system with one bright sun and one fainter one. Most of the stars in the sky, in fact, are double stars.

Write a story describing what it might be like to live on a planet in a double star system. How would you adapt such concepts as day and night and the year? A famous science fiction story by Isaac Asimov, entitled Nightfall, imagines what happens to a planet in a multiple star system, when all the suns set and the beings who live there experience the unaccustomed darkness.

KAO Connection

One of the most significant discoveries in the history of infrared astronomy was that of the brightness of Jupiter at longer wavelengths. Jupiter is actually producing more energy than it receives from the sun. This energy is probably coming from a gradual gravitational shrinking of the planet, a residual effect of the process which made the planet in the first place. Saturn and Neptune, the solar system's two other giant, gaseous planets, also produce more energy than they receive from the sun, however Uranus does not.

QUESTION: Have the people on the plane seen anything weird?

ANSWER from Ted Dunham:

We see plenty of weird things, usually each other after staying up all night! We have seen some really terrific thunderstorms (they look great from above at night), satellites passing across our TV screens, sometimes other airplanes, lots of brightly-lit cities. Sometimes we see our own strobe lights blinking off thin clouds as we fly through them. Sunsets and sunrises are also really pretty, seen from a high-altitude airplane. Nobody has seen any UFO's though.

We don't see these things as cool pictures like you might see in a comic book. Mainly we see a few stars on a TV screen. Often the thing we are really looking at with the telescope will be invisible to our eyes and TV cameras, and the only way we know we are looking at the right place is that the infrared equipment shows a signal. The astronomers record their information on computer disks or tapes and take it back home where they analyze it very carefully. They talk things over with their friends and come up with ideas about what could make their results turn out the way they do. This is where pictures of exploding stars or forming stars begin to appear, but the pictures form in the imaginations of the astronomers, not on a TV screen.

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