# Jupiter's Giant Moons

Both Cisto and Ganymede are very large moons, much bigger than our moon. Ganymede is the largest moon in the solar system. Both are made mostly of ice at more than 200 degrees F. below zero. At this temperature, ice is as hard as quartz. Fresher ice in cratered areas is lighter in color. Europa is perhaps the smoothest moon in the solar system. Its icy surface may melt and refreeze. Sulfur compounds give lo's surface a brilliant red and orange color. Lava flows and erupting volcanoes are also visible.

# The energy equation

In this research, you are going to predict which of jupiter's four large moons will be the 'brightest" in the infrared. During the October 12th flight, KAO astronomers will locate and measure the brightness of these moons. You can use their data to modify your predictions.

# Prediction from Appearance:

Look at each moon in in the collage above. The moons are displayed to scale. Read the accompanying descriptions and look for clues about which moon will be the brightest and which will be the faintest in the infrared. Then rank the moons beginning with the brightest.

```1.___________________  2.___________________

3.___________________  4.___________________
```
Note. the Albedo Data-- Albedo is an index of how bright or dark a surface is in visible light (the lower the number, the brighter.)

# Prediction from Data

Study the table of moon sizes and magnitudes. List the moons in size firom largest to smallest:

```1.___________________  2.___________________

3.___________________  4.___________________
```
Visual magnitude is an inversed scale. Lower magnitudes indicate brighter objects. List the moons in order of magnitude from brightest to dimmest:

```1.___________________  2.___________________

3.___________________  4.___________________
```
Which moon is unusually faint for its large size?

Using these data, predict the ranking of the the moons in IR brightness. You may modify your earlier prediction.

```1.___________________  2.___________________

3.___________________  4.___________________
```
```
Moon		Diameter	Albedo	Magnitude*

lo		1.2 arc sec.	.55	5.0

Europa		1.0 arc sec.	.5	5.3

Ganymede	1.7 arc sec.	.3	4.6

Callisto	1.6 arc sec.	.15	5.6

*Relative brightness
```

# A Jovian Challenge

Jupiter's moons reflect some of the sun's energy they receive and absorb the rest. The absorbed energy warms up the moons and is later released as infrared radiation. The total amount of energy shining on each moon is balanced by the energy reflected plus the energy absorbed and re-emtted at longer wavelength. Jupiter, however, emits more infrared radiation than expected from analyzing the energy received from the sun, minus the energy reflected. During the flight, KAO astronomers will report on the excess infrared radiation they detect from jupiter. Listen to their explanations for what may be causing this extra energy output.

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