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