Rowan Introduction to Astronomy
Activity #7: How Much Rock Is in an Icy Moon?*
Name: _______________________________________________
Score: __________________________________
f
Acknowledgement
This activity is adapted from an exercise created by
Hawai’
i Institute of Geophysics and Planetology, University of Hawai
’
i.
f
Objective
The outer planets
—
Jupiter, Saturn, Uranus, Neptune
—
and the dwarf planet Pluto have icy, rocky satellites (moons). Given
the densities of the satellites, calculate the percentage of rock and ice in their compositions.
f
Rock and Ice Ratios [87 pts]
1. Silicate rock has a density of about 3.0 g/cm
3
(grams per cubic centimeter). Look at the first table on page 2. Based only
on density, are any of the moons composed
entirely
of rock?
yes
no
[1 pt]
2. Which two moons are
closest
to being composed entirely of rock? ______________________________________ [2 pts]
3. Water ice has a density of about 0.9 g/cm
3
(exactly 0.934 cm
3
). Again, look at the first table on page 2. Are any of the
moons composed
entirely
of ice?
yes
no
[1 pt]
4. Which two moons (are)
closest
to being composed entirely of ice? ______________________________________ [2 pts]
5. We can make a graph to help figure out the percentages of rock and ice in the moons of the outer planets. Use the equations
shown below (especially the
second
equation) to compute the density resulting from different percentages of rock and ice.
Write your answers in the second table on page 2 (i.e., the third column). [Round your answers to
1
decimal place.]
Density =
(Percentage of rock × Density of rock) + (Percentage of ice × Density of ice)
100
࠵?
Moon
=
(࠵?
rock
×࠵?
rock
) + (࠵?
ice
×࠵?
ice
)
100
=
(࠵?
rock
)(3.0) + (࠵?
ice
)(0.9)
100
6. Next, using the grid found on page 3, plot the percentage of rock (column 1 of the second table) on the
x
-axis and density
of the moon (column 3 of the second table) on the
y
-axis.
7. From this graph you have plotted, estimate the percentage of rock for ea
ch moon listed in the first table given that moon’s
density (column 3 of first table). Write this value for the percentage of rock in column 4 of the first table.

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