Astronomy 120: Fall 2008
Homework 5: Due in October 10/13 recitation
Name ___________________________ Section _______
It is often said that the Earth has a relatively large Moon but what exactly
does this mean?
Q2: If you go outside and pick up a rock (almost any rock will do) and
measure its density, you'll find that it is probably about 3
times denser than water. This is true in Ames, in Des Moines, in Colorado,
at the floor of the ocean, and just about anywhere else.
- Using the data found in the Appendix E of your textbook how many moons
you find that are larger than our Moon? Name them and their host planet.
- For each of the moons you found in part (a) calculate the ratio of their
diameter to the diameter of the planet they orbit. Comment on the value you
for the Moon-Earth system compared to the other values.
- Which other terrestrial planet has moons?
With this fact, we concluded that the Earth is centrally concentrated -
the material that is in the center is much denser than what we find at the
The mean density of our Earth's moon is about 3.3 times that of water
which is just slightly greater than that of Earth rocks. Given this, answer
these two questions: What does this imply for the central concentration and
composition of the Moon? What does this tell you about the possiblity of
joint origin of the Moon and Earth?
- Jupiter's moon Ganymede has a mostly ice surface (ice has a mean density
slightly less than water).
Ganymede's mean density is only about twice that of water. Comment on the
composition of Ganymede, and on the state of matter inside of it.
There are four main processes that have modified the
surfaces of planets and moons since their surfaces first hardened.
- List those four processes. For each process, name the terrestrial
planet whose surface most clearly shows its effects.
- Why do the surface of Mercury and the highlands of the Moon suggest
that in its early history, our solar system was a violent and dangerous
place, compared to modern times?
- Suggest a reason why the surface of Mars shows many more
craters than the surface of the Earth.
Which terrestrial planet has the strongest magnetic field? For each of the
other terrestrial planets explain why their magnetic field is so weak. (Hint:
consider what characteristics are required for a planet to have a strong
magnetic field and which of these caracteristics is missing in each case).
Suppose Venus rotated as fast at the Earth did. How would this change its
relative levels of volcanism, tectonics, and erosion? Explain why in each