Astronomy 120: Fall 2003

Homework 2: Due in October 17/20 recitation

Name ___________________________ Section _______

Q1. Fill in this table of the planets in the solar system in order of increasing distance from the Sun. Use your textbook and lecture notes to provide the requested information about each planet:

Name Dist. from Sun (AU) Mass / Jupiter mass Density (water=1) Mag. field (Y/N,big/small) # of moons Rings? (Y/N)

Of the planets, which are rocky objects?


Which are gas-balls?


Which are icy?


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.

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 surface.

  1. 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?

  2. Jupiter's moon Ganymede has a mostly ice surface (ice has a mean density of 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.


Q3. There are four main processes that have modified the surfaces of planets and moons since their surfaces first hardened.

  1. List those four processes. For each process, name the terrestrial planet whose surface most clearly shows its effects.

  2. Why does 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?

  3. Suggest a reason why the surface of Mars shows many more craters than the surface of the Earth?


Q4. We expect that liquid water once existed on the surface of Mars. List two distinct pieces of evidence that this is true. Where might the water be now? Explain.