Chapter 12 Rings, Moons, and Pluto

12.8 Questions and Exercises

Review Questions

1: What are the moons of the outer planets made of, and how is their composition different from that of our Moon?

2: Compare the geology of Callisto, Ganymede, and Titan.

3: What is the evidence for a liquid water ocean on Europa, and why is this interesting to scientists searching for extraterrestrial life?

4: Explain the energy source that powers the volcanoes of Io.

5: Compare the properties of Titan’s atmosphere with those of Earth’s atmosphere.

6: How was Pluto discovered? Why did it take so long to find it?

7: How are Triton and Pluto similar?

8: Describe and compare the rings of Saturn and Uranus, including their possible origins.

9: Why were the rings of Uranus not observed directly from telescopes on the ground on Earth? How were they discovered?

10: List at least three major differences between Pluto and the terrestrial planets.

11: The Hubble Space Telescope images of Pluto in 2002 showed a bright spot and some darker areas around it. Now that we have the close-up New Horizons images, what did the large bright region on Pluto turn out to be?

12: Saturn’s E ring is broad and thin, and far from Saturn. It requires fresh particles to sustain itself. What is the source of new E-ring particles?

Thought Questions

13: Why do you think the outer planets have such extensive systems of rings and moons, while the inner planets do not?

14: Ganymede and Callisto were the first icy objects to be studied from a geological point of view. Summarize the main differences between their geology and that of the rocky terrestrial planets.

15: Compare the properties of the volcanoes on Io with those of terrestrial volcanoes. Give at least two similarities and two differences.

16: Would you expect to find more impact craters on Io or Callisto? Why?

17: Why is it unlikely that humans will be traveling to Io? (Hint: Review the information about Jupiter’s magnetosphere in The Giant Planets.)

18: Why do you suppose the rings of Saturn are made of bright particles, whereas the particles in the rings of Uranus and Neptune are black?

19: Suppose you miraculously removed all of Saturn’s moons. What would happen to its rings?

20: We have a lot of good images of the large moons of Jupiter and Saturn from the Galileo and Cassini spacecraft missions (check out NASA’s Planetary Photojournal site, at, to see the variety). Now that the New Horizons mission has gone to Pluto, why don’t we have as many good images of all sides of Pluto and Charon?

21: In the Star Wars movie Star Wars Episode VI: Return of the Jedi, a key battle takes place on the inhabited “forest moon” Endor, which supposedly orbits around a gas giant planet. From what you have learned about planets and moons of the solar system, why would this be an unusual situation?

Figuring for Yourself

22: Which would have the longer orbital period: a moon 1 million km from the center of Jupiter, or a moon 1 million km from the center of Earth? Why?

23: How close to Uranus would a spacecraft have to get to obtain the same resolution as in Example 12.1 with a camera that has an angular resolution of 2 arcsec?

24: Saturn’s A, B, and C Rings extend 75,000 to 137,000 km from the center of the planet. Use Kepler’s third law to calculate the difference between how long a particle at the inner edge and a particle at the outer edge of the three-ring system would take to revolve about the planet.

25: Use the information in Appendix G to calculate what you would weigh on Titan, Io, and Uranus’ moon Miranda.

26: The average distance of Enceladus from Saturn is 238,000 km; the average distance of Titan from Saturn is 1,222,000 km. How much longer does it take Titan to orbit Saturn compared to Enceladus?


Icon for the Creative Commons Attribution 4.0 International License

Astronomy Copyright © 2017 by OpenStax is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

Share This Book