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 http://photojournal.jpl.nasa.gov, 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 [link] 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?

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