Chapter 14 Cosmic Samples and the Origin of the Solar System

14.8 Questions and Exercises

Review Questions

1: A friend of yours who has not taken astronomy sees a meteor shower (she calls it a bunch of shooting stars). The next day she confides in you that she was concerned that the stars in the Big Dipper (her favorite star pattern) might be the next ones to go. How would you put her mind at ease?

2: In what ways are meteorites different from meteors? What is the probable origin of each?

3: How are comets related to meteor showers?

4: What do we mean by primitive material? How can we tell if a meteorite is primitive?

5: Describe the solar nebula, and outline the sequence of events within the nebula that gave rise to the planetesimals.

6: Why do the giant planets and their moons have compositions different from those of the terrestrial planets?

7: How do the planets discovered so far around other stars differ from those in our own solar system? List at least two ways.

8: Explain the role of impacts in planetary evolution, including both giant impacts and more modest ones.

9: Why are some planets and moons more geologically active than others?

10: Summarize the origin and evolution of the atmospheres of Venus, Earth, and Mars.

11: Why do meteors in a meteor shower appear to come from just one point in the sky?

Thought Questions

12: What methods do scientists use to distinguish a meteorite from terrestrial material?

13: Why do iron meteorites represent a much higher percentage of finds than of falls?

14: Why is it more useful to classify meteorites according to whether they are primitive or differentiated rather than whether they are stones, irons, or stony-irons?

15: Which meteorites are the most useful for defining the age of the solar system? Why?

16: Suppose a new primitive meteorite is discovered (sometime after it falls in a field of soybeans) and analysis reveals that it contains a trace of amino acids, all of which show the same rotational symmetry (unlike the Murchison meteorite). What might you conclude from this finding?

17: How do we know when the solar system formed? Usually we say that the solar system is 4.5 billion years old. To what does this age correspond?

18: We have seen how Mars can support greater elevation differences than Earth or Venus. According to the same arguments, the Moon should have higher mountains than any of the other terrestrial planets, yet we know it does not. What is wrong with applying the same line of reasoning to the mountains on the Moon?

19: Present theory suggests that giant planets cannot form without condensation of water ice, which becomes vapor at the high temperatures close to a star. So how can we explain the presence of jovian-sized exoplanets closer to their star than Mercury is to our Sun?

20: Why are meteorites of primitive material considered more important than other meteorites? Why have most of them been found in Antarctica?

Figuring for Yourself

21: How long would material take to go around if the solar nebula in Example 14.1 became the size of Earth’s orbit?

22: Consider the differentiated meteorites. We think the irons are from the cores, the stony-irons are from the interfaces between mantles and cores, and the stones are from the mantles of their differentiated parent bodies. If these parent bodies were like Earth, what fraction of the meteorites would you expect to consist of irons, stony-irons, and stones? Is this consistent with the observed numbers of each? (Hint: You will need to look up what percent of the volume of Earth is taken up by its core, mantle, and crust.)

23: Estimate the maximum height of the mountains on a hypothetical planet similar to Earth but with twice the surface gravity of our planet.


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