21st Century Astronomy

Laura Kay, Stacy Palen, Brad Smith

Chapter 8

The Terrestrial Planets and Earth's Moon - all with Video Answers

Educators

Chapter Questions

Problem 1

_______,_______, and _________, build up structures on the terrestrial planets, while _______ tears them down.
a. impacts, erosion, volcanism; tectonism
b. impacts, tectonism, volcanism; erosion
c. tectonism, volcanism, erosion; impacts
d. tectonism, impacts, erosion; volcanism

Zachary Warner

Zachary Warner

Numerade Educator

Problem 2

If crater $\mathrm{A}$ is inside crater $\mathrm{B}$, we know that
a. crater A was formed before crater B.
b. crater B was formed before crater A.
c. both craters were formed at about the same time.
d. crater B formed crater A.
e. crater A formed crater B.

Zachary Warner

Numerade Educator

Problem 3

If radioactive element A decays into radioactive element B with a half-life of 20 seconds, then after 40 seconds
a. none of element A will remain.
b. none of element B will remain.
c. half of element A will remain.
d. one-quarter of element A will remain.

Zachary Warner

Numerade Educator

Problem 4

Scientists can learn about the interiors of the terrestrial planets from
a. seismic waves.
b. satellite observations of gravitational fields.
c. physical arguments about cooling.
d. satellite observations of magnetic fields.
e. all of the above

Zachary Warner

Numerade Educator

Problem 5

_______ waves are compressional, while _________ waves oscillate perpendicular to their line of travel.
a. longitudinal; transverse
b. transverse; longitudinal
c. $P$ waves; $S$ waves
d. S waves; P waves
e. both a and c
f. both b and d

Zachary Warner

Numerade Educator

Problem 6

Earth's interior is heated by
a. angular momentum and gravity.
b. radioactive decay and gravity.
c. radioactive decay and tidal effects.
d. angular momentum and tidal effects.
e. gravity and tidal effects.

Zachary Warner

Numerade Educator

Problem 7

Lava flows on the Moon and Mercury created large, smooth plains. We don't see similar features on Earth because
a. Earth has less lava.
b. Earth had fewer large impacts in the past.
c. Earth has plate tectonics that recycle the surface.
d. Earth is large compared to the size of these plains, so they are not as noticeable.
e. Earth rotates much faster than either of these other worlds.

Zachary Warner

Numerade Educator

Problem 8

Rank the following worlds by the strength of wind erosion currently operating on their surfaces, from greatest to least:
a. Mercury
b. Venus
c. Earth
d. Moon
e. Mars

Zachary Warner

Numerade Educator

Problem 9

Differentiation, in the context of planets, means
a. comparing a planet to others to better understand its features.
b. that different parts of the planet have different compositions.
c. that different planets have different compositions.
d. calculating the slope of the trajectory.

Zachary Warner

Numerade Educator

Problem 10

Scientists know the history of Earth's magnetic field because
a. the magnetic field hasn't changed since the formation of Earth.
b. they see how it's changing today, and project backward in time.
c. the magnetic field becomes frozen into rocks, and plate tectonics spreads those rocks out.
d. they compare the magnetic fields on other planets to Earth's.
e. there are written documents of magnetic field measurements since the beginning of Earth.

Zachary Warner

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Problem 11

$\mathbf{T} / \mathbf{F}:$ Volcanism has been present on all the terrestrial planets.

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Problem 12

$\mathbf{T} / \mathbf{F}:$ Impact cratering no longer affects the terrestrial planets.

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Problem 13

T/F: The geological processes that shape a planet have ceased on Earth.

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Problem 14

T/F: Large worlds remain geologically active longer than small ones.

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Problem 15

T/F: Wind erosion is an important process on Venus.

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Problem 16

Of the four processes that shape the surface of a terrestrial world, the one with the greatest potential for catastrophic rearrangement is
a. impact cratering.
b. volcanism.
c. tectonism.
d. erosion.

Zachary Warner

Numerade Educator

Problem 17

Geologists can determine the relative age of features on a planet because
a. the ones on top must be older.
b. the ones on top must be younger.
c. the larger ones must be older.
d. the larger ones must be younger.
e. all the features we can see are the same age.

Zachary Warner

Numerade Educator

Problem 18

Geologists can determine the actual age of features on a planet by
a. radiometric dating of rocks retrieved from the planet.
b. comparing cratering rates on one planet to those on another.
c. assuming that all features on a planetary surface are the
same age.
d. both a and b
e. both b and c

Zachary Warner

Numerade Educator

Problem 19

Impacts on the terrestrial planets and the Moon
a. are more common than they used to be.
b. have occurred at approximately the same rate since the Solar System formed.
c. are less common than they used to be.
d. periodically become more common and then are less common for a while.
e. never occur anymore.

Zachary Warner

Numerade Educator

Problem 20

Comparative planetology is a particularly useful approach to a study of planets because
a. physical explanations should apply to more than one object.
b. very few data have been collected.
c. all the planets are alike.
d. we can't actually travel to other planets.

Zachary Warner

Numerade Educator

Problem 21

Earth has fewer craters than Venus. Why?
a. Earth's atmosphere provides better protection than Venus's.
b. Earth is a smaller target than Venus.
c. Earth is closer to the asteroid belt.
d. Earth's surface experiences more erosion.

Zachary Warner

Numerade Educator

Problem 22

Imagine that you are rock collecting in Arizona and you find rock containing shock-modified quartz. You immediately know that the rock
a. formed during an impact.
b. formed in a volcano.
c. has been heavily eroded.
d. was crushed by tectonic plates.

Zachary Warner

Numerade Educator

Problem 23

Scientists propose an early period of heavy bombardment in the Solar System because
a. the Moon is heavily cratered.
b. all the craters on the Moon are old.
c. the smooth part of the Moon is nearly as old as the heavily cratered part.
d. all the craters on the Moon are young.

Zachary Warner

Numerade Educator

Problem 24

Scientists know that Earth was once completely molten because
a. the surface is smooth.
b. the interior layers are denser.
c. the chemical composition indicates that.
d. volcanoes exist today.

Zachary Warner

Numerade Educator

Problem 25

Earth's magnetic field cannot be due to permanent magnets, because
a. the core is too hot.
b. the field changes its strength.
c. the field changes its orientation.
d. all of the above

Zachary Warner

Numerade Educator

Problem 26

In discussing the terrestrial planets, why do we include Earth's Moon?

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Problem 27

Can all rocks be dated with radiometric methods? Explain.

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Problem 28

Explain how scientists know that rock layers at the bottom of Arizona's Grand Canyon are older than those found on the rim.

Zachary Warner

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Problem 29

What evidence supports the theory suggesting that a mass extinction occurred as a consequence of an enormous impact on Earth 65 million years ago?

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Problem 30

Describe the sources of heating that are responsible for generating Earth's magma.

Zachary Warner

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Problem 31

Explain why the Moon's core is cooler than Earth's.

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Problem 32

Explain the difference between longitudinal waves and transverse waves.

Zachary Warner

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Problem 33

How do we know that Earth's core includes a liquid zone?

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Problem 34

Explain hydrostatic equilibrium.

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Problem 35

Compare and contrast tectonism on Venus, Earth, and Mercury.

Zachary Warner

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Problem 36

Explain plate tectonics and identify the only planet on which this process has been observed.

Zachary Warner

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Problem 37

Volcanoes have been found on all of the terrestrial planets. Where are the largest volcanoes in the inner Solar System?

Zachary Warner

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Problem 38

Name and explain the criteria you would apply to images (assume adequate resolution) in order to distinguish between a crater formed by an impact and one formed by a volcanic eruption.

Zachary Warner

Numerade Educator

Problem 39

What are the primary reasons that the surfaces of Venus, Earth, and Mars have been determined to be younger than those of Mercury and the Moon?

Zachary Warner

Numerade Educator

Problem 40

Explain some of the geological evidence suggesting that Mars once had liquid water on its surface.

Zachary Warner

Numerade Educator

Problem 41

Study Figure 8.10
a. How has the cratering rate changed over time? Has it fallen off gradually or abruptly?
b. At present, what is the cratering rate compared to about 4 billion years ago?
c. Explain why this falloff in cratering rate fits nicely in the theory of planet formation.

Zachary Warner

Numerade Educator

Problem 42

Study Figure $8.9 .$ Are the vertical and horizontal axes linear or logarithmic? After how many half-lives will the number of parent isotopes equal the number of daughter isotopes? Is this result unique to this example? Why or why not?

Zachary Warner

Numerade Educator

Problem 43

Study Figure $8.9 .$ The destruction of the parent isotope is an example of exponential decay. Is the growth of the daughter isotope an example of exponential growth? How can you tell?

Zachary Warner

Numerade Educator

Problem 44

Compare Figures 8.21 and $8.27 .$ Which of these regions is older?

Zachary Warner

Numerade Educator

Problem 45

Assume that Earth and Mars are perfect spheres with radii of $6,371 \mathrm{km}$ and $3,390 \mathrm{km}$, respectively.
a. Calculate the surface area of Earth.
b. Calculate the surface area of Mars.
c. If 0.72 (72 percent) of Earth's surface is covered with water, compare the amount of Earth's land area to the total surface area of Mars.

Zachary Warner

Numerade Educator

Problem 46

Compare the kinetic energy of a 1-gram piece of ice (about half the mass of a dime) entering Earth's atmosphere at a speed of $50 \mathrm{km} / \mathrm{s}$ to that of a 2 -metric-ton SUV $\left(\text { mass }=2 \times 10^{3} \mathrm{kg}\right)$ speeding down the highway at $90 \mathrm{km} / \mathrm{h}$

Zachary Warner

Numerade Educator

Problem 47

The object that created Arizona's Meteor Crater was estimated to have a diameter of 50 meters and a mass of 300 million kg. Calculate the density of the impacting object, and explain what that may tell you about its composition.

Zachary Warner

Numerade Educator

Problem 48

Using the information in Table 8.1 , determine the relative rates of internal energy loss experienced by Earth and the Moon.

Zachary Warner

Numerade Educator

Problem 49

Although oceans cover 72 percent of Earth's surface, they represent but a tiny fraction of its mass. Earth's mass is $6.0 \times 10^{24} \mathrm{kg},$ and its oceans have a total mass of $1.5 \times 10^{21} \mathrm{kg}$
a. What fraction of Earth's total mass do the oceans represent?
b. Does surface and atmospheric water represent Earth's total mass of water? Explain.

Zachary Warner

Numerade Educator

Problem 50

Earth's mean radius is $6,371 \mathrm{km},$ and its mass is $6.0 \times 10^{24} \mathrm{kg}$
a. Calculate Earth's average density. Show your work; do not look this value up.
b. The average density of Earth's crust is $2,600 \mathrm{kg} / \mathrm{m}^{3}$. What does this value tell you about Earth's interior?
c. Compute the Moon's average density. Show your work; do not look this value up.
d. Compare the average densities of the Moon, Earth, and Earth's crust. What do these values tell you about the Moon's composition compared to that of Earth and of Earth's crust?

Zachary Warner

Numerade Educator

Problem 51

Suppose you find a piece of ancient pottery and take it to the laboratory of a physicist friend. He finds that the glaze contains radium, a radioactive element that decays to radon and has a half-life of 1,620 years. He tells you that there could not have been any radon in the glaze when the pottery was being fired, but that it now contains three atoms of radon for each atom of radium. How old is the pottery?

Zachary Warner

Numerade Educator

Problem 52

Archaeological samples are often dated by radiocarbon dating. The half-life of carbon-14 is 5,700 years.
a. After how many half-lives will the sample have only $1 / 64$ as much carbon-14 as it originally contained?
b. How much time will have passed?
c. If the daughter product of carbon-14 is present in the sample when it forms (even before any radioactive decay happens), you cannot assume that every daughter you see is the result of carbon-14 decay. If you did make this assumption, would you overestimate or underestimate the age of a sample?

Zachary Warner

Numerade Educator

Problem 53

Different radioisotopes have different half-lives. For example, the half-life of carbon-14 is 5,700 years, the half-life of uranium-235 is 704 million years, the half-life of potassium-40 is 1.3 billion years, and the half-life of rubidium-87 is 49 billion years.
a. Why wouldn't you use an isotope with a half-life similar to that of carbon-14 to determine the age of the Solar System?
b. The age of the universe is approximately 14 billion years. Does that mean that no rubidium- 87 has decayed yet?

Zachary Warner

Numerade Educator

Problem 54

Assume that the east coast of South America and the west coast of Africa are separated by an average distance of 4,500 km. Assume also that GPS measurements indicate that these continents are now moving apart at a rate of $3.75 \mathrm{cm} /$ year. If this rate has been constant over geological time, how long ago were these two continents joined together as part of a supercontinent?

Zachary Warner

Numerade Educator

Problem 55

Shield volcanoes are shaped something like flattened cones. The volume of a cone is equal to the area of its base multiplied by one-third of its height. The largest volcano on Mars, Olympus Mons, is $27 \mathrm{km}$ high and has a base diameter of 550 km. Compare its volume with that of Earth's largest volcano, Mauna Loa, which is $9 \mathrm{km}$ high and has a base diameter of $120 \mathrm{km}$

Zachary Warner

Numerade Educator

Problem 56

Go to the U.S. Geological Survey's "Latest Earthquakes in the World" website (http://earthquake.usgs.gov/ earthquakes/map) and look at the earthquakes for the past week. Were there any really large ones? Compare the map of recent earthquakes with Figure 8.20 in the text. Are any of them in surprising locations? Where was the most recent one? Set "data feed" to 30 days, M2.5 $+$ and click on "US" above the map. Where in the U.S. has there been seismic activity?

Kayla Day

Numerade Educator

Problem 57

Use the Google Earth platform to explore the Moon, Mercury, and Mars.
a. View all sides of the Moon. Does one hemisphere look more heavily cratered than others, and if so, why?
b. View the planet Mercury. In what ways is Mercury similar to and in what ways different from the Moon? (You might need to get the Mercury KMZ file:
http://messenger.jhuapl.edu/the_mission/google.html)
c. View all sides of the planet Mars. What differences can you see between the northern and southern hemispheres?

Zachary Warner

Numerade Educator

Problem 58

In his project Full Moon, artist Michael Light digitized many of the $A$ pollo mission photographs. Some prints are hanging in museums; many can be seen on his website (http:// michaellight.net/workFullMoon.html). Click on "Explore Full Moon" to bring up the images. What does the surface of the Moon look like? Why does the footprint in image 48 look unchanged after 40 years? Why is there no color except for in the objects brought from Earth?

Zachary Warner

Numerade Educator

Problem 59

The International Astronomical Union adopted a plan to have all features on Venus (with a few exceptions for large features discovered earlier) named after historical or mythological women. Categories of features are paired with specific subcategories of women; for example, large craters (greater than about $15 \mathrm{km}$ ) are named after famous women, smaller craters have female first names, mountains are named after goddesses, and so on. Go to the Venus Crater Database (http://lpi.usra.edu/resources/vc/vchome.html), click on "Craters by Image Map," click on a region to zoom in on, and then select a few craters. For each crater, consider these questions: What is the "morphologic" class of the crater? Is there another crater very close by? What is the crater's diameter? How high is the elevation? Who was the large crater named after (if you didn't get a large one, go back to the starting address and click on "Craters by Descending Diameter")

Zachary Warner

Numerade Educator

Problem 60

Go to the website for Moon Zoo (http://moonzoo.org), a project that lets everyone participate in the analysis of images from NASA's Lunar Reconnaissance Orbiter. Read through the FAQ; then click on "Tutorials" and select "How to Take Part." (You will need to create an account if you haven't already done so for PlanetHunters in Chapter $7 ;$ all of these Zooniverse projects use the same log-in.) You will be counting craters on the Moon, noting where there are boulders, classifying some of these features, and looking for hardware left over from exploration missions.

Zachary Warner

Numerade Educator

Problem 61

Space missions:
a. Go to NASA's GRAIL mission website (http://solarsystem .nasa.gov/grail/home.cfm). The two spacecraft entered lunar orbit in 2012 and are studying the gravitational field and thermal history of the Moon. Are there any mission results? What has been learned?
b. Go to the website for NASA's Messenger mission to Mercury (http://messenger.jhuapl.edu). Click on "Gallery" and then "Science Images," and look at a few of the pictures. Why are some taken with the narrow-angle camera and some with the wide-angle camera? Are the color images using real or false colors? Click on "News Center." Is the mission still collecting data? Describe a recent result. How does this result correspond to one of the six goals of the mission (listed under "Why Mercury?")?
c. Go to the website for the Mars Science Laboratory (http://mars.jpl.nasa.gov/msl), which landed in 2012 What are the latest science results?
d. The Chandrayaan-2 Moon lander and rover, a joint IndiaRussia mission, is scheduled to launch in $2013 .$ Chang'e 3 another Moon lander and rover, is scheduled for launch from China in $2013 .$ Do a news search to find the status of these missions. Are there any scientific results yet? What are these countries' plans for future lunar exploration?

Samantha Baker

Numerade Educator

Problem 62

Do a news search to see the latest news story about water on the Moon or water on Mars. What is the story based on-new space data? improved analysis of old data? If the information comes from a current space mission, go to the mission website and read the original press release. How does the news story compare with the press release? Is it just a summation? Did the writer get comments from scientists who were not directly involved in the study? How certain are the results about water?

Zachary Warner

Numerade Educator

Problem 63

The Google Lunar X Prize (http://googlelunarxprize.org) goes to the first privately funded team to send a robot to the Moon. The winning robot must travel some distance on the Moon's surface, and send back pictures, by December 2015 On the website, click on "The Teams" and read about a few of the teams. For each team, consider these questions: What kind of people and companies are on the team? What is their plan to go to the Moon? Aside from this prize, why do they want to go to the Moon; what commercial opportunities on the Moon do they anticipate?

Samantha Baker

Numerade Educator

Problem 64

Watch one of the available documentaries about the Apollo missions to the Moon (for example, In the Shadow of the Moon, 2008 ). Why did the United States decide to send astronauts to the Moon? Why did the Apollo program end? Are there current plans-in the United States or elsewhereto send people to the Moon?

Zachary Warner

Numerade Educator

Problem 65

The first science fiction film, the short Voyage to the Moon (George Méliès, 1902 ), is in the public domain and can be viewed at http://archive.org/details/Levoyagedanslalune (a newer, digitized version was released in 2011 ). Where do the "Selenians" live on the Moon? In this first cinematic depiction of contact with life from outside of Earth, what do the human astronomers do to the Selenians? Contrast what the astronomers in the film find on the Moon with what the Apollo astronauts actually saw.

Zachary Warner

Numerade Educator