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Chapter Review
Planets and other objects form a system
around our Sun.
CONTENT REVIEW
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KEY CONCEPTS SUMMARY
1
Planets orbit the Sun at different distances.
The planets have different sizes and distances from the
Sun. The solar system formed from a disk of dust and gas.
Massive objects became round.
outer solar system
Jupiter, Saturn, Uranus,
Neptune, Pluto, comets
inner solar system
Mercury, Venus, Earth,
Mars, asteroids
2
The inner solar system has rocky planets.
VOCABULARY
• The terrestrial planets are round and have layers.
• Atmospheres came from volcanoes and impacts.
• Four processes produce surface features.
terrestrial planet
p. 725
tectonics p. 726
volcanism p. 726
tectonics
3
VOCABULARY
astronomical unit
(AU) p. 721
ellipse p. 721
volcanism
weathering
and erosion
impact cratering
The outer solar system has four
giant planets.
VOCABULARY
gas giant p. 734
ring p. 737
• The gas giants have very dense, deep
atmospheres with layers of clouds.
• All four giant planets have ring systems.
Close-up of Saturn’s rings
4
Small objects are made of ice
and rock.
VOCABULARY
asteroid p. 743
comet p. 744
meteor p. 745
meteorite p. 745
• Objects in the inner solar system are rocky.
• Pluto and most other objects in the outer
solar system are made of ice and rock.
• Rocky asteroids and icy comets orbit the
Sun and produce tiny fragments that may
become meteors.
The asteroid Eros
748 Unit 5: Space Science
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Reviewing Vocabulary
Make a Venn diagram for each pair of terms.
Put an important similarity in the overlapping
part. Use the rest of the diagram to show an
important difference.
Example:
Ring
many small
chunks
Moon
orbits a
planet
one solid
object
1. terrestrial planet, gas giant
2. volcanism, impact cratering
3. erosion, tectonics
4. asteroid, comet
5. meteor, meteorite
9. Which of these appears in Earth’s atmosphere?
a. a moon
c. a meteor
b. an asteroid
d. a comet
10. How did planets and other objects in the solar
system form?
a. After the Sun formed, it threw off hot
pieces that spun and cooled.
b. The Sun captured objects that formed in
other places in the galaxy.
c. Two stars collided, and the broken pieces
went into orbit around the Sun.
d. Material in a disk formed large clumps as
the Sun formed in the center of the disk.
11. Which process occurs only when a small space
object interacts with a larger space body?
a. tectonics
c. erosion
b. volcanism
d. impact cratering
12. Which processes occur because a planet or
another space body is hot inside?
a. tectonics and volcanism
b. volcanism and erosion
c. erosion and impact cratering
d. impact cratering and tectonics
6. comet, meteor
Reviewing Key Concepts
Multiple Choice Choose the letter of the
best answer.
7. Even though orbits are ellipses, what shape is
a typical planet’s orbit most like?
a. a short rectangle
b. an egg-shape with a pointy end
c. a long, narrow oval
d. a circle
8. How is a moon different from a planet?
a. A moon is smaller than any planet.
b. A moon is less massive than any planet.
c. A moon is in orbit around a planet.
d. A moon is unable to have an atmosphere.
13. What do all four gas giants have that terrestrial
planets do not have?
a. atmospheres
c. moons
b. solid surfaces
d. rings
14. What are the white stripes of Jupiter and the
white spots of Neptune?
a. clouds high in the atmosphere
b. smoke from volcanoes
c. continents and islands
d. holes in the atmosphere
Short Answer Write a short answer to
each question.
15. The solid part of a comet is small in comparison
with a planet. However, sometimes a comet
appears to be larger than the Sun. What
makes it seem so large?
16. Why do all nine major planets orbit the Sun
in the same direction?
Chapter 21: Our Solar System 749
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Thinking Critically
Use the image of Jupiter’s moon Ganymede
to answer the next five questions.
25. INFER Some comets orbit in a direction opposite
to that of the planets. Why might this make
some scientists wonder if they formed with the
rest of the solar system?
26. HYPOTHESIZE Scientists calculate the mass of a
planet from the effects of its gravity on other
objects, such as moons. However, Mercury and
Venus have no moons. What other objects in
space could have been used to determine the
planets’ masses?
A
B
27. COMPARE AND CONTRAST Images of Earth from
space show white clouds above darker land
and water. In what ways are they like and
unlike images of Jupiter?
17. OBSERVE Which crater, A or B, is more eroded?
Explain why you think so.
18. COMPARE AND CONTRAST Describe the differences between the surface in the upper half
of the image and the long, triangular area
near the bottom of the image.
19. INFER Explain which area of the surface, the
smooth part or the heavily cratered part, is
probably older.
20. APPLY The lighter area was produced by
tectonic processes and may have been covered
with molten material. What can you infer
about the inside of this moon?
21. SEQUENCE A crack runs through part of crater
A. Explain how you can tell whether the crack
or the crater formed first. Hint: Think about
what would have happened if the other
feature had formed first.
22. PREDICT Suppose the Moon were hotter inside.
How might its surface be different?
23. IDENTIFY CAUSE Mercury’s surface is not as hot
as Venus’s, even though Mercury is closer to the
Sun. In addition, the night side of Mercury gets
very cold, while the night side of Venus is about
as hot as the day side. Why are the temperature
patterns on these two planets so different?
24. EVALUATE Would it be easier to design a lander
mission for the surface of Venus or the surface
of Mercury? Explain your reasoning.
750 Unit 5: Space Science
Earth
Jupiter
28. ANALYZE Scientists sometimes use round
numbers to compare quantities. For example,
a scientist might say that the Sun’s diameter is
about 100 times Earth’s diameter, even though
she knows that the precise value is 109 times.
Why might she use such an approximation?
29. APPLY Look back at pages 716–717. Think
about the answer you gave to the question
about the large image of a planet and moon.
How would you answer this question
differently now?
30. SYNTHESIZE Ice is generally less dense than
rock, which is generally less dense than metal.
Use what you know about materials in the
solar system to estimate whether a moon of
Mars, a moon of Uranus, or the planet Mercury
should be the least dense.
Check your schedule for your unit project. How
are you doing? Be sure that you have placed data
or notes from your research in your project folder.
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Standardized Test Practice
For practice on your
state test, go to . . .
TEST PRACTICE
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Interpreting a Passage
Read the following passage. Then answer the questions that follow.
Life in Extreme Environments
Could living organisms survive in the crushing, hot atmosphere of Venus? Could they
thrive on a waterless asteroid or get their energy from tides in the dark ocean that might
be beneath the surface of Europa? Scientists are looking for answers to these questions
right here on Earth. They study extremophiles, which are life forms that can survive in
extreme environments—very high or low temperatures or other difficult conditions.
These environments have conditions similar to those on other planets, and those on
moons, asteroids, and comets.
Scientists have found tiny organisms that grow in the scalding water of hot vents on
the ocean floor, deep inside rock, and in miniature ponds within glaciers. Scientists have
also found organisms that were dormant because they were frozen solid for thousands
of years but that were still capable of living and growing after warming up. By studying
extremophiles, scientists learn more about the conditions needed to support life.
Choose from the following four environments to
answer each of the next three questions.
• the dark ocean that might be underneath
Europa’s surface
• the flood channels on Mars, which have been
dry and frozen for a long time
• the very hot, high-pressure environment of Venus
• the dry rock of an asteroid that alternately heats
and cools
1. Some organisms survive deep underwater, where
photosynthesis does not occur because little or no
sunlight reaches those depths. Which environment
can these organisms teach about?
a. under Europa’s surface c. Venus
b. Martian flood channels d. an asteroid
2. Some organisms survive in very deep cracks in
rocks, where they are protected from changing
temperatures. Where else might scientists look
for these types of organisms?
a. under Europa’s surface c. Venus
b. Martian flood channels d. an asteroid
3. Where might scientists look for tiny organisms that
are dormant but that might revive if given warmth
and water?
a. under Europa’s surface c. Venus
b. Martian flood channels d. an asteroid
4. Where, outside Earth, should scientists look for
tiny ponds of water within solid ice?
a. the other terrestrial planets
b. the gas giants
c. small space objects in the inner solar system
d. small space objects in the outer solar system
Extended Response
Answer the two questions in detail.
5. A class was given a sample of ordinary dormant,
dry yeast that had been exposed to an extreme
environment. Describe ways the students might
test the yeast to see if it remained undamaged,
or even survived, the conditions.
6. Imagine that scientists have found extremophiles in
clouds of frozen water crystals high in Earth’s
atmosphere. How might this discovery affect a
search for organisms on the gas giants?
Chapter 21: Our Solar System 751