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Table of Contents
The Solar System
Section 1 • Planet Motion
Section 2: The Inner Planets
Section 3: The Outer Planets
Section 4: Life in the Solar System
Section
1
Planet Motion
Models of the Solar System
• In the geocentric
model of the solar
system, Earth is
considered the center
and everything else
revolves around it.
• This model was developed
by the Greek philosopher
Ptolemy.
Section
1
Planet Motion
Heliocentric Model
• Earth-centered model held until 1543 when Polish
astronomer Nicholas Copernicus proposed a different
view.
• Copernicus stated that the Moon revolves around
Earth.
• Earth and the other planets revolve around the
Sun.
Section
1
Planet Motion
Heliocentric Model
• The apparent motion
of the planets, the
stars, and the Sun is
due to Earth’s
rotation. This is the
heliocentric model,
or Sun-centered
model of the solar
system.
Section
Planet Motion
1
Galileo
• Using his telescope, Italian astronomer Galileo Galilei
discovered evidence to support Copernicus’s model.
• He observed that Venus went through phases like the
Moon’s.
• He also saw moons in orbit around Jupiter.
Section
1
Planet Motion
Understanding the Solar System
• In the early 1600’s, the German astronomer Johannes
Kepler discovered the planets travel around the Sun in
ellipses, not perfect spheres.
• Planets travel at different speeds in their orbits.
• The closer a planet is to the Sun, the faster it completes
its orbit.
• The astronomical unit (AU) equals the average
distance from Earth to the Sun, about 150 million km.
Section
1
Planet Motion
Classifying the Planets
• One system uses size, structure, and composition.
• Those similar to Earth are called terrestrial planets.
Giant planets are jovian planets.
• Two other systems classify planets by location.
Section
1
Planet Motion
Classifying the Planets
• Planets whose orbits are between the Sun and the
asteroid belt are classified as inner planets and those
beyond the asteroid belt are outer planets.
• Another system classifies planets whose orbits are
between Earth’s orbit and the Sun as inferior planets,
and those whose orbits are beyond Earth’s orbit as
superior planets.
Section
1
Planet Motion
Other Solar Systems
• Extrasolar planets—planets in orbit around other
stars—are helping astronomers learn how planetary
systems form.
• As of 2009, astronomers have discovered more than
300 extrasolar planets in the universe.
Section
1
Section Check
Question 1
Who was responsible for developing the geocentric
model of the solar system?
A. Aristotle
B. Copernicus
C. Galileo
D. Ptolemy
Section
1
Section Check
Answer
The answer is D.
Ptolemy presented
his geocentric
model of the solar
system in 140 A.D.
Section
Section Check
1
Question 2
What is the length of an astronomical unit?
A. 100 km
B. 100 million km
C. 150 million km
D. 200 billion km
Section
1
Section Check
Answer
The answer is C. One astronomical unit equals the
average distance from Earth to the Sun, about 150
million km.
Section
1
Section Check
Question 3
_______ are planets in orbit around stars other than our
Sun.
A. Extrasolar planets
B. Extrasensory planets
C. Intersolar planets
D. Intrasolar planets
Section
1
Section Check
Answer
The answer is A. Scientists have discovered extrasolar
planets around Upsilon Andromedae.
Section
2
The Inner Planets
Planets Near the Sun
• The smallest and closest planet to the Sun is
Mercury.
• Mercury is covered by craters.
• Mercury has a much larger iron core than would be
expected and is missing some lighter materials.
Section
2
The Inner Planets
Planets near the Sun
• Mercury has a large iron core and thin outer layers.
• Mercury’s surface is covered with craters and cliffs up to
3km high.
• Mercury has no true atmosphere.
• Surface temperatures vary from 430ºC to -170ºC.
Section
The Inner Planets
2
Venus
• Venus is the second planet from the Sun.
• Venus is often referred to as Earth’s sister planet
because their sizes and masses are almost identical.
• Venus is blanketed by a dense atmosphere.
Section
2
The Inner Planets
The Greenhouse Effect
• The clouds on Venus are so dense that only two
percent of sunlight reaches the surface.
• Heat radiated from Venus’s surface is absorbed by the
carbon dioxide gas, causing what is called a greenhouse
effect.
• Due to this intense greenhouse effect, temperatures on
the surface of Venus are between 450ºC and 475ºC.
Section
The Inner Planets
2
Earth
• The third planet from the Sun is Earth.
• Temperatures on Earth allow water to exist as a solid,
a liquid, and a gas.
• Ozone in Earth’s atmosphere protects life from the
Sun’s intense radiation.
Section
2
The Inner Planets
Life on Earth
• Life has been discovered in extreme environments on
Earth.
• These environments include vents on the seafloor,
acidic hot springs, and ice in dark, cold polar waters
Section
The Inner Planets
2
Mars
• The fourth planet from the Sun, Mars, is called the red
planet because of iron oxide in some of the weathered
rocks.
• Other Martian features are the polar ice caps, composed
of frozen carbon dioxide and frozen water.
• Changes in the coloration and size of ice caps have
been observed.
• Coloration changes are seasonal due to wind blowing
lighter colored dust off the darker colored dust below.
Section
The Inner Planets
2
Mars
• The Martian atmosphere is much thinner than Earth’s
and is composed mostly of carbon dioxide, some
nitrogen and, argon.
• Mars has two small, heavily cratered moons
called Phobos and Deimos.
Section
2
The Inner Planets
Was Mars Once Wet?
• In late 2003, NASA sent martian landers Spirit and
Opportunity in search of liquid water.
• NASA’s Mars Reconnaissance Orbiter discovered
sediment layering and gullies in 2009.
Section
2
The Inner Planets
NASA on Mars
• The Mariner 9 space probe orbited Mars in 1971-1972.
• Valles Marineris is a large canyon that was discovered
by this early mission.
• Mariner 9 also found large, extinct volcanoes on Mars.
Section
2
The Inner Planets
The Viking Probes
• In 1976, the Viking 1 and Viking 2 probes landed on
Mars.
• The Viking 1 and Viking 2 orbiters photographed the
entire surface of Mars from orbit.
• Landers conducted meteorological, chemical, and
biological experiments on the planet’s surface.
Section
2
The Inner Planets
Global Surveyor, Pathfinder, and Odyssey
• In 1996, Global Surveyor showed that the walls of
Valles Marineris have distinct layers similar to those of
the Grand Canyon in Arizona.
• Mars Odyssey, provided evidence for water as frost
beneath a thin layer of soil in the far northern and
southern parts of Mars.
• The Mars Pathfinder and its rover, Sojourner,
gathered data that indicated that iron in Mar’s crust
may have been leached out by groundwater.
Section
2
Section Check
Question 1
Which planet is closest to the Sun?
A. Mars
B. Mercury
C. Earth
D. Venus
Section
2
Section Check
Answer
The answer is B. Mercury is the closest planet to
the Sun. Venus is the second planet from the
Sun.
Section
Section Check
2
Question 2
Which planet has a size and a mass similar
to Earth’s?
A. Jupiter
B. Mercury
C. Pluto
D. Venus
Section
2
Section Check
Answer
The answer is D. Venus has similar size and mass but
the temperatures on its surface are between 450º C
and 475º C.
Section
2
Section Check
Question 3
Earth is the __________ planet from the Sun.
A. second
B. third
C. fourth
D. fifth
Section
2
Section Check
Answer
The answer is B. Mercury and Venus are closer to the Sun
than Earth.
Section
The Outer Planets
3
Jupiter
• The largest and fifth planet from the Sun is
Jupiter.
• It is composed mostly of hydrogen and helium.
• Continuous storms of swirling, high-pressure gas have
been observed on Jupiter.
• The Great Red Spot is the most spectacular of these
storms.
Section
3
The Outer Planets
The Voyager Probes and Galileo
• In 1979, Voyager1 and Voyager 2 flew past Jupiter,
and the Galileo space probe reached Jupiter in 1995.
• The major discoveries of these probes include
information about the composition and motion of
Jupiter’s atmosphere, characteristics of some of its
moons and the discovery of new moons and faint
rings.
Section
3
The Outer Planets
Jupiter’s Moons
• Jupiter has 63 known moons. Many are small, rocky
bodies that could be captured asteroids.
• Four are large enough to be considered small planets.
• These Galilean moons of Jupiter are Io, Europa,
Ganymede, and Callisto.
• NASA scientists believe liquid water exists beneath
Europa, Ganymede, and Callisto’s surfaces.
Section
3
The Outer Planets
Jupiter’s Moons
• Ganymede is larger than the planet Mercury and is the
largest moon in the solar system.
• Io is under a constant tug-of-war between the
gravities of Jupiter and Europa.
• This heats up the interior of Io and causes it to be
the most volcanically active body in the solar
system.
• Europa is ice-covered.
Section
The Outer Planets
3
Saturn
• Saturn is the sixth planet from the Sun and has the
largest and most complex ring system of any outer
planet.
• Saturn is a large planet with a thick outer atmosphere
composed of hydrogen mostly and helium with some
ammonia, methane, and water vapor.
Section
3
The Outer Planets
Saturn’s Rings
• Saturn’s rings are composed of billions of ice and rock
particles ranging in size from a speck of dust to tens of
meters across.
• The ring system is over 280,000 km wide and only 1 km
thick.
Section
3
The Outer Planets
Cassini-Huygens
• The Cassini-Huygens spacecraft approached
Saturn in 2004 to collect data about Saturn, its ring
system and many moons.
• In January 2005, Huygens passed by Saturn’s
largest moon Titan in search of hydrocarbons.
Section
The Outer Planets
3
Uranus
• Uranus is the seventh planet from the Sun.
• It is four times larger than Earth with 27 moons.
• The atmosphere of Uranus contains hydrogen, helium,
and about two percent methane.
• The methane gives the planet its blue-green color.
• Uranus’s axis of rotation is tilted, so that it is nearly
parallel to the plane of its orbit.
Section
The Outer Planets
3
Neptune
• Neptune is the eighth planet from the Sun.
• Neptune’s atmosphere is similar to that of Uranus, but
has a little more methane—about 3 percent—causing
it to look bluer.
• Voyager 2 passed by Uranus in 1986 and Neptune in
1989, the only spacecraft to fly-by each planet.
Section
3
The Outer Planets
Dwarf Planets
• In 2005, astronomers discovered Eris, an object
beyond Pluto, that is larger than Pluto.
• This discovery led to a change in the definition of a
planet.
• Pluto, Eris and a large asteroid named Ceres are now
classified as dwarf planets.
• Dwarf planets are nearly round objects in orbit around
the Sun that are not satellites and have not cleared the
debris in their orbits.
Section
3
The Outer Planets
Comets and Other Objects
• A comet, is composed of dust and rock particles
mixed with frozen water, methane, and ammonia.
• As a comet approaches the Sun, it begins to
vaporize. The vaporized dust and gases form a
bright cloud called a coma around the nucleus. The
solar wind pushes on the vaporized coma, forming
a tail that always points away from the Sun.
Section
3
The Outer Planets
Comets and Other Objects
• Most comets come from two places—a vast disk of
icy comets called the Kuiper Belt near Neptune’s
orbit and the Oort cloud.
• Once in orbit around the Sun, comets reappear at
predictable times.
Section
The Outer Planets
3
Asteroids
• Rocky objects formed from material similar to that of
the planets are called asteroids.
• Most asteroids are found in a belt between the orbits
of Mars and Jupiter.
• Asteroids range in size from tiny particles to objects
500 km in diameter.
Section
The Outer Planets
3
Meteoroids
• Sand-to-boulder sized objects within the solar
system are called meteoroids.
• Meteoroids may enter the atmosphere.
• Most burn up completely and we see them as meteors or
“shooting stars.”
• Others do not burn completely and strike Earth.
• These are called meteorites.
Section
The Outer Planets
3
Sedna
• Sedna has been
labeled a distant
planetoid and with a
diameter of 1,200 to
1,700 km, it is smaller
than Pluto, but larger
than comets in the
Kuiper Belt.
Artist rendition
Section
3
Section Check
Question 1
The fifth planet from the Sun is __________.
A. Jupiter
B. Neptune
C. Saturn
D. Pluto
Section
3
Section Check
Answer
The answer is A. Jupiter is also the largest planet in the
solar system.
Section
3
Section Check
Question 2
Which of Jupiter’s four largest moons most volcanically
active object in the solar system?
A. Callisto
B. Europa
C. Ganymede
D. Io
Section
3
Section Check
Answer
The answer is D. Jupiter exerts tremendous gravitational
pull on Io.
Section
3
Section Check
Question 3
Which one of the following is NOT classified as a
dwarf planet?
A. Pluto
B. Eris
C. Ganymede
D. Ceres
Section
3
Section Check
Answer
The answer is C. Ganymede is one of Jupiter’s four
largest moons.
Section
4
Life in the Solar System
Life as We Know It
• A research submarine, named Alvin, found some
interesting life-forms while exploring hot, volcanic
vents on the ocean floor.
• Life-forms found included crabs, clams, and
tubeworms.
• Alvin also discovered colonies of bacteria living off the
superheated, chemically enriched fluids erupting from
volcanic vents.
Section
4
Life in the Solar System
Can life exist on other worlds?
• Extraterrestrial life is life beyond Earth.
• Let’s take a look at some places where scientists are
searching for extraterrestrial life.
Section
Life in the Solar System
4
Mars
• Evidence from recent missions to Mars has shown that
the planet probably had large amounts of water on its
surface in the past.
• If life existed and left evidence, future landers or
astronauts will find it.
Section
4
Life in the Solar System
Europa
• Europa’s ocean could hold more than twice the
amount of water that Earth’s oceans hold.
• If life can exist in extremely hot liquid flowing from
volcanic vents on Earth’s ocean floor, could it not
exist in a similar environment if it exists on Europa?
Section
Life in the Solar System
4
Titan
• Saturn’s moon, Titan, is larger than Mercury and
has an atmosphere composed mostly of nitrogen,
with some argon and methane.
• The presence of hydrocarbons on the surface
of Titan interests exobiologists, scientists who
search for evidence of life on other worlds.
Section
Life in the Solar System
4
Titan
• The apparent absence of large impact craters
indicates that Titan has experienced internal
geologic activity.
• This activity could provide the energy needed for
organic molecules to develop into the building blocks
of life.
Section
4
Section Check
Question 1
What is extraterrestrial life?
Answer
Extraterrestrial life is life that exists beyond Earth.
Section
4
Section Check
Question 2
What makes scientists think that Europa’s subsurface ocean could contain life?
Answer
Scientists think that the ocean might be deep and longlasting, possibly even liquid water that is warmed by
Jupiter’s gravitational pull on Europa.
Section
4
Section Check
Question 3
Which performed tests for water on Mars?
A. Alvin
B. Huygens probe
C. Galileo probe
D. Spirit and Opportunity
Section
4
Section Check
Answer
The answer is D. Spirit and Opportunity discovered
evidence of hematite, which forms in the presence of
water.
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Image Bank
Chapter Summary
Chapter Review Questions
Standardized Test Practice
Image Bank
Click on individual
thumbnail images to
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Image Bank
Geocentric Model
THUMBNAILS
Image Bank
Heliocentric Model
THUMBNAILS
Image Bank
Our Solar System
THUMBNAILS
Image Bank
Sedna (artist rendition)
THUMBNAILS
Reviewing Main Ideas
Planet Motion
• In the geocentric model of the solar system, Earth is in
the center. In the heliocentric model, the Sun is in the
center.
• The position of a planet in orbit around the Sun can be
shown by heliocentric longitude.
Reviewing Main Ideas
Planet Motion
• Inner planets have orbits closer to the Sun than the
asteroid belt; outer planets have orbits beyond the
asteroid belt.
• A large nebula fragmented into smaller ones, one of
which later condensed and flattened to form the solar
system.
Reviewing Main Ideas
The Inner Planets
• Mercury has a larger iron core than expected for a
planet its size.
• The carbon dioxide in Venus’s dense atmosphere has
caused an extreme greenhouse effect that produces
very high surface temperatures.
• Mars landers have provided evidence that Mars once
had more water on its surface than it does today.
Reviewing Main Ideas
The Outer Planets
• Jupiter is the largest planet in the solar system
and has many moons. Four of these moons were
first seen by Galileo.
• Saturn has the most complex ring system of all
outer planets and is the second largest planet.
Reviewing Main Ideas
The Outer Planets
• The green-blue color of Uranus and the blue color of
Neptune are caused by methane in their atmosphere.
• Pluto, Eris and Ceres are dwarf planets.
• Comets, asteroids, and meteoroids also orbit the
Sun.
Reviewing Main Ideas
Life in the Solar System
• Life exists in extreme environments on Earth and
may be able to survive in extreme environments on
other planets.
• Europa is considered the most promising location in
the solar system to look for extraterrestrial life.
• Mars and Titan might have harbored life sometime in
the past.
Chapter Review
Question 1
What view of the solar system was prevalent among
early Greek scientists?
Answer
Many early Greeks thought that the Sun and Moon
rotated around Earth, and that the stars were in a
separate sphere that also rotated around Earth.
Chapter Review
Question 2
Which of these planets has a very thin atmosphere?
A. Earth
B. Mars
C. Mercury
D. Venus
Chapter Review
Answer
The answer is C. Mercury has a low gravitational pull
and most gases that could form an atmosphere
escape into space.
Chapter Review
Question 3
The most well-studied planet in our solar system other
than Earth is _____.
A. Mars
B. Mercury
C. Saturn
D. Venus
Chapter Review
Answer
The answer is A. Missions to Mars have long been a
focus of NASA.
Chapter Review
Question 4
What is the Great Red Spot of Jupiter?
Answer
The Great Red Spot of Jupiter is a continuous storm of
high-pressure gas.
Chapter Review
Question 5
__________ gives Neptune a bluish-green color.
A. Ammonia
B. Methane
C. Nitrogen
D. Oxygen
Chapter Review
Answer
The answer is B. Neptune’s atmosphere is similar to that
of Uranus. Its methane content gives it a bluish-green
color.
Standardized Test Practice
Question 1
Which two adjacent planets have the greatest distance
between them?
Standardized Test Practice
Question 1
A. Jupiter and Saturn
B. Mars and Jupiter
C. Uranus and Neptune
D. Venus and Earth
Standardized Test Practice
Answer
The answer is C. Uranus and Neptune are nearly 11 AUs
apart.
Standardized Test Practice
Question 2
Which planet has an orbital
speed closest to that of
Earth?
A. Jupiter
B. Mars
C. Mercury
D. Venus
Standardized Test Practice
Answer
The answer is D. The
orbital speed of Venus and
Earth differ by 5 km/s.
Standardized Test Practice
Question 3
The area between Mars and Jupiter that contains the
particles shown in the diagram is the __________.
A. asteroid belt
B. comet belt
C. meteor shower
D. Oort cloud
Standardized Test Practice
Answer
The answer is A. Most
asteroids are located in
the asteroid belt
between the orbits of
Mars and Jupiter.
Standardized Test Practice
Question 4
This diagram illustrates that as Mercury’s core began to
solidify, __________ resulted from breaks in the crust.
A. cliffs
B. craters
C. maria
D. storms
Standardized Test Practice
Answer
The answer is A. The cliffs on the surface provide
evidence that Mercury shrank.
Standardized Test Practice
Question 5
On which Sol was
the low temperature
the warmest?
A. 1
B. 3
C. 4
D. 5
Standardized Test Practice
Answer
The answer is D.
After the fifth Sol,
the low
temperature was
about 10º C
warmer than on
the other four
days.
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