Chapter Introduction
Lesson 1 The Structure of
the Solar System
Lesson 2 The Inner Planets
Lesson 3 The Outer Planets
NASA/JPL/USGS
Lesson 4 Dwarf Planets and Other
Objects
Chapter Wrap-Up
What kinds of
objects are in the
solar system?
What do you think?
Before you begin, decide if you agree or
disagree with each of these statements.
As you view this presentation, see if you
change your mind about any of the
statements.
Do you agree or disagree?
1. Astronomers measure distances
between space objects using
astronomical units.
2. Gravitational force keeps planets in
orbit around the Sun.
3. Earth is the only inner planet that has a
moon.
Do you agree or disagree?
4. Venus is the hottest planet in the solar
system.
5. The outer planets also are called the
gas giants.
6. The atmospheres of Saturn and Jupiter
are mainly water vapor.
Do you agree or disagree?
7. Asteroids and comets are mainly rock
and ice.
8. A meteoroid is a meteor that strikes
Earth.
The Structure of the Solar System
• How are the inner planets different
from the outer planets?
• What is an astronomical unit and why
is it used?
• What is the shape of a planet’s orbit?
The Structure of the Solar System
• asteroid
• comet
• astronomical unit
• period of revolution
• period of rotation
What is the solar system?
• Almost all of the specks of light you
can see in the night sky are stars.
• A few of the tiny lights are part of our
solar system.
• Stars are much farther away than
objects in our solar system.
Objects in the Solar System
The largest object in the solar system is
the Sun, a star.
star
Science Use an object in space made of
gases in which nuclear fusion reactions
occur that emit energy
Common Use a shape that usually has
five or six points around a common center
Objects in the Solar System (cont.)
• Planets orbit the Sun and have nearly
spherical shapes.
• The mass of a planet must be much
larger than the total mass of all other
objects whose orbits are close by.
Objects in the Solar System (cont.)
Eight of the objects in the solar system
are planets.
• Mercury
• Jupiter
• Venus
• Saturn
• Earth
• Uranus
• Mars
• Neptune
• Mercury, Venus, Earth, and Mars are the
inner planets.
• The inner planets are mostly solid, rocky
material.
• Jupiter, Saturn, Uranus, and Neptune are
the outer planets.
• The outer planets are mostly ice and
gases, such as hydrogen and helium.
Objects in the Solar System (cont.)
Describe how the inner planets
differ from the outer planets.
Objects in the Solar System (cont.)
• A dwarf planet is a spherical object that
orbits the Sun and is not a moon or
another planet.
• Dwarf planets are in regions of the solar
system where there are many objects
orbiting nearby.
Ceres, a dwarf planet, orbits the Sun as
planets do.
Objects in the Solar System (cont.)
• Millions of small, rocky objects called
asteroids orbit the Sun in the asteroid
belt between the orbits of Mars and
Jupiter.
• Asteroids vary in size and are usually not
spherical.
• A comet is made of gas, dust, and ice
and moves around the Sun in an ovalshaped orbit.
Objects in the Solar System (cont.)
• Distances between objects in the solar
system are extremely large.
• Astronomers do not use meters or
kilometers to describe these distances.
• A more convenient unit is used—
the astronomical unit (AU).
• One AU is Earth’s average distance from
the Sun—about 150,000,000 km.
It is easier to express very large
distances using astronomical units
rather than kilometers.
Objects in the Solar System (cont.)
Define what an astronomical unit
is and explain why it is used.
The Motion of the Planets
• The time it takes an object to travel
once around the Sun is its period of
revolution.
• The time it takes an object to complete
one rotation is its period of rotation.
The Motion of the Planets (cont.)
• A planet’s orbit is an ellipse—
a stretched-out circle.
• Focus points, or foci, determine the
shape of the ellipse.
The Motion of the Planets (cont.)
Describe the shape of a
planet’s orbit.
• The solar system contains the Sun,
the inner planets, the outer planets,
the dwarf planets, asteroids, and
comets.
• An astronomical
unit (AU) is a
unit of distance
equal to about
150 million km.
• The speeds of
the planets
change as they
move around the
Sun in elliptical
orbits.
What are most of the specks that
you can see in the night sky?
A. asteroids
B. comets
C. planets
D. stars
What is a spherical object that
orbits the Sun and is not a moon
or another planet?
A. asteroid
B. astronomical unit
C. comet
D. dwarf planet
Which refers to the time it takes
an object to complete one
rotation?
A. astronomical unit
B. focus
C. period of revolution
D. period of rotation
Do you agree or disagree?
1. Astronomers measure distances
between space objects using
astronomical units.
2. Gravitational force keeps planets in
orbit around the Sun.
The Inner Planets
• How are the inner planets similar?
• Why is Venus hotter than Mercury?
• What kind of atmospheres do the
inner planets have?
The Inner Planets
• terrestrial planet
• greenhouse effect
Planets Made of Rock
• Earth and the other inner planets—
Mercury, Venus, and Mars—are also
called the terrestrial planets.
• Like Earth, the other terrestrial planets
are made of rock and metallic materials
and have a solid outer layer.
Planets Made of Rock (cont.)
terrestrial
from Latin terrestris, means
“earthly”
The inner planets are roughly similar in
size, with Earth being about two and half
times larger than Mercury.
Mercury: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Venus: NASA
Earth: NASA Goddard Space Flight Center
Mars: NASA/JPL/Malin Space Science Systems
Mercury is the smallest planet and the
planet closest to the Sun.
Mercury
• Mercury’s gravity is not strong enough to
hold an atmosphere.
• Mercury’s temperatures are as high as
450°C on the side toward the Sun and
as low as –170° on the side away from
the Sun.
• Like all inner planets, Mercury has a core
made of iron and nickel.
Mercury (cont.)
How are the inner planets
similar?
Venus is the second planet from the Sun
and is about the same size as Earth.
Venus
• The atmosphere of Venus is about
97 percent carbon dioxide.
• The pressure of Venus’s dense
atmosphere is 90 times greater than
that of Earth’s atmosphere.
• A thick layer of acid clouds covers
Venus.
Venus (cont.)
• The greenhouse effect occurs when a
planet’s atmosphere traps solar energy
and causes the surface temperature to
increase.
• Because of its greenhouse effect, Venus
is the hottest planet in the solar system,
with an average temperature of about
460°C.
Venus (cont.)
Why is Venus hotter than
Mercury?
Earth is the third planet from the Sun.
Earth
• A mixture of gases, including water
vapor, make up Earth’s atmosphere and
produce a greenhouse effect that raises
its surface temperature.
• A protective atmosphere, moderate
surface temperatures, and the presence
of liquid water support a variety of life on
Earth.
Mars is the fourth planet from the Sun and
is about half the size of Earth.
Mars
• Images of Mars show features that might
have been made by water, though no
evidence of liquid water or life has been
found.
• The atmosphere of Mars is thin and made
of about 95 percent carbon dioxide.
• Temperatures on Mars range from about –
125°C at the poles to about 20°C at the
equator during the summer.
Mars (cont.)
Describe the atmosphere of
each inner planet.
• The terrestrial planets include
Mercury, Venus, Earth, and Mars.
Mercury: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Venus: NASA
Earth: NASA Goddard Space Flight Center
Mars: NASA/JPL/Malin Space Science Systems
• The inner planets
all are made of
rocks and minerals,
but the
characteristics of
the planets are
different. Earth is
the only planet with
water.
NASA Goddard Space Flight Center
• The greenhouse
effect greatly
increases the
surface temperature
of Venus.
NASA
Which planet’s greenhouse effect
makes it the hottest planet in the
solar system?
A. Earth
B. Mars
C. Mercury
D. Venus
Which is the only planet with
large bodies of liquid water?
A. Earth
B. Mars
C. Mercury
D. Venus
Which planet is the fourth planet
from the Sun and about half the
size of Earth?
A. Mars
B. Mercury
C. Venus
D. none of these
Do you agree or disagree?
3. Earth is the only inner planet that has
a moon.
4. Venus is the hottest planet in the solar
system.
The Outer Planets
• How are the outer planets similar?
• What are the outer planets made of?
The Outer Planets
• Galilean moons
The Gas Giants
• The outer planets, also known as the gas
giants, are primarily made of hydrogen
and helium.
• The outer planets are extremely
massive. They apply strong gravitational
forces.
• The interiors of the outer planets are
mainly liquid.
• These gas giants generally have gas and
liquid layers around a small solid core.
The outer planets are large compared to
the inner planets. The size of Earth is
shown for reference.
Earth: NASA Goddard Space Flight Center
Jupiter: NASA/JPL/USGS
Saturn: NASA and The Hubble Heritage Team (STScI/AURA)Acknowledgment: R.G. French (Wellesley College), J. Cuzzi (NASA/Ames), L. Dones (SwRI), and J.
Uranus, Neptune: NASA/JPL
The Gas Giants (cont.)
How are the outer planets
similar?
• Jupiter is the largest planet in the solar
system.
• Jupiter has a diameter 11 times larger
than the diameter of Earth.
Jupiter
• Jupiter’s atmosphere is about 90 percent
hydrogen and 10 percent helium.
• The planet itself is about 80 percent
hydrogen and 20 percent helium.
• Jupiter is a ball of gas swirling around a
thick liquid layer that conceals a solid
core. Scientists are not certain what
makes up the core.
Jupiter (cont.)
Describe what makes up each of
Jupiter’s three distinct layers.
Jupiter (cont.)
• Jupiter has at least 63 moons, more than
any other planet.
• The four largest moons of Jupiter—
Io, Europa, Ganymede, and Callisto—
are known as the Galilean moons.
• The Galilean moons are made of rock
and ice.
Saturn is the sixth planet from the Sun.
It rotates rapidly and has horizontal bands
of clouds.
Saturn
• Saturn is mostly hydrogen and helium.
• Saturn has an outer gas layer, a thick
layer of liquid hydrogen, and a solid core.
• Saturn has seven bands of rings, each
containing thousands of narrower ringlets.
Saturn (cont.)
The ice particles in the rings are possibly
from a moon that was shattered in a
collision with another icy object.
Describe what makes up Saturn
and its ring system.
Saturn has at least 60 moons. Titan is
the only moon in the solar system with
a dense atmosphere.
Cassini, Rhea, Iapetus, Dione, Tethys: NASA/JPL/Space Science Institute
Saturn (cont.)
titan
from Green titan, means “member
of a mythological race of giants”
NASA/ESA and Erich Karkoschka, University of Arizona
Uranus is the seventh planet from the Sun,
with a system of narrow, dark rings and a
diameter about four times that of Earth.
Uranus
• Uranus has a deep atmosphere
composed mostly of hydrogen and
helium and a small amount of methane.
• Beneath Uranus’s atmosphere is a thick,
slushy layer of water, ammonia, and
other materials.
• Uranus has a tilted axis or rotation that
might have been caused by a collision
with an Earth-sized object.
Uranus (cont.)
Uranus has at least 27 moons.
Identify the substances that make
up the atmosphere and the thick
slushy layer on Uranus.
Like Uranus, Neptune’s atmosphere is
mostly hydrogen and helium, with a trace
of methane.
NASA/JPL
Neptune
• Neptune’s interior is also like Uranus’s,
made of partially frozen water and
ammonia with a rock and iron core.
• Neptune has at least 13 moons and a
faint, dark ring system.
Neptune (cont.)
How does the atmosphere and
interior of Neptune compare with
that of Uranus?
• All of the outer planets are primarily
made of materials that are gases on
Earth. Colorful clouds of gas cover
Saturn and Jupiter.
Earth: NASA Goddard Space Flight Center
Jupiter: NASA/JPL/USGS
Saturn: NASA and The Hubble Heritage Team (STScI/AURA)Acknowledgment: R.G. French (Wellesley College), J. Cuzzi (NASA/Ames), L. Dones (SwRI), and J.
Uranus, Neptune: NASA/JPL
• Jupiter is the largest
outer planet. Its four
largest moons are
known as the
Galilean moons.
NASA/JPL/USGS
• Uranus has an
unusual tilt, possibly
due to a collision
with a large object.
NASA/ESA and Erich Karkoschka, University of Arizona
The outer planets are primarily
made of what?
A. oxygen
B. methane
C. hydrogen and helium
D. carbon dioxide
What are Jupiter’s Galilean
moons made of?
A. rock and ice
B. hydrogen and helium
C. gas
D. carbon dioxide
Which planet is the seventh from
the Sun and has a system of
narrow, dark rings?
A. Jupiter
B. Neptune
C. Saturn
D. Uranus
Do you agree or disagree?
5. The outer planets also are called the
gas giants.
6. The atmospheres of Saturn and Jupiter
are mainly water vapor.
Dwarf Planets and Other Objects
• What is a dwarf planet?
• What are the characteristics of comets
and asteroids?
• How does an impact crater form?
Dwarf Planets and Other Objects
• meteoroid
• meteor
• meteorite
• impact crater
Dwarf Planets
According to the International Astronomical
Union (IAU), a dwarf planet is an object that
orbits a star and has enough mass and
gravity to pull itself into a spherical shape.
Dwarf Planets (cont.)
• Unlike a planet, a dwarf planet has
objects similar in mass orbiting nearby
or crossing its orbital path.
• Ceres is the smallest dwarf planet with
a diameter of about 950 km.
• Pluto is so far from the Sun that it takes
about 248 years to complete one orbit.
• Eris is the largest dwarf planet.
All of the dwarf planets are smaller than
Earth’s moon.
Pluto: Dr. R. Albrecht, ESA/ESO Space Telescope European Coordinating Facility; NASA
Ceres: NASA, ESA, and J. Parker (Southwest Research Institute)
Eris: NASA, ESA, and M. Brown (California Institute of Technology)
Dwarf Planets (cont.)
Describe the characteristics of
a dwarf planet.
Most asteroids orbit the Sun in the
asteroid belt between the orbits of Mars
and Jupiter.
Asteroid: NASA/JPL/JHUAPL
Ida: NASA/JPL/USGS
Vesta: Ben Zellner (Georgia Southern University), Peter Thomas (Cornell University), NASA/ESA
Eros: NASA/Goddard Space Flight Center Scientific Visualization Studio
Asteroids
• Asteroids are chunks of rock and ice that
never clumped together to form a planet.
• Some astronomers think the strength of
Jupiter’s gravitational field might have
caused the chunks to collide so violently
that they broke apart instead of sticking
together.
Asteroids (cont.)
Where do the orbits of most
asteroids occur?
Comets are mixtures of rock, ice, and dust.
Comet: Roger Ressmeyer/Getty Images
Wild 2: NASA/JPL-Caltech
Comets
• The particles in a comet are loosely held
together by the gravitational attractions
among the particles.
• Comets orbit the Sun in stretched out
elliptical orbits.
• The solid, inner part of a comet is its
nucleus.
• As a comet moves closer to the Sun, it
heats up and can develop a bright tail.
Comets (cont.)
Describe the characteristics of
a comet.
Meteoroids
• A meteoroid is a small rocky particle
that moves through space.
• A meteor is a streak of light in Earth’s
atmosphere made by a glowing
meteoroid.
Meteoroids (cont.)
• A meteorite is a meteoroid that strikes a
planet or a moon.
• An impact crater is a round depression
formed on the surface of a planet, moon,
or other space object by the impact of a
meteorite.
Meteoroids (cont.)
What causes an impact crater
to form?
• An asteroid, such as Ida, is a chunk
of rock and ice that orbits the Sun.
NASA/JPL/USGS
• Comets, which are
mixture of rock, ice,
and dust, orbit the Sun.
A comet’s tail is
caused by its
interaction with
the Sun.
Roger Ressmeyer/Getty Images
• When a large meteorite strikes a
planet or moon, it often makes an
impact crater.
Which term refers to chunks of
rock and ice that never clumped
together to form a planet?
A. meteoroid
B. meteor
C. comet
D. asteroid
Which is a round depression
formed on the surface of a planet,
moon, or other space object by the
impact of a meteorite?
A. coma
B. impact crater
C. meteor
D. meteoroid
Which objects orbit the Sun in
stretched out elliptical orbits?
A. asteroids
B. comets
C. meteoroids
D. meteors
Do you agree or disagree?
7. Asteroids and comets are mainly rock
and ice.
8. A meteoroid is a meteor that strikes
Earth.
Key Concept Summary
Interactive Concept Map
Chapter Review
Standardized Test Practice
The solar system
contains planets,
dwarf planets, comets,
asteroids, and other
small solar system
bodies.
Lesson 1: The Structure of the Solar
System
• The inner planets are made mainly of solid materials.
The outer planets, which are larger than the inner
planets, have thick gas and liquid layers covering a
small solid core.
• Astronomers measure vast distances
in space in astronomical units;
an astronomical unit is about
150 million km.
• The speed of each planet changes as
it moves along its elliptical orbit around the Sun.
Lesson 2: The Inner Planets
• The inner planets—Mercury, Venus,
Earth, and Mars—are made of rock
and metallic materials.
• The greenhouse effect makes
Venus the hottest planet.
• Mercury has no atmosphere.
The atmospheres of Venus and Mars are almost
entirely carbon dioxide. Earth’s atmosphere is a
mixture of gases and a small amount of water vapor.
Lesson 3: The Outer Planets
• The outer planets—Jupiter,
Saturn, Uranus, and Neptune—
are primarily made of hydrogen
and helium.
• Jupiter and Saturn have thick
cloud layers, but are mainly
liquid hydrogen. Saturn’s rings
are largely particles of ice.
Uranus and Neptune have thick atmospheres of
hydrogen and helium.
Lesson 4: Dwarf Planets and Other
Objects
• A dwarf planet is an object that orbits a star, has
enough mass to pull itself into a spherical shape,
and has objects similar in mass orbiting nearby.
• An asteroid is a small rocky
object that orbits the Sun.
Comets are made of rock, ice,
and dust and orbit the Sun in
highly elliptical paths.
• An impact crater is formed by
the impact of a meteorite.
Roger Ressmeyer/Getty Images
What term refers to the small,
rocky objects that orbit the Sun
between the orbits of Mars and
Jupiter?
A.
B.
C.
D.
asteroids
comets
dwarf planets
planets
How many objects in the solar
system are classified as planets?
A. 8
B. 10
C. 12
D. 14
The greenhouse effect occurs when
a planet’s atmosphere traps solar
energy and causes which of these?
A. decrease in surface temperature
B. decreased number of plant species
C. increase in surface temperature
D. increased number of plant species
Which planet has a tilted axis that
might have been caused by a
collision with an Earth-sized
object?
A. Jupiter
B. Neptune
C. Saturn
D. Uranus
Which term refers to a small
rocky particle that moves
through space?
A. asteroid
B. meteor
C. meteorite
D. meteoroid
Which term refers to an object made
of gas, dust, and ice that moves
around the Sun in an oval-shaped
orbit?
A. asteroid
B. comet
C. dwarf planet
D. star
What is a term used to describe
the four planets closest to the
Sun?
A. dwarf planets
B. gas giants
C. inner planets
D. outer planets
Which planet is fourth from the
Sun and about half the size of
Earth?
A. Mars
B. Mercury
C. Neptune
D. Venus
How many moons does Saturn
have?
A. 1
B. at least 60
C. less than 4
D. at most 27
Which of these describes a
meteoroid that strikes a planet
or a moon?
A. meteorite
B. meteor
C. impact crater
D. asteroid