1. Lesson 1 The Structure of the Solar System Lesson 2 The Inner Planets
Chapter Introduction
Lesson 1 The Structure of the Solar System
Lesson 2 The Inner Planets
Lesson 3 The Outer Planets
Lesson 4 Dwarf Planets and Other Objects
Chapter Wrap-Up
NASA/JPL/USGS
Chapter Menu

2. What kinds of objects are in the solar system?
Chapter Introduction

3. 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.
Lesson 1-1

4. 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
Lesson 1-2

5. 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.
Lesson 1-2

6. Objects in the Solar System (cont.)
Eight of the objects in the solar system are planets.
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Lesson 1-2

7. Mercury, Venus, Earth, and Mars are the inner planets.
The inner planets are mostly solid, rocky material.
Lesson 1-2

8. Jupiter, Saturn, Uranus, and Neptune are the outer planets.
The outer planets are mostly ice and gases, such as hydrogen and helium.
Lesson 1-2

9. 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.
Lesson 1-2

10. Ceres, a dwarf planet, orbits the Sun as planets do.
Lesson 1-2

11. 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 oval-shaped orbit.
Lesson 1-2

12. 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.
Lesson 1-2

13. It is easier to express very large distances using astronomical units rather than kilometers.
Lesson 1-2

14. 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.
Lesson 1-3

15. 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.
Lesson 1-3

16. The solar system contains the Sun, the inner planets, the outer planets, the dwarf planets, asteroids, and comets.
Lesson 1 - VS

17. An astronomical unit (AU) is a unit of distance equal to about 150 million km.
Lesson 1 - VS

18. The speeds of the planets change as they move around the Sun in elliptical orbits.
Lesson 1 - VS

19. What are most of the specks that you can see in the night sky?
A. asteroids
B. comets
C. planets
D. stars
Lesson 1 – LR1

20. 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
Lesson 1 – LR2

21. 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
Lesson 1 – LR3

22. 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.
Lesson 2-1

23. Planets Made of Rock (cont.)
terrestrial
from Latin terrestris, means “earthly”
Lesson 2-1

24. 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
Lesson 2-1

25. Mercury is the smallest planet and the planet closest to the Sun.
Lesson 2-2

26. 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.
Lesson 2-2

27. Venus is the second planet from the Sun and is about the same size as Earth.
Lesson 2-3

28. 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.
Lesson 2-3

29. 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.
Lesson 2-3

30. Earth is the third planet from the Sun.
Lesson 2-4

31. 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.
Lesson 2-4

32. Mars is the fourth planet from the Sun and is about half the size of Earth.
Lesson 2-5

33. 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.
Lesson 2-5

34. 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
Lesson 2 - VS

35. 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
Lesson 2 - VS

36. The greenhouse effect greatly increases the surface temperature of Venus.
NASA
Lesson 2 - VS

37. Which planet’s greenhouse effect makes it the hottest planet in the solar system?
A. Earth
B. Mars
C. Mercury
D. Venus
Lesson 2 – LR1

38. Which is the only planet with large bodies of liquid water?
A. Earth
B. Mars
C. Mercury
D. Venus
Lesson 2 – LR2

39. 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
Lesson 2 – LR3

40. 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.
Lesson 3-1

41. The outer planets are large compared to the inner planets
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
Lesson 3-1

42. Jupiter is the largest planet in the solar system.
Jupiter has a diameter 11 times larger than the diameter of Earth.
Lesson 3-2

43. 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.
Lesson 3-2

44. 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.
Lesson 3-2

45. Saturn is the sixth planet from the Sun
Saturn is the sixth planet from the Sun. It rotates rapidly and has horizontal bands of clouds.
Lesson 3-3

46. 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.
Lesson 3-3

47. 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.
Lesson 3-3

48. Saturn has at least 60 moons
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
Lesson 3-3

49. Saturn (cont.)
titan
from Green titan, means “member of a mythological race of giants”
Lesson 3-3

50. Uranus is the seventh planet from the Sun, with a system of narrow, dark rings and a diameter about four times that of Earth.
NASA/ESA and Erich Karkoschka, University of Arizona
Lesson 3-4

51. 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.
Lesson 3-4

52. Uranus (cont.) Uranus has at least 27 moons.
Identify the substances that make up the atmosphere and the thick slushy layer on Uranus.
Lesson 3-4

53. Like Uranus, Neptune’s atmosphere is mostly hydrogen and helium, with a trace of methane.
NASA/JPL
Lesson 3-5

54. 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.
Lesson 3-5

55. 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
Lesson 3 - VS

56. Jupiter is the largest outer planet
Jupiter is the largest outer planet. Its four largest moons are known as the Galilean moons.
NASA/JPL/USGS
Lesson 3 - VS

57. Uranus has an unusual tilt, possibly due to a collision with a large object.
NASA/ESA and Erich Karkoschka, University of Arizona
Lesson 3 - VS

58. The outer planets are primarily made of what?
A. oxygen
B. methane
C. hydrogen and helium
D. carbon dioxide
Lesson 3 – LR1

59. What are Jupiter’s Galilean moons made of?
A. rock and ice
B. hydrogen and helium
C. gas
D. carbon dioxide
Lesson 3 – LR2

60. Which planet is the seventh from the Sun and has a system of narrow, dark rings?
A. Jupiter
B. Neptune
C. Saturn
D. Uranus
Lesson 3 – LR3

61. 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.
Lesson 4-1

62. 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.
Lesson 4-1

63. 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)
Lesson 4-1

64. 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
Lesson 4-2

65. 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.
Lesson 4-2

66. Comets are mixtures of rock, ice, and dust.
Comet: Roger Ressmeyer/Getty Images Wild 2: NASA/JPL-Caltech
Lesson 4-3

67. 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.
Lesson 4-3

68. 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.
Lesson 4-4

69. 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.
Lesson 4-4

70. An asteroid, such as Ida, is a chunk of rock and ice that orbits the Sun.
NASA/JPL/USGS
Lesson 4 - VS

71. Comets, which are mixture of rock, ice, and dust, orbit the Sun
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.
Lesson 4 - VS

72. 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
Lesson 4 – LR1

73. 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
Lesson 4 – LR2

74. Which objects orbit the Sun in stretched out elliptical orbits?
A. asteroids
B. comets
C. meteoroids
D. meteors
Lesson 4 – LR3

75. 7. Asteroids and comets are mainly rock and ice.
Do you agree or disagree?
7. Asteroids and comets are mainly rock and ice.
8. A meteoroid is a meteor that strikes Earth.
Lesson 4 - Now

76. Gravity and energy influence the formation of objects in the solar system, including planets, dwarf planets, comets, asteroids, and other small solar system bodies.
The BIG Idea

77. 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.
Key Concepts 1

78. 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.
Key Concepts 2

79. 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.
Key Concepts 3

80. 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
Key Concepts 4

81. What term refers to the small, rocky objects that orbit the Sun between the orbits of Mars and Jupiter?
A. asteroids
B. comets
C. dwarf planets
D. planets
Chapter Review – MC1

82. How many objects in the solar system are classified as planets?
Chapter Review – MC2

83. A. decrease in surface temperature
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
Chapter Review – MC3

84. 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
Chapter Review – MC4

85. Which term refers to a small rocky particle that moves through space?
A. asteroid
B. meteor
C. meteorite
D. meteoroid
Chapter Review – MC5

86. 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
Chapter Review – STP1

87. 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
Chapter Review – STP2

88. Which planet is fourth from the Sun and about half the size of Earth?
A. Mars
B. Mercury
C. Neptune
D. Venus
Chapter Review – STP3

89. How many moons does Saturn have?
B. at least 60
C. less than 4
D. at most 27
Chapter Review – STP4

90. Which of these describes a meteoroid that strikes a planet or a moon?
A. meteorite
B. meteor
C. impact crater
D. asteroid
Chapter Review – STP5