1. NEW CHAPTER Our Solar System CHAPTER the BIG idea Planets and other objects form a system around our Sun. Planets orbit the Sun at different distances. The inner solar system has rocky planets. The outer solar system has four giant planets. CHAPTER OUTLINE Small objects are made of ice and rock. 21.1 21.2 21.3 21.4 CHAPTER RESOURCES

2. VOCABULARY KEY CONCEPT CHAPTER HOME SECTION OUTLINE SECTION OUTLINE astronomical unit (AU) Planets orbit the Sun at different distances. ellipse The planets have different sizes and distances from the Sun. 21.1 CHAPTER RESOURCES CHAPTER RESOURCES VISUALIZATION CLASSZONE.COM Take a virtual spaceflight through the solar system. inner solar system Mercury, Venus, Earth, Mars, asteroids outer solar system Jupiter, Saturn, Uranus, Neptune, Pluto, comets

3. VOCABULARY KEY CONCEPT CHAPTER HOME SECTION OUTLINE SECTION OUTLINE astronomical unit (AU) Planets orbit the Sun at different distances. ellipse 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. 21.1 CHAPTER RESOURCES CHAPTER RESOURCES

4. VOCABULARY KEY CONCEPT CHAPTER HOME Earth’s average distance from the Sun, which is approximately 150 million kilometers (93 million mi). astronomical unit (AU) KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY Planets orbit the Sun at different distances. astronomical unit (AU) ellipse 21.1 CHAPTER RESOURCES CHAPTER RESOURCES

5. VOCABULARY KEY CONCEPT CHAPTER HOME An oval or flattened circle. ellipse KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY Planets orbit the Sun at different distances. astronomical unit (AU) ellipse 21.1 CHAPTER RESOURCES CHAPTER RESOURCES

6. VOCABULARY KEY CONCEPT CHAPTER HOME terrestrial planet The inner solar system has rocky planets. SECTION OUTLINE SECTION OUTLINE The terrestrial planets are round and have layers. Atmospheres came from volcanoes and impacts. Four processes produce surface features. tectonics volcanism 21.2 CHAPTER RESOURCES CHAPTER RESOURCES impact cratering tectonics weathering and erosion volcanism

7. VOCABULARY KEY CONCEPT CHAPTER HOME Earth or a planet similar to Earth that has a rocky surface. The four planets in the inner solar system, Mercury, Venus, Earth, and Mars, are terrestrial planets. terrestrial planet KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY The inner solar system has rocky planets. terrestrial planet tectonics volcanism 21.2 CHAPTER RESOURCES CHAPTER RESOURCES

8. VOCABULARY KEY CONCEPT CHAPTER HOME The processes in which the motion of hot material under a crust changes the crust of a space body. Earth has a specific type of tectonics called plate tectonics. tectonics KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY The inner solar system has rocky planets. terrestrial planet tectonics volcanism 21.2 CHAPTER RESOURCES CHAPTER RESOURCES

9. VOCABULARY KEY CONCEPT CHAPTER HOME The process of molten material moving from a space body’s hot interior onto its surface. volcanism KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY The inner solar system has rocky planets. terrestrial planet tectonics volcanism 21.2 CHAPTER RESOURCES CHAPTER RESOURCES

10. VOCABULARY KEY CONCEPT CHAPTER HOME SECTION OUTLINE SECTION OUTLINE The outer solar system has four giant planets. ring gas giant 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 21.3 CHAPTER RESOURCES CHAPTER RESOURCES

11. VOCABULARY KEY CONCEPT CHAPTER HOME A large planet that consists mostly of gases in a dense form. The four large planets in the outer solar system (Jupiter, Saturn, Uranus, and Neptune) are gas giants. gas giant KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY The outer solar system has four giant planets. ring gas giant 21.3 CHAPTER RESOURCES CHAPTER RESOURCES

12. VOCABULARY KEY CONCEPT CHAPTER HOME In astronomy, a wide, flat zone of small particles that orbit around a planet’s equator. ring KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY The outer solar system has four giant planets. ring gas giant 21.3 CHAPTER RESOURCES CHAPTER RESOURCES

13. VOCABULARY KEY CONCEPT CHAPTER HOME SECTION OUTLINE SECTION OUTLINE Small objects are made of ice and rock. comet asteroid meteor 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. meteorite 21.4 CHAPTER RESOURCES CHAPTER RESOURCES The asteroid Eros

14. VOCABULARY KEY CONCEPT CHAPTER HOME A small, solid, rocky body that orbits the Sun. Most asteroids orbit in a region between Mars and Jupiter called the asteroid belt. asteroid KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY Small objects are made of ice and rock. comet asteroid meteor meteorite 21.4 CHAPTER RESOURCES CHAPTER RESOURCES

15. VOCABULARY KEY CONCEPT CHAPTER HOME A body that produces a coma of gas and dust; a small, icy body that orbits the Sun. comet Small objects are made of ice and rock. KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY comet asteroid meteor meteorite 21.4 CHAPTER RESOURCES CHAPTER RESOURCES

16. VOCABULARY KEY CONCEPT CHAPTER HOME A brief streak of light produced by a small particle entering Earth’s atmosphere at a high speed. meteor Small objects are made of ice and rock. KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY comet asteroid meteor meteorite 21.4 CHAPTER RESOURCES CHAPTER RESOURCES

17. VOCABULARY KEY CONCEPT CHAPTER HOME A small object from outer space that passes through Earth’s atmosphere and reaches the surface. meteorite Small objects are made of ice and rock. KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY comet asteroid meteor meteorite 21.4 CHAPTER RESOURCES CHAPTER RESOURCES

18. VOCABULARY KEY CONCEPT CHAPTER HOME I. Planets orbit the Sun at different distances. A. Planets have different sizes and distances. 1. Distances KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY B. The solar system formed from a swirling cloud of gas and dust. 2. Orbits Planets orbit the Sun at different distances. astronomical unit (AU) ellipse 21.1 CHAPTER RESOURCES CHAPTER RESOURCES

19. VOCABULARY KEY CONCEPT CHAPTER HOME B. Craters cover the surface of Mercury. II. The inner solar system has rocky planets. A. The terrestrial planets have rocky crusts. KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY 1. Processes and Surface Features 2. Atmospheres The inner solar system has rocky planets. C. Volcanoes shape the surface of Venus. D. Erosion changes the appearance of Mars. 1. Surface of Mars terrestrial planet tectonics volcanism 2. Gases and Water on Mars 21.2 CHAPTER RESOURCES CHAPTER RESOURCES

20. VOCABULARY KEY CONCEPT CHAPTER HOME D. Uranus and Neptune are extremely cold. III. The outer solar system has four giant planets. A. The gas giants have very deep atmospheres. 1. Uranus 2. Neptune KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY The outer solar system has four giant planets. B. Jupiter is a world of storms and clouds. C. Saturn has large rings. ring gas giant 21.3 CHAPTER RESOURCES CHAPTER RESOURCES

21. VOCABULARY KEY CONCEPT CHAPTER HOME IV. Small objects are made of ice and rock. A. Pluto and most objects in the outer solar system are made of ice and rock. B. Asteroids and comets orbit the Sun. 1. Pluto and Charon 2. Moons of Gas Giants Small objects are made of ice and rock. 1. Asteroids 2. Comets 3. Meteors and Meteorites KEY CONCEPT SUMMARY KEY CONCEPT SUMMARY comet asteroid meteor meteorite 21.4 CHAPTER RESOURCES CHAPTER RESOURCES

22. CHAPTER HOME Image Gallery Click on the icons to see a larger image or animation. VISUALIZATION CLASSZONE.COM Take a virtual spaceflight through the solar system.

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36. CHAPTER HOME Image Gallery BACK TO IMAGE GALLERY Neptune’s orbit Pluto and Charon’s orbit

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41. BACK TO CHAPTER Click on the items below to access resources on Standardized Test Practice Practice state standardized tests Math Tutorial Review math concepts Resource Centers Get more information on select science topics Content Review Review key concepts and vocabulary Audio Readings Hear chapter audio readings CLASSZONE.COM Chapter Resources CHAPTER HOME Animations Link to all the McDougal Littell Science animations Review Game Play a fun interactive review game Image Gallery Click here to review chapter images and animations