Chapter: The Solar System

2. Table of Contents Chapter: The Solar System Section 1: Planet Motion Section 2: The Inner Planets Section 3: The Outer Planets Section 4: Life in the Solar System

3. Planet Motion 1 Models of the Solar System Geocentric Model • In the geocentric model of the solar system, Earth is considered the center and everything else revolves around it.

4. Planet Motion 1 Heliocentric Model • Earth-centered model held until 1543. • Nicholas Copernicus published a different view. • Copernicus stated that the Moon revolves around Earth. • Earth and the other planets revolve around the Sun.

5. Planet Motion 1 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.

6. Planet Motion 1 Heliocentric Model • Galileo Galilei found evidence that supported the ideas of Copernicus. • He observed that Venus went through phases like the Moon’s. • He also saw moons in orbit around Jupiter.

7. Planet Motion 1 Understanding the Solar System • In the early 1600’s, Kepler discovered that the planets travel around the Sun in ellipses, not circles. • Planets travel at different speeds in their orbits. • The astronomical unit (AU) equals the average distance from Earth to the Sun, about 150 million km.

8. Planet Motion 1 Classifying Planets • One system uses sizes and other characteristics. • Those similar to Earth are called terrestrial planets, giant planets are jovian planets. • Two other systems classify planets by location.

9. Planet Motion 1 Classifying Planets • Planets whose orbits are between the Sun and the asteroid belt as inner planets and those beyond the asteroid belt as outer planets. • The other 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.

10. Planet Motion 1 Other Solar Systems • Extrasolar planets—planets in orbit around other stars—are helping astronomers learn how planetary systems form. • Astronomers have devised new techniques and instruments to find planets around other stars.

11. Section Check 1 Question 1 Who was responsible for developing the geocentric model of the solar system? A. Aristotle B. Copernicus C. Galileo D. Ptolemy

12. Section Check 1 Answer The answer is D. Ptolemy presented his geocentric model of the solar system in 140 A.D.

13. Section Check 1 Question 2 Approximately how long is an astronomical unit? A. 100 km B. 100 million km C. 150 million km D. 200 billion km

14. Section Check 1 Answer The answer is C. One astronomical unit equals the average distance from Earth to the Sun, about 150 million km.

15. Section Check 1 Question 3 _______ are planets in orbit around stars other than our Sun. A. Extrasolar planets B. Extrasensory planets C. Intersolar planets D. Intrasolar planets

16. Section Check 1 Answer The answer is A. Scientists have discovered extrasolar planets around Upsilon Andromedae.

17. The Inner Planets 2 Planets near the Sun • The second-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.

18. The Inner Planets 2 Planets near the Sun • Mercury’s large, solid core shrank much more rapidly than its thin outer layers. • As the outer layers adjusted, they wrinkled, forming dramatic cliffs as high as 3 km. • Mercury has no true atmosphere. • Surface temperatures vary from 427ºC to -170ºC.

19. The Inner Planets 2 Venus • Venus is the second planet from the Sun. • Venus is blanketed by a dense atmosphere.

20. The Inner Planets 2 Venus • 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.

21. 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.

22. 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 and changes in the coloring of Mars’s surface.

23. The Inner Planets 2 Mars • The polar ice caps are made of frozen carbon dioxide and frozen water.

24. The Inner Planets 2 Mars • The Martian atmosphere is much thinner than Earth’s and is composed mostly of carbon dioxide with some nitrogen and argon. • Mars has two small, heavily cratered moons called Phobos and Deimos.

25. The Inner Planets 2 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.

26. The Inner Planets 2 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.

27. The Inner Planets 2 Global Surveyor, Pathfinder, and Odyssey • Global Surveyor showed that the walls of Valles Marineris have distinct layers similar to those of the Grand Canyon. • Mars Odyssey, provided evidence for water as frost beneath a thin layer of soil in the far northern and southern parts of Mars.

28. The Inner Planets 2 Global Surveyor, Pathfinder, and Odyssey • The Mars Pathfinder and its rover, Sojourner, gathered data that indicated that iron in Mar’s crust may have been leached out by groundwater.

29. Section Check 2 Question 1 Which planet is closest to the Sun? A. Mars B. Mercury C. Earth D. Venus

30. Section Check 2 Answer The answer is B. Mercury is the closest planet to the Sun. Venus is the second planet from the Sun.

31. Section Check 2 Question 2 Which planet has size and mass similar to Earth’s? A. Jupiter B. Mercury C. Pluto D. Venus

32. Section Check 2 Answer The answer is D. Venus has similar size and mass but the temperatures on its surface are between 450º C and 475º C.

33. Section Check 2 Question 3 Earth is the __________ planet from the Sun. A. second B. third C. fourth D. fifth

34. Section Check 2 Answer The answer is B. Mercury and Venus are closer to the Sun than Earth.

35. The Outer Planets 3 Jupiter • The largest and fifth planet from the Sun is Jupiter. • It is composed mostly of hydrogen and helium.

36. The Outer Planets 3 Jupiter • Continuous storms of swirling, high-pressure gas have been observed on Jupiter. • The Great Red Spot is the most spectacular of these storms.

37. The Outer Planets 3 Space Probes to Jupiter • 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.

38. The Outer Planets 3 Jupiter’s Moons • Four are large enough to be considered small planets. • These Galilean moons of Jupiter are Io, Europa, Ganymede, and Callisto.

39. The Outer Planets 3 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.

40. The Outer Planets 3 Saturn • Saturn is the sixth planet from the Sun and is known as the ringed planet. • Saturn is a large planet with a thick outer atmosphere composed mostly of hydrogen and helium with some ammonia, methane, and water vapor.

41. The Outer Planets 3 Saturn’s Rings • Saturn’s rings are composed of countless ice and rock particles ranging in size from a speck of dust to tens of meters across. • Pictures of these rings showed a density wave and areas where the ring material bends up and down.

42. The Outer Planets 3 Uranus • Uranus, is the seventh planet from the Sun. • It is a large planet with 27 moons. • The atmosphere of Uranus contains hydrogen, helium, and about two percent methane. • The methane gives the planet its blue-green color.

43. The Outer Planets 3 Neptune • Neptune, another large planet similar in size to Uranus, 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.

44. The Outer Planets 3 Pluto • Pluto, is farther from the Sun than Neptune during most of its orbit, it is considered the ninth planet from the Sun.

45. The Outer Planets 3 Comets and Other Objects • A comet, is composed of dust rock particles mixed with frozen water, methane, and ammonia. • As a comet approaches the Sun, it begins to vaporize. The released 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.

46. The Outer Planets 3 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.

47. The Outer Planets 3 Comets and Other Objects • 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 940 km in diameter.

48. The Outer Planets 3 Comets and Other Objects • Other rocky objects orbiting within the solar system are 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.

49. The Outer Planets 3 Comets and Other Objects • 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.

50. Section Check 3 Question 1 The fifth planet from the Sun is __________. A. Jupiter B. Neptune C. Saturn D. Pluto