Objectives

1. Distinguish between planets and dwarf planets. Identify the oldest members of the solar system. Describe meteoroids, meteors, and meteorites. Determine the structure and behavior of comets. Section 28.4 Objectives Other Solar System Objects

2. Section 28.4 Other Solar System Objects Rocks, dust, and ice compose the remaining 2 percent of the solar system. Review Vocabulary smog: air polluted with hydrocarbons and nitrogen oxides

3. Section 28.4 New Vocabulary Other Solar System Objects dwarf planet meteoroid meteor meteorite Kuiper belt comet meteor shower

4. Section 28.4 Dwarf Planets Other Solar System Objects In the early 2000s, astronomers began to detect large objects in the region of the planet Pluto, about 40 AU from the Sun, called the Kuiper belt.

5. Classification in order of decreasing size • 1. Planets • 2. Dwarf planets • 3. Other solar system objects.

6. Section 28.4 Dwarf Planets Other Solar System Objects In 2003 an object, now known as Eris, was discovered that appeared to be the same size, or larger, than Pluto. At that time, the scientific community began to take a closer look at the planetary status of Pluto and other solar system objects.

7. Section 28.4 Dwarf Planets Other Solar System Objects Ceres In 1801, Giuseppe Piazzi discovered a large object, which was given the name Ceres, in orbit between Mars and Jupiter. Ceres is the largest asteroid. Scientists had predicted that there was a planet somewhere in that region, and it seemed that this discovery was it. However, Ceres was extremely small for a planet.

8. Section 28.4 Dwarf Planets Other Solar System Objects Ceres In the century following the discovery of Ceres, hundreds of thousands of other objects were discovered in the area between Mars and Jupiter. Therefore, Ceres was no longer thought of as a planet, but as the largest of the asteroids in what would be called the asteroid belt.

9. Section 28.4 Dwarf Planets Other Solar System Objects Pluto Since its discovery by Clyde Tombaugh in 1930, Pluto has been an unusual planet. It is not a terrestrial or gas planet; it is made of rock and ice.

10. Section 28.4 Dwarf Planets Other Solar System Objects Pluto Pluto has a long, elliptical orbit that overlaps the orbit of Neptune. It is also smaller than Earth’s Moon. It has three moons, two of which orbit at widely odd angles from the plane of the ecliptic.

11. Section 28.4 Dwarf Planets Other Solar System Objects How many others? With the discovery of objects close to and larger than Pluto’s size, the International Astronomical Union (IAU) chose to create a new classification of objects in space called dwarf planets.

12. Section 28.4 Dwarf Planets Other Solar System Objects How many others? The IAU has defined a dwarf planet as an object that, due to its own gravity, is spherical in shape, orbits the Sun, is not a satellite, and has not cleared the area of its orbit of smaller debris.

13. Section 28.4 Dwarf Planets Other Solar System Objects How many others? Currently the IAU has limited the dwarf planet classification to Pluto, Eris, and Ceres, but there are at least 12 other objects whose classifications are undecided.

14. Section 28.4 Visualizing the Kuiper Belt Other Solar System Objects Recent findings of objects beyond Pluto, in a vast disk called the Kuiper belt, have forced scientists to rethink what features define a planet.

15. Section 28.4 Small Solar System Bodies Other Solar System Objects Once the IAU defined planets and dwarf planets, they had to identify what was left. In the early 1800s, a name was given to the 1)rocky planetesimals between Mars and Jupiter— the asteroid belt.

16. Section 28.4 Small Solar System Bodies Other Solar System Objects 2)Objects beyond the orbit of Neptune have been called trans-Neptunian objects, Kuiper belt objects, comets, and members of the Oort cloud. The IAU calls all these objects, collectively, small solar system bodies.

17. Section 28.4 Small Solar System Bodies Other Solar System Objects Asteroids There are thousands of asteroids orbiting the Sun between Mars and Jupiter. As asteroids orbit, they occasionally collide and break into fragments. When an asteroid fragment, or any other interplanetary material, enters Earth’s atmosphere, it is called a meteoroid.

18. Section 28.4 Small Solar System Bodies Other Solar System Objects Asteroids As a meteoroid passes through the atmosphere, it is heated by friction and burns, producing a streak of light called a meteor. If the meteoroid does not burn up completely and part of it strikes the ground, the part that hits the ground is called a meteorite.

19. Section 28.4 Small Solar System Bodies Other Solar System Objects Kuiper belt The Kuiper belt is a group of small solar system bodies that are mostly rock and ice. Most of these bodies probably formed in this region—30 to 50 AU from the Sun—from the material left over from the formation of the Sun and planets.

20. Section 28.4 Small Solar System Bodies Other Solar System Objects Kuiper belt The Kuiper belt appears as the outermost limit of the planetary disk. The Oort cloud surrounds the Sun, echoing its solar sphere.

21. Section 28.4 Comets Other Solar System Objects Comets are small, icy bodies that have highly eccentric orbits around the Sun. Located in Kuiper belt and Oort cloud. Ranging from 1 to 10 km in diameter, most comets orbit in a continuous distribution that extends from the Kuiper belt to 100,000 AU from the Sun. The outermost region is known as the Oort cloud.

22. Section 28.4 Comets Other Solar System Objects Comet structure When a comet comes within 3 AU of the Sun, it begins to evaporate and forms a head and one or more tails. The head is surrounded by an envelope of glowing gas, and it has a small solid core.

23. Section 28.4 Comets Other Solar System Objects Comet structure A comet’s tail always points away from the Sun and is driven by a stream of particles and radiation.

24. Section 28.4 Comets Other Solar System Objects Periodic comets Comets that repeatedly return to the inner solar system are known as periodic comets. Each time a periodic comet comes near the Sun, it loses some of its matter, leaving behind a trail of particles.

25. Section 28.4 Comets Other Solar System Objects Periodic comets When Earth crosses the trail of a comet, particles left in the trail burn in Earth’s upper atmosphere, producing bright streaks of light called a meteor shower. Most meteors are caused by dust particles from comets.

26. 28 Section 28.4 Other Solar System Objects Study Guide Key Concepts Rocks, dust, and ice compose the remaining 2 percent of the solar system. • Dwarf planets, asteroids, and comets formed from the debris of the solar system formation. • Meteoroids are planetesimals that enter Earth’s atmosphere.

27. 28 Section 28.4 Other Solar System Objects Study Guide Key Concepts • Mostly rock and ice, the Kuiper belt objects are currently being detected and analyzed. • Periodic comets are in regular, permanent orbit around the Sun, while others might pass this way only once. • The outermost regions of the solar system house the comets in the Oort cloud.

28. 28 28.1 Section Questions Our Solar System Which scientist first observed the moons of Jupiter with a telescope? a. Nicolaus Copernicus b.Tycho Brahe c.Isaac Newton d.Galileo Galilei

29. 28 28.1 Section Questions Our Solar System Which observation provided evidence for the heliocentric model of the solar system? a. the nightly motion of the stars b.the rising and setting of the Sun c.the retrograde motion of planets d.the occurrence of meteor showers

30. 28 28.1 Section Questions Our Solar System Kepler determined the relationship between a planet’s orbital period (P) and the length of its semimajor axis (a). Which equation correctly represents this relationship? a. P3 = a2 b.P2 = a3 c.P = a2 d.P2 = a

31. 28 28.2 Section Questions Our Solar System Earth is the only planet known to have life. a.true b. false

32. 28 28.2 Section Questions Our Solar System Which inner planet has the highest average surface temperature? a. Mercury b.Venus c.Earth d.Mars

33. 28 28.2 Section Questions Our Solar System Which hypothesis has been suggested to explain the scarps on Mercury? a. Mercury’s crust shrank and cracked. b.Mercury once had plate tectonics. c.Mercury was eroded by flowing water. d.Mercury’s surface was covered by lava.

34. 28 28.3 Section Questions Our Solar System Which gas gives Uranus and Neptune their blue color? a.hydrogen b.helium c.methane d.nitrogen

35. 28 28.3 Section Questions Our Solar System How many of the four gas giant planets have rings? a.one b.two c.three d.four

36. 28 28.3 Section Questions Our Solar System Which elements have the highest abundance in gas giant planets? a.iron and nickel b.hydrogen and helium c.silicon and oxygen d.calcium and magnesium

37. 28 28.4 Section Questions Our Solar System Which solar system object is most abundant in the Oort cloud? a.rocky planets b.asteroids c.comets d.dwarf planets

38. 28 28.4 Section Questions Our Solar System What causes most meteor showers? a.dust from the paths of comets b.asteroids breaking up in the atmosphere c.pieces from the Moon or Mars d.particles left from the interstellar cloud

39. 28 28.4 Section Questions Our Solar System Which characteristic must a dwarf planet have? a.It must be smaller than Pluto. b.It must be beyond Neptune. c.It must be rocky. d.It must be spherical.

40. 28 Chapter Assessment Questions Our Solar System Which inner planet has retrograde rotation? a.Mercury b.Venus c.Earth d.Mars

41. 28 Chapter Assessment Questions Our Solar System Suppose that two objects in space move apart until the distance between them is double. How does the gravitational force between these objects change? a.It decreases by a factor of two. b.It decreases by a factor of four. c.It decreases by a factor of eight. d.It decreases by a factor of ten.

42. 28 Chapter Assessment Questions Our Solar System Which statement describes the gas giant planets? a.They have a high density. b.They have a thin atmosphere. c.They have a cratered surface. d.They have many moons.

43. 28 Chapter Assessment Questions Our Solar System Which planet has an axis of rotation that is nearly in its orbital plane? a.Jupiter b.Saturn c.Uranus d.Neptune

44. 28 Chapter Assessment Questions Our Solar System How do comet tails form?

45. 28 Chapter Assessment Questions Our Solar System Possible answer: As a comet approaches the Sun, ices in the comet vaporize, or turn to gas. Dust is also released as the comet dissipates. Particles and radiation streaming away from the Sun then push the gas and dust away from the Sun. The gas often forms a blue tail that points directly away from the Sun. The dust sometimes forms a separate white tail because it is not pushed as much by the solar particles and radiation.

46. 28 Standardized Test Practice Our Solar System Who described the behavior of gravity? a.Tycho Brahe b.Clyde Tombaugh c.Nicolaus Copernicus d.Isaac Newton

47. 28 Standardized Test Practice Our Solar System Which characteristic distinguishes Earth from the other inner planets? a.the presence of an atmosphere b. the presence of an iron core c.the presence of volcanoes d.the presence of surface oceans

48. 28 Standardized Test Practice Our Solar System Examine the illustration. What relationship exists between the areas of the segments of the planet’s orbit?

49. 28 Standardized Test Practice Our Solar System Answer: Kepler’s second law states that a planet sweeps out equal amounts of area in equal amounts of time. Therefore, each segment of the planet’s orbital ellipse has the same area.

50. 28 Standardized Test Practice Our Solar System Where are most of the asteroids in the solar system? a.between the orbits of Mercury and Venus b.between the orbits of Earth and Mars c.between the orbits of Mars and Jupiter d.between the orbits of Uranus and Neptune