New Vocabulary

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

2. Section 28.4 Other Solar System Objects Dwarf Planets 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.

3. Section 28.4 Other Solar System Objects Dwarf Planets 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.

4. Section 28.4 Other Solar System Objects Dwarf Planets Ceres In 1801, Giuseppe Piazzi discovered a large object, which was given the name Ceres, in orbit between Mars and Jupiter. 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.

5. Section 28.4 Other Solar System Objects Dwarf Planets 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.

6. Section 28.4 Other Solar System Objects Dwarf Planets 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.

7. Section 28.4 Other Solar System Objects Dwarf Planets 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.

8. Section 28.4 Other Solar System Objects Dwarf Planets 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.

9. Section 28.4 Other Solar System Objects Dwarf Planets 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.

10. Section 28.4 Other Solar System Objects Dwarf Planets 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.

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

12. Section 28.4 Other Solar System Objects Please click the image above to view the video.

13. Section 28.4 Other Solar System Objects Small Solar System Bodies 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 rocky planetesimals between Mars and Jupiter—the asteroid belt.

14. Section 28.4 Other Solar System Objects Small Solar System Bodies 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.

15. Section 28.4 Other Solar System Objects Small Solar System Bodies 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.

16. Section 28.4 Other Solar System Objects Small Solar System Bodies 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.

17. Section 28.4 Other Solar System Objects Small Solar System Bodies 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.

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

19. Section 28.4 Other Solar System Objects Comets Comets are small, icy bodies that have highly eccentric orbits around the Sun. 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.

20. Section 28.4 Other Solar System Objects Comets 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.

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

22. Section 28.4 Other Solar System Objects Comets 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.

23. Section 28.4 Other Solar System Objects Comets 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.

24. 28 Study Guide Key Concepts Section 28.1 Formation of the Solar System The solar system formed from the collapse of an interstellar cloud. • A collapsed interstellar cloud formed the Sun and planets from a rotating disk. • The inner planets formed closer to the Sun than the outer planets, leaving debris to produce asteroids and comets.

25. 28 Study Guide Key Concepts Section 28.1 Formation of the Solar System • Copernicus created the heliocentric model and Kepler defined its shape and mechanics. • Newton explained the forces governing the solar system bodies and provided proof for Kepler’s laws. • Present-day astronomers divide the solar system into three zones.

26. 28 Study Guide Key Concepts Section 28.2 The Inner Planets Mercury, Venus, Earth, and Mars have high densities and rocky surfaces. • Mercury is heavily cratered and has high cliffs. It has a hot surface and no real atmosphere. • Venus has clouds containing sulfuric acid and an atmosphere of carbon dioxide that produces a strong greenhouse effect.

27. 28 Study Guide Key Concepts Section 28.2 The Inner Planets • Earth is the only planet that has all three forms of water on its surface. • Mars has a thin atmosphere. Surface features include four volcanoes and channels that suggest that liquid water once existed on the surface.

28. 28 Study Guide Key Concepts Section 28.3 The Outer Planets Jupiter, Saturn, Uranus, and Neptune have large masses, low densities, and many moons and rings. • The gas giant planets are composed mostly of hydrogen and helium. • The gas giant planets have ring systems and many moons.

29. 28 Study Guide Key Concepts Section 28.3 The Outer Planets • Some moons of Jupiter and Saturn have water and experience volcanic activity. • All four gas giant planets have been visited by space probes.

30. 28 Study Guide Key Concepts Section 28.4 Other Solar System Objects 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.

31. 28 Study Guide Key Concepts Section 28.4 Other Solar System Objects • 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.

32. 28 Our Solar System 28.1 Section Questions Which scientist first observed the moons of Jupiter with a telescope? a. Nicolaus Copernicus b.Tycho Brahe c.Isaac Newton d.Galileo Galilei

33. 28 Our Solar System 28.1 Section Questions 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

34. 28 Our Solar System 28.1 Section Questions 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

35. 28 Our Solar System 28.2 Section Questions Earth is the only planet known to have life. a.true b. false

36. 28 Our Solar System 28.2 Section Questions Which inner planet has the highest average surface temperature? a. Mercury b.Venus c.Earth d.Mars

37. 28 Our Solar System 28.2 Section Questions 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.

38. 28 Our Solar System 28.3 Section Questions Which gas gives Uranus and Neptune their blue color? a.hydrogen b.helium c.methane d.nitrogen

39. 28 Our Solar System 28.3 Section Questions How many of the four gas giant planets have rings? a.one b.two c.three d.four

40. 28 Our Solar System 28.3 Section Questions 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

41. 28 Our Solar System 28.4 Section Questions Which solar system object is most abundant in the Oort cloud? a.rocky planets b.asteroids c.comets d.dwarf planets

42. 28 Our Solar System 28.4 Section Questions 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

43. 28 Our Solar System 28.4 Section Questions 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.

44. 28 Our Solar System Chapter Assessment Questions Which inner planet has retrograde rotation? a.Mercury b.Venus c.Earth d.Mars

45. 28 Our Solar System Chapter Assessment Questions 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.

46. 28 Our Solar System Chapter Assessment Questions 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.

47. 28 Our Solar System Chapter Assessment Questions Which planet has an axis of rotation that is nearly in its orbital plane? a.Jupiter b.Saturn c.Uranus d.Neptune

48. 28 Our Solar System Chapter Assessment Questions How do comet tails form?

49. 28 Our Solar System Chapter Assessment Questions 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.

50. 28 Our Solar System Standardized Test Practice Who described the behavior of gravity? a.Tycho Brahe b.Clyde Tombaugh c.Nicolaus Copernicus d.Isaac Newton