Prepared by Lisa M. Will, San Diego City College

1. Lecture Slides CHAPTER 8: The Giant Planets Understanding Our Universe SECOND EDITION Stacy Palen, Laura Kay, Brad Smith, and George Blumenthal Prepared by Lisa M. Will, San Diego City College

2. The Giant Planets We will learn how the giant planets are different from the terrestrial planets. We will learn the similarities and differences between the giant planets themselves.

3. Comparative Planetology

4. Comparative Planetology: Physical Properties of the Giant Planets • Jupiter and Saturn: easily seen by naked eye. • Uranus (1781) and Neptune (1846) were discovered after invention of telescope. • These worlds are all larger and more massive than the terrestrial planets. • Their orbits span a large distance: 5-30 AU. • Called “giant planets” because of their mass (15 - 318 Earth masses) and also their physical size (4-11 Earth radii).

5. Properties of the Giant Planets • Astronomers determine diameters by observing how long it takes for a planet to pass over a star: stellar occultation. • Masses can be found by gravitational effects (Kepler’s laws!) on moons and planetary spacecraft.

6. Properties of the Giant Planets: Gas and Ice Giants • Jupiter and Saturn are primarily hydrogen and helium - gas giants. • Uranus and Neptune contain more water ice and other ices than Jupiter and Saturn - ice giants. • No solid surfaces: we just see the cloud layers in the atmospheres.

7. Properties of the Giant Planets:Composition and Comparison • The giant planets are less dense than the terrestrial planets—in fact, Saturn would float in a large enough vat of water. • Jupiter’s chemistry is like the Sun: mostly hydrogen and helium. • Saturn has more heavy elements than Jupiter. • Uranus and Neptune have a significantly larger fraction of massive elements in their composition than either Saturn or Jupiter.

8. Properties of the Giant Planets: Axial Tilt All giants have rapid rotation. Each as a different axial tilt, ranging from: Jupiter: 3°, effectively no seasonal variation Uranus: 98°, which results in extreme seasons.

9. Jupiter: strong dark bands (belts) and light bands (zones). A long-lasting giant storm (Great Red Spot). Many smaller storms. Complex behavior including “cloud cannibalism.” The colors of the bands on Jupiter are determined by their chemical composition. Jupiter: Properties

10. Jupiter: Properties (Cont.)

11. Jupiter: Properties (Cont.)

12. Jupiter: Properties (Cont.)

13. Jupiter: Properties (Cont.)

14. The colors of the bands on Jupiter are determined by their chemical composition. Jupiter: Properties (Cont.)

15. Has lightning-producing storms, as well as a strong wind pattern similar to Earth’s jet stream. Saturn: similar band structure to Jupiter, but less obvious. The cloud layers on Saturn are thicker than Jupiter because of the lower gravity of Saturn. Saturn: Properties

16. Saturn: Properties (Cont.)

17. Saturn: Properties (Cont.)

18. Saturn: similar band structure to Jupiter, but less obvious. The cloud layers on Saturn are thicker than Jupiter because of the lower gravity of Saturn. Saturn: Properties (Cont.)

19. Uranus & Neptune Uranus and Neptune: infrared observations show weak patterns of bands. Small, scattered bright or dark clouds. Transient large storms (Great Dark Spot on Neptune).

20. Uranus & Neptune (Cont.)

21. Uranus & Neptune (Cont.)

22. Uranus & Neptune: Presence of Methane Highest clouds on Uranus and Neptune: methane ice. Bluish-green color because of presence of methane in their atmospheres (methane absorbs red, orange, yellow).

23. Properties of the Giant Planets: Wind Speeds Rapid planetary rotation results in strong Coriolis forces, giving storms a rotation. Most extreme winds are in Saturn’s atmosphere (1,690 km/hr).

24. Properties of the Giant Planets: Circulation Patterns The alternating east/west winds make the prominent banded cloud pattern on Jupiter. Circulation patterns differ from planet to planet for reasons not yet understood.

25. Properties of the Giant Planets: Depths and Pressure Jupiter/Saturn: At depths of a few 1,000 km, gases are compressed so much they liquefy. At higher pressure and temperature, this liquid hydrogen can act like a metal.

26. Properties of the Giant Planets: Composition Uranus/Neptune: Have much less hydrogen and helium. Have more water and ices (ammonia, methane).

27. Properties of the Giant Planets: Cores All four giant planets have large, dense “rocky” cores. The cores are molten, because of the very high temperatures and pressures.

28. Properties of the Giant Planets: Magnetic Fields Strong magnetic fields are generated by the motion of the conducting liquids. =>Stronger than those of the terrestrial planets. The shapes of the magnetic field are similar to that of a bar magnet.

29. Properties of the Giant Planets: Magnetic Fields (Cont.)

30. Properties of the Giant Planets: Magnetic Fields (Cont.)

31. Properties of the Giant Planets: Magnetic Fields (Cont.)

32. Properties of the Giant Planets: Magnetic Fields (Cont.)

33. Properties of the Giant Planets: Magnetospheres Magnetospheres are huge. They interact with the solar wind. Create radiation belts and auroras. Emit radio waves.

34. Rings All four gas giants have ring systems. The rings are composed of countless tiny particles. Ring particles orbit their planet following Kepler’s laws.

35. Rings: Shepherd Moons The rings are influenced and maintained by shepherd moons. Particles most likely came from moons disrupted by tidal stresses.

36. Rings: Shepherd Moons (Cont.)

37. Rings: Shepherd Moons (Cont.)

38. Rings: Shepherd Moons (Cont.)

39. Rings: Shepherd Moons (Cont.)

40. Rings: Ringlets Saturn has the most complex rings. A very complicated system, composed of thousands of ringlets. There are bright and dark rings, “gaps,” and divisions.

41. Rings: Facts Gaps are not empty. Brightness/darkness reflects the amount of material in each ring. Though wide, the ring system is extremely thin.

42. Rings: Ring Arcs The other giants’ rings are mostly narrow and diffuse. Backlighting brings them into view. Neptune has denser sections known as ring arcs.

43. Rings: Ring Arcs (Cont.)

44. Rings: Ring Arcs (Cont.)

45. Rings: Visual Comparison • Saturn: bright rings because they are made of mostly water ice. • Uranus and Neptune: dark rings from organic material (darker than coal). • Jupiter: not as dark as the ice giants, nor as bright as Saturn’s, likely composed of silicates, and possibly caused by asteroid collisions with one or more moons. • Volcanism on moons can also contribute ring material.

46. Rings: Lifespan Rings do not last forever. Collisions and sunlight destroy the rings. Shepherd moons can help stabilize the rings.

47. Class Question If you could measure the velocities of ring particles at each distance from Saturn, you would find: Particles closer to Saturn orbit at slower speeds. Particles farther from Saturn orbit at slower speeds. Orbital speed is the same at all distances.

48. Class Question Which of the following statements about the giant planets compared to terrestrial planets is correct? The giant planets have more mass and higher densities. The giant planets have larger radii and weaker magnetic fields. The giant planets have more mass, larger radii, lower densities, and stronger magnetic fields. The giant planets and terrestrial planets have overall similar characteristics.

49. Chapter Summary • The giant planets are larger and less dense than the terrestrial planets and consist primarily of light elements rather than rock. • Temperatures and pressures in the cores of the giant planets are very high. • All four giant planets have ring systems.

50. Nebraska Applet Planetary Formation Temperatures Plot Click the image to launch the Nebraska Applet(Requires an active Internet connection)