1. Lecture 12

2. Key Words liquid metallic hydrogen noble gases oblate, oblateness
plasma
tidal force

3. Outline
Jupiter and Saturn
Orbit
Surface
Atmosphere
Rings
Moons

4. It is difficult to see!

9. Inferior planets
superior planets

13. A planet’s synodic period is measured with respect to the Earth and the Sun (for example, from one opposition to the next)

14. Periods Rotational Orbital Sidereal Synodic
Measured with respect to something that is not rotating or orbiting

15. Question Which is longer, Jupiter’s synodic or orbital period?
Which is longer, Jupiter’s synodic or Saturn’s synodic period?
Guess Jupiter’s and Saturn’s synodic period.

16. Kepler’s Third Law P2 = a3 P = planet’s sidereal period, in years
a = planet’s semimajor axis, in AU

17. Long orbital periods of Jupiter and Saturn cause favorable viewing times to shift

18. The best time to observe Saturn from Earth is when it is
at opposition and it is midnight at your location on Earth.
at opposition and it is sunset or sunrise at your location on Earth.
at conjunction and it is midnight at your location on Earth.
at conjunction and it is sunset or sunrise at your location on Earth.
at opposition and it is just before sunrise at your location on Earth.

19. Outline
Jupiter and Saturn
Orbit
Surface
Atmosphere
Rings
Moons

20. How to get Oblate
hoop

21. What happens to ornaments when hoop is spun?

22. The oblateness of Jupiter and Saturn reveals their rocky cores
Jupiter probably has a rocky core several times more massive than the Earth
The core is surrounded by a layer of liquid “ices” (water, ammonia, methane, and associated compounds)

23. The oblateness of Jupiter and Saturn reveals their rocky cores
On top of this is a layer of helium and liquid metallic hydrogen and an outermost layer composed primarily of ordinary hydrogen and helium
Saturn’s internal structure is similar to that of Jupiter, but its core makes up a larger fraction of its volume and its liquid metallic hydrogen mantle is shallower than that of Jupiter

24. Metallic hydrogen inside Jupiter and Saturn endows the planets with strong magnetic fields
Jupiter and Saturn have strong magnetic fields created by currents in the metallic hydrogen layer
Jupiter’s huge magnetosphere contains a vast current sheet of electrically charged particles
Saturn’s magnetic field and magnetosphere are much less extensive than Jupiter’s

25. Jupiter and Saturn have extensive magnetospheres
The Jovian magnetosphere encloses a low-density plasma of charged particles
The magnetosphere exists in a delicate balance between pressures from the plasma and from the solar wind
When this balance is disturbed, the size of the magnetosphere fluctuates drastically

26. Synchrotron Radiation
Charged particles in the densest portions of Jupiter’s magnetosphere emit synchrotron radiation at radio wavelengths

27. Auroras on Jupiter and Saturn are caused by
charged particles from the magnetosphere colliding with molecules in the upper atmosphere.
ionized hydrogen.
ionized helium.
tidal interactions with the largest moons.
gas circulating at the poles.

28. Outline
Jupiter and Saturn
Orbit
Surface
Atmosphere
Rings
Moons

29. Atmospheres
gravity and escape velocity

30. Atmospheres
gravity and escape velocity

31. Atmospheres
The visible “surfaces” of Jupiter and Saturn are actually the tops of their clouds

32. Atmospheres
The rapid rotation of the planets twists the clouds into dark belts and light zones that run parallel to the equator

33. The chemical composition of Jupiter and Saturn is difficult to measure
The chemical composition of Jupiter and Saturn is difficult to measure. Why?

34. Atmospheres
The outer layers of both planets’ atmospheres show differential rotation
The equatorial regions rotate slightly faster than the polar regions

35. Atmospheres
For both Jupiter and Saturn, the polar rotation rate is nearly the same as the internal rotation rate

36. Spacecraft images show remarkable activity in the clouds of Jupiter and Saturn

37. Storms
Both Jupiter and Saturn emit more energy than they receive from the Sun
Presumably both planets are still cooling
The colored ovals visible in the Jovian atmosphere represent gigantic storms
Some, such as the Great Red Spot, are quite stable and persist for many years

39. Storms in Saturn’s atmosphere seem to be shorter-lived

40. The internal heat of Jupiter and Saturn has a major effect on the planets’ atmospheres

41. A space probe has explored Jupiter’s deep atmosphere
There are presumed to be three cloud layers in the atmospheres of Jupiter and Saturn
The reasons for the distinctive colors of these different layers are not yet known
The cloud layers in Saturn’s atmosphere are spread out over a greater range of altitude than those of Jupiter, giving Saturn a more washed-out appearance
Saturn’s atmosphere contains less helium than Jupiter’s atmosphere
This lower abundance may be the result of helium raining downward into the planet
Helium “rainfall” may also account for Saturn’s surprisingly strong heat output

43. Spacecraft images show remarkable activity in the clouds of Jupiter and Saturn

44. In the news: Hurricane on Saturn?
Hurricane-like vortex at Saturn's south pole, where the vertical structure of the clouds is highlighted by shadows. Such a storm, with a well-developed eye ringed by towering clouds, is a phenomenon never before seen on another planet.

45. Both Jupiter and Saturn emit more energy than they receive from the Sun. What does this tell us?

46. Jupiter radiates more energy into space than it receives from the Sun
Jupiter radiates more energy into space than it receives from the Sun. What is the primary source of the excess energy that Jupiter radiates?
Decay of radioactive materials in Jupiter's core
Tidal forces from Jupiter's moons
Jupiter is still contracting, and the contraction releases energy
Jupiter's rotation is slowing down dramatically, and this slowdown releases energy
All of the above are the energy sources

47. What can you say about these planets?
Figure 7-11 Planet Size and Cratering
Of these two hypothetical planets, the
smaller one (#2) has less volume and less internal heat, as well as less
surface area from which to radiate heat into space. But the ratio of
surface area to volume is greater for the smaller planet. Hence, the
smaller planet will lose heat faster, have a colder interior, and be less
geologically active. It will also have a more heavily cratered surface, since
it takes geologic activity to erase craters.
What can you say about these planets?

48. If Jupiter and Saturn formed at the same time, which should be emitting more heat?

51. Outline
Jupiter and Saturn
Orbit
Surface
Atmosphere
Rings
Moons

52. Why can’t the rings be solid?
Roche limit

53. Link

54. Something is Fishy
How can a planet be solid?

55. Pebbles, snowballs and boulder size
How was this determined?

56. Earth-based observations reveal three broad rings encircling Saturn

57. Saturn is circled by a system of thin, broad rings lying in the plane of the planet’s equator
This system is tilted away from the plane of Saturn’s orbit, which causes the rings to be seen at various angles by an Earth-based observer over the course of a Saturnian year

58. Saturn’s rings are composed of numerous icy fragments, while Jupiter’s rings are made of small rocky particles
The principal rings of Saturn are composed of numerous particles of ice and ice-coated rock ranging in size from a few micrometers to about 10 m
Jupiter’s faint rings are composed of a relatively small amount of small, dark, rocky particles that reflect very little light

60. Most of its rings exist inside the Roche limit of Saturn, where disruptive tidal forces are stronger than the gravitational forces attracting the ring particles to each other
Each of Saturn’s major rings is composed of a great many narrow ringlets

61. Saturn’s rings consist of thousands of narrow, closely spaced ringlets

63. Saturn’s inner satellites affect the appearance and structure of its rings

64. The faint F ring, which is just outside the A ring, is kept narrow by the gravitational pull of shepherd satellites

67. Outline
Jupiter and Saturn
Orbit
Surface
Atmosphere
Rings
Moons

68. Preview Already discussed influence on Saturn’s rings.
Jupiter’s moons are even more interesting