1. The Jovian Planets (“Gas Giants”): Jupiter, Saturn, Uranus, Neptune
Chapters 23 and 24:
The Jovian Planets (“Gas Giants”):
Jupiter, Saturn, Uranus, Neptune

2. Galileo’s view of Saturn
Galileo’s view of Saturn. He could not see that the “lobes” were rings, and did not understand why they sometimes disappeared.

3. Images of Saturn taken by students at Seattle University
Ming-Hua Chang
Matthew Day

4. Saturn -- Hubble Space Telescope

5. Saturn: Voyager 2
Saturn’s most striking feature is its ring system

6. Cassini Spacecraft View of Saturn

7. Saturn’s Ring system, by Cassini

8. Close-up of clouds on Saturn

9. Gas giants (Jovian planets)
Are mostly gases (H, He, H2O, CH4, NH3); the rest = ice + rock
Have no solid surface: gases --> solid at high pressure
Have ring systems and many moons
Form faster, and in a different way, compared to terrestrial planets: large enough to accumulate gas directly from the solar nebula
They are far from the Sun (in the case of the solar system)
So far, all known extrasolar planets are gas giants, but they are all close to their parent star (why?)

10. Jupiter, imaged with the
Hubble Space Telescope
Colorful cloud bands are the most striking characteristic of the planet, and the Great Red Spot

11. Neptune: Its existence was predicted because Uranus did not seem to obey Kepler’s Law!
Images taken by the Voyager 2 spacecraft

12. The giant planets are much more massive and less dense than Earth
They rotate much faster than Earth
95 MEarth
318 MEarth
15 MEarth
17 MEarth
Gas giants rotate differentially: rotation is faster at their equator than their poles (like which other object in the solar system??
They all have magnetic fields (molten interiors)

13. Belts and zones on Jupiter
Differential rotation

14. Jupiter’s most distinguishing features:
The Great Red Spot
Cloud bands
the “Galilean moons”
Storms on gas giants last so long because there are no continents over which they can lose their energy and dissipate

15. What causes Jupiter’s cloud bands?
Strong winds and Jupiter’s differential rotation produce bands parallel to equator
hydrogen, helium, water (H2O), ammonia (NH3) and methane (CH4)
These gases are colorless, and their ices are white
Colors due to sulfur compounds and organic hazes particles (?)
Sunlight and lightning affect the chemistry of Jupiter’s atmosphere

16. Clouds and convection in Jupiter’s atmosphere
Zones: high pressure, lighter
Belts: Lower pressure,
darker color
Rotation channels the winds into east-west pattern that wraps around entire planet
Zonal flow: stable eastward and westward winds deeper in the atmosphere
300 km/hour easterly, at equator
0 at poles - bands disappear

17. Entry site of Galileo Probe: the first man-made object to enter the atmosphere of a giant planet

18. Saturn is not as colorful as Jupiter, but does have bands and storms
Saturn has less hydrogen and helium than Jupiter, and the ratio of helium to hydrogen is much lower: why?
Helium seems to have liquified and sank to Saturn’s center
Helium precipitation seems to be the cause of Saturn’s energy output

19. color enhanced
Like Jupiter, Saturn has:
bands
oval storm systems
turbulent flow patterns
stable east–west zonal flow
wind speed is > Jupiter with fewer east–west alternations.
The equatorial eastward jet stream = 1500 km/h

20. Storms on Saturn are more rare than on Jupiter
In 1990, a storm developed in Saturn’s equatorial region and soon completely encircled the planet.
The storm dissipated in a few weeks.

21. Uranus
Neptune
Both worlds are composed mostly of hydrogen and helium
Ammonia is in the form of ice crystals (snow), not as a gas
Methane gives these planets their blue color : absorbs red and yellow photons from sunlight, reflects blue
Neptune has more methane than Uranus

22. Does not have distinct atmospheric features (storms, bands, etc
Does not have distinct atmospheric features (storms, bands, etc.) the way Jupiter does
No high-altitude clouds; deeper features are obscured by haze layer
Clouds move around planet in same direction as rotation ( km/hour)
colder than Jupiter & Saturn (53 K)
has a thin ring
Uranus
computer enhanced

23. Uranus’ axial tilt is 98o -- compared to Earth’s 23o tilt
New hypothesis of Uranus and Neptune formation: they originally formed between Jupiter and Saturn (5-9 AU) and migrated outward!

24. Neptune
Slightly warmer than Uranus even though further from Sun
temperature = 59 K
Haze layer not as thick
Has more obvious features than Uranus: storms, spots, bands
slightly more massive than Uranus
2000 km/hour winds -- much faster than Uranus
The Great Dark Spot lasted only a few years

25. Using a telescope with a spectrometer, we can observe the wavelength at which Neptune radiates most of its photons. From Wien’s law,
max =
0.29 T cm
Neptune, max = cm, so Neptune’s temperature = 59 K
if it were only heated by the Sun, Neptune should be 50 K.
Neptune has an internal source of energy: unknown at this time!

26. Neptune’s Great dark Spot, discovered by Voyager 2 in 1989
Neptune, imaged by the Hubble Space Telescope
Great Dark Spot is gone by 1994
Atmospheric structure changes over just a few days’ time

27. Computer-enhanced images of Neptune from Hubble Space Telescope
Seasons are changing!

28. Laws of physics and chemistry + observations = model for giant planets

29. All 4 giant planets have about the same mass rocky core (10 Mearth)
J & S have much more hydrogen & helium than U & N
J & S have metallic hydrogen
J & S & N radiate away more energy than they receive from Sun

30. Aurorae on earth: Interaction of solar wind with Earth’s magnetic field

31. The Earth has the properties of a big magnet
Solar wind (charged particles) respond to this magnetic field

32. The giant planets all have magnetic fields, & atmospheres, so we expect them to have aurorae too!

34. Jupiter’s magnetosphere is affected by the solar wind
We can measure the strength of J’s magnetic field : much stronger than Earth’s

35. Formation of the gas giant planets:
Gas giants form via core accretion followed by accumulating H and He gases from the solar nebula.
In the solar nebula, ice was an abundant core-building material > 5 AU from the Sun, because temperatures drops as you go further from the Sun

36. Gas giants must form before the solar nebula dissipates (< 10 million years)
Disks are seen around many young stars

37. Earth
Jupiter

38. Jupiter and Saturn’s atmospheres to scale
cooler than Jupiter, less dense atmosphere, thicker cloud layers