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

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

2. 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! Uranus 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.) the way Jupiter does • No high-altitude clouds; deeper features are obscured by haze layer • Clouds move around planet in same direction as rotation (200-500 km/hour) • colder than Jupiter & Saturn (53 K) • has a thin ring computer enhanced Uranus

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. 0.29 T max = cm Using a telescope with a spectrometer, we can observe the wavelength at which Neptune radiates most of its photons. From Wien’s law, Neptune, max = 0.005 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