Chapter 8 Jovian Planets

1. Chapter 8Jovian Planets

2. Mass: 1.9 × 10^27 kg (twice as much as all other planets put together) • Radius: 71,500 km (112 times Earth's) • Density: 1300 kg/m - cannot be rocky or metallic as inner planets are • Rotation rate: Problematic, as Jupiter has no solid surface; different parts of atmosphere rotate at different rates • From magnetic field, rotation period is 9 hr, 55 min Orbital and Physical Properties

3. Major visible features: Bands of clouds; Great Red Spot The Atmosphere of Jupiter

4. Atmosphere has bright zones and dark belts • Zones are cooler, and are higher than belts • Stable flow underlies zones and bands, called zonal flow • Simplified model:

5. Composition of atmosphere: Mostly molecular hydrogen and helium; small amounts of methane, ammonia, and water vapor These cannot account for color; probably due to complex chemical interactions The Atmosphere of Jupiter

6. No solid surface; take top of troposphere to be at 0 km Lowest cloud layer cannot be seen by optical telescopes Measurements by Galileo probe show high wind speeds even at great depth—probably due to heating from planet, not from Sun The Atmosphere of Jupiter

7. Great Red Spot has existed for at least 300 years, possibly much longer Color and energy source still not understood Lightning-like flashes have been seen; also shorter-lived rotating storms One example: Brown Oval, really a large gap in clouds The Atmosphere of Jupiter

8. Jupiter radiates more energy than it receives from the Sun: • Core is still cooling off from heating during gravitational compression Internal Structure • Could Jupiter have been a star? • It would need to be about 80 times more massive to be even a very faint star.

9. Jupiter is surrounded by belts of charged particles, much like the Van Allen belts but vastly larger. Magnetosphere is 30 million km across Intrinsic field strength is 20,000 times that of Earth Magnetosphere can extend beyond the orbit of Saturn Jupiter's Magnetosphere

10. 63 moons have now been found orbiting Jupiter, but most are very small • The four largest are the Galilean moons, so called because they were first observed by Galileo: • Io, Europa, Ganymede, Callisto • Galilean moons have similarities to terrestrial planets: largest is somewhat larger than Mercury, and density decreases as distance from Jupiter increases The Moons of Jupiter

11. Io is the densest of Jupiter's moons, and the most geologically active object in the solar system: • Many active volcanoes, some quite large • Can change surface features in a few weeks • No craters; they fill in too fast—Io has the youngest surface of any solar system object • Europa has no craters; surface is water ice, possibly with liquid water below The Moons of Jupiter

12. Ganymede is the largest moon in the solar system—larger than Pluto and Mercury History similar to Earth's Moon, but water ice instead of lunar rock Callisto is similar to Ganymede; no evidence of plate activity The Moons of Jupiter

13. Jupiter has been found to have a small, thin ring Jupiter's Ring

14. Saturn Orbital and Physical Properties Mass: 5.7 × 10^26 kg Radius: 60,000 km Density: 700 kg/m — less than water! Rotation: Rapid and differential, enough to flatten Saturn considerably Rings: Very prominent; wide but extremely thin

15. Saturn's atmosphere also shows zone and band structure, but coloration is much more subdued than Jupiter's Mostly molecular hydrogen, helium, methane, and ammonia; helium fraction is much less than on Jupiter Saturn's Atmosphere

16. Similar to Jupiter's, except pressure is lower Three cloud layers Cloud layers are thicker than Jupiter's; see only top layer Saturn's Atmosphere

17. Wind patterns on Saturn are similar to those on Jupiter, with zonal flow Jupiter-style “spots” rare on Saturn; don't form often and quickly dissipate if they do As expected for a planet with an atmosphere, there is a vortex at Saturn's south pole. Saturn's Atmosphere

18. Saturn also radiates more energy than it gets from the Sun, but not because of cooling: • Helium and hydrogen are not well mixed; helium tends to condense into droplets and then fall • Gravitational field compresses helium and heats it up • Saturn also has a strong magnetic field, but only 5% as strong as Jupiter's Saturn's Interior and Magnetosphere

19. Ring particles range in size from fractions of a millimeter to tens of meters • Composition: Water ice—similar to snowballs • Why rings? • Too close to planet for moon to form—tidal forces would tear it apart • Details of formation are unknown: • Too active to have lasted since birth of solar system • Either must be continually replenished, or are the result of a catastrophic event Saturn's Spectacular Ring System

20. Saturn's many moons appear to be made of water ice • In addition to the small moons, Saturn has: • Six medium-sized moons (Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus) • One large moon (Titan) which is almost as large as Ganymede The Moons of Saturn

21. Titan has been known for many years to have an atmosphere thicker and denser than Earth's; mostly nitrogen and argon Makes surface impossible to see; the upper picture at right was taken from only 4000 km away Trace chemicals in Titan's atmosphere make it chemically complex The Moons of Saturn

22. Uranus and Neptune

23. Uranus was discovered in 1781 by William Herschel; first planet to be discovered in more than 2000 years Little detail can be seen from Earth; arrows point to three of Uranus's moons: The Discoveries of Uranus and Neptune

24. Neptune was discovered in 1846, after analysis of Uranus's orbit indicated its presence Details of Neptune cannot be made out from Earth either; arrows again point to moons: 13.1 The Discoveries of Uranus and Neptune

25. Uranus and Neptune are very similar Orbital and Physical Properties

26. Uranus Neptune Orbital and Physical Properties Mass 14.5 x Earth 17.1 x Earth Radius 4.0 x Earth 3.9 x Earth Density 1300 kg/m^3 1600 kg/m^3

27. Peculiarity of Uranus: Axis of rotation lies almost in the plane of its orbit. Seasonal variations are extreme. Uranus and Neptune are cold enough that ammonia freezes; methane dominates and gives the characteristic blue color Orbital and Physical Properties

28. Outer atmospheres of Uranus and Neptune are similar to those of Jupiter and Saturn The Atmospheres of Uranus and Neptune

29. Uranus and Neptune both have substantial magnetic fields, but at a large angle to their rotation axes. Magnetospheres and Internal Structure

30. The Moon Systems of Uranus and Neptune Uranus has 27 moons, five of which are major: Miranda, Ariel, Umbriel, Titania, and Oberon Similar to Saturn's medium-sized moons, except that all are much less reflective Umbriel is the darkest

31. Neptune has 13 moons, but only two can be seen from Earth: Triton and Nereid Triton is in a retrograde orbit; Nereid’s is highly eccentric Triton’s surface has few craters, indicating an active surface. There appear to be ice volcanoes andNitrogen geysers The Moon Systems of Uranus and Neptune

32. Uranus and Neptune have faint ring systems, recently detected via stellar occultation The Rings of the Outermost Jovian Planets

33. Neptune has five rings: three narrow and two wide The Rings of the Outermost Jovian Planets