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The Giant Planets

The Giant Planets. The Jovian Worlds. Saturn. Neptune. Uranus. Jupiter. Exploration. First spacecrafts: Pioneer 10 (1972) & 11 (1973) Can we navigate through the asteroid belt? What are the radiation hazards near the planets?

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The Giant Planets

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  1. The Giant Planets AST 2010: Chapter 10

  2. The Jovian Worlds Saturn Neptune Uranus Jupiter AST 2010: Chapter 10

  3. Exploration • First spacecrafts: Pioneer 10 (1972) & 11 (1973) • Can we navigate through the asteroid belt? • What are the radiation hazards near the planets? • Pioneer 10 flew by Jupiter in 1973 and flew out the solar system • Pioneer 11 flew by Jupiter in 1974 and was deflected towards Saturn which it reached in 1979 AST 2010: Chapter 10

  4. Exploration • Voyager 1 & 2 (launched 1977) • Highly productive Missions • Carried 11 scientific instruments including cameras and spectrometers, devices for measuring magnetospheres • Voyager 1 • Reached Jupiter (1979) and Saturn (1980) • Used gravity assist towards Saturn • Voyager 2 • Reached Jupiter four month later than Voyager 1 • Reached Saturn (1981), Uranus (1986), Neptune (1989) • Multiple Flybys possible thanks to approximate alignment of the planets • Such an alignment occurs once in 175 years Voyager 2 AST 2010: Chapter 10

  5. Exploration • Galileo space probe • Launched 1989 • Reached Jupiter December 1995 • Deployed a small entry probe for a direct study of Jupiter’s atmosphere • Sept. 2003, probe sent into Jupiter’s atmosphere to end its mission • Cassini • Launched 1997 • Reached Saturn in 2004, now in orbit • Deployed entry probe for Titan in Jan. 2005 AST 2010: Chapter 10

  6. Galileo Space Probe

  7. Galileo – Jupiter Entry Probe • Mass 339 kg • Plunged at shallow angle into Jupiter at speed of 50 km/s • Slowed down by friction against Jupiter atmosphere • Temperature of its shield reached 15,000°C • Speed dropped to 2500 km/h • Deployed parachute for actual entry in the atmosphere • Transmitted data to orbiter, for retransmission to Earth AST 2010: Chapter 10

  8. Some Results of the Galileo Mission • The discovery of a satellite (Dactyl) of an asteroid (Ida) • Jovian wind speeds in excess of 600 km/hour (400 mph) were detected • Far less water was detected in Jupiter's atmosphere than estimated from earlier Voyager observations and from models of the Comet Shoemaker-Levy 9 impact • Far less lightning activity (about 10% of that found in an equal area on Earth) than anticipated. The individual lightning events, however, are about ten times stronger on Jupiter than the Earth • Helium abundance in Jupiter is very nearly the same as its abundance in the Sun (24% compared to 25%) • Extensive resurfacing on Io due to continuing volcanic activity since the 1979 Voyagers fly-bys • Evidence for liquid water ocean under Europa's ice AST 2010: Chapter 10

  9. Huygens Probe Dropped by Cassini Orbiter AST 2010: Chapter 10

  10. Basics Properties of the Jovian Planets Planet Distance (AU) Period (years) Diameter (km) Mass (Earth=1) Density (g/cm3) Rotation (hours) Jupiter 5.2 11.9 142800 318 1.3 9.9 Saturn 9.5 29.5 120540 95 0.7 10.7 Uranus 19.2 84.1 51200 14 1.2 17.2 Neptune 30.1 164.8 49500 17 1.6 16.1 Basic Facts of Jovian Planets • Large distances from the sun • Long periods • Jupiter and Saturn similar in composition and internal structure • Uranus and Neptune smaller and differ in composition and structure

  11. Appearance • Only the upper atmosphere of the giant planets is visible to us • Astronomers believed that their interiors are composed primarily of hydrogen and helium • The uppermost clouds of Jupite and Saturn are composed of ammonia (NH3) crystals • Neptune’s upper clouds are made of methane (CH4) • Uranus has no obvious clouds, only deep and featureless haze AST 2010: Chapter 10

  12. Rotation • How does one determine the rotation rate of the giants? • For Jupiter: • 1st option: use dynamic surface features (storms) • However the cloud rotation may have nothing to do with the rotation of the mantle and core… • 2nd option: look at periodic variations of radio waves associated with the magnetic field produced deep inside the planet • This gave rotation period of 9 h 56 m • The same technique is used to measure the rotation of other giant planets: • Saturn has 10 h 40 m • Uranus and Neptune have about 17 hours AST 2010: Chapter 10

  13. Seasons on the Giants • Jupiter is tilted by 3o • No seasons to speak of • Saturn is tilted by 27o • Long seasons • Neptune is tilted by 27o • Long seasons • Uranus is Tilted by 98o • Practically orbiting on its side • Rings and satellites follow same pattern • 21 year seasons!!! • Why this odd tilt? • A giant impact in the past could be the cause Seasons on Uranus

  14. Giant Planets – Giant Pressure • Giant planets composed mainly of hydrogen (H) and helium (He) • But because of its enormous size, the H and He in the center of Jupiter are compressed enormously • Estimated pressure: 100 million bars. • Central density of 31 g/cm3 • Earth by contrast has 4 million bars and 17 g/cm3 in its center • Giant Planet implies giant pressure!! AST 2010: Chapter 10

  15. Consequences of the Pressure • Few thousand km below the surface, hydrogen is in a liquid state • Still deeper, the liquid is further compressed and begins to act like a metal • On Jupiter, part of the interior is metallic hydrogen! • Saturn is less massive • Most of its interior is liquid, but not metallic • Neptune and Uranus are probably too small to liquefy hydrogen AST 2010: Chapter 10

  16. More about Composition • The planets also have a core composed of heavier materials • Possibly the original rock/ice bodies that formed before gas were abundantly captured by the planets AST 2010: Chapter 10

  17. Internal Heat Source (1) • Because of their large sizes, all the giant planets are believed to be strongly heated during their formation • Jupiter was the hottest • Some of the primordial heat still remains • Giant planets may also generate energy internally by slowly contracting • Even a small amount of shrinkage can generate significant heat • This probably raises the temperature of the core and atmosphere above the temperature due to the Sun’s heat • Jupiter has the largest internal source of energy • 4x1017 W • A cross between a planet (like earth) and a star • Internal heat probably primordial heat AST 2010: Chapter 10

  18. Magnetic Fields • All four giant planets have strong magnetic fields and associated magnetospheres • The magnetospheres are large • They extend for millions of km in space • Jupiter’s field was discovered in the late 1950’s • Radio waves detected from Jupiter • Electrons circulating in the magnetosphere produce the radio waves by a process called synchrotron emission • Magnetic fields of Saturn, Uranus, and Neptune discovered by flyby spacecraft AST 2010: Chapter 10

  19. Magnetospheres • Jupiter’s magnetic field is not aligned with its axis of rotation • It is tipped by 10o • Uranus and Neptune have tilts of 60o and 55o • Saturn’s field is perfectly aligned with its axis of rotation AST 2010: Chapter 10

  20. Atmospheres of the Giant Planets • The part of the planets accessible to direction observation • Dramatic examples of weather patterns • Storms on these planets can be larger than Earth! AST 2010: Chapter 10

  21. Atmospheric Composition • Methane (CH4) and ammonia (NH3) were first believed to be the primary constituents of the atmospheres • We know today that hydrogen and helium are actually the dominant gases • First based on far-infrared measurements by Voyager • Less helium in Saturn’s atmosphere • Precipitation of helium? Energy source of Saturn? • Best measurements of composition by Galileo spacecraft (1995) upon entry to atmosphere AST 2010: Chapter 10

  22. Clouds and Atmospheric Structure • Jupiter’s clouds are spectacular in color and size • Color: orange, red, brown • Fast motion • Saturn is more “subdued” • Clouds have nearly uniform butterscotch hue AST 2010: Chapter 10

  23. Atmospheric Structure of the Jovian Planets AST 2010: Chapter 10

  24. Winds and Weather • Many regions of high/low pressures • Air flow between these regions sets up wind patterns distorted by the fast rotation of the planet • Wind speeds measurable by tracking cloud patterns • Differences with Earth • Giant planets spin much faster than Earth • Rapid rotation smears out air circulation into horizontal (east-west) patterns parallel to the equator • No solid surface • No friction or loss of energy – this is why tropical storms on Earth eventually die out… • Internal heat contributes as much energy to the atmosphere as sunlight (except for Uranus) AST 2010: Chapter 10

  25. Winds on The Giant Planets • Winds on Uranus and Neptune are rather similar to those on Jupiter and Saturn • True on Uranus in spite of the 98O tilt AST 2010: Chapter 10

  26. Storms • Omni-present on the giant planets • Superimposed on the regular circulation patterns • Large oval-shaped high-pressure regions on both Jupiter and Neptune • Most famous: Jupiter’s Great Red Spot • In the southern hemisphere • 30,000 km long (when Voyager flew by) • Present since first seen 300 years ago • Changes in size, but never disappears AST 2010: Chapter 10 From Voyager 1 in 1979

  27. Great Red Spot • Counterclockwise rotation with rotation period of 6 days • Similar disturbances formed in the 1930s on Jupiter • Smaller circles near the red spot • Cause unknown • Long-lived because of • absence of ground • their size • Expected lifetime: centuries AST 2010: Chapter 10

  28. Neptune Great Dark Spot • First seen in 1989 by Voyager • About 10,000-km long • 17-day period • Had disappeared (faded?) in mid 1990s • New dark spot seen in Nov. 1994 • Faded by 1995 • Do storms form and disappear quicker on Neptune? AST 2010: Chapter 10

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