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The Gas Giants

The Gas Giants

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The Gas Giants

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  1. The Gas Giants Astronomy 311 Professor Lee Carkner Lecture 16

  2. Which of the following is not a distinguishing feature of meteorites? • A dark outer crust • Widmanstatten Patterns • Long parallel grooves on the surface • Thumbprint-like depressions on the surface • Small glassy inclusions

  3. Where do iron meteorites come from? • A very high energy collision of two stony meteorites • The Kuiper belt • Near the orbit of Mercury • A large, differentiated asteroid that got broken up • The collision that made the Moon

  4. Gas Giant Basics • The 4 largest planets of the solar system are the gas giants • All have small cores and large hydrogen outer layers • The gas giants have no real surface, all we see is atmosphere

  5. Missions to the Outer Planets • 1972 Pioneer 10 -- • first spacecraft to the outer planets • 1973 Pioneer 11 -- Jupiter/Saturn flyby • 1977 Voyager 1 -- Jupiter/Saturn flyby • 1977 Voyager 2 – • 1989 Galileo -- Jupiter orbiter and probe • 1997 Cassini -- • arrived 2004, currently taking data

  6. Voyager 2 • Launched August 20 1977 • Only mission to Uranus or Neptune • Used gravity of each planet to change orbit to get to the next • Is still taking data on the edge of the solar system

  7. Voyager 2’s Grand Tour

  8. Jupiter Diameter: 11.21 Mass: 317.83 Orbital Radius: 5.20 Saturn Diameter: 9.42 Mass: 95.16 Orbital Radius: 9.54 Uranus Diameter: 4.01 Mass: 14.50 Orbital Radius: 19.19 Neptune Diameter: 3.88 Mass: 17.20 Orbital Radius: 30.06 Gas Giant Facts • Numbers are relative to the Earth

  9. Orbits • Compare to 0.4-1.5 AU for the inner planets • Orbital periods are also much larger (12-165 years)

  10. Sizes of the Gas Giants • Gas giants are all very large compared to the terrestrial planets • Jupiter a little larger • Uranus a little larger • Jupiter itself contains 71% • Volume and mass go as radius cubed

  11. Densities • Average density (kg/m3) • Jupiter: 1330 • Saturn: 700 • Uranus: 1300 • Neptune: 1760 • Saturn is less dense than water (it floats)

  12. Composition • The gas giants have a low density because they are made up mostly of hydrogen and helium, the 2 lightest elements • Hydrogen is the lightest and most abundant element in the universe (1 proton + 1 electron) • Total composition • ~5% heavier elements (methane, ammonia, water vapor etc.)

  13. Atmospheric Features • Clouds • small amounts of trace elements may produce the colors • Bands • adjacent bands move in opposite directions • Storms • some are very long lived (e.g. Great Red Spot)

  14. Odyssey to Jupiter Jupiter at Conjunction Spaceship Direct Boost Earth Spacecraft Least Energy Orbit Jupiter at Opposition

  15. Structure • Degree of oblateness depends on mass distribution • Gas giants also have strong magnetic fields • Must have conducting liquid interiors

  16. Internal Structure of Jupiter

  17. Moons • Number of satellites (larger than 10 km) • Jupiter -- 16 • Saturn -- 18 • Uranus -- 27 • Neptune -- 13 • Including the very small ones, about 160 total

  18. Moon Properties • Satellites tend to be composed of rock and ice • The satellites are very diverse: • Titan has a denser atmosphere than the Earth • Europa may have a liquid water ocean

  19. Rings • All of the gas giants have rings of small particles • The rings of the other planets are made of smaller darker particles and were only discovered by spacecraft • This is the region where the tidal force from the planet is greater than the gravitational force holding the object together

  20. Differences Between the Gas Giants • Uranus and Neptune are smaller, cooler and have less distinct cloud features

  21. Next Time • Read 11.1-11.4, 11.6

  22. Summary • Size: ~4-11 times Earth diameter • Mass: ~15-318 Earth masses • Composition: mostly hydrogen and helium • Atmosphere: clouds of methane and ammonia • also have large, long-lived storm systems and oppositely moving bands

  23. Summary: The Jovian Systems • The gas giants have extensive satellite systems • Many moons have icy exteriors with rocky cores • Some are very large (~size of Earth’s Moon) • All of the outer planets (not just Saturn have ring systems) • rings composed of small particles • Ring properties different for each planet