The Gas Giants

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

2. Gas Giant Basics • The 4 largest planets of the solar system are the gas giants • Does not include Pluto • The gas giants have no real surface, all we see is atmosphere

3. Missions to the Outer Planets • 1972 Pioneer 10 -- Jupiter flyby • 1973 Pioneer 11 -- Jupiter/Saturn flyby • 1977 Voyager 1 -- Jupiter/Saturn flyby • 1989 Galileo -- Jupiter orbiter and probe • 1997 Cassini -- Saturn orbiter and Titan probe (Huygens) • arrived 2004, currently taking data

4. Voyager 2 • Launched August 20, 1977 • Only mission to Uranus or Neptune • Most successful space probe ever launched • Is still taking data on the edge of the solar system

5. Voyager 2’s Grand Tour

6. 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

7. Orbits • Orbital radii for the outer planets range from ~5-30 AU • The outer planets cover a much larger region • Gas giants don’t move much in the sky from our viewpoint

8. Sizes of the Gas Giants • Gas giants are all very large compared to the terrestrial planets • Jupiter a little larger • Uranus a little larger • The gas giants contain 99% of the mass of the solar system (not including the Sun) • Volume and mass go as radius cubed

9. Densities • The gas giants have very low densities • Average density (kg/m3) • Jupiter: • Saturn: • Uranus: • Neptune: • For comparison Earth’s density is 5515 • Saturn is less dense than water (it floats)

10. 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.)

11. 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)

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

13. Structure • Degree of oblateness depends on mass distribution • Models indicate that gas giants have a small, dense, rock-ice core • Must have conducting liquid interiors

14. Internal Structure of Jupiter

15. Moons • Number of satellites (larger than ~10 km) • Jupiter -- • Saturn -- • Uranus -- • Neptune -- • Range in size from Ganymede (larger then Mercury) to small pieces of rock • Including the very small ones, about 170 total

16. Moon Properties • Satellites tend to be composed of rock and ice • Many have rocky cores and icy surfaces • Io is very active and covered with volcanoes • Europa may have a liquid water ocean

17. Jupiter’s Satellites

18. Saturn’s Satellites

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