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The Gas Giants Astronomy 311 Professor Lee Carkner Lecture 16
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Gas Giant Basics The 4 largest planets of the solar system are the gas giants
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Missions to the Outer Planets 1972 Pioneer 10 -- 1973 Pioneer 11 -- 1977 Voyager 1 -- 1977 Voyager 2 -- 1989 Galileo -- 1997 Cassini --
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Voyager 2 Launched August 20 1977 Used gravity of each planet to change orbit to get to the next Is still taking data on the edge of the solar system
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Voyager 2’s Grand Tour
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Gas Giant Facts 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 Numbers are relative to the Earth
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Orbits Orbital radii for the outer planets range from ~5-30 AU
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Sizes of the Gas Giants Gas giants are all very large compared to the terrestrial planets Jupiter and Saturn about 10 Earth diameters Uranus and Neptune about 4 Earth diameters The gas giants contain 99% of the mass of the solar system (not including the Sun)
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Densities The gas giants have very low densities Average density (kg/m 3 ) Jupiter: Saturn: Uranus: Neptune: For comparison Earth’s density is 5515
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Composition The gas giants have a low density because they are made up mostly of hydrogen and helium the 2 lightest elements Total composition
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Surface and Atmosphere The gas giants do not have a real “surface”
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Atmospheric Features Clouds Bands Storms
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Jupiter’s Great Red Spot
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Neptune’s Great Dark Spot
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Hurricane on Earth
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Saturn’s Atmosphere
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Traveling Through the Solar System
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Structure The gas giants are not perfectly round, they are oblate due to rotation Degree of oblateness depends on mass distribution Gas giants also have a magnetic field
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Internal Structure of Jupiter
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Moons Number of satellites (larger than 10 km) Range in size from Ganymede (larger then Mercury) to small pieces of rock
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Moon Properties Satellites tend to be composed of rock and ice Many have rocky cores and icy surfaces The satellites are very diverse:
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Jupiter’s Satellites
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Saturn’s Satellites
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Rings All of the gas giants have rings of small particles Rings consist of material that has fallen inside the Roche limit
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Saturn’s A Ring
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Differences Between the Gas Giants Jupiter and Saturn are larger,warmer and have more distinct cloud features
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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
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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
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