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Transcript
The Gas Giants Astronomy 311 Professor Lee Carkner Lecture 16 Which of the following is not a distinguishing feature of meteorites? a) b) c) d) A dark outer crust Widmanstatten Patterns Long parallel grooves on the surface Thumbprint-like depressions on the surface e) Small glassy inclusions Where do iron meteorites come from? a) A very high energy collision of two stony meteorites b) The Kuiper belt c) Near the orbit of Mercury d) A large, differentiated asteroid that got broken up e) The collision that made the Moon 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 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 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 Voyager 2’s Grand Tour 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 Orbits Compare to 0.4-1.5 AU for the inner planets Orbital periods are also much larger (12-165 years) 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 Densities Average density (kg/m3) Jupiter: 1330 Saturn: 700 Uranus: 1300 Neptune: 1760 Saturn is less dense than water (it floats) 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.) 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) Jupiter at Conjunction Spacecraft Least Energy Orbit Earth Spaceship Direct Boost Jupiter at Opposition Odyssey to Jupiter Structure Degree of oblateness depends on mass distribution Gas giants also have strong magnetic fields Must have conducting liquid interiors Internal Structure of Jupiter Moons Number of satellites (larger than 10 km) Jupiter -- 16 Saturn -- 18 Uranus -- 27 Neptune -- 13 Including the very small ones, about 160 total 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 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 Differences Between the Gas Giants Uranus and Neptune are smaller, cooler and have less distinct cloud features Next Time Read 11.1-11.4, 11.6 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 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
