The Gas Giants Astronomy 311 Professor Lee Carkner Lecture 16

Which of the following is not a distinguishing feature of meteorites? a)A dark outer crust b)Widmanstatten Patterns c) Long parallel grooves on the surface d)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  first spacecraft to the outer planets  1973 Pioneer 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   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:  Mass:  Orbital Radius: 5.20  Saturn  Diameter: 9.42  Mass:  Orbital Radius: 9.54  Uranus  Diameter: 4.01  Mass:  Orbital Radius:  Neptune  Diameter: 3.88  Mass:  Orbital Radius:  Numbers are relative to the Earth

Orbits   Compare to AU for the inner planets   Orbital periods are also much larger ( 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/m 3 )  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)

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

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  Saturn  Uranus  Neptune   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 , 11.6

Summary  Size: ~4-11 times Earth diameter  Mass: ~ 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