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Transcript
Planet Jupiter o Fifth planet from Sun. o Largest planet. o Twice as massive of all the other planets combined. Earth Comparison o Orbit: 5.20 AU o Diameter: 11.2 Earths o Mass: 318 Earths History o Jupiter (Jove) was the King of the Gods (Zeus). o Fourth brightest object in the sky from Earth. o Known as a “wandering star” since prehistoric times. o Galileo (1610) used telescope to discover four moons: Io, Europa, Ganymede, Callisto o Moons were first discovery of a center of motion not associated with Earth. o Satellite motions and phases of Venus helped support Copernicus's heliocentric theory. Visiting Spacecraft o First visited by Pioneer 10 in 1973 o Pioneer 11 o Voyager 1 o Voyager 2 o Ulysses o Galileo orbited Jupiter for eight years. o JUNO, launched in 2011 and will arrive at Jupiter in 2016 Structure o No solid surface, the gaseous materials simply get denser with depth. o 90% hydrogen o 10% helium o Traces of methane, water, and ammonia. o Similar to primordial Solar Nebula from which the solar system formed. o Saturn has a similar composition. o Uranus and Neptune have much less hydrogen and helium. Interior – “Core” o Knowledge of Jupiter’s interior is indirect. o Galileo’s atmospheric probe only went to 150 km below the cloud tops. o Jupiter probably has a core of rocky material amounting to 10 to 15 Earth-masses. Interior – “Mantle" o Liquid metallic hydrogen above the core makes up most of the planet. o This exotic form of hydrogen is possible only at pressures exceeding 4 million Earth atmospheres. o Liquid metallic hydrogen consists of ionized protons and electrons. o It’s an electrical conductor and the source of Jupiter's magnetic field. Outer “Layer” (atmosphere) o The outermost layer is composed primarily of ordinary hydrogen and helium gas. o Also includes: o Water o Carbon Dioxide o Methane o The atmosphere we see is just the very top of this deep layer. Lack of “Layers” o Experiments show that hydrogen does not change phase suddenly. o Therefore there are no boundaries between the various interior layers. Clouds o Three layers of clouds consist of o Ammonia Ice, o Ammonium Hydrosulfide, o and a mixture of ice and water. Weather o High velocity winds are confined in wide bands of latitude. o Winds blow in opposite directions in adjacent bands. o The Galilean probe indicates winds are more than 400 mph and extend down as far as the probe was able to observe. o Winds may extend down thousands of kilometers into the interior. Band Characteristics o Chemical and temperature differences between bands create colored effects. o Light colored bands are called zones; the dark ones belts. o Bands have been known for some time on Jupiter, but complex vortices in the boundary regions between the bands were first seen by Voyager. o Cloud colors correlate with altitude: o Blue = lowest o Brown = higher o Whites = higher yet o Red = highest o Sometimes we see the lower layers through holes in the upper ones. The Red Spot o The Great Red Spot (GRS) has been seen for more than 300 years. o Discovered by Cassini or Robert Hooke. o The GRS is a 12,000 by 25,000 km oval, big enough to hold two Earths. o Infrared observations and its rotation direction indicate that the GRS is a high-pressure region whose cloud tops are significantly higher and colder than the surrounding regions. o There are other spots such as Red Spot Junior. o It is not known how such structures can persist for so long. Radiation o Jupiter radiates more energy into space than it receives from the Sun. o The interior is hot: the core is about 20,000 K. o Slow gravitational compression heats the planet. o Interior heat causes convection deep within Jupiter's liquid layers and is probably responsible for the complex motions we see in the cloud tops. o Jupiter does NOT produce energy by nuclear fusion as in the Sun; it is much too small and hence its interior is too cool to ignite nuclear reactions. o If Jupiter were 80 times more massive, it would be a small star. Magnetic Field o Jupiter has a huge magnetic field, much stronger than Earth's. o Its magnetosphere extends past the orbit of Saturn! o Jupiter's moons therefore lie within it. o Designers of the Voyager and Galileo spacecraft had to take in account the high levels of energetic particles trapped by Jupiter's magnetic field. o It would be immediately fatal to an unprotected human being. Rings! o Jupiter has rings like Saturn's, but much fainter and smaller. o Unexpected and were only discovered when two of the Voyager 1 scientists insisted that after traveling 1 billion km it was at least worth a quick look to see if any rings might be present. o Unlike Saturn's, Jupiter's rings are dark. o Composed of very small grains of rocky material. o Particles don't stay there long due to atmospheric and magnetic drag. o The Galileo spacecraft found clear evidence that the rings are continuously resupplied by dust formed by micrometeor impacts on the four inner moons. Comet Impact! o In July 1994, Comet Shoemaker-Levy 9 collided with Jupiter with spectacular results. o The effects were clearly visible even with small telescopes. o The debris from the collision was visible for nearly a year afterward with HST. The Moons o Galilean moons are easily visible with binoculars; a few bands and the Great Red Spot can be seen with a small telescope. o Jupiter has 67 known satellites (as of 2013): the four large Galilean moons plus many more small ones some of which have not yet been named: o Jupiter's satellites are named for other figures in the life of Zeus (mostly his numerous lovers) o Like the Earth-Moon system, Jupiter’s rotation is very gradually slowing down due to the tidal drag produced by the Galilean satellites. o Also, the same tidal forces are changing the orbits of the moons, very slowly forcing them farther from Jupiter. o Io, Europa and Ganymede are locked together in a 1:2:4 orbital resonance. o In a few hundred million years, Callisto will be locked in too, orbiting at exactly twice the period of Ganymede (eight times the period of Io). o Jupiter's satellites are named for other figures in the life of Zeus (mostly his numerous lovers).