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Cassini Imaging Team, NASA, a nice picture which shows the belts (dark bands) and zones (light bands) which encircle Jupiter. Also, the Great Red Spot stands out clearly in the southern hemisphere. |
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Galileo was launched on October 18, 1989 entering the Jupiter system December 7, 1995. The Galileo mission ended when Galileo plunged into Jupiter's crushing atmosphere on Sept. 21, 2003, deliberately destroyed to protect one of its own discoveries - the possible ocean beneath the icy crust of Europa. Galileo was the first probe to fly past an asteroid and to then discover a moon around an asteroid. It made direct observations of a comet colliding with a planet. Galileo was the first to measure Jupiter's atmosphere with a descent probe. The probe made the most difficult planetary atmospheric entry ever attempted, entering Jupiter's atmosphere on 7 December 7 1995, it survived entry speeds of over 106,000 mph, temperatures twice those on the surface of the Sun and forces up to 230 times greater than the strength of gravity on Earth, surviving for a remarkable 57 minutes as it descended into Jupiter. |
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The impacts occurred at night and Galileo was the only obesrvatory to observe the direct impact of Comet Shoemaker-Levy 9 on Jupiter. Because of Jupiter's rapid rotation, the impact sites were quickly brought into view (within a few minutes). To the right is shown the impact of Fragment W. |
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| ![]() The above shows the small moon Tethys slipping behind the large moon Titan. Cassini has always shown great interest in Titan, the giant, haze-enshrouded moon of Saturn. Cassini studied the structure and complex organic chemistry of Titan's smog-filled atmosphere. Cassini revealed vast methane lakes and widespread stretches of wind-driven hydrocarbon sand dunes on Titan's surface. Cassini researchers also deduced the presence of an internal, liquid water-ammonia ocean. As Cassini continues to study Titan, it will search for signs of seasonal changes such as storms, flooding, or changes in lake levels, as well as evidence of volcanic activity.
The lower left image shows the plumes on Enceladus. The middle image shows the chemical make-up of the plumes and the far right image shows the Tiger Stripes on Enceladus, cracks in the ice shell of Enceladus.
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Jupiter and Saturn are the two most massive planets in the Solar System; Jupiter is 318 times as massive as the Earth (with a rocky core may be as massive as 20-40 times the mass of the Earth, although Galileo suggested that it also may be as small as 5 times the mass of the Earth). JUNO suggests that its core is from ten to tens of Earth masses. Saturn is 94 times as massive as the Earth. Both Jupiter and Saturn have low density, roughly the density of water (as is the Sun) which implies they are composed of simple elements such as hydrogen and helium. Jupiter and Saturn are both gaseous with no solid surfaces; when a probe was sent to Jupiter it simply sank into the planet ( see Galileo Home Page). Both Jupiter and Saturn have short spin (rotation) periods, on the order of 10 hours. Translated into the speed of an observer standing on the equator of Jupiter, this corresponds to a speed of ~25,000 miles per hour! Recall that for the Earth, an observer would move with a speed of ~ 1,100 miles per hour. This rapid spin has profound effects on the appearance of Jupiter and Saturn.
In the following lectures, we will look at the properties of Saturn and Jupier in more detail especially highlighting results obtained from the Galileo, Juno, and Cassini missions mentioned above. In partcular, we consider results that pertained to our models for the formation of our Solar System and planetary systems in general and to our searches for extra-Terrestrial life in our Solar System on moons of Jupiter and Saturn.