|Grand Tour of the Outer Planets|
Saturn, the second largest planet in our solar system, orbits the Sun every 29½ Earth years. Both Voyager 1 and Voyager 2 measured a day on Saturn to be 10 hours, 39 minutes long.
Saturn's most recognizable feature is its rings, which Voyager demonstrated are far more intricate than scientists had realized. The rings are composed of ice and rock that probably broke off from large moons colliding with comets or meteoroids. The ring system extends 100's of thousands of miles from Saturn.
Voyager 1 image of Saturn and three of its moons taken from a distance of 106 million km. North is at 1:30. Bands can be seen in the northern hemisphere and structure can be identified in the rings, including the Cassini Division, towards the outer edge of the rings. The satellites that can be seen in this image are Enceladus, near the left edge of the rings, Dione, below Saturn, and Tethys, at the right edge of the frame. Saturn is 120,000 km in diameter.
From the Earth, Saturn is never seen as a crescent, as in this image taken by Voyager 1 on November 16, 1980.
Voyager 1 image of Saturn from 5.3 million km four days after its closest approach. This perspective allows a view of Saturn looking back towards the sun. The shadow of Saturn can be seen on the rings, and Saturn can be seen through the rings as well. Some of the spoke-like ring features are visible as bright patches. Saturn has a diameter of about 12,000 km. North is at 1:00.
Because some of Saturn's rings are translucent, we can see Saturn through parts of the rings. Saturn's rings have been named in the order in which they were discovered. Moving outward from the planet are the main rings, A, B, and C. The large division between rings B and A is known as the Cassini Division, after the astronomer who first reported it in 1675. Closest to Saturn, is the very faint D ring.
Left: False color image, taken by Voyager 1, showing the unlit side of Saturn's rings. The brightest part of the image is the Cassini division. The B ring is the darkest ring in the image. The F ring is also visible. Right: This enhanced false color Voyager 2 image was put together from clear, orange and ultraviolet frames. The color variations reflect possible variations in chemical composition within Saturn's ring system. The C ring appears blue. The picture also shows color differences between the inner B ring and the outer region, where the spokes form, and between the B and the A rings. The B ring contains spokes that were first observed by amateur astronomers and later confirmed by Voyager. Researchers believe that the spoke-like appearance is due to small grains of dust kept hovering above larger particles by electrostatic forces that eventually dissipate.
Voyager 2's image of the B ring in forward-scattered light. The spokes appear as bright streaks, which means that the spokes are due to tiny dust grains, about one wavelength of light in size.
This movie, showing the motion of the B ring spokes, is composed of a series of time-lapse images taken by Voyager.
Outside the A ring lies the fascinating F ring which, from Voyager 1 images, appeared braided. Nine months later Voyager 2 took images of the F ring that showed it to consist of a more regular ring made up of parallel strands that did not intersect one another. Later examination of the Voyager data showed that the ring consists of at least four strands, each with slightly different orbits, which explains the changing appearance.
The left image is from Voyager 1 and shows the apparently braided F ring as two bright strands enclosing a fainter strand. The right image is a high-resolution image from Voyager 2, showing that the ring is made up of at least four distinct components. The small black dots are camera reference marks, while the small bright dash in the middle right of the image is a star trail.
Beyond the F ring are the faint G and E rings.
One of Voyager 1's main tasks on its flyby of Saturn was to study its largest moon, Titan. However, the dense haze surrounding Titan prevented Voyager 1 from taking images of Titan's surface. Voyager did discover that Titan's atmosphere consists mainly of nitrogen and is 1.6 times as dense as Earth's atmosphere at sea level. Researchers believe that Titan's atmosphere today may resemble that of Earth before the evolution of life.
Voyager 1 image of Titan, taken in 1980
Saturn is the only planet less dense than water. It consists of approximately 75% hydrogen and 25% helium, similar to Jupiter. One of the mysteries about Saturn was that it radiates 80 percent more heat than it receives solar energy. Voyager determined that only 7% of Saturn's upper atmosphere is helium, compared with Jupiter's 11%. This may mean that Saturn's helium may be falling through the less dense hydrogen and causing Saturn's luminosity.
Saturn's atmosphere appears far more peaceful than does Jupiter's, and Saturn has only a quarter as much energy for storm systems as has Jupiter. Scientists were, therefore, amazed to learn from Voyager that Saturn has an equatorial jet stream blowing at 1,100 miles per hour, six times faster than Jupiter's storm system.
Right: A false-color image, taken through green, violet, and ultraviolet filters, shows three large storms in Saturn's northern hemisphere.
Voyager has now passed the baton to Cassini, which was launched in 1997 and, in 2004, will be the first spacecraft to visit Saturn since 1981.
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