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Full-disk image of Saturn and its rings.
A Hubble Space Telescope image of Saturn in true color.

Saturn is the most distant of the five planets known to ancient stargazers. In 1610, Italian Galileo Galilei was the first astronomer to gaze at Saturn through a telescope. To his surprise, he saw a pair of objects on either side of the planet, which he later drew as "cup handles" attached to the planet on each side. In 1659, Dutch astronomer Christiaan Huygens announced that this was a ring encircling the planet. In 1675, Italian-born astronomer Jean Dominique Cassini discovered a gap between what are now called the A and B rings.

Like Jupiter, Uranus, and Neptune, Saturn is a gas giant. It is made mostly of hydrogen and helium. Its volume is 755 times greater than Earth's. Winds in the upper atmosphere reach 500 meters per second in the equatorial region. (In contrast, the strongest hurricane-force winds on Earth top out at about 110 meters per second.) These super-fast winds, combined with heat rising from within the planet's interior, cause the yellow and gold bands visible in its atmosphere.

Saturn's ring system is the most extensive and complex in our solar system; it extends hundreds of thousands of kilometers from the planet. In fact, Saturn and its rings would just fit in the distance between Earth and the Moon. In the early 1980s, NASA's two Voyager spacecraft revealed that Saturn's rings are made mostly of water ice, and they found "braided" rings, ringlets, and "spokes" - dark features in the rings that seem to circle the planet at a different rate from that of the surrounding ring material. Some of the small moons orbit within the ring system as well. Material in the rings ranges in size from a few micrometers to several tens of meters.

Titan's atmosphere is visible as a thick purple haze around the moon.
A Cassini spacecraft image of Titan's thick atmosphere.
Saturn has 46 known natural satellites (moons) and there are probably many more waiting to be discovered. The largest, Titan, is a bit bigger than the planet Mercury. Titan is shrouded in a thick nitrogen-rich atmosphere that might be similar to what Earth's was like long ago. Further study of this moon promises to reveal much about planetary formation and, perhaps, about the early days of Earth as well.

In addition to Titan, Saturn has many smaller icy satellites. From Enceladus, which shows evidence of surface changes, to Iapetus, with one hemisphere darker than asphalt and the other as bright as snow, each of Saturn's satellites is unique.

Saturn, the rings, and many of the satellites lie totally within Saturn's enormous magnetosphere, the region of space in which the behavior of electrically charged particles is influenced more by Saturn's magnetic field than by the solar wind. Images taken by NASA's Hubble Space Telescope show that Saturn's polar regions have aurorae similar to Earth's Northern and Southern Lights. Aurorae occur when charged particles spiral into a planet's atmosphere along magnetic field lines.

The next chapter in our knowledge of Saturn is already under way. The Cassini- Huygens spacecraft arrived at Saturn on July 1, 2004 and immediately began sending back surprising new information about the planet, rings and moons. The Cassini orbiter is carrying the European Space Agency's Huygens probe, which will descend through Titan's atmosphere in January 2005 and collect data on the atmosphere and surface of the moon. Cassini will orbit continue to orbit Saturn during a four-year primary mission.
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Last Updated: 06.27.05