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An Introduction to the Ringed Giant
Saturn in false color With its stunning rings and dozen of moons, Saturn is an intriguing planet for many reasons. Barely smaller than Jupiter, it formed four billion years ago and it is made mainly of gas. It is also the only known planet that is less dense than water, meaning that if it could be placed inside an imaginary gigantic bathtub it would float. Saturn has a huge magnetosphere and a stormy atmosphere, with winds clocked at 1,800 kilometers (1,118 miles) per hour near its equator.

Image right: Saturn's atmosphere in false-color.
Image credit: NASA/JPL

Of the 31 known moons orbiting Saturn, Titan is the largest. Bigger than the planet Mercury and our own moon, Titan is of particular interest to scientists because it is the only moon in the solar system with its own atmosphere.

But what sets Saturn apart from the rest of the planets in the solar system are its picturesque rings. Made up by billions of ice and rock particles of all sizes -- from small debris to boulders as big as houses -- these rings orbit Saturn at varying speeds. There are hundreds of these rings, believed to be pieces of shattered comets, asteroids or moons that broke apart before they reached the planet. The rings are so big that they would fill most of the distance between Earth and the Moon.

For centuries, Saturn and its rings puzzled observers, in particular, Italian astronomer Galileo Galilei. The first to use a telescope to explore the wonders of the heavens, Galileo couldn't understand why Saturn looked different in the night sky at varying times -- a phenomenon that we now know is caused by the shifting of our view of the ring plane. Because of this, when the rings face Earth edge-on they are virtually invisible. They seem to reappear months later when our angle of view changes. Despite major advances in lens technology since Galileo's time, many questions still need to be answered through exploration of Saturn's rings.

Saturn's rings Launched from Kennedy Space Center on Oct. 15, 1997, the Cassini-Huygens spacecraft will reach the Saturnian region in July 2004. The mission is composed of two elements: The Cassini orbiter that will orbit Saturn and its moons for four years, and the Huygens probe that will dive into the murky atmosphere of Titan and land on its surface. The sophisticated instruments onboard these spacecraft will provide scientists with vital data to help understand this mysterious, vast region.

Image left: View of Saturn's rings.
Image credit: NASA/JPL

Cassini-Huygens is an international collaboration between three space agencies. Seventeen nations contributed to building the spacecraft. The Cassini orbiter was built and managed by NASA's Jet Propulsion Laboratory. The Huygens probe was built by the European Space Agency. The Italian Space agency provided Cassini's high-gain communication antenna. More than 250 scientists worldwide will study the data collected.
Cassini Mission
NASA's Jet Propulsion Laboratory