Introduction to Saturn

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.

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.

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.

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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.

Source: NASA