Saturn; Magnificent Cosmos; Scientific American Presents; by Staff Editor; 2 Page(s)
Saturn's rings make it one of the most familiar, and spectacular, images of astronomy, not to mention science fiction. When Galileo trained a primitive telescope on the planet for the first time in 1610, he was misled. From the poorly resolved image in his viewfinder, he believed Saturn to be a triple-system, with a large body in the center and smaller ones on each side. The rings may be much younger than the planet itself, and great mathematicians have found them worthy of contemplation. Laplace and James Clerk Maxwell calculated that Saturn's rings must consist of many smaller objects. Although the planet is almost the size of Jupiter, its mass is but one third as great, giving Saturn the lowest mean density of any solar system object.
As a gas giant, the planet has no single rotation period but rather a variety depending on latitude. Upper atmosphere clouds travel around the equator in as little as 10 hours and 10 minutes; clouds in high latitudes may take half an hour longer to pass across the planet. Based on gravitational field data, Saturn appears to have a solid core with a mass equivalent to up to 20 Earths. As the most oblate planet, the pull of gravity at its equator is less than three quarters of that at the poles.