Known still today as the "ringed planet," Saturn is one of the giant planets of our solar system. Its rings, seen through fairly powerful telescopes on Earth succeed in providing endless fascination. With the Pioneer and Voyager spacecraft, astronomers got their first close-up at the rings. Though these photographs answered some questions, there are still many important issues left unresolved.
Photo. Saturn, seen from the Hubble Space Telescope with its rings edge-on, tilted only slightly. Most often, we see Saturn with its rings more angled, but in this photo Earth was close to the flat plane of the rings. Courtesy Space Telescope Science Institute, Erich Karkoschka/University of Arizona Lunar & Planetary Lab, NASA.
Saturn is the second largest planet in the Solar System, after Jupiter, and could fit some 750 Earths. For all of its size, Saturn is actually less dense than water because it is made up mostly of gases and liquids.
Rotating around the sun from an average distance of 890 million miles, Saturn is the sixth closest planet to the sun and takes 30 Earth years to complete one full orbit. Like the other giant planets, Saturn rotates twice as fast as Earth: once every ten hours on Earth, the planet completes another spin. As on Jupiter, this rapid spinning swirls around winds that gust at up to 1120 miles per hour.
Saturn's clouds are much more pale than those of Jupiter and are covered by a haze which obscures the formations and which hides the strong storm activity taking place on the surface. Astronomers have used special filters to see through the haze and have viewed close-up pictures taken by the two Voyager spacecraft of the clouds being whipped around by the strong winds on Saturn's surface.
The haze that conceals the planet's surface is one of the most interesting features of the clouds. When the Voyager 1 spacecraft passed by Saturn, its view of Saturn's cloud formations was much the Voyager 2 craft, which arrived nine months later. This suggests, astronomers say, that the transparency of the haze, composed largely of ammonia, varies over time. The clouds themselves are made up largely of crystallized, poisonous gases, like ammonia and methane.
Below the clouds storms swirl about, with winds whipping at over 1100 miles per hour. Many astronomers believe that no solid surface lies below the clouds and that Saturn is instead covered by a churning ocean of liquid hydrogen, presumably condensed under the great weight of the clouds. It core is believed to be a rocky, metallic one.
When Galileo first viewed Saturn through his low-powered telescope, he thought that there were two small globes on either side of the planet. In just 50 years, it was found that these two "globes" were in fact a flat ring around the planet that had appeared to be rounded only because of their tilt. Until the 1970's astronomers were confounded by why Saturn was the only planet with rings, but we know have confirmed the existence of rings around Jupiter and Uranus and strongly believe that there are rings around Neptune as well.
Photo. Saturn's rings at sunset. This is a rare, stunning photograph taken by the Hubble Space Telescope in November 1995. Usually, we see Saturn's rings fully illuminated, but here the Sun had set below the plane of the rings. Courtesy Space Telescope Science Institute, Phil Nicholson/Cornell University, Steve Larson/University of Arizona, NASA.
The Pioneer and Voyager spacecraft provided astronomers with the first close-up pictures of Saturn's rings. We now know that what appear as four or five rings through a high-powered, Earth-bound telescope are actually thousands of little ringlets that combine into several main rings, or "zones," that are identified by letter. The rings visible from Earth are actually the A, B and C zones, each of which is made up of many of these individual ringlets. With particles of ice that range in size from small grains to large boulders, the rings extend for some 46,000 miles. Even at this great distance, the rings are kept in place by the gravity that pulls objects towards the center of the planet. Though wide, the rings are only several miles thick -- a mystery that still perplexes astronomers today.
Though much was learned through the Voyager probes, many questions remain unanswered. Why are the rings so thin? Why are the rings grouped into certain zones? And above all, how did the rings themselves form? One leading theory proposed to answer the last question is the possibility that the rings are the remnants of a small satellite -- perhaps only 60 miles in diameter -- that smashed into the planet.