The pioneer of astronomy Galileo first spotted Saturn's rings in 1610—and for the next 370 years, astronomers believed Saturn was the only ringed planet in our solar system.
In the years of exploration following, however, modern-day Galileos have discovered that Saturn is not alone. Telescopic observations of Uranus show rings orbiting its equator, and Voyager 1 revealed a bright, narrow ring around Jupiter.
Photographs from the Voyager missions have also multiplied the number of known rings around Saturn. Astronomers now estimate that 1,000 individual rings may be orbiting the planet. Even the apparent gaps in the rings, including the famous Cassini Division, are filled with narrow ringlets.
The photos of Jupiter's and Saturn's rings are both valuable scientific data and beautiful space art. Astronomers and astrophysicists continue to study information gathered by Voyagers 1 and 2 to learn more about these rings, and also well as the rings surrounding Uranus, which were discovered and studied when Voyager 2 flew past that planet in January 1986. These photos and drawings on these pages illustrated the majority of what we knew—or suspected—about the ring systems of these three outer planets up until the Cassini–Huygens reached Saturn in 2005.
Galileo saw Saturn's rings, but he thought they were attached to the planet, like handles on a sugar bowl. The changes in the rings observed by Galileo were the effect of viewing the rings from different angles as the Earth and Saturn both moved through their orbits.
How Big Are Saturn’s Rings?
If Saturn's rings are viewed edge-on, they seem to disappear. Estimates put their maximum thickness at 600 feet. The rings are more likely to be only 90 to 150 feet thick in most places. Compared to the distance across the entire main ring system—about 170,000 miles—this is extremely thin.
To get an idea of how thin the rings are, imagine that the main ring system is the size of a football field. At that scale, the rings would be about as thick as a single sheet of tissue paper.
What Are the Rings Made Of?
Saturn's rings don't really look like they do in the above picture. This image was made by a computer, using three separate black-and-white pictures taken through different colored filters (ultraviolet, clear, and green).
The purpose of creating this color picture was to find differences in material within the rings. The C-ring, which looks yellow in this photo, would look grey if you could see it with your own eyes. The color is very similar to that of dirty ice, which is probably what the rings are made of. The black spots in this photograph are reference marks that were made by Voyager's cameras.
The presence of different materials in the rings has led scientists to think that the rings were formed by two separate moons that disintegrated early in Saturn's history. Another theory suggests that the ring particles were leftover material that began to orbit Saturn when the solar system was formed.
Observing Saturn’s Rings
Much of our information about Saturn's rings comes from stellar occultation. During an occultation, a planet or satellite moves between the Earth (or observing spacecraft) and a distant star; The star is eclipsed, or occulted, and then reappears. The star appears to blink off and on. Occultations give valuable information on the diameter, orbit, and possible atmosphere of the planet or satellite. When Saturn's rings pass in front of a bright star, the star's light seems to become dimmer. By measuring the star's brightness before, during, and after occultation, scientists can estimate the thickness and density of the rings. Radio waves can also be used. When the Voyager spacecraft moved behind Saturn, their radio signal so dimmed as the waves passed through the ring material.
The spokes in Saturn's rings seem to appear where the rings emerge into daylight from the planet's shadow. This location is called the "ansa." Scientists do not know exactly how the spokes form, but the process is probably related to electrical and magnetic activity. At the ansa for Saturn's rings, scientists have detected radiation and sudden changes in the magnetic field; These may also be related to the formation of spokes in Saturn's rings.
Scientists think that the separation of the F-ring into smaller twisted strands of material with slightly different orbits may be caused by two "shepherding"” satellites. The shepherd moons closely follow the orbit of the rings; The gravitational attraction of the moons pulls some of the ring particles out of their main orbit. Computer models suggest the F-ring has a narrow core of marble-sized pieces of material. Outside this core, some F-ring particles may be as much as 6 miles across.
Researchers know very little about what the individual ring particles are like. Theories for behavior of the rings depend on the size, shape, and composition of these particles. Computer models are being used to figure out what types of particles form the rings around Saturn.
Computer models of Saturn's rings have given more clues about the sizes and shapes of the particles that form them. The smallest particles have diameters just a little thicker than a fingernail; much larger particles were also observed in the A-ring.
Other Ringed Planets
Scientists were surprised when Pioneer 11 data showed evidence of a ring around Jupiter. When the ring appeared in Voyager 1 photos, it was unexpectedly bright, probably due to sunlight bouncing off small ring particles. Some details in the pictures indicated that Jupiter's ring has structure like Saturn's rings, but the long exposures and spacecraft motion blurred the pictures. Researchers were able to "de-smear" some of the pictures, however, revealing that the structure does exist.
Astronomers were also surprised to discover the rings around Uranus in 1977. The rings seem to be as different from Saturn's as they could possibly be. Uranus's rings are narrow, elliptical ribbons of varying width, and they consist of black rock.
Scientists now know that Uranus has a total of nine rings, seven of which are tilted to the planet's equator. The maximum tilt of the rings creates a 30 mile offset from the other rings. Such a small irregularity is hard to measure in a ring system that is almost 1.8 billion miles away from Earth. The precise measurements are possible only through star occultations.
Traditional theories do not explain why some of Uranus's rings are tilted. One possible answer is that Uranus has shepherd satellites that orbit the planet in tilted orbits. The gravitational effects of these shepherds could help keep the ring particles in a tilted orbit also.
Saturn's rings are stunning, but they don't scrape the surface of the beauties to be seen in space. Explore Saturn along with the vast expanses of space through the eyes of great artists in The Art of Space: The History of Space Art, from the Earliest Visions to the Graphics of the Modern Era.
The Art of Space profiles the development of space-based art through various forms of media. Containing over 350 photorealistic images, the volume documents how artists worked with the knowledge and research available to portray space. Each chapter includes one profile of an artist or group of artists of particular influence and one sidebar discussion of general cultural topics.