Shop Windows to the Universe

The Winter 2010 issue of The Earth Scientist includes a variety of educational resources, ranging from astronomy to glaciers. Check out the other publications and classroom materials in our online store.
This image shows the different rings of Saturn. The dotted lines represent the paths of Saturn's moons.
Click on image for full size
Windows to the Universe original image

Ring Structure of Saturn

We have a lot to learn before we fully understand planetary rings. Saturn's rings are the brightest and therefore more famous than Jupiter's and Uranus' rings. The total number of rings is seven, and each one was given a letter between A and G for its name. Three of the rings, A, B and C, are visible from Earth with a telescope.

Saturn's rings were first discovered by Galileo in the 1600's, although at the time he didn't know what they were. In 1655, the astronomer Christian Huygens predicted that Galileo had seen rings. Later on, more powerful telescopes proved Huygens right.

In 1675, a scientist named Cassini found what appeared to be a gap between the A and B rings. This gap was later called the Cassini division. In the 1800's a third, faint ring was found and named C. It wasn't until 1979 that we found the E, F, and G rings, when the Pioneer 11 and Voyager spacecrafts flew by Saturn. They also found a smaller gap between the A and F rings, called the Encke division.

These rings still remain somewhat of a mystery to scientists. We now know that Saturn's gravity keeps the small particles that make up the rings in place. It also prevents the chunks of ice and rock from combining to form moons. Every planet has something called a Roche limit, which is a specific distance away from the planet. Depending on the planet's gravitational force, anything inside the limit can't combine to create larger objects. That is why the rock particles are mostly a few centimeters in size. However, most of Saturn's moons are outside of the Roche limit, which is why they stay together.

Two of Saturn's moons, Prometheus and Pandora, are called shepherd satellites. They are both tiny moons located on either side of the F ring. They work against each other, pushing the particles inside the F ring towards the middle of the ring. The result is a small, compact F ring.

An enormous new "ring" was discovered in 2009. The tenuous Phoebe Ring is about 100 times larger than the main ring system. The ice and dust in the ring apparently comes from the odd moon Phoebe, and may cause the strange coloration of the surface of Iapetus.

Last modified October 9, 2009 by Randy Russell.

Shop Windows to the Universe Science Store!

Our online store includes issues of NESTA's quarterly journal, The Earth Scientist, full of classroom activities on different topics in Earth and space science, ranging from seismology, rocks and minerals, oceanography, and Earth system science to astronomy!

Windows to the Universe Community



You might also be interested in:

Cool It! Game

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Galileo Discovers Origin of Jupiter's Rings

Scientists recently discovered the origin of Jupiter's rings. With the help of the Galileo spacecraft, it has been deduced that the rings are made from dust and debris that was kicked off of the small...more


The rare geometric arrangement of planets Jupiter, Saturn, Uranus, and Neptune in the 1980's made it possible for the Voyager spacecrafts to visit them over a 12 year span instead of the normal 30. They...more

The Phoebe Ring Around Saturn

The Phoebe Ring is much larger than Saturn's other rings. Saturn's main ring system starts a few thousand kilometers above the top of Saturn's atmosphere and extends outward a few hundred thousand kilometers....more

Saturn's Rings

Many people are fascinated by Saturn's rings. Although Saturn isn't the only planet with rings, it is the only planet famous for them. Almost every image or drawing of the planet has the rings included....more


The Cassini probe began its journey to Saturn on October 15, 1997. It flew by Earth in August, 1999, before heading towards the distant planet. Cassini passed Jupiter in 2000 and then burned towards its...more

Cassini arrives at Saturn

The Cassini spacecraft will arrive at Saturn on June 30, 2004. Cassini's engine will make a critical 96-minute burn starting at 7:36 p.m. Pacific Time (10:36 p.m. EDT) on June 30. The burn will slow Cassini...more


Pandora is a small moon of Saturn. It was discovered by S. Collins and others in 1980 from photos taken by the Voyager 1 spacecraft. Pandora's name comes from Greek mythology. Pandora was the first woman,...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA