Why Does Saturn Have Rings Around It?

Dramatic image of Saturn.
Surely one of the most gorgeous sights the solar system has to offer, Saturn sits enveloped by the full splendor of its stately rings. NASA/JPL/Space Science Institute

Saturn's striking rings make it one of the most beautiful objects for stargazers to pick out in the skies. The magnificent ring system is visible even through a small telescope, although not with a great deal of detail. The best views have come from spacecraft, such as the Voyagers, and the Cassini missions. From these close encounters, planetary scientists have gained a great deal of information that helps illuminate the origin, motions, and evolution of Saturn's rings. 

Key Takeaways

  • Saturn's rings are made largely of ice, interspersed with dust particles. 
  • Saturn boasts six major ring systems, with divisions between them.
  • The rings may have formed when a small moon wandered too close to Saturn and broke into pieces, but particles may have come from stray comets or asteroids, too.
  • The rings are thought to be fairly young, only a few hundred million years old, and according to NASA, they could dissipate in the next hundred million years or so.

Through a telescope, the rings of Saturn almost look solid. Some early astronomers, such as Jean-Dominique Cassini, were able to identify what looked like "gaps" or breaks in the rings. The largest of these was named after the famed astronomer, the Cassini Division. At first, people thought the breaks were empty areas, but 20th-century spacecraft views showed them to be filled with material, too. 

How Many Rings Does Saturn Have?

There are six major ring regions. The main ones are the A, B, and C rings. The others, D (the closest one), E, F, and G are much fainter. A map of the rings shows them in the following order, starting at just above the surface of Saturn and moving outward: D, C, B, Cassini Division, A, F, G, and E (the most distant). There's also a so-called "Phoebe" ring that is the same distance as the moon Phoebe. The rings are named alphabetically according to the order in which they were discovered.

Diagram of Saturn's rings with labels.
This image made by the Cassini spacecraft captures nearly the entire ring system's various regions. NASA/JPL/Space Science Institute/Wikimedia Commons/Public Domain

The rings are broad and thin, with the widest extending up to 282,000 kilometers (175,000 miles) from the planet, but only a few tens of feet thick in most places. There are thousands of rings in the system, each made up of billions of bits of ice that orbit the planet. The ring particles are made largely of very pure water ice. Most pieces are fairly small, but some are the size of mountains or even small cities. We can see them from Earth because they're bright and reflect a lot of sunlight. 

Artist rendering of ring particles.
Artist's conception of clumping ring material in orbit around Saturn. Some ring particles are large while others are small. NASA/JPL/University of Colorado/Wikimedia Commons/Public Domain

Ring particles are kept in place by gravitational interactions with each other and with small moons embedded in the rings. These "shepherding satellites" ride herd on the ring particles.

How Saturn Got Its Rings

While scientists have always known that Saturn has rings, they do not know how long the rings have existed and when they came into being. There are two main theories.

Born This Way, Theory One

For many years, scientists assumed that the planet and its rings came into being early in the history of the solar system. They believed the rings were created from existing materials: dust particles, rocky asteroids, comets, and large ice boulders.

That theory held sway until the first spacecraft explorations made by the Voyager missions beginning in 1981. Images and data showed changes in the rings, even over short time periods. The Cassini Mission provided additional information that scientists are still analyzing, indicating that ring particles are lost over short time periods. Another clue about the age of the rings comes from the very pure water-ice makeup of the particles. Scientists argue that this means the rings are much, much younger than Saturn. Older ice particles would be darkened by dust over time. If that's true, then the rings we see now may not date back to Saturn's origins.

A Broken Moon, Theory Two

Alternatively, the current ring system might have been created when a moon the size of Mimas strayed too close to Saturn about 200 million years ago and broke apart, due to Saturn's immense gravity. The resulting pieces then would have fallen into orbit around Saturn, creating the rings we see today. It's possible that this moon breakup scenario has played out many times over the 4.5 billion year lifespan of the planet. The rings we see today are just the most recent set, according to this theory.

It's also possible that a very early "Titan-like" world could have been involved in the creation of the rings, forming a system much larger and more massive than the ones seen today.

Did You Know?

Saturn is not the only planet with rings. Giant Jupiter, mysterious Uranus, and chilly Neptune have them as well.

No matter how they formed, Saturn's rings continue to change over time, gaining material as smaller objects wander too close. Based on data collected during the Cassini mission, scientists think that the rings attract interplanetary dust, which helps replenish materials that are lost over time. Activity within the rings by the shepherding moons also causes changes in the rings.

Locating the propellers.
This collection of Cassini images provides context for understanding the location and scale of propeller-shaped features observed within Saturn's A ring. NASA/JPL/Space Science Institute/Wikimedia Commons/Public Domain

The Future of Saturn's Rings

Scientists have a number of theories on how the current rings might dissipate, but most agree they probably won't last very long. New rings would form only if something got close enough to get torn apart. Other smaller particles, while being herded by the nearby moons, might spread out to space and be lost to the system. As the moons themselves migrate outward, the ring particles they "herd" will spread out.

Particles could "rain" into Saturn, or dissipate to space. In addition, bombardment by and collisions with meteoroids could knock particles out of orbit. Over time, these actions could cause the rings to lose mass and eventually disappear completely. Cassini data point to the idea that the current rings might be a few hundred million years old at the very most. They may only last another hundred million years before dissipating to space or into the planet. That means Saturn's rings are ephemeral when compared to the planet itself, and that the planet could have had many sets of rings as smaller worlds wandered too close over Saturn's lifetime.

One thing scientists do agree on — time means different things for the lifetime of a planet, and we will be able to appreciate Saturn's stunning rings for many millennia more.

Sources

Grossman, Lisa. “Saturn's Rings Might Be Shredded Moons.” Science News for Students, January 24, 2018. 

"How thick are Saturn's rings?" Reference Desk, Hubblesite.

"Saturn." NASA, April 25, 2019.

Steigerwald, Bill. "NASA Research Reveals Saturn is Losing Its Rings at 'Worst-Case-Scenario' Rate." Nancy Jones, NASA, December 17, 2018, Greenbelt, Maryland.