Homepage Educators and Developers Homepage

Discussion questions

All about Star Witness icon

Star Witness news stories

> Closing in on Saturn's Rings

AUG. 2004

Closing in on Saturn's Rings


Saturn's ringed world
As viewed by Hubble from a billion miles away

Hundreds of years before telescopes were invented, ancient sky watchers were gazing into the night sky to view Saturn, which shines more brightly than most of the stars in the sky. But it was not until Galileo pointed his telescope at Saturn in 1610 that those famous "hula-hoop" rings were seen.

Although Galileo saw the rings, he did not know what they were. He thought the rings were two moons, one on each side of the planet. These "moons" seemed to play "hide-and-seek" with him, appearing and disappearing over several years of observations.

Dutch astronomer Christiaan Huygens solved the mystery in the 1650s. In his book, Huygens described Saturn as being "surrounded by a thin flat ring." The discovery of Saturn's mysterious ring system led to a rush of observations of the planet during Huygens' time.

Saturn's unique rings

Today, astronomers are still studying Saturn, the sixth planet from the Sun, in an attempt to understand the planet and its ring system. After hundreds of years of Saturn watching, there is still much information that astronomers do not know about the planet and its signature rings.

Other planets have rings, but they are so faint that we cannot easily see them. Saturn's rings stand out because they are very bright and contain lots of material. Their brightness is due to their makeup. The rings are made of icy material that reflects sunlight, just as ice does on Earth.

A popular destination spot

Saturn and its ring system are so special that three spacecraft have visited the planet over the past 30 years to take some close-up views. None of the spacecraft, however, has landed on the ringed planet. Saturn, like Jupiter, is a gas giant and does not have a solid surface.


A first portrait:
Pioneer 11's view from about 585,000 miles away

The first spacecraft to fly by Saturn was Pioneer 11 in the late 1970s. In the early 1980s, Voyager 1 and 2 flew by the ringed planet. Even the Earth-orbiting Hubble Space Telescope has been "eyeing" the planet, snapping several spectacular pictures since its launch in 1990.

Finding the keys to the rings

Observations from Hubble, the three spacecraft, and many ground-based telescopes have yielded valuable information about Saturn and its famous rings. The planet's ring system is made up of about 10,000 rings, called ringlets. The ring system is about 175,000 miles (280,000 km) across, yet only about half a mile (1 km) thick. These measurements may seem very large, but remember, the rings orbit a huge planet. So, compared with Saturn's size, the rings appear paper-thin.

The rings are not made up of solid sheets of material. Astronomers believe the rings are made of pieces of dusty water ice, which range in size from dust grains to boulders. These particles gently collide with each other as they go around Saturn. The rings orbit Saturn just as our Moon goes around the Earth. If our Moon broke apart, the pieces would form a ring around our planet. The collisions between the ring particles are what make the ring system so thin.

And now … ringside seats


Cassini's views:
Taken while orbiting Saturn

Although astronomers have spent about 400 years looking at Saturn, they do not know everything about its ring system. Now a new spacecraft designed to study Saturn, its moons, and its complex ring system has settled into orbit around the planet. Named Cassini, for the Italian astronomer who studied the planet in the late 1600s, the spacecraft spent nearly seven years traveling to Saturn.

On July 1, 2004, the seasoned traveler finally arrived. The spacecraft flew through the faint, wispy outer rings and settled into orbit around the second largest planet in the solar system. It will spend four years studying the planet. Scientists hope Cassini will help explain how and when Saturn's rings were formed, why there are gaps between the rings, and even why Saturn has such a spectacular ring system.


The Star Witness

brings you "tele-scoops" from the Hubble Space Telescope