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
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
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.