Saturn – Then & Now

The View from Galileo’s Telescope

Galileo first observed Saturn through his telescope in July, 1610. He had already announced his discovery of the moons of Jupiter, but Saturn, the furthest planet then known and twice as far away as Jupiter, was even more mysterious and difficult to understand. To Galileo’s surprise, Saturn wasn’t just one planet, but three! A big middle planet with a small planet or moon on each side, and the three were almost touching. Galileo drew it like this:

Other astronomers, whose telescopes were not as good as Galileo’s, saw a single oval planet. After a few years, Galileo again studied Saturn, and in 1616 made this sketch:

Above: Galileo’s sketch of Saturn from 1616. Does it look like a ring to you? . (Image credit: Albert Van Helden/Science History Publications Ltd.)

Galileo described the appearance as a planet with handles. How would you describe the planet in his sketch? Although we can easily make out the appearance of a ring, Neither Galileo nor fellow astronomers guessed that Saturn’s shape was due to a ring. Theories of handles and ovals and triple planets lasted another 40 years, until Dutch astronomer Christian Huygens finally discovered the rings of Saturn.

What did YOU See with MicroObservatory?

How does Saturn appear in your image taken by MicroObservatory? Can you tell that the planet has rings or, like Galileo, can you imagine them more as handles, or even a triple planet? To see your image of Saturn more clearly, you may want to open it in our MicroObservatory image processing software.

Above: Archive MicroObservatory image of Saturn. Do you see rings or handles?

Saturn – 400 Years Later

Saturn has been explored by four NASA spacecraft since 1979, and close-up views of the rings have shown how complex and spectacular they are. We now know that the rings are made up of billions of particles of ice and rock, varying in size between a few centimeters to a few meters. Despite the fact that the rings are 250,000km across (Ring-tip to ring-tip would stretch from the Earth to the Moon!) the rings are less than a kilometer thick, and in some places much thinner. The brightness of the rings depends on their thickness, and also how big the ring material particles are. This image from the Cassini probe shows the amazing structure and variation in the rings.

Above: An eclipse of the Sun – by Saturn! This was taken by the Cassini spacecraft as it passed around the night side of the planet. (Image credit: JPL/NASA)

The rings of Saturn seem to be held in place by many tiny moons, called Shepherding moons, which use their gravity to shape and redistribute the ring material. It is still not clear how the rings were made, or how old they are, but it is probable that the ring material needs to be replenished or the rings will fade over millions of years. The new material could come from the dozens of moons in Saturn’s family, when collisions or meteorite impacts throw clouds of rock and ice into space.

Find Out More

2009 is International Year of Astronomy, chosen to commemorate the 400^th anniversary of Galileo’s discoveries with the telescope. Find out what else is happening by visiting these web sites:

The World site for International Year of Astronomy.

The United States national site for International Year of Astronomy.

NASA’s International Year of Astronomy website.

For more information on the Cassini Mission, go to:

http://saturn.jpl.nasa.gov/home/index.cfm/

For more information on the planets of the Solar System, go to:

http://solarsystem.nasa.gov/planets/index.cfm

The space probes that have visited Saturn are Pioneer 11 (1979), Voyager 1 (1980), Voyager 2 (1981) and Cassini-Huygens (2004). To read about all NASA’s missions, go to http://www.nasa.gov/missions/index.html

Take a look at the full list of objects in MicroObservatory’s Galileo activity, and see how our understanding has evolved over the last four centuries.