Saturn

The most distant of the five planets known to the ancients, Saturn is one of the most beautiful and unique objects in the Solar System, due to its dramatic system of rings.

"I have observed the highest planet tri-form." -- Galileo, writing on Saturn

Saturn's Rings

These are swarms of small pieces of ice, from tiny grains up to boulders, each orbiting the planet. The structure in the rings comes from the gravitational influence of the many moons of Saturn, which pull these particles into different orbits, but the precise details are not completely understood.

Galileo was the first human to turn a telescope towards Saturn. The telescope was a new invention, and Galileo's instrument was not of the quality to discern more than, well, an odd appearance. He saw what he thought were "handles" around the planet. Observations of the rings were not correctly interpreted until 1655 by Christian Huygens.

Saturn is not the only planet with rings in our solar system, but the rings that have been found around Jupiter, Neptune and Uranus are very faint and are not nearly as striking as Saturn's.

The rings make fine viewing from Earth-based telescopes, but the best pictures come from space probes. The first to fly by was Pioneer 11 in 1979, followed by Voyager 1 and 2 in 1980 and 1981. In summer 2004 the Cassini-Huygens mission entered Saturn orbit for an extended survey of the planet, its rings and its moons.

Information about these missions can be found at the following websites:

Voyager 1 and 2
- NSSDC: Voyager Project Information :
  http://nssdc.gsfc.nasa.gov/planetary/voyager.html
- NASA/JPL Voyager Project Summary :
  http://www.solarviews.com/eng/vgrsat.htm
The Cassini-Huygens Mission
- Cassini-Huygens Mission to Saturn:
  http://saturn.jpl.nasa.gov/home/index.cfm
- Article from Astrobiology online magazine:
  http://www.astrobio.net/news/article849.html

Saturn's Composition

Saturn's atmosphere is mostly hydrogen and helium, with smaller quantities of ammonia, water and sulfur compounds. You can see stripes or bands in the outer atmosphere, which represent regions of different chemical composition and wind speed, which can reach 1000 mph. One reason for this extreme weather is that Saturn generates its own heat internally, and in fact it radiates more energy than it receives from sunlight. The heat is thought to come from a very slow collapse of the planet inwards, under its gravity. We don't know what the center of Saturn is like. Perhaps there is a core of rock, surrounded by hydrogen compressed to a liquid under intense pressure. Near the center, under extreme conditions, liquid hydrogen becomes an electrical conductor, like a molten metal, and its motion generates Saturn's powerful magnetic field.

Due to its fluid state and the speed of its spinning around its axis, Saturn does not look like a perfect sphere, but has a bit of a flattened appearance. Saturn also is the only planet with a density lighter than water. If there was a body of water big enough for the planet, it would float.

Saturn's Moons

We know of 31 moons orbiting Saturn, and likely more will be discovered. The largest is Titan, which could make a planet in its own right. It is larger than Mercury, and has its own hazy atmosphere of nitrogen and hydrocarbons. This is similar to what we think the early Earth's atmosphere was like, and study of Titan may give clues about the evolution of own atmosphere and the perhaps the origins of life. In January 2005 Cassini will land a probe on Titan, whose surface is invisible to us because of clouds of condensed methane.

Images used on this page are courtesy NASA/JPL-Caltech.