Launched in 1997 from Cape Canaveral in Florida, the C assini s pacecraft, with the Huygens probe on board, began a journey to Saturn that would cover over 2 billion miles (3.5 billion kilometers). The objectives of the Cassini-Huygens mission are to analyze the composition and atmosphere of Saturn, investigate Saturn's rings and several of its moons, and study the planet's magnetosphere - the region of space that's influenced by Saturn’s magnetic field.

To fulfill its scientific objectives, Cassini carries two groups of complex instruments. The first consists of remote sensing devices, including visible light and infrared cameras. The second contains instruments that will directly investigate charged particles and magnetic fields.

On June 11, 2004, Cassini came within about 1,200 miles (2,000 kilometers) of Phoebe, the largest of Saturn's outermost moons. An analysis of the data gathered during the flyby has led scientists to conclude that Phoebe is a relic from more than four billion years ago. This little moon seems to have been one of the abundant icy planetesimals (small bodies) that helped form the giant outer planets.

Cassini began orbiting Saturn on July 1, 2004, Universal Time (June 30 in U.S. time zones). The orbiter is expected to circle Saturn more than seventy times during the next four years, transmitting a wealth of information to Earth daily.

In December 2004, Huygens separated from Cassini and begin coasting toward Titan, Saturn's largest moon and the only moon in the solar system that has an atmosphere. Huygens entered Titan's atmosphere in January 2005 and gathered a variety of atmospheric data before landing on the moon's surface. [See Updates to find out what sceintists learned from the remarkable Huygens mission.]

The orbiter is named for Jean-Dominique (or Giovanni Domenico) Cassini (1625-1712), a French-Italian astronomer who discovered four of Saturn's moons and a gap in the ring system known as the Cassini division. The probe honors Dutch scientist Christiaan Huygens (1629-1695), who correctly theorized that Saturn was surrounded by rings and also discovered Titan.

This mission represents a major collaborative effort between three international space agencies and many countries. The Cassini orbiter was built and managed by NASA's Jet Propulsion Laboratory, the Huygens probe was constructed by the European Space Agency, and the Agenzia Spaziale Italiana (the Italian Space agency) supplied Cassini 's high-gain communications antenna. In addition, seventeen nations helped build the spacecraft, and hundreds of scientists worldwide are evaluating the data sent back to Earth.