THE EXPLORATION OF SATURN

Saturn was first observed using a telescope by Galileo in the early 17th century. The first spacecraft to visit Saturn was Pioneer 11 that flew within 3,500 kilometres of the outer edge of Saturn’s A ring. Pioneer 11 gathered significant new data about Saturn’s complex magnetic field.

The Voyager spacecraft returned high quality pictures that reveal the complex structure of Saturn’s rings, with each of the major rings made up of a numerous minor rings. Sequences of pictures taken by Voyager showed winds travelling at 1,500 kilometres an hour; several times faster than winds on Jupiter.

Some of the most dramatic results of the Voyagers’ visit to Saturn came from pictures revealing the great diversity of the surfaces of Saturn’s major moons. Saturn has 19 known moons ranging in size from 15 kilometres across up to Titan; larger than Mercury, with a radius of 2,575 kilometres.

Before the Voyager mission it was assumed that the surfaces of Mimas and Enceladus were very similar. In fact they represent two extremes with Mimas’ cratered surface to be as old as the formation of the moon and Enceladus to have a much younger, geologically active surface.

Voyager views of Tethys reveal the huge 1,000 kilometre Ithaca chasm that runs round 75% of the moon and a 400 kilometre impact crater (Ulysses) that covers 40% of its surface.

Apart from Titan, Rhea and Iapetus are the two largest moons of Saturn. Although similar in size these two moons show distinct differences with Rhea’s surface dominated by heavily worn craters similar to those on Earth’s Moon and Iapetus with dark material that my have erupted from the interior.

It was hoped that Voyager might find a break in the cloud cover of Saturn’s largest moon, Titan, to provide a glimpse of the surface. This did not occur and the Voyager pictures of Titan show only a uniform layer of photochemical smog.

Future exploration

The joint ESA/NASA Cassini mission was launched on 15 October 1997 and is scheduled to arrive at Saturn on 1 July 2004. Weighing over six tons, the Cassini spacecraft is the largest ever launched by NASA. After 4 months in orbit around Saturn, Cassini will launch the Huygens Titan probe that during its three hour descent will study the atmosphere and after touch down, the surface of this largely unexplored moon.