With its famous rings, Saturn is the most distant planet clearly visible to the naked eye. But how did the rings get there and when were they formed? To study the planet in detail, scientists needed to get closer. So on 15 October 1997, the Cassini-Huygens spacecraft was launched.

The Cassini-Huygens is one of the most ambitious spacecraft ever launched, taking seven years to reach Saturn. The mission itself consists of two separate probes. The first is the enormous Cassini probe, designed to gather information about all aspects of the Saturnian system, from its many rings to its 33 moons. The second is the Huygens probe, a smaller wok-shaped craft, attached to the side of Cassini. Its task is to plunge through the atmosphere of Titan, Saturn’s largest and most mysterious moon.

The project is a joint NASA, European Space Agency (ESA) and Italian Space Agency venture. It has cost $3.27 billion and involves over 17 countries. It was inspired by another successful mission- the launch of the two Voyager Deep Space probes. These left Earth in 1977, and arrived separately at Saturn in 1980 and 1981. They sent back revolutionary data, changing what scientists thought about the Saturnian system.

They revealed that Saturn’s rings are far more complex and dynamic than any one had ever imagined. They also suggested that the rings had been formed after the planet itself. Why? And how old were they? But the Voyager probes had to move on, past Uranus and Neptune and beyond, leaving these fundamental questions about the rings unanswered.