The Huygens landing remains an amazing achievement, and long in the coming for those scientists like Jean-Pierre Lebreton who had been with the project since the 1980s. Of the pictures sent back by the camera, Roger Bonnet says: “When I saw the first images of 'rivers' on this moon of Saturn, I said: 'My goodness. We promised that, and we got it'.” Other onboard experiments profiled the atmosphere, including its temperature, pressure, density and composition, as well as wind strength and direction. In addition, the probe carried a CD-Rom with drawings, paintings, messages and poems from people around the world. It also carried music created specially for the disc by two French musicians. “Huygens is still sitting quietly on Titan's surface waiting for Nasa and Esa to recover the CD,” says Dr Bonnet, although this isn’t likely to happen for decades or even centuries.

One of the two data discs

(Nasa)

This was mirrored by Nasa’s decision to attach a DVD to Cassini carrying the signatures of 616,400 people from 81 countries. The signatures had been scanned from postcards and letters containing messages of support sent to Nasa. The effort was described as a “message in a bottle” to Saturn. While Huygens provided ground truth, Cassini's radar was able to peer through Titan's clouds from further away. This revealed a world with its own seasonal cycle, where wind and rain shaped the surface to form river channels, seas, dunes and shorelines.

A false-colour mosaic of Titan made from infrared data - revealing differences in the composition of surface materials around hydrocarbon lakes

(Nasa)

Titan is a mind-bending, through-the-looking-glass version of Earth. The average temperature of -179C means that mountains are made of ice, sand is made of plastic and liquid methane assumes many of the roles played by water on Earth. Around Titan's northern pole are three dark methane seas, the largest of which is bigger than Lake Superior in North America. Cassini even resolved gentle (2cm-high) waves and the glint of sunlight reflecting off liquid hydrocarbons. “The orbiter and the probe really provided a very complementary data-set. They will surely be used for the next 20 years - maybe the next 50,” says Dr Lebreton. Cassini's looping, elliptical orbit around Saturn was carefully choreographed to enable multiple close flybys of Saturn's many moons. “Because Saturn's such a rich system, one instrument will want to look one place, another instrument will want to look another,” says Earl Maize. “It's taken an awful lot of human engineering to integrate all those different scientific objectives into one seamless series of activities.” During its tour of Saturn, Cassini made a total of 127 close passes of Titan during its mission and 22 of an icy saturnian moon called Enceladus. It was undoubtedly Enceladus that served up the biggest surprise of the mission. Pictures from Voyager 2 revealed a smooth, crater-less surface, hinting at some ongoing geological activity. But Cassini’s instruments detected jets of icy particles gushing out into space from fissures at the south pole known as “tiger stripes”. What's more, scientists showed that these jets of water were coming from a deep global ocean beneath the outer shell. “Cassini has been the validation of the theory that you can make liquid water beneath an icy crust even though you are very far from the Sun,” says Nicolas Altobelli, Esa's Cassini project scientist. Cassini even flew through Enceladus' plumes and used one of its instruments to “taste” what was in it. “It's got organic material in it, and a variety of rocky dust,” says Jim Green. “That tells us that underneath that ice crust, water is being heated just like the hydrothermal vents heating oceans on Earth.”

Cassini's view of the icy crust on Enceladus

(Nasa)

All of this suggested Enceladus could be one of the best targets in our Solar System to look for extra-terrestrial life. Indeed, the decision to destroy Cassini is in part because Nasa can't risk the orbiter one day crashing into moons like Enceladus and contaminating them with terrestrial microbes. As for Saturn itself, Jim Green explains: “It looks a lot like Jupiter in many ways - it’s mostly hydrogen and helium – and there are huge storms that we don’t quite understand the origin of.” The huge storm at Saturn’s north pole is surrounded by a unique six-sided jet stream known as “the hexagon”.

False-colour image of a giant spinning storm at Saturn's north pole - it resembles a deep red rose

(Nasa)

Wider view of Saturn's north pole showing the hexagon-shaped jet stream

(Nasa)

And then there are those majestic pieces of planetary ornamentation - the rings. How and when the rings formed remains one of the giant planet's biggest mysteries.

Cassini's view of Saturn's spiralling rings

(Nasa)