Awesome in its power and beauty, the planet Saturn has gripped the collective imagination of humankind from the day of its discovery, but its extraordinary remoteness has made it inaccessible to telescopes on Earth. Two decades ago, a team led by the Jet Propulsion Laboratory in Pasadena, California, started planning the mission that changed that. 7 years and 2.2 billion miles in transit to Saturn, the spacecraft Cassini arrived in July 2004 for a four-year tour to observe the planet in depth. On board was a probe developed by the European Space Agency, which descended through the thick atmosphere on Saturn's largest moon, Titan, sending back the first photographs of a distant world. Images of astounding beauty and enough data to keep hundreds of scientists engrossed for decades have since come streaming back to Earth. Cassini has recorded supercharged storm systems, hurricane-force jet streams and more than forty battered and frozen moons.