The Cassini mission to Saturn is one of the most ambitious efforts in planetary space exploration ever mounted. A joint endeavor of NASA, the European Space Agency (ESA) and the Italian space agency, Agenzia Spaziale Italiana (ASI), Cassini is a sophisticated robotic spacecraft orbiting the ringed planet and studying the Saturnian system in detail. Cassini also carried a probe called Huygens, which parachuted to the surface of Saturn's largest moon, Titan, in January 2005 and returned spectacular results. After two decades in space, NASA's Cassini spacecraft is nearing the end of its remarkable journey of exploration. Having expended almost every bit of the rocket propellant it carried to Saturn, operators are deliberately plunging Cassini into the planet to ensure Saturn's moons will remain pristine for future exploration.