Cassini has had an impressive journey since its launch in 1997. During its journey to Saturn, it made two Venus flybys and an Earth-Moon flyby, and then swung by Jupiter. Cassini didn’t even wait to go into orbit around Saturn before beginning observations that led to the discovery of two new moons and some initial close-ups of Saturn’s storms. Now the Cassini Grand Finale is set to begin on April 26 and end with a plunge into Saturn’s atmosphere on September 15.
As impressively, Cassini has been making close flybys of the Mercury-sized moon, Titan, and released the Huygens probe, which made observations of Titan’s nitrogen atmosphere and sent back images of the surface that had been previously hidden by Titan’s thick cloud cover.
Other notable discoveries include the possibility of a liquid salt water ocean under Enceladus’ icy surface and Enceladus’ contribution to Saturn’s E ring in the form of icy material from vents that indicate hydrothermal activity under the moon’s surface. Cassini has also observed Saturn’s jet streams, storms, radio, and plasma waves in ways that would have been impossible from Earth. Its most famous Saturn observation is a hexagon on this planet’s north pole that is the result of jet stream activity. The hexagon was first observed by the Voyager probes, but Cassini revealed that it is a long-lived phenomenon.
It took Cassini a while to spot lightning on Saturn during the day. Night observations of lightning was a little easier, but not by much because Saturn’s night never gets very dark. When it did finally spot lightning during the day, the observation was made during a “seasonal” megastorm that began in December 2010. These megastorms occur every 28 to 30 Earth years and can last for up to 2/3 of an Earth year and can produce lightning that is as powerful as the most powerful lightning that Earth storm’s produce.
Cassini has been orbiting Saturn since the summer of 2004 and has been through two mission extensions since then. Now the probe is beginning to run low on fuel and NASA has planned the Cassini Grand Finale as a way of ensuring that the probe won’t inadvertently damage Saturn’s moons. The probe will make its final close flyby of Titan on April 22 and begin a series of close orbits that take it between Saturn and its innermost rings on April 26. The Cassini team hopes that it will make as many as 22 of these close orbits and take readings that will help scientists improve their understanding of the evolution of worlds like Saturn and their systems. Then it will begin its plunge into Saturn’s atmosphere on September 15, hopefully sending back as much data as possible before it is crushed by the pressures under the surface of Saturn’s atmosphere.