Enceladus
Enceladus was discovered on August 28, 1789, by William Herschel. Little was known about it until the two Voyager spacecraft, Voyager 1 and Voyager 2, passed nearby in 1980 and 1981. In 2005, the Cassini spacecraft started multiple close flybys of Enceladu. In particular, Cassini discovered water-rich plumes venting from the south polar region.