Short answers, pulled from the story.
Enceladus was discovered by William Herschel on the 28th of August 1789, during the first use of his new 1.2 m telescope at Observatory House in Slough, England. The moon was observed during a Saturnian equinox, when Earth is within Saturn's ring plane and the rings' glare is reduced enough to spot faint moons nearby.
Enceladus has a global subsurface ocean approximately 26 to 31 km deep, an energy source from hydrothermal activity, complex organic molecules including hydrogen cyanide and nitrogen-bearing amines, and phosphates, completing the basic chemical ingredients for life. Molecular hydrogen detected in the plumes is consistent with hydrothermal reactions that on Earth underpin the process known as methanogenesis.
The tiger stripes are four fractures bounded by ridges near Enceladus's south pole. They are surrounded by coarse-grained crystalline water ice that may be less than 1,000 years old. The fissures are the source of Enceladus's geysers, which open and close as Saturn's tidal forces alternately compress and stretch them during each orbit.
Enceladus's geysers expel roughly 200 kg of material per second into space, including water vapour, molecular hydrogen, sodium chloride crystals, ice particles, and organic molecules. Jets move at speeds up to 2,189 km/h, and more than 100 individual geysers have been identified.
Enceladus is the primary source of material in Saturn's E ring. Water vapour and ice particles ejected by Enceladus's south polar geysers escape into space and replenish the ring continuously. Mathematical models show the E ring is unstable with a lifespan between 10,000 and 1 million years, so it requires constant replenishment, which Cassini confirmed Enceladus provides.
The 2022 Planetary Science Decadal Survey recommended the Enceladus Orbilander, a roughly 5 billion dollar NASA flagship mission designed to orbit Enceladus for eighteen months before landing for two Earth years of astrobiology research. In 2024, ESA named a mission to Enceladus its top priority, designating the L4 orbiter-lander for proposed launch in 2042 and arrival in 2053.