Cassini's successful mission of exploration to the Saturn system is over, but planetary scientists are left with a cornucopia filled with important new information that Cassini/Huygens sent back to Earth before its mission ended. A collaborative NASA/European Space Agency/Italian Space Agency mission, the robotic spacecraft was made up of two components. The first was the European Space Agency's (ESA's) Huygens Probe, that had been named in honor of the Dutch mathematician and astronomer Christiaan Huygens (1629-1695), who discovered Titan. The Huygens Probe also closely observed Saturn's lovely system of gossamer rings. The second component, the NASA-designed Cassini Orbiter, was named after the Italian-French astronomer Giovanni Dominico Cassini (1625-1712), who discovered four of Saturn's other intriguing, numerous, and icy moons.
Enceladus: Enceladus has shown geysers of water that were confirmed by the Cassini spacecraft in 2005. Gravimetric data obtained from 2010 to 2011 confirmed the existence of a subsurface ocean. Even though originally it was thought to be localized, most likely in a region of the icy moon's southern hemisphere, evidence collected in 2015 indicates the subsurface ocean is actually global. Furthermore, in additon to water, these geysers from vents located near the south pole of Enceladus contain tiny quantities of salt, nitrogen, carbon dioxide, and volatile hydrocarbons. Tidal flux from Saturn is apparently responsible for the melting of the ocean water, as well as the geysers.
The twin spacecraft flew in an almost-circular orbit until the mission ended on December 17, 2012, when the probes were intentionally sent down to the lunar surface. NASA ultimately named the impact site in honor of the late astronaut Sally K. Ride, who was America's first woman in space and a member of the GRAIL mission team.