"Cassini's seven-plus years... have shown us how beautifully dynamic and unexpected the Saturn system is," commented project scientist Dr. Linda Spilker of NASA's JPL to Time Magazine's online edition on March 23, 2012. Europa: Planetary scientists generally think that a layer of liquid water swirls around beneath Europa's surface, and that heat from tidal flexing causes the subsurface ocean to remain liquid. It is estimated that the outer crust of solid ice is about 6 to 19 miles thick, including a ductile "warm ice" layer that hints that the liquid ocean underneath may be 60 miles deep. This means that Europa's oceans would amount to slightly more than two times the volume of Earth's oceans. The findings of the two missions are presented in papers published on April 13, 2017, by planetary scientists with NASA's Cassini mission to Saturn and the venerable Hubble Space Telescope (HST). In one of the papers, Cassini scientists announced their discovery that a form of chemical energy life can feed on appears to exist on Enceladus. In the second paper, HST researchers report additional evidence of plumes erupting from Jupiter's moon, Europa, whose fascinating frozen crust of ice resembles a cracked eggshell. It has long been recognized by planetary scientists that beneath Europa's bizarre cracked shell of ice, there is a sloshing global ocean of liquid water.