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ScienceShot: Life on Enceladus?

Spouting plumes of ice and water vapor certainly make Enceladus one of the solar system's liveliest places. But continuing studies of the composition of those plumes are now making Saturn's icy moon the most promising place to look for extraterrestrial life. Researchers reported at a May meeting and online today in Nature that the best sampling yet of the plumes by the Cassini spacecraft reveals strong evidence for liquid water beneath the deeply frigid surface—an ocean, a sea, or at least water-filled cracks. Solid ice had been a contender to explain the gases and particles found in the plumes. But Cassini observations, including ever-rising estimates of the amount of heat given off by the moon, were challenging the ice-only source. Now analyses of Cassini data from a flyby through the heart of the plumes show that 99% of the mass of plume ice-particles is salt-rich. That alone strongly implies that the water in plume ice came from salty liquid water somewhere beneath the surface, say the researchers. Direct proof of a watery interior must likely await another mission, which may not come for decades.

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