Enceladus is ripe for life. In one final pass through the icy moon’s liquid plumes, NASA’s Cassini spacecraft found molecular hydrogen, which indicates favourable conditions for life in Enceladus’s subsurface sea.

For over a decade, Cassini has been exploring Saturn and its moons, sending back the best pictures and measurements we’ve ever had of the system. It dropped off the Huygens probe at hazy Titan, scrutinised the structure of Saturn’s rings, and revealed that Enceladus was much stranger than anyone expected.

Enceladus’s south pole has strange, warm fractures, and plumes of liquid water coming from an internal ocean many believed was impossible in such a small, cold world. The plumes also contain enticing compounds like organics and carbon dioxide, all necessary for life as we know it on Earth.

Those things represent tantalising hints of habitability. But there was no evidence for an energy source to feed potential life, until now. In extreme environments on Earth, hydrogen can play that role.

“What was missing to complete the story of habitability was an energy source,” says Chris McKay at NASA’s Ames Research Center in California. “This completes that story.”

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