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What lives in the seas of Enceladus? Despite 10 years orbiting Saturn’s icy moon and sampling the material gushing from its plumes, NASA’s Cassini spacecraft is far from having an answer. Now two proposed missions hope to change that by searching for life more directly.

Cassini has made a series of fly-bys through water-rich plumes erupting from deep inside the icy moon out of cracks in the surface. These have yielded tantalising clues that the ingredients for life might be buried there.

The subsurface ocean is probably an alkaline solution with a pH of 11 or 12, which could have been produced by water reacting with certain iron-rich types of rock – a process called serpentinisation. This creates hydrogen, a source of energy that is favourable for life and probably powered ancient life on Earth.

But despite focusing on these details during its most recent fly-by on 28 October, Cassini researchers haven’t been able to determine precise hydrogen levels because of complications in how the probe’s instruments take measurements.

The final fly-by on 19 December will offer more data, but it won’t be able to confirm whether microbes live in the salty sea: the instruments on board, designed more than 20 years ago, simply don’t have the capability.

That’s where the Enceladus Life Finder (ELF), proposed by Jonathan Lunine at Cornell University in Ithaca, New York, aims to step in. Equipped with better instruments, the solar-powered probe would follow in Cassini’s footsteps by flying through the plumes and building on what we already know.

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