Enceladus
Hydrothermal vents

On April 13, 2017, NASA announced the discovery of possible hydrothermal activity on Enceladus's sub-surface ocean floor. In 2015, the Cassini probe made a close fly-by of Enceladus's south pole, flying within 48.3 km (30.0 mi) of the surface, as well as through a plume in the process. A mass spectrometer on the craft detected molecular hydrogen (H) from the plume, and after months of analysis, the conclusion was made that the hydrogen was most likely the result of hydrothermal activity beneath the surface. It has been speculated that such activity could be a potential oasis of habitability.

The presence of ample hydrogen in Enceladus's ocean means that microbes – if any exist there – could use it to obtain energy by combining the hydrogen with carbon dioxide dissolved in the water. The chemical reaction is known as " methanogenesis " because it produces methane as a byproduct, and is at the root of the tree of life on Earth, the birthplace of all life that is known to exist.
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