NASA has found hydrogen on Saturn's moon, Enceladus
Scientists found hydrogen around hydrothermal vents, similar to those found at the bottom of Earth’s oceans.
The “exciting” discovery was made after the Cassini space probe flew through spray bursting from Enceladus, one of Saturn’s 62 named moons.
Chris Glein, Cassini INMS team associate at SwRI, said he was hopeful organisms such as shrimp could be found at the bottom of the vents.
Chemical analysis of the plume suggested conditions favourable for methanogenesis – the generation of methane by microbes that use hydrogen and carbon dioxide to obtain energy.
On Earth, methane-making bugs flourish in the vicinity of hydrothermal vents, fissures in the ocean floor that gush water heated by volcanic activity.
Like Jupiter's moon Europa, Enceladus is believed to be surrounded by a global watery ocean covered by thick ice.
Beneath Enceladus' icy ocean surface there are thermal plumes, NASA found
In 2015, the American space agency's Cassini probe made a deep dive into a geyser-like plume of water and other material erupting from cracks in the south polar region of Enceladus.
The spacecraft's instruments registered molecular hydrogen and carbon dioxide, two ingredients critical for methanogenesis.
Hydrogen levels were high enough to imply a continual source, and were consistent with hydrothermal activity.
Writing in the journal Science, the US team led by Dr Hunter Waite, from the Southwest Research Institute in San Antonio, Texas, concluded: "Our analysis supports the feasibility of methanogenesis as an energy-releasing process that can occur over a wide range of geochemical conditions plausible for Enceladus' ocean."
However, the scientists pointed out that just because Enceladus has conditions suitable for methanogenesis, that does not prove anything is living there.
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Leading British expert Professor Andrew Coates, from University College London, said: "This is an exciting and remarkable result which shows that Enceladus may actually be habitable.
"We know that the four requirements for life as we know it are liquid water, the right chemistry, a source of energy and enough time for life to develop.
"But now, we know that three of the four conditions are there on Enceladus – and this distant moon now joins Mars and Europa as the best potential locations for life beyond Earth in our solar system."
David Rothery, Professor of Planetary Geosciences at the Open University, said: "Life has not been discovered on Enceladus, but we do now have the last piece of evidence needed to demonstrate that life is possible there."
Professor Jeffrey Kargel, from the University of Arizona, US, said: "As the authors model and describe, the hydrogen gas does indeed appear to be a tell-tale signature of hydrothermal activity occurring on the seafloor.
"This finding does not mean that life exists there, but it makes life more plausible and potentially quite abundant if a fraction of the hydrogen is used to drive biology. The combination of volatiles is extremely interesting with regard to potential biology.
"It's a very exciting finding."