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The researchers also uncovered evidence that the ocean, which is hiding below the moon’s icy outer shell and supplies the plume, holds a powerful source of chemical energy. Unidentified until now, the energy source is in the form of several organic compounds, some of which, on Earth, serve as fuel for organisms.
The findings, published on December 14, in Nature Astronomy, indicate there may be much more chemical energy inside this tiny moon than previously thought. The more energy available, the more likely that life might proliferate and be sustained.
“Our work provides further evidence that Enceladus is host to some of the most important molecules for both creating the building blocks of life and for sustaining that life through metabolic reactions,” said lead author Jonah Peter, a doctoral student at Harvard University who performed much of the research while working at NASA’s Jet Propulsion Laboratory in Southern California. “Not only does Enceladus seem to meet the basic requirements for habitability, we now have an idea about how complex biomolecules could form there, and what sort of chemical pathways might be involved.”
Versatile and Energetic
“The discovery of hydrogen cyanide was particularly exciting, because it’s the starting point for most theories on the origin of life,” Peter said. Life as we know it requires building blocks, such as
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“The more we tried to poke holes in our results by testing alternative models,” Peter added, “the stronger the evidence became. Eventually, it became clear that there is no way to match the plume composition without including hydrogen cyanide.”
In 2017, scientists found evidence at Enceladus of chemistry that could help sustain life, if present, in its ocean. The combination of carbon dioxide, methane, and hydrogen in the plume was suggestive of methanogenesis, a metabolic process that produces methane. Methanogenesis is widespread on Earth, and may have been critical to the origin of life on our planet.
The new work uncovers evidence for additional energy chemical sources far more powerful and diverse than the making of methane: The authors found an array of organic compounds that were oxidized, indicating to scientists that there are many chemical pathways to potentially sustain life in Enceladus’ subsurface ocean. That’s because oxidation helps drive the release of chemical energy.
“If methanogenesis is like a small watch battery, in terms of energy, then our results suggest the ocean of Enceladus might offer something more akin to a car battery, capable of providing a large amount of energy to any life that might be present,” said