April 13, 2017
NASA's Cassini spacecraft discovered hydrogen in the plume of gas and icy particles spraying from Saturn's moon Enceladus. The discovery means the small, icy moon — which has a global ocean under its surface — has a source of chemical energy that could be useful for microbes, if any exist there. The finding also provides further evidence that warm, mineral-laden water is pouring into the ocean from vents in the seafloor. On Earth, such hydrothermal vents support thriving communities of life in complete isolation from sunlight. Enceladus now appears likely to have all three of the ingredients scientists think life needs: liquid water, a source of energy (like sunlight or chemical energy), and the right chemical ingredients (like carbon, hydrogen, nitrogen, oxygen).
Cassini is not able to detect life, and has found no evidence that Enceladus is inhabited. But if life is there, that means life is probably common throughout the cosmos; if life has not evolved there, it would suggest life is probably more complicated or unlikely than we have thought. Either way the implications are profound. Future missions to this icy moon may shed light on its habitability.
White smoker video courtesy of: NOAA-OER / C.German (WHOI)
Ingredients for Life at Enceladus
In 2015 NASA's Cassini spacecraft made the deepest dive ever through a plume of gas and ice spraying from the south pole of Saturn's moon Enceladus. A Cassini science instrument "sniffed" the plume and detected hydrogen.
Hunter Waite, Ion and Neutral Mass Spectrometer Team Lead, Southwest Research Institute: “The instrument acts like a human nose, analyzing the smell, so to speak, or the composition of the gases in the environment. There was a significant amount of molecular hydrogen.”
What makes this hydrogen important?
Waite: “The existence of molecular hydrogen, at least within the Earth's ocean system, is a... like a food source. It's candy for microbes. They eat the hydrogen; they turn it into methane. And with our findings we were able to not only find out that there was H2 in the system, but to examine the chemistry that's associated with that process of taking hydrogen and turning it into methane.”
Cassini previously discovered there's a salty, global ocean under Enceladus' icy crust and that hot ocean water was coming into contact with a rocky sea floor.
Waite: “Here on Earth the hydrothermal systems known as white smokers have water-rock interactions that lead to the release of molecular hydrogen in a similar fashion to, apparently, what's going on at Enceladus.”
Life requires three primary ingredients:
Source of energy.
Right chemical ingredients.
Waite: “This is just the final step that shows that there's molecular hydrogen being produced by these same hydrothermal processes. And that molecular hydrogen has the chemical energy to support microbial systems in the interior ocean. It's not demonstration of finding life, but it shows the potential for the existence of life in this interior ocean.”