Vapor plumes emerging through cracks in the icy shell of Saturn’s moon Enceladus contain abundant molecular hydrogen, a finding that has surprised scientists and could indicate the presence of microbial life in the moon’s subsurface ocean.
Molecular hydrogen is a source of fuel for microbial life. Scientists did not expect to find a lot of it on Enceladus because the moon is too small for its gravity field to trap large hydrogen reserves, noted Cassini co-investigator Scott Bolton, who is also co-author of a study on the findings published in Science magazine.
Bolton and his research team believe the molecular hydrogen is being produced by a process much like the hydrothermal activity in Earth’s oceans through which hydrogen is released.
Hydrothermal vents on Earth release either black or white “smoke” beneath the oceans via the interaction between iron-rich materials and water. In addition to releasing hydrogen, this process also forms new minerals.
Whether the “smoke” is black or white depends on its sulfur content.
“The idea that we’ve proposed–and we’ve researched a lot of different ideas trying to come up with an alternative theory–is that actually there’s hydrothermal activity going on deep in the ocean on Enceladus, and it may be producing white and black smokers, kind of like what we see on Earth,” Bolton said.
“In other words, under the deep sea, the water meets rock, and some chemistry occurs, and hydrogen is released.”
Based on data sent back by NASA’s Cassini Saturn orbiter, scientists know Enceladus’ subsurface ocean sits on top of a rocky core, meaning similar interactions could be occurring there.
Hydrothermal vents hosted some of the earliest life on Earth, and scientists continue to discover new species inside them that do not require sunlight as an energy source because they feed off the hydrogen instead.
By flying a probe through Enceladus’ plumes, scientists would be able to determine whether amino acids and even microbes are present in the waters that make up the plumes.
While no such mission is yet being planned, NASA’s Europa Clipper, scheduled for a 2020s launch, may fly through similar plumes emerging from that moon, first imaged by the Hubble Space Telescope.
Like Enceladus, Jupiter’s moon Europa contains a subsurface salty ocean beneath its icy crust.