The ice volcanoes of Saturn’s moon Enceladus erupt in ice plumes—but could the chemical makeup of these plumes mean there is actually something swimming in the vast subsurface oceans of the frozen moon?
Saturn orbiter Cassini discovered evidence of molecular hydrogen, or H2, inside one of those ice plumes on its last flyby of Enceladus. The find was explosive enough to be published in the journal Science by Cassini scientist Hunter Waite and his colleagues at the Southwest Research Institute in San Antonio. The spacecraft’s find means that the H2 is probably the result of endless hydrothermal reactions going on under the ice. When hot water interacts with rock in which reduced and organic minerals are embedded, the reaction creates what could be a feeding frenzy for potential alien microbes.
Don’t say “Aliens!”—yet. Molecular hydrogen spewing from the watery depths of Enceladus doesn’t necessarily equate to some strange and unknown form of extraterrestrial life, but is rather an indicator for the possibility of life.
“The fact that there is molecular hydrogen there — and a lot of it — can be interpreted in two different ways with regard to life,” explained Waite. “One is that there is so much hydrogen because there are no microbes there to eat it... The more positive way is that there is H2 there, there is plenty of food for them, but there’s probably some other limiting growth factor so that there is excess H2 in the system.”
Hydrothermal systems on Earth reflect how scientists like Waite imagine hypothetical undersea life on Enceladus. Microbes here multiply around hydrothermal vents gushing hot water on the ocean floor (bacterial mats that flourish around those tube worms that look like giant lipsticks) because of a chemical reaction between water and iron-bearing minerals that produces H2. These processes disrupt the ocean’s equilibrium, and the chemical chaos is advantageous to certain microscopic deep-sea life-forms that use the H2 as fuel to produce methane from carbon dioxide through methanogenesis.
“There is every reason to believe we’re moving toward Enceladus’s ocean being habitable,” Waite said. “But we’re not making any claims at this point about it being inhabited.”
Could the same thing be happening on an ocean floor 790 million miles away in space? Even if Cassini was immortal, it could only go so far. It was able to use its Ion Neutral Mass Spectrometer to prove the presence of molecular hydrogen and measure the ratio of H2 to CO2, but it is not equipped with more specific instruments that would be able to detect other chemical reactions which might provide evidence of life on Enceladus (if there is any). NASA wants to get under the ice to sample the moon’s mysterious ocean somehow. The literal way of doing this would be drilling, though a more cost-effective mission would use a more advanced spacecraft to sample specimens by flying through the plumes.
NASA has an entire list of processes for this future spacecraft to detect, any one of which could mean a chemical relationship that could be indicative of a microbial food source. Finding certain ratios of amino acids and structural patterns in fatty acids could even be indicative of the microbes themselves. While there are no official plans to launch an Enceladus explorer just yet, NASA’s planned Europa mission will search for similar signs on the Jovian moon of ice, which also has a saltwater ocean beneath its surface. As a candidate for the New Frontiers program, Enceladus may not have to wait long for its own satellite. Just keep dreaming up sci-fi fantasies about what might lurk beneath the surface until then.