Scientists have detected molecules of hydrogen in plumes of watery material erupting from cracks in the ice of Enceladus, a moon of Saturn – and that suggests an ocean beneath the ice has hydrothermal vents that just might be capable of sustaining life.
“We’ve always wondered, ‘Are we alone in the universe?'” Linda Spilker, project scientist for the Cassini mission at NASA’s Jet Propulsion Laboratory, told GeekWire. “Now, as we look out from our own planet, we find worlds in our own solar system that might have life.”
The direct evidence is still wanting, however. The research team, headed by the Southwest Research Institute’s Hunter Waite and Christopher Glein, made their conclusions based on a chain of evidence that started with observations from Cassini’s Ion Neutral Mass Spectrometer.
The researchers focused on Enceladus’ plumes – intriguing sprays of water vapor, ice and other material that emanate from deep fissures in the ice-covered moon’s surface.
The mere existence of the plumes suggests that a watery ocean lies beneath the ice, and scientists had already suspected that the ocean was fed by hydrothermal activity. The newly announced findings provide strong support for that suspicion.
Cassini’s spectroscopic readings revealed significant levels of molecular hydrogen in the plume material, and the researchers said that chemical activity from hydrothermal vents provides the best explanation for those levels.
What’s more, the team could use those hydrogen levels to calculate how much energy might be available for organisms in Enceladus’ sea.
“We have made the first calorie count in an alien ocean,” Glein told Geekwire.
In Earth’s oceans, reactions between the water from hydrothermal vents and the surrounding rocks produce chemicals that can sustain microbes. Glein said the potential chemical energy in Enceladus’ ocean should be “very similar to the amount … that hydrothermal vents pump out on Earth.”
Such findings come as thrilling news to Spilker. “The excitement here is that now you have something that can chemically interact with the rock to produce the kind of chemistry that can be used by microbes,” she said.
The fact that the findings are being published just as the Cassini mission is in its final months, almost 20 years after the orbiter’s launch, adds to the appeal. “This is really a capstone finding for the mission,” Spilker said.
But the question about life on Enceladus is still an unsolved mystery.
“I would say this is a very provocative result, supports what we know already and could very well be right,” Carolyn Porco, a planetary scientist who heads Cassini’s imaging team but was not involved in the newly published research, told GeekWire in an email.
“But for me, its power is that it begs to be confirmed by a return to Enceladus with instruments that are designed for the express purpose of sampling a tenuous plume of material and returning a higher-fidelity result than we have now,” Porco said.
A follow-up mission to Enceladus has been under discussion for years. However, NASA has been focusing instead on sending a probe to Europa, an ice-covered moon of Jupiter that’s also thought to harbor a hidden, potentially habitable ocean.
Porco makes no secret of her preference.
“I say we press on with a return mission to Enceladus, to learn if Cassini’s indications and our readings of them are correct,” she said. “The next steps at Enceladus could be the most consequential ever taken in the history of planetary exploration.”
In addition to Waite and Glein, the authors of the Science study, “Cassini Finds Molecular Hydrogen in the Enceladus Plume: Evidence for Hydrothermal Processes,” include Rebecca Perryman, Ben Teolis, Brian Magee, Greg Miller, Jacob Grimes, Mark Perry, Kelly Miller, Alexis Bouquet, Jonathan Lunine, Tim Brockwell and Scott Bolton.