Life on Earth developed slowly over billions of years, and often it seems the modern process of looking for life beyond our own planet moves at a similarly glacial pace. But on Thursday, scientists announced another tantalizing lead in our species-wide quest to answer that great existential question: Is anyone or anything else alive beyond this rock of ours?
Researchers from NASA's Cassini mission say something's happening in a hidden ocean beneath the icy shell of Saturn's moon Enceladus. It's too early to say anything is swimming around down there, but it's becoming clearer that many of the ingredients that allow life to survive in deep, dark underwater environments on Earth can also be found on the Saturnian satellite.
Specifically, the scientists say something's releasing molecular hydrogen (H2) in large amounts into its subsurface sea.
"We think that hydrothermal reactions between liquid water and rock is making the hydrogen," Christopher Glein, a member of the Cassini team at the Southwest Research Institute, said by phone. He's also co-author of a paper in the upcoming issue of the journal Science about the findings. "When you compare that to what we find on the Earth, the most obvious comparison are these hydrothermal vents that emit hydrogen-rich water into the ocean."
According to Woods Hole Oceanographic Institution senior scientist and geochemist Jeffrey Seewald, who's written a companion commentary in Science, the presence of H2 combined with previous research that found things like salt and sodium carbonate in the plumes "suggests a state of chemical disequilibria in the Enceladus ocean that represents a chemical energy source capable of supporting life."
Glein adds that it's also possible tidal processes play a role in whatever is happening on the water world. He's also quick to point out there's no evidence that any type of hydrothermal vents or life exist on Enceladus just yet.
"We've discovered very encouraging signs that this is a habitable environment, which is great because it moves us one step closer to understanding Enceladus, but we're not quite at the stage of determining whether life is present."
Cassini detected the hydrogen at the center of these new insights in an icy plume issuing forth from cracks in Enceladus' surface. The NASA spacecraft flew directly through the spray about a year and a half ago to take measurements and collect the data that Glein and his colleagues analyzed and found contained significant amounts of H2 and carbon dioxide.
"This is just the latest example of how Enceladus never ceases to surprise and amaze us," Glein said.
Before Cassini arrived on the scene, Enceladus seemed to be just another frozen snowball moon in the outer solar system. Then observations by the spacecraft made it clear the plumes belied the presence of a covered ocean. Next came revelations about potential heat sources and the chemistry needed to support life.
Glein says there's still much more to learn about the distant moon and plenty of work for geophysicists, geochemists and biologists to do along the way. Ultimately, though, he says figuring out what is really happening beneath Enceladus' intriguing icy curtain will require a return trip.
"I think there's just so many tantalizing questions that are raised from this study as well as the history of Cassini's exploration that we're compelled to go back," he said.
It may be a while before a spacecraft returns though. Cassini is scheduled to end its mission with a spectacular descent into Saturn later this year, and NASA has plans to visit Europa in the next decade, but nothing is currently in the budget for Enceladus.
And so the discovery of extraterrestrial life remains at once inevitable and still several years away. Perhaps someone ought to see how Elon Musk feels about sending a Falcon Heavy rocket in the direction of Saturn sometime soon.
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