Saturn’s moon Enceladus might have the right elements to sustain Earth-like life

On its deepest dive through the spray that shoots up from Saturn’s icy moon Enceladus, NASA’s Cassini spacecraft picked up signs of molecular hydrogen and carbon dioxide — two ingredients that feed many microbes living around hydrothermal vents on Earth.

The findings, described in the journal Science, break ground in showing that an icy world beyond our own might truly have the right environment for Earth-like life.

“It is life-friendly,” lead author J. Hunter Waite, a planetary scientist at the Southwest Research Institute, said in an interview. He ticked off several of the ingredients necessary for life that have been found on Enceladus, including water and key elements such as carbon, hydrogen, nitrogen and oxygen. “This drives Enceladus to the top of the heap on conditions that demonstrate habitability.”

Ever since Enceladus was spotted shooting what turned out to be plumes of water vapor and ice from cracks in its icy crust, scientists have wondered what lies beneath the Saturnian moon’s surface. Data gathered by Cassini have shown that this tiny world may host a salty global ocean; the spacecraft’s Cosmic Dust Analyzer also recently discovered the presence of silica in the plume, a hint that geothermal activity may be happening beneath the surface.

The chemical energy released by geothermal activity could be a key food source for any hypothetical microbes in the ocean beneath Enceladus, given that the little water world is too far from the sun for photosynthesis to be an option.

The presence of silica was a hopeful sign that water was indeed interacting with rock, though it didn’t prove that the right chemical ingredients were present. But Waite and his colleagues used the onboard mass spectrometer to study the plumes, and discovered molecular hydrogen — which happens to be a key food source for microbes living around hydrothermal vents on Earth.

“Silicon is not very appetizing, apparently — but H₂ is,” Waite said.

On Earth, certain microbes living in the dark, high-pressure depths of the ocean where oxygen is scarce actually consume hydrogen and carbon dioxide, producing methane in the process. Cassini’s discovery that the plume could contain as much as 1.4 volume percent molecular hydrogen and 0.8 volume percent carbon dioxide shows that the same thing could theoretically happen at Enceladus.

“If correct, this observation has fundamental implications for the possibility of life on Enceladus; chemical disequilibrium that is known to support microbial life in Earth’s deep oceans is also available to support life in the Enceladus ocean,” Jeffrey Seewald of the Woods Hole Oceanographic Institution, who was not involved in the study, wrote in a commentary.

This paper can’t say whether any microbes do or ever did exist beneath the moon’s icy crust, Waite was quick to add — only that the right ingredients are there. Researchers are not even sure whether the exact same hydrothermal process seen on Earth is responsible for all that hydrogen, or whether it’s more similar to a different process that has been produced in the lab.

Still, he added, the findings show that scientists should continue looking to water worlds — both in our solar system and beyond — as some of the best possible places to look for life.

“We still have a long way to go in our understanding of processes regulating the exchange of mass and heat across geological interfaces that define the internal structure of Enceladus and other ice-covered planetary bodies,” Seewald wrote. “Future missions to explore oceans beyond Earth will answer many of these questions and further constrain the possibility of life elsewhere in our solar system.”

amina.khan@latimes.com