"Some of the most primitive metabolic pathways utilized by microbes in these environments involve the reduction of carbon dioxide (CO2) with H2 to form methane (CH4) by a process known as methanogenesis," Seewald wrote.
The inferred presence of H2 and CO2 in Enceladus' ocean therefore suggests that similar reactions could well be occurring deep beneath the moon's icy shell. Indeed, the observed H2 levels indicate that a lot of chemical energy is potentially available in the ocean, Glein said.
"It's quite a bit larger than the minimum energy required to support methanogenesis," he said.
Glein stressed, however, that nobody knows whether such reactions are actually occurring on Enceladus.
"This is not a detection of life," Glein said. "It increases the habitability, but I would never suggest that this makes Enceladus more or less likely to have life itself. I think the only way to answer that question is, we need data."
Seewald also counseled caution on astrobiological interpretations. He noted, for example, that molecular hydrogen is rare in Earth's seawater, because hungry microbes quickly gobble it up.