Potential Energy Source for Life Spotted on Saturn Moon Enceladus By Mike Wall, Space.com Sen

In that year, NASA's Saturnorbiting Cassini spacecraft first spotted geysers of water ice erupting from "tiger stripe" fissures near Enceladus' south pole. Scientists think these geysers are blasting material from a sizeable ocean buried beneath the satellite's ice shell.

More than 100 individual geysers blast water ice, organic molecules and other material into space from the south polar region of Saturn’s moon Enceladus, as seen here by NASA’s Cassini spacecraft.

Credit: NASA/JPL/SSI

So, Enceladus has liquid water, one of the key ingredients required for life as we know it. (This ocean stays liquid because Saturn's immense gravitational pull twists and stretches the moon, generating internal "tidal" heat.) And the new study suggests that the satellite possesses another key ingredient as well: an energy source.

A team of researchers led by Hunter Waite, of the Southwest Research Institute (SwRI) in San Antonio, analyzed observations made by Cassini during an October 2015 divethrough Enceladus' geyser plume.

This plunge was special in several ways. For one thing, it was Cassini's deepest-ever dive through the plume; the probe got within a mere 30 miles (49 km) of Enceladus' surface. In addition, Cassini's Ion and Neutral Mass Spectrometer (INMS) instrument alternated between "open-source" and "closed-source" modes during the encounter, rather than sticking to closed source (the usual routine).

INMS is just 0.25 percent as sensitive in open-source mode as it is in closed-source mode, Waite and his colleagues wrote in the new Science paper. But open source has a key advantage: It minimizes artifacts that have complicated previous attempts to measure H2 levels in the plume.

With this analytical hurdle cleared, Waite and his team were able to calculate that H2 makes up between 0.4 percent and 1.4 percent of the volume of Enceladus' geyser plume. Further calculations revealed that carbon dioxide (CO2) makes up an additional 0.3 percent to 0.8 percent of the plume's volume. [Inside Enceladus, Icy Moon of Saturn (Infographic)]

The molecular hydrogen is most likely being produced continuously by reactions between hot water and rock in and around Enceladus' core, Waite and his colleagues concluded. They considered other possible explanations and found them wanting. For example, neither Enceladus' ocean nor its ice shell are viable long-term reservoirs for volatile H2, the authors wrote, and processes that disassociate H2 from water ice in the shell don't seem capable of generating the volume measured in the plume.

The hydrothermal explanation is also consistent with a 2016 study by another research group, which concluded that tiny silica grains detected by Cassini could have been produced only in hot water at significant depths.