Saturn’s moon Enceledus may harbour life: study

Scientists have unveiled the pH of water spewing from a geyser-like plume on Saturn’s moon Enceladus, a discovery that suggests it is a promising candidate to harbour life.

The finding from a team including Carnegie Mellon University’s Christopher Glein is an important step towards determining whether life could exist, or could have previously existed, on the planet’s sixth-largest moon.

Enceladus is geologically active and thought to have a liquid water ocean beneath its icy surface.

The hidden ocean is the presumed source of the plume of water vapour and ice that the Cassini spacecraft has observed venting from the moon’s south polar region.

The team developed a new chemical model based on mass spectrometry data of ice grains and gases in Enceladus’ plume gathered by Cassini, in order to determine the pH of Enceladus’ ocean.

The pH tells us how acidic or basic the water is. It is a fundamental parameter to understanding geochemical processes inside the moon that are considered important in determining Enceladus’ potential for acquiring and hosting life.

The model shows that the plume, and by inference the ocean, is salty with an alkaline pH of about 11 or 12, which is similar to that of glass-cleaning solutions of ammonia.

It contains the same sodium chloride (NaCl) salt as our oceans here on Earth. Its additional substantial sodium carbonate (Na2CO3) makes the ocean more similar to our planet’s soda lakes such as Mono Lake in California.

The model suggests that the ocean’s high pH is caused by a metamorphic, underwater geochemical process called serpentinisation.

On Earth, serpentinisation occurs when certain kinds of so-called “ultrabasic” or “ultramafic” rocks (low in silica and high in magnesium and iron) are brought up to the ocean floor from the upper mantle and chemically interact with the surrounding water molecules.

On Enceladus, serpentinisation would occur when ocean water circulates through a rocky core at the bottom of its ocean.

“Why is serpentinization of such great interest? Because the reaction between the metallic rocks and the ocean water also produces molecular hydrogen (H2), which provides a source of chemical energy that is essential for supporting a deep biosphere in the absence of sunlight inside moons and planets,” Glein said.

“This process is central to the emerging science of astrobiology, because molecular hydrogen can both drive the formation of organic compounds like amino acids that may lead to the origin of life, and serve as food for microbial life such as methane-producing organisms.

“As such, serpentinisation provides a link between geological processes and biological processes. The discovery of serpentinisation makes Enceladus an even more promising candidate for a separate genesis of life,” said Glein.

The research was published in the journal Geochimica et Cosmochimica Acta.

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