Researchers have found a geochemical process on Saturn's sixth largest moon that suggests life could exist on it, or could have previously existed.
The team, including Christopher Glein from the Carnegie Mellon University, has revealed the pH of water spewing from a geyser-like plume on Saturn's moon Enceladus.
The pH tells us how acidic or basic the water is.
Enceladus is geologically active and thought to have a liquid water ocean beneath its icy surface.
"Knowledge of the pH improves our understanding of geochemical processes in Enceladus' 'soda ocean,'" Glein explained.
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.
Whenever there's the possibility of liquid water on another planetary body, scientists begin to ask whether or not it could support life.
The present team, including lead author Glein and John Baross of the University of Washington, 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 team's 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 salt as our oceans here on the Earth.
Its additional substantial sodium carbonate makes the ocean more similar to our planet's soda lakes such as Mono Lake in California or Lake Magadi in Kenya.
The scientists refer to it as a "soda ocean."
The model suggests that the ocean's high pH is caused by a metamorphic, underwater geochemical process called serpentinisation.
On the Earth, serpentinisation occurs when certain kinds of 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.
This process is central to the emerging science of astrobiology.
"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," the authors wrote.
The work demonstrates that it is possible to determine the pH of an extraterrestrial ocean based on chemical data from a spacecraft flying through a plume.
This may be a useful approach to searching for habitable conditions in other icy worlds, such as Jupiter's moon Europa.
"The results open the door to an exciting new era of chemical oceanography in the solar system and beyond," Glein concluded.
Their work was published in the journal Geochimica et Cosmochimica Acta.
