Hot water activity found on Enceladus

Chuck Bednar for redOrbit.com – @BednarChuck

Add Enceladus to the growing list of candidates that may be capable of supporting life, as an international team of researchers has discovered evidence of an active hydrothermal system on the icy Saturn moon that could be capable of supporting microbial life.

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Hsiang-Wen Hsu, a planetary scientist at the University of Colorado-Boulder’s Laboratory for Atmospheric and Space Physics (LASP), and his colleagues reported Wednesday in the journal Nature that they had discovered tiny grains of silicon-rich dust in orbit around Saturn.

Mysterious, tiny grains

While those grains, which were using the Cassini spacecraft’s Cosmic Dust Analyzer, are no larger than a strand of human DNA, they are similar to sand and quartz found that are found on Earth and are typically formed by processes that require the presence of heated water.

“It’s a peculiar thing to find particles enriched with silicon,” Hsu told the Los Angeles Times. Since water ice is dominant in Saturn’s rings and its moons, the discovery of the unusual grains caught his attention, and he and his colleagues traced their origins to the E-ring of Saturn, which contains ice particles that originate from Enceladus.

They analyzed the particles, which tended to be uniformly small instead of ranging in size, and their work revealed that the grains were made of silicon dioxide (silica), a material which is not common in space. Silica is a product of water interacting with rock, and since its properties were well known, it allowed the scientists to work backwards to determine what type of environment is responsible for creating these unusual particles, the newspaper explained.

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Next, they ran a series of experiments to figure out how those particles came to be. Given that they had a specific makeup and a set size distribution, very specific conditions would have been required for them to form, the authors found. The silica particles would had to have formed in water that had less than four percent salinity, was slightly alkaline in nature (a pH of between 8.5 and 10.5) and temperatures of at least 190 degrees Fahrenheit (90 degrees Celsius).

Hsu’s team reasoned that the heat was likely being generated in part by the effect of Saturn’s tidal forces on Enceladus. Those forces also likely created the surface cracks that allowed the water vapor to escape into space, indicating that somewhere within the icy moon, there had to be some form of hydrothermal activity – salty warm water interacting with rocks. This is similar to the conditions found here on Earth, and is extremely conducive to microbial life.

Hydrothermal processes at work on the seafloor

Thus, as the ESA explained in a statement, they believe that the silicon-rich grains originate on the seafloor of Enceladus, where hydrothermal processes are at work. On the seafloor, hot water dissolves minerals from the rocky interior of the minerals. While the origins of this energy are not fully understood, the researchers believe that it is some combination of tidal heating taking place as the moon orbits Saturn, chemical reactions, and radioactive decay in the core.

As the hot water moves upwards, it comes into contact with cooler H2O, causing minerals to become condensed and form into nano-scale grains of silica floating in the ocean. They have to spend at least a few months rising from the seafloor to avoid growing too large. Eventually, they become part of larger ice grains in the vents connecting the ocean to Enceladus’ surface, and once they are ejected into space, the ice grains erode and the silica particles are freed.

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“It’s very exciting that we can use these tiny grains of rock, spewed into space by geysers, to tell us about conditions on – and beneath – the ocean floor of an icy moon,” said Hsu.

“This moon has all the ingredients – water, heat, and minerals – to support habitability in the outer Solar System, confirming the astrobiological potential of Enceladus,” added ESA Cassini project scientist Nicolas Altobelli. “Enceladus may even represent a very common habitat in the Galaxy: icy moons around giant gas planets, located well beyond the ‘habitable zone’ of a star, but still able to maintain liquid water below their icy surface.”

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