Enceladus Has Potentially Life-Giving Hydrothermal Activity

Saturn’s icy moon Enceladus is showing definite signs of hydrothermal activity — similar activity that is found along deep sea vents on Earth where water is heated and minerals are formed. Known to have a sub-surface ocean of salty water, the new findings described in two recent papers have boosted the moon’s life-giving potential.

“These findings add to the possibility that Enceladus, which contains a subsurface ocean and displays remarkable geologic activity, could contain environments suitable for living organisms,” said John Grunsfeld, associate administrator of NASA’s Science Mission Directorate in Washington D.C. “The locations in our solar system where extreme environments occur in which life might exist may bring us closer to answering the question: are we alone in the universe.”

Enceladus is already known for its famous geysers blasting water vapor from beneath the moon’s icy crust. Long fractures in the moon’s south pole allow liquid water to escape into space, a sure sign that some kind of heating process is going on deep inside the icy world.

Now, through the analysis of minerals contained within the water vapor detected during flybys of NASA’s Cassini mission, the nature of this heated water has been revealed. And it’s great news if you happen to be a deep-sea dwelling microbe.

Hydrothermal Hothouses

On Earth, hydrothermal vents on ocean floors are hothouses of chemical reactions, providing a vital energy resource to marine life. Often, the lifeforms found at the bottom of oceans do not require sunlight to survive; they have evolved next to these hydrothermal vents, thriving in the dark with the energy the vents provide.

Now, through new analysis of Cassini data, scientists writing in the journal Nature have discovered microscopic grains of silica (the mineral quartz that is found on Earth) and related what that means in laboratory experiments. This discovery indicates that hot water, at a temperature of at least 194 degrees Fahrenheit (90 degrees Celsius), containing dissolved minerals from the moon’s core has been forced through cooler layers of water. Tiny rock grains then form during this process.

“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 lead author Sean Hsu, a postdoctoral researcher at the University of Colorado at Boulder.

The small size of the grains of minerals found in Enceladus’ water vapor hints at the speed at which they are formed. The largest grains were only 6 to 9 nanometers in size, showing that they must have formed very quickly as the hot water the minerals were dissolved in came into contact with the comparatively cooler layers of water at the bottom of the moon’s ocean. The distance from seafloor to outer space is around 30 miles, so from formation to release, the grains would have spent only a few months to a few years in transit otherwise they would have had time to grow much larger.

This first line of evidence of hydrothermal activity suggests Enceladus has a porous, rocky core where liquid water from the ocean has the freedom to percolate through the core, forming water-borne mineral particles.

Methane Clues

In a second paper published by the journal Geophysical Research Letters, researchers investigating the curious abundance of methane in Enceladus’ plumes also suggest hydrothermal activity is at play.

In the pressures associated with Enceladus’ deep ocean, the team was investigating how methane gas is likely locked inside water ice crystals called clathrates. According to the authors, the Enceladus clathrate-forming process should be so efficient that the ocean is almost entirely depleted of methane. If this is the case, why is Cassini seeing an abundance of methane in the plumes?

There are two possibilities. The first is that the clathrates in the ocean are being dragged to the surface by the erupting plumes, venting the methane as they go. The second possibility is that hydrothermal activity is creating more methane than the clathrate-formation process can lock away. Although both proceses are likely occurring, the fact that another study has found rock minerals associated with hydrothermal activity suggests there may also be a hydrothermal answer to the methane puzzle.

“We didn’t expect that our study of clathrates in the Enceladus ocean would lead us to the idea that methane is actively being produced by hydrothermal processes,” said Alexis Bouquet, a graduate student at the University of Texas at San Antonio and lead author of the second paper.

On Earth, hydrothermal vents heated by volcanic activity deep within our planet’s core provide the necessary ingredients for life to form at the bottom of the ocean, devoid of light. On Enceladus, with a core heated by Saturn’s tidal squeezing, it seems an identical process is occurring — water loaded with minerals is heated and rocky particles condense from the mix.

Read more at Discovery News