Europa’s ocean may have chemistry to sustain life

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An enhanced-colour view from NASA’s Galileo spacecraft shows an intricate pattern of linear fractures on the icy surface of Jupiter’s moon Europa.

The chemistry of the ocean beneath the surface of Jupiter’s moon Europa could sustain life, according to a new model developed by NASA scientists.

Scientists are almost sure that a deep, salty sea lies beneath the moon’s frozen surface and have long speculated that it could harbour life.

But questions have remained over whether the Europa has the necessary raw materials or chemistry to support biological processes.

The new study, which took place in the NASA’s Jet Propulsion Laboratory in Pasadena, compared Europa’s potential for producing hydrogen and oxygen with that of Earth, and found the proportions remarkable similar – with oxygen production about 10 times higher than hydrogen.

“We’re studying an alien ocean using methods developed to understand the movement of energy and nutrients in Earth’s own systems,” says Steve Vance, lead author of the study.  

“The cycling of oxygen and hydrogen in Europa’s ocean will be a major driver for Europa’s ocean chemistry and any life there, just as it is on Earth.”

The researchers considered how cracks in Europa’s seafloor likely open up over time.

Vance and his colleagues calculated how much hydrogen that could potentially be produced in Europa’s ocean as seawater reacts with rock, in a process called serpentinisation.

In this process, water percolates into spaces between mineral grains and reacts with the rock to form new minerals, releasing hydrogen in the process.

The researchers considered how cracks in Europa’s seafloor likely open up over time, where hydrogen-producing reactions can take place.

On Earth, similar fractures are believed to penetrate to a depth of about six kilometres. On Europa, the researchers expect water could reach as deep as 25 kilometres into the rocky interior.

Scientists are also investigating oxidants – oxygen and other compounds split from water molecules that could react with the hydrogen – being cycled into Europa’s ocean from the surface.

“The oxidants from the ice are like the positive terminal of a battery, and the chemicals from the seafloor, called reductants, are like the negative terminal,” says planetary scientist Kevin Hand.

“Whether or not life and biological processes complete the circuit is part of what motivates our exploration of Europa.”

Researchers have previously speculated that volcanoes were essential for creating a habitable environment in Europa’s ocean. Without it, they have thought that the oxidants from the surface would make the ocean too acidic for life.

“But actually, if the rock is cold, it’s easier to fracture. This allows for a huge amount of hydrogen to be produced by serpentinisation that would balance the oxidants in a ratio comparable to that in Earth’s oceans,” says Vance.

The team next wants to study the cycling other major elements in the ocean – carbon, nitrogen, phosphorus and sulfur.

The study was published in the journal Geophysical Research Letters

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