A new study modeling conditions in Europa’s global liquid ocean suggests that the necessary balance of chemical energy for life could exist there.
Europa. Image credit: NASA / JPL-Caltech.
Europa, the sixth-closest moon of Jupiter and the smallest of its four Galilean satellites, is believed to hide an ocean of salty liquid water beneath its frozen surface.
Whether Europa has the raw materials and chemical energy in the right proportions to support biology is a topic of intense scientific interest.
The answer may hinge on whether Europa has environments where chemicals are matched in the right proportions to power biological processes. Life on Earth exploits such niches.
In the new study, planetary researchers from NASA compared Europa’s potential for producing hydrogen and oxygen with that of Earth, through processes that do not directly involve volcanism.
According to the scientists, the balance of these two elements is a key indicator of the energy available for life.
The study, published online in the journal Geophysical Research Letters, found that the amounts would be comparable in scale; on both worlds, oxygen production is about ten times higher than hydrogen production.
“We’re studying an alien ocean using methods developed to understand the movement of energy and nutrients in Earth’s own systems,” said study lead author Dr. Steve Vance, from NASA’s Jet Propulsion Laboratory.
“The cycling of oxygen and hydrogen in Europa’s ocean will be a major driver for its chemistry and any life there, just it is on Earth.”
As part of the study, Dr. Vance and co-authors calculated how much hydrogen could potentially be produced in Europa’s ocean as seawater reacts with rock in a process called serpentinization.
In this process, water percolates into spaces between mineral grains and reacts with the rock to form new minerals, releasing hydrogen in the process.
They considered how cracks in Europa’s seafloor likely open up over time, as the moon’s rocky interior continues to cool following its formation billions of years ago. New cracks expose fresh rock to seawater, where more hydrogen-producing reactions can take place.
In Earth’s oceanic crust, such fractures are believed to penetrate to a depth of 3 to 4 miles (5 to 6 km).
On Europa, the team expects water could reach as deep as 15 miles (25 km) into the rocky interior, driving these key chemical reactions throughout a deeper fraction of moon’s seafloor.
The other half of Europa’s chemical-energy-for-life equation would be provided by oxidants — oxygen and other compounds that could react with the hydrogen — being cycled into the Europan ocean from the icy surface above.
“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,” said co-author Dr. Kevin Hand, also from JPL.
“Whether or not life and biological processes complete the circuit is part of what motivates our exploration of Europa.”
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S.D. Vance et al. Geophysical controls of chemical disequilibria in Europa. Geophysical Research Letters, published online May 17, 2016; doi: 10.1002/2016GL068547
