Can methane on Saturn’s moon Enceladus is a sign of life?

(Credit: NASA)

Some hardy Earth microbes would likely survive in the Saturn moon Enceladus’ buried ocean, gobbling up hydrogen produced by the interaction between seawater and rock, a new study suggests.

And the microbes tested in the study churn out methane as a metabolic byproduct. That is intriguing, because NASA’s Cassini spacecraft discovers methane in the plume of the particles blown into space by Enceladus’ powerful south-pole geysers.

“We were able to show that, under the alleged Enceladus conditions, biological methane production occurs in the lab,” said study co-author Simon Rittmann, of the Department of Ecogenomics and Systems Biology at the University of Vienna in Austria. [Amazing Photos of Saturn’s icy moon Enceladus]

“Therefore, some of the methane found on Enceladus, it would, in principle, of biological origin,” said Rittmann via e-mail.

The researchers, under the leadership of Ruth-Sophie Taubner, also of the University of Vienna — the first experiments were performed on three species of methane-producing archaean microbes. Archaea are similar to bacteria in that the absence of a nucleus or any other membrane-bound internal structures, but the former critters represent an entirely separate line that can go all the way back to the dawn of life on Earth.

This exploratory research showed that one of the microbes, Methanothermococcus okinawensis, as the most suitable for more in-depth study of the Enceladus-like conditions. So the team exposed to M. okinawensis to a variety of gas compositions and the (relatively high) pressure, 150 degrees Fahrenheit (65 degrees Celsius) — basically what you would expect to find in hydrothermal vents on Enceladus’ on the seabed.

Astronomers have inferred the existence of such openings on Enceladus from different observations of Cassini. For example, the Saturn orbiter spotted tiny silica particles and molecular hydrogen (H2) in the moon, the plume, both of which are best explained by reactions between hot water and rock.

M. okinawensis grew well and produced methane in the team of the experiments, which may not be very surprising, given the fact that the organism isolated from a hydrothermal vent off the island of Okinawa, at a depth of about 3,200 feet (975 meters).

n addition, Taubner and her colleagues modeled the water-rock reactions likely occurring in Enceladus’ interior. They found that such reactions are likely to be the production of a lot of H2 — enough to sustain the methanogenic organisms such as M. okinawensis, if present on the Saturn satellite. [In Enceladus, Icy Moon of Saturn (Infographic)]

To be clear, the study of the team members do not claim that Enceladus’ methane is organic; after all, the substance can be produced geologically (by reactions between rock and hot water, in fact). But the new results may help to inform the search for life on the ocean moons in the solar system, Rittmann said.

“From an astronomical perspective, future missions to Enceladus or other icy moons should be equipped to be able to detect methanogenic biosignatures in connection with methanogens, such as certain lipids or ratios of certain carbon isotopes,” he said.

There are currently no Enceladus missions on the books of the NASA or other space agency. But both NASA and the European Space Agency (ESA) to develop missions to explore the icy ocean moons of Jupiter.

NASA’s entry, called Europa Clipper, will assess the habitability of the buried ocean on the Jovian satellite Europa, in the course of tens of minutes. ESA ‘ s mission, called Jupiter Icy Moons Explorer (JUICE), will also study Europe, but it will focus more on Ganymede and, to a lesser extent, Callisto.

Europa Clipper and JUICE are both scheduled to launch in 2020. NASA is also working on a separate Europa lander mission, even though that project remains a concept at this time.

The new study today, published online (Feb. 27) in the journal Nature Communications.

Scientists have spotted methane in the atmosphere of Mars, and they’re not sure where the Red Planet’s store of the stuff comes from. But more information should be coming soon: The Trace Gas Orbiter, part of the European-Russian ExoMars exploration program, is planned to begin measuring and mapping Mars methane in the middle of April.

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