Saturn's watery moon Enceladus might harbour methane-belching microb... http://www.abc.net.au/news/science/2018-02-28/enceladus-microbes-me...
ABC Science By science reporter Belinda Smith Updated Tuesday at 20:20 First posted Tuesday at 19:35
Could anything live beneath Enceladus' tortured, cratered, icy surface? For the moment, we can only speculate. (Supplied: NASA/JPL /Space Science Institute)
Enceladus is only 500 kilometres wide, but the tiny icy moon is a massive contender in the search for extra-terrestrial life.
Now, lab experiments suggest it's possible the right kind of microbe could, in theory, call the small satellite home. Key points: The work was reported in Nature Communications today. Saturn's moon Enceladus is believed to have a subsurface
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Saturn's sixth largest moon has been a target for ocean and hydrothermal vents astrobiologists since the Cassini mission pointed to the Methane-producing microbes live in such environments on presence of a salty ocean under its cracked and cratered Earth crust. New research suggests they can also survive in Enceladus- like conditions The surface of Enceladus' south pole, too, is marked by a series of fractures, from which jets of gas and dust are But water worlds like Enceladus lack dry spots which life blasted up to 80 kilometres into the atmosphere. needs to arise
When the Cassini spacecraft flew through these jets, it sniffed out compounds related to life, such as hydrogen gas and methane.
The Cassini spacecraft snapped this image of Enceladus' jets, near the moon's south pole, in 2009. (Supplied: NASA/JPL/Space Science Institute)
This caused a stir in astrobiology circles. The jets, it was thought, might be powered by hydrothermal vents: openings on the sea bed that spew hot, mineral-rich water.
On Earth, hydrothermal vents crawl with organisms, including microbes that produce methane known as methanogens. If similar environments are found on extra-terrestrial ocean worlds, they too, might harbour such life.
To test this theory, a team from Austria and Germany examined three species of methane-producing microbes to see if they could survive in Enceladus' subsurface ocean.
The problem is, despite Cassini's reams of data, planetary scientists don't know exactly what is in the subsurface ocean, let alone how warm it is, and how pressure changes with depth.
So, the researchers had to test a range of conditions suspected to be present below Enceladus' crust. Cassini finale: NASA spacecraft ends "The important thing for us was to be as broad as possible
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with all the experiments," said lead researcher Simon 20-year mission with crash into Saturn Rittmann, a microbiologist from the University of Vienna.
Dr Rittmann and crew cultivated methane-producing archaea — primitive organisms that churn out methane from carbon dioxide and hydrogen gas — in 120-millilitre bottles filled with different compounds and topped up with gases.
Some bottles were pressurised, to mimic different depths of the ocean.
And then the researchers measured the microbial mass that grew, and the amount of methane they produced. The 7.9-billion-kilometre journey to explore the distant planet has come to a crashing end, having discovered moons One microbe, Methanothermococcus okinawensis, thrived in that might hold the key ingredients for life. Enceladus-like conditions to crushing pressures of 50 bars. That's equivalent to being 500 metres underwater on Earth.
This isn't too surprising, as the microbe was harvested from a hydrothermal vent 972 metres beneath the waves, south of Japan.
Methane may not be produced by microbes
Even though these microbes can thrive and produce methane in Enceladus-like environments, that's not to say they or any other life forms actually exist on the moon itself, Dr Rittmann said.
Microbes aren't the only source of methane. Chemical reactions in rocks, for instance, can make the gas — no life required.
Differentiating this geological methane and biological methane from microbes is no easy feat — especially on an icy moon, more than a billion kilometres away.
Further studies to detect chemical signatures of biological organisms would be needed.
"You could look at different isotopes of carbon dioxide or methane, maybe in combination with proteins or lipids from microorganisms," Dr Rittmann said.
"Then we might have an indication that there could be life on Enceladus."
Barriers to life on water worlds 'insurmountable'
Some experts are unconvinced that the methane detected on Enceladus is from living organisms.
There's an "insurmountable problem" when it comes to life on water worlds like Enceladus, said Martin Van Kranendonk, head of the Australian Centre for Astrobiology at the University of New South Wales.
"If there was life and it evolved into something like a methanogen, it could survive on Enceladus," he agreed.
"The tricky question is: how did life get started?"
Professor Van Kranendonk pointed to the "water problem". For instance, sugars are made from amino acids, but the process cannot take place in water.
"The best is an environment that undergoes wetting and drying, and for that you need a surface," he said.
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And Enceladus simply lacks the land needed to create the building blocks of life.
Astrobiologists and planetary scientists might get answers on the source of methane on Enceladus sooner rather than later.
NASA and the European Space Agency have made noises about sending a probe to Enceladus — although they might be beaten by Russian billionaire Yuri Milner, who said in November that he is considering one too. This artist's impression shows a cutaway view of Meanwhile, Dr Rittmann and his colleagues will continue Enceladus. Its rocky core is likely completely enveloped by an ocean, leaving no land for life to arise. (Supplied: creating miniature icy worlds in the lab and growing NASA/JPL-Caltech) microbes in conditions like those found on other planetary bodies.
"We'll focus on the icy moons, definitely. They're very fascinating."
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Topics Science and Technology Chemistry Microbiology Planets and Asteroids Geology Space Exploration
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