From the moment scientists spotted plumes of water erupting from Enceladus, one of Saturn’s moons, it became the most tantalising place in the solar system to search for life beyond Earth.
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it → spot → Earth
Now the case is even more compelling after researchers found that organisms that live in deep-sea waters off Japan can survive the harsh conditions expected in the briny ocean that lurks beneath Enceladus’s icy crust.
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that → find → crust
The microbes, which thrive near hydrothermal vents on the seafloor by converting hydrogen and carbon dioxide into methane, survived in a brine that mimicked the Saturnian moon’s ocean.
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that → thrive → ocean
The work suggests the distant world may be habitable, if not exactly hospitable, to at least some forms of life.
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world → suggest → life
“If we use the cellular definition of life that we understand on Earth today, the experiments tell us that if this organism, or something similar to it, was on Enceladus, there’s a good chance it could survive,” said William Orsi, a professor of geomicrobiology at Ludwig-Maximilian University in Munich.
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Orsi → use → Munich
Saturn has more moons than any other planet in the solar system, with nearly 300 known to orbit the gas giant.
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300 → have → giant
For more than two centuries, Enceladus, a 300-mile-wide ice ball, did not seem particularly remarkable.
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Enceladus → seem → centuries
But that changed with the arrival of robotic spacecraft.
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that → change → spacecraft
The seafloor is thought to be dotted with hydrothermal vents that warm the water around them.
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that → think → them
Last year, scientists found organic substances in samples collected by Cassini as it swooped through one of Enceladus’s spectacular plumes.
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it → find → plumes
Orsi and his colleagues wanted to see if they could concoct a miniature version of Enceladus’s ocean to study in the laboratory.
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they → want → laboratory
By combining water with salts and carbonates and adding powdered rock, they recreated not only the extremely alkaline environment of the ocean but also crucial reactions that take place between the water and the rocky seafloor.
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that → combine → water
The rock-water reactions were active enough to start churning out hydrogen, a process that seems to happen in the ocean on Enceladus.
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that → start → Enceladus
It led the researchers to wonder whether Earthly microbes called methanogens, which survive by converting hydrogen and carbon dioxide into methane, could survive in the solution.
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which → lead → solution
“It was a long shot,” said Orsi.
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Orsi → say → ?
To find out, the scientists turned to microbes originally found near deep-sea hydrothermal vents in the Okinawa trough between Japan and Taiwan.
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scientists → find → Japan
Hydrothermal vents are hot springs on the seafloor that release hot, mineral-rich water.
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that → release → water
Surprisingly, the microbes grew in the simulated ocean despite its pH reaching 11, which is far more alkaline than the organisms’ known limit.
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which → grow → limit
The microbes even adapted their metabolism to cope with low concentrations of carbon dioxide in the water.
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microbes → adapt → water
Details are published in Science Advances.
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Details → publish → Advances
David Rothery, a professor of planetary geosciences at the Open University, said that by showing that methanogenesis – the process that sustains the microbes – was possible in the simulated Enceladus ocean, the work “removes another barrier to the viability of microbial life there”.
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work → say → life
Orsi stressed that if life ever evolved on Enceladus it could be radically different from that on Earth.
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it → stress → Earth
Even if similar bugs did somehow arise, it is not clear if methane-making microbes would thrive in the moon’s ocean: his experiments lasted only days.
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experiments → arise → ocean
“Could they survive for a year?
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they → survive → year
Could they survive for a million years?
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they → survive → years
We don’t know,” Orsi said.
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Orsi → know → ?
In a second paper in the journal, some of the same researchers describe how ice grains in Enceladus’s plumes freeze and fragment in a way that separates the different constituents of the ocean.
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that → describe → ocean
If ocean droplets contained bits of alien microbes, these might turn up in a small fraction of ice particles but be highly concentrated within them.
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these → contain → them
That would be “great news” for the search for life, said Frank Postberg, a professor of planetary sciences at the Free University of Berlin, who said it would be relatively easy to identify signs of life with today’s technology.
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it → say → technology
The tantalising science around Enceladus has fuelled interest in a return trip.
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science → fuel → trip
The European Space Agency’s L4 mission aims to combine a Saturn orbiter with an Enceladus lander that would touch down at the moon’s south pole and hunt for biosignatures in the plumes erupting from its ocean.
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that → aim → ocean
But scientists face a long wait: with a launch proposed for about 2042, it would not reach Saturn until the 2050s.
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it → face → 2050s
Dr Rachael Hamp, also at the Open University, who has worked on Enceladus’s plumes, said: “It’s fantastic to see new research pushing our understanding further and providing additional evidence for the potential habitability of this little icy world.
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research → work → world
I think this makes the European Space Agency’s proposed mission to Enceladus even more exciting.”
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mission → think → Enceladus
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