- Enceladus, an ice-encrusted moon of Saturn, hides an ocean of saltwater that blasts ice into space.
- NASA flew its Cassini spacecraft through the ice geysers in 2015.
- Scientists continue to analyze the data, and on Wednesday a group announced that it had detected complex organic molecules.
- Though not definitive proof of alien life, the molecules are a good sign for the habitability of Enceladus.
Two years before NASA destroyed its Cassini spacecraft in the clouds of Saturn, the space agency flew the robot through geysers of ice blasting out of the planet's moon Enceladus.
The plumes come from a giant saltwater ocean hidden beneath the moon's icy crust. The water seeps through cracks at Enceladus' south pole, where it boils into the vacuum of space and forms 300-mile-tall curtains of ice particles.
Ever since Cassini's nuclear-powered geyser-dive in October 2015, scientists have pored over the probe's trove of data. They've found all sorts of eyebrow-raising chemicals, including small organic (carbon-containing) molecules such as acetylene, formaldehyde, methane, and propane.
But this week, researchers announced the detection of long, messy strings of organic molecules that could be indicative of water that's habitable to life — or perhaps something even more exciting.
"We cannot decide whether the origin of this complex material is biotic or not, but there is astrobiological potential," Nozair Khawaja, a researcher at Heidelberg University, told Gizmodo.
Translation: The chemicals might be signs of microbial aliens, though it's too soon to say.
Khawaja and 20 other space scientists published a study in the journal Nature on Wednesday about their discovery of the organic molecules, which they call macromolecular compounds.
"The discovery of macromolecular compounds originating from a moderately warm water environment will fuel interest worldwide in such icy moons as possible habitats for extraterrestrial life," Mario Trieloff, another author of the study, said in a press release.
How Enceladus might brew complex organic muck
Life as we know it is carbon-based. The element makes it possible to store and copy genetic information, is essential to building proteins, and helps store and shuttle energy. Liquid water is an essential ingredient too — so when scientists find the two together in space, the stakes become interesting.
A warm, salty ocean with organic molecules is no guarantee of alien life, of course. Some oceans, such as the one under Pluto's icy crust, are most likely deadly to us. But researchers keep finding more evidence that Enceladus' environment is conducive to life, rather than dangerous.
Recent studies using Cassini's water-spray data suggest hydrogen is bubbling up from the moon's ocean bottom, possibly from structures called hydrothermal vents. Khawaja said in the press release that gas bubbles that most likely hail from Enceladus' seafloor "probably transport the molecules to the surface, where they form an organic film."
He added that the bubbles are hydrophobic, or water-repelling, which is why they form a film on top of the water as opposed to dissolving.
"From there," he said, the film "is launched into space together with ocean water droplets."
Hydrothermal vents can generate hydrogen gas. They litter Earth's seafloor near volcanically active regions, spewing nutrient-rich hot water that may make them bastions of life. In fact, scientists last year announced the discovery of what may be 3.77- to 4.28-billion-year-old fossils that originated at hydrothermal vents on Earth.
But the new study in Nature is far from definitive proof of organic alien goop.
Water is being pulled toward Enceladus' core and heated up under pressure, so it's possible that carbon that's been present in Enceladus since its formation (every world contains a little) is reacting with minerals to form more complex molecules. Ancient asteroids that drift through space also harbor complex organic molecules but are almost certainly devoid of life.
Cassini's instruments weren't designed to analyze organic molecules for alien or non-alien origins, and the spacecraft is now gone.
It may be decades before we find out for sure. There's no funded mission to return to Enceladus, and Saturn's increasingly famous moon is roughly 890 million miles away, so it can take nearly seven years to get a probe there.
Seeking signs of life at Europa
Those hoping to find signs of alien life shouldn't despair, though.
Both NASA and the European Space Agency are planning to send spacecraft to Jupiter's moon Europa. That ice-covered world has an even larger subsurface ocean, is spraying water, and might also be rich with a soup of organic molecules that alien microbes could feed on or generate.
The ESA's probe, called the Jupiter Icy Moons Explorer, is scheduled to launch in 2022 and reach Jupiter in 2030. The mission calls for two flybys of Europa from about 200 miles away.
The other mission is NASA's roughly $2 billion Europa Clipper probe, which may launch sometime between 2022 and 2025 and arrive about five years later.
The Europa Clipper is expected to make 47 flybys and come within 20 miles of Europa's surface. That would give the probe unprecedented access to water plumes and the ability to sample the water for salts, organic compounds, and other chemicals.
"The instruments are designed with Europa's plumes in mind, allowing us to infer the ocean's composition and thus its suitability for life, and even to look for direct chemical signs of extant life," Steve Vance, a planetary scientist at NASA's Jet Propulsion Laboratory, previously told Business Insider.
Bob Pappalardo, another JPL scientist, also previously told Business Insider that oceans on moons like Europa may be the most common habitats for life that exist in the universe.
"If there's life at Europa, it'd almost certainly be an independently evolved form of life," Pappalardo said. "Would it use DNA or RNA? Would it use the same chemistry to store and use energy? Discovering extraterrestrial life would revolutionize our understanding of biology."
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