- 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 they’ve detected complex organic molecules.
- Though not proof of alien life, that’s a good sign for the habitability of Enceladus.
Before NASA destroyed its Cassini spacecraft in the clouds of Saturn, the space agency flew the robot through geysers of ice that shoot 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 they boil off into the vacuum of space and form 300-mile-tall curtains of ice particles.
Ever since Cassini’s nuclear-powered geyser-dive in October 2015, scientists have pored over the trove of data the probe collected. They’ve found all sorts of eyebrow-raising chemistry, 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 an environment in which alien life could thrive.
Translation: It just might be signs of microbial aliens, though it’s too soon to say.
Khawaja and a multi-national group of 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 study author, said in a press release.
How Enceladus might brew complex organic muck
Life as we know it is carbon-based. The atom 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 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 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 why they form a film on top of the water as opposed to dissolving.
“From there, [the film] is launched into space together with ocean water droplets,” he said.
Hydrothermal vents can generate hydrogen gas. They litter Earth’s seafloor near volcanically active regions, spewing out nutrient-rich hot water that may make them bastions of life. In fact, scientists in 2017 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 evidence 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 not yet a mission funded 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 icy moon Europa. That ice-covered world has an even larger subsurface ocean, is spraying out water, and might also be rich with a soup of organic molecules that alien microbes could feed on or generate.
The ESA probe, called the Jupiter Icy Moons Explorer (JUICE), 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 will 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 oceans 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 (JPL), previously told Business Insider.
“If there’s life at Europa, it’d almost certainly be an independently evolved form of life. Would it use DNA or RNA?” Pappalardo said. “Would it use the same chemistry to store and use energy? Discovering extraterrestrial life would revolutionize our understanding of biology.”