Saturn’s moon Enceladus is one of the most important extraterrestrial sites in the solar system for life to thrive. It hosts a global saline ocean that theoretically keeps internal warming at temperatures hospitable to an alien marine ecosystem.
However, discovering this life is not so easy. The moon is surrounded by an estimated ice sheet 5 kilometers thick (3.1 miles) at its thinnest point, and the ocean below is 10 kilometers deep. That would be quite a challenge here on Earth, let alone a moon half a solar system away.
But maybe we don’t need to bother piercing Enceladus’s armor after all. A new study finds we should be able to spot life on the icy moon in the plumes of salt water erupting from its surface — even if there’s not much life there.
“Obviously, having a robot crawl through ice crevices and dive deep to the sea floor wouldn’t be easy,” he says. says evolutionary biologist Regis Ferrière the University of Arizona.
“By simulating the data that a better prepared and more advanced orbiting spacecraft would collect from the plumes alone, our team has now shown that this approach would be sufficient to determine with certainty whether or not there is life in Enceladus’ ocean.” , without actually having to investigate the depths of the moon. It’s an exciting prospect.”
Enceladus is very different from Earth; It’s hardly likely to be teeming with cows and butterflies. But deep beneath Earth’s ocean, far from the sun’s life-giving light, a different kind of ecosystem emerged. Life, which clusters around vents in the sea floor that give off heat and chemicals, does not rely on photosynthesis but on harnessing the energy of chemical reactions.
What we know about Enceladus suggests that similar ecosystems may be lurking on its seafloor. It orbits Saturn every 32.9 hours in an elliptical orbit that bends the moon‘s interior and generates enough heat to keep the water closest to the core liquid.
This isn’t just theory: At the South Pole, where the ice sheet is thinnest, huge plumes of water are hundreds of kilometers high seen break out emerges from under the ice and spits out water that scientists believe contributes to the ice in Saturn’s rings.
When Saturn’s Cassini probe flew through those cloud plumes over a decade agoit discovered several strange molecules – including high concentrations of a cluster associated with Earth’s hydrothermal vents: methane and smaller amounts of dihydrogen and carbon dioxide. These can be associated with methane production Archaea Here on earth.
“Our planet is teeming with life, large and small, in hydrothermal vents, despite darkness and insane pressure,” Ferrière said. “The simplest creatures there are microbes called methanogens, which fuel themselves without sunlight.”
Methanogens metabolize hydrogen and carbon dioxide, releasing methane as a by-product. Ferrière and his colleagues modeled the methanogenic biomass we might expect to find on Enceladus if the biomass existed near hydrothermal vents like those found on Earth.
Then they modeled the likelihood that cells and other biological molecules would be ejected through the openings, and how much of those materials we were likely to find.
“We were surprised to find that the hypothetical cell abundance would only correspond to the biomass of a single whale in the Enceladus global ocean,” says evolutionary biologist Antonin Affholdernow from the University of Arizona but at the time of the research at the University of Paris Sciences et Lettres in France.
“Enceladus’ biosphere may be very sparse. And yet our models suggest it would be productive enough to feed the feathers with just enough organic molecules or cells to be picked up by instruments onboard a future spacecraft.”
Armed with the expected abundance of these connections, an orbiting spacecraft could potentially spot them — if it could make multiple Plume passes to collect enough material.
Even then, there might not be enough biological material, and the chance of a cell surviving the journey through the ice and being ejected into space is probably pretty slim.
In the absence of such a smoking gun, the team propose that amino acids such as glycine would serve as an alternative, indirect signature when the abundance exceeds a certain threshold.
“Considering that by the calculations any life on Enceladus would be extremely sparse, there’s still a good chance we’ll never find enough organic molecules in the feathers to conclusively conclude it’s there.” says Ferriere.
“So instead of focusing on how much is enough to prove life exists, we asked ourselves, ‘What is the maximum amount of organic matter that could exist in the absence of life?'”
Those numbers, the researchers say, could help shape future missions in the years to come. In the meantime, we’ll just be here on Earth wondering what an ecosystem deep under the ocean might look like on a moon orbiting Saturn.
The team’s research was published in The Planetary Science Journal.