Saturn’s moon Enceladus is a top candidate in our solar system’s search for extraterrestrial life. However, it remains a mystery whether microbial alien life could inhabit Enceladus.

Enceladus appeared to NASA’s Voyager 1 spacecraft as a small, inconspicuous “snowball” in the sky when it was first observed in 1980. Later, from 2005 to 2017, NASA’s Cassini probe flew through the Saturnian System, conducting unprecedented in-depth research to Saturn’s intricate rings and moons. Cassini’s discovery that Enceladus’s thick ice cover hides a large, warm, saltwater ocean that emits methane, a gas generally derived from microbial life on Earth, astounded scientists.

A new study by researchers at the University of Arizona suggests that the mystery of whether microbial alien life could inhabit Enceladus could be solved by a space probe in orbit. Researchers outlined how a fictitious space mission could yield conclusive solutions.

A group of researchers from the Universities of Arizona and the Université Paris Sciences et Lettres of Paris concluded last year that there is a good chance that Enceladus has life and that this life could be the cause of the moon’s methane emissions.

Régis Ferrière, senior author of the new paper and an associate professor in the UArizona Department of Ecology and Evolutionary Biology, said: “To know if that’s the case, we’ll have to go back to Enceladus and see.”

According to the most recent analysis, even if the total mass of potentially living bacteria in Enceladus’s ocean were minimal, a visit from an orbiting spacecraft would be enough to definitively determine whether Earth-like microbes are present in the water from Enceladus. under his shell.

water interacts with rock
This image shows how scientists think water interacts with rocks on the bottom of Enceladus’s ocean to create hydrothermal vent systems. These same chimney-like vents are found along tectonic plate boundaries in Earth’s oceans, about 2,200 meters below the surface.NASA/JPL-Caltech/Southwest Research Institute

Ferriere said, “Obviously getting a robot to crawl through ice cracks and dive deep to the sea floor wouldn’t be easy. More realistic missions have been designed using improved instruments to sample the plumes as Cassini did, or even land on the lunar surface.”

“By simulating the data that a more prepared and advanced spacecraft would collect from the plumes alone, our team has now shown that this approach would be enough to confidently determine whether there is life in Enceladus’s ocean without actually having to investigate. the depths of the moon This is an exciting perspective.”

Enceladus, about 800 million miles from Earth, orbits Saturn every 33 hours. The moon is the only object in the solar system that reflects light like the moon, even though it’s not even as wide as the state of Arizona. The moon’s surface makes it stand out in the sky like a frozen pond in the sunlight. At least 100 huge plumes of water erupt from the frozen surface of the moon’s south pole, resembling lava from an raging volcano.

According to scientists, one of Saturn’s famous rings is believed to be the result of water vapor and ice particles spewed out by these geyser-like features. The Cassini mission sampled this ejected combination, which contains gases and other grains deep in Enceladus’s ocean.

The excess methane found in the plumes by Cassini is reminiscent of hydrothermal vents, unique ecosystems found in the dark interior of Earth’s oceans. Here, heated magma under the seafloor heats the ocean water in porous rock at the boundaries of two nearby tectonic plates, creating “white smokers,” vents that spout red-hot, mineral-rich salt water. Because they don’t have access to sunlight, organisms must survive using the energy in the chemicals that white smokers release into the environment.

Ferriere said, “On our planet, hydrothermal vents teem with life, large and small, despite the darkness and frenzied pressure. The simplest living things are microbes called methanogens, which power themselves even in the absence of sunlight.”

“Methanogens convert dihydrogen and carbon dioxide into energy, releasing methane as a by-product. Ferrière’s research group modeled its calculations based on the hypothesis that Enceladus has methanogens that inhabit oceanic hydrothermal vents similar to those on Earth. In this way, the researchers calculated what the total mass of methanogens on Enceladus would be, as well as the likelihood that their cells and other organic molecules could be ejected by the plumes.”

The paper’s first author, Antonin Affholder, a postdoctoral research fellow at UArizona who was with Paris Sciences & Lettres when he conducted this research, said: “We were surprised to find that the hypothetical abundance of cells would only amount to the biomass of a single whale in the global ocean of Enceladus. The Enceladus biosphere may be very sparse. And yet our models indicate that it would be productive enough to feed the plumes with just enough organic molecules or cells to be picked up by instruments aboard a future spacecraft.”

“Our research shows that if a biosphere is present in Enceladus’s ocean, signs of its existence could be picked up in plume material without the need for landing or drilling, but such a mission would require an orbiter to flying through the plume several times to collect a lot of oceanic material.”

“The chances of finding true cells may be slim because they would have to survive the outgassing process to carry them through the plumes of the deep ocean into the vacuum of space — quite a journey for a small cell.”

Instead, the authors suggest that detected organic molecules, such as certain amino acids, would serve as circumstantial evidence for or against an environment rich in life.

“Given that any life on Enceladus is calculated to be extremely scarce, there’s still a good chance we’ll never find enough organic molecules in the plumes to conclude unequivocally that it’s there,” said Ferriere. “So instead of focusing on how much is enough to prove life, we asked, ‘What is the maximum amount of organic matter that could be present if there was no life?'”

Authors said, “If all measurements were to rise above a certain threshold again, that could be a signal that life is a serious possibility.”

“Definitive evidence of living cells trapped in an alien world may remain elusive for generations. Until then, it’s probably the best we can do that we can’t rule out the existence of life on Enceladus.”

Magazine reference:

  1. Antonin Affholder et al. Putative methanogenic biosphere in the deep ocean of Enceladus: biomass, productivity and implications for sensing. The journal Planetary Science. DOI 10.3847/PSJ/aca275