Enceladus is the sixth-largest moon of Saturn, with a diameter roughly equivalent to the width of the state of Arizona. It is believed that a vast ocean lies beneath its surface, ejecting plumes of water into space. Enceladus, one of 145 known moons orbiting the planet, has captivated scientists searching for extraterrestrial life within our Solar System. And according to fresh research, they might be looking in the right spot. New findings, presented across several scientific papers, suggest that microscopic life could exist in Enceladus’s ocean, and that its water emissions essentially “organize” the compounds and minerals within them. This implies that exploring the moon’s ocean might be easier than previously thought. The results have been published in the journal Science Advances.
“This is fantastic news for the search for life,” stated study co-author Professor Frank Postberg from the Free University of Berlin. “Future spacecraft will need to analyze numerous individual ice particles within the plume. But if they encounter a particle containing microbial material, they can identify biosignatures within it relatively easily using existing technology.”
Enceladus is not the only location in our Solar System with water, so what makes it so intriguing for the search for life? The key lies at the bottom of its vast liquid ocean.
Scientists believe that at great depths, on the floor of this water body, hydrothermal processes occur—meaning the movement or reactions of hot water beneath the surface. The plumes rising from the ocean also contain traces of salts and organic compounds. NASA’s Cassini spacecraft detected these traces over a decade ago while flying through the plumes. Thanks to hydrothermal activity, along with organic substances and minerals in the water, this moon’s ocean possesses several characteristics that could be linked to supporting life.
Moreover, in Postberg’s new study, which used a combination of Cassini data, theoretical models, and laboratory experiments, the team discovered that water droplets shooting into space at speeds up to 1,000 kilometers per hour do not freeze as quickly as expected. Scientists previously thought that freezing happened instantly once the droplets reached space, but Postberg and his colleagues argue that the freezing process is actually much slower.
They also found that during freezing, salt, organic compounds (and potentially signs of life) within the water droplets separate from each other. Furthermore, according to the researchers, when particles are ejected into space, they often collide with icy fissures on the moon’s surface. This ultimately leaves behind tiny fragments of frozen droplets with components neatly separated.
Essentially, it’s as if the moon is organizing its oceanic components into minuscule, frozen particle fragments.
“Enceladus is effectively doing much of the work for us in preparing samples for analysis—work that typically requires significant effort in chemical laboratories on Earth,” said Postberg. “The composition of the oceanic environment is separated from itself and simultaneously concentrated into individual ice particles.”
Looking ahead, researchers could theoretically use this knowledge to more easily collect samples from the moon. With missions to Enceladus currently in development, such as the European Space Agency’s L4, we could learn more about what lies within Enceladus’s oceans—and whether life exists there—sooner rather than later.
While we await the ability of future spacecraft to gather fragments of frozen droplets from Enceladus’s ocean, researchers in a separate study recreated the moon’s ocean conditions in a laboratory and tested how well life could survive there.
Although we don’t know everything about this ocean, and it remains a mystery whether it harbors life—or even the ingredients to sustain it—we do have some knowledge from prior observations by missions like Cassini. For example, we know the ocean is fairly alkaline, contains very little oxygen, and is characterized by abundant carbonates and hydrothermal activity.
A second research group incorporated all these elements to create a miniature Enceladus ocean in the lab. To test whether life could survive in this artificial ocean, the team added a microscopic species: Methanothermococcus okinawensis. On Earth, this microbe is commonly found near hydrothermal vents. Additionally, this species does not require oxygen (it uses hydrogen and carbon dioxide instead). This was a very clever choice of species to introduce, given that Enceladus also exhibits hydrothermal activity and has very little oxygen.
The group of microbes actually thrived in the artificial Enceladus ocean, multiplying and consuming hydrogen from the environment. Moreover, even with a limited amount of carbon dioxide in the tank, the microbes survived, adapting to the conditions relatively quickly.
“This came as a real surprise to us,” said study co-author Nozair Khawaja from the Free University of Berlin. “We did not expect such a successful outcome from this experiment.”
With one study showing the potential for life to exist in an environment similar to Enceladus’s ocean, and another demonstrating how easily future spacecraft might examine samples from this moon, these new findings are inspiring hope among scientists to continue the search for life there.
“On Enceladus, specific geochemical conditions could allow one of the oldest known metabolic systems on Earth to function, even in a very alkaline environment,” said Postberg. “While this does not mean there is life on Saturn’s moon, our first study shows that—if it is there—future space missions might have a good chance of detecting its traces if they analyze individual ice grains from Enceladus’s plume.”
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