New experiments simulating the surface of Saturn’s icy moon Enceladus show organic compounds found in plumes emanating from its subsurface ocean may form on the moon’s surface and not within the ocean itself.
Although the findings do not rule out biological activity as the origin of these “precursors of life” compounds, the scientists behind the experiments suggest astrobiologists should remain cautious when making that assumption.
Discovery of Subsurface Ocean on Enceladus Sparks Hopes for Life
When NASA’s Cassini spacecraft first imaged Enceladus, some of the shots of the south polar region revealed large plumes of material shooting out into space. Further analysis showed these plumes were coming from rows of cracks on the moon’s surface that scientists compared to tiger stripes. Ultimately, scientists determined that Enceladus must have a subsurface ocean of liquid water sustained by the heavy gravitational pull of Saturn that is being ejected into space through the tiger stripes, resulting in the plumes.
Curious if they might find signs of life in the plumes since liquid water is critical to life forms on Earth, NASA scientists flew Cassini through them and used its onboard sensors to sample the ejected material. Analysis of the samples found the presence of salts and several organic compounds.
NASA/JPL/Space Science Institute.
In a statement announcing the new experiments, the research team behind the study noted that “these findings were of great interest to astrobiologists” since organic compounds are the building blocks of life. The discovery also led to several potential mission proposals to further explore the possible habitability of Enceladus.
Experiments Show Plume Organics Could Form Without an Ocean
To test whether these compounds could originate from Enceladus’ surface rather than an ocean, the Europlanet research team led by Dr Grace Richards, of the Istituto Nazionale di Astrofisica e Planetologia Spaziale (INAF) in Rome, visited facilities at the HUN-REN Institute for Nuclear Research in Hungary. There, the team was able to take advantage of the facility’s ability to simulate ice on the moon’s surface and within the walls of the Tiger Stripes.
To best approximate Enceladus’ surface ice, the team made ice with a mixture of water, methane, carbon dioxide, and ammonia. After cooling the mixture to -200 degrees Celsius, the team used specialized equipment to bombard the ice with ions to replicate the radiation that the moon’s surface experiences naturally.
As expected, the ions reacted with the ice samples, resulting in the creation of carbon monoxide, ammonium, and cyanate. Along with these organic molecules, the ion bombardment created molecular precursors to amino acids. In organic life forms, amino acids make up the peptide chains in proteins that drive metabolic reactions, repair damaged cells, and transport nutrients, making them critical for life.
The team notes that several of these compounds have been detected on the surface of the icy moon, while others “have also been identified in the plumes.” Critically, they did not require a liquid ocean to form but instead could have been made by ion radiation interacting with surface ice.
“Molecules considered prebiotic could plausibly form in situ through radiation processing, rather than necessarily originating from the subsurface ocean,” Richards explained.
Icy Moon’s Habitability and Future Missions
In the study’s conclusion, Richards and colleagues acknowledge that the presence of organic molecules remains a crucial indicator of Enceladus’ potential habitability. However, Richards noted, the team’s experimental results show that radiation-driven chemical reactions “could also create these molecules.”
“Although this doesn’t rule out the possibility that Enceladus’s subsurface ocean may be habitable, it does mean we need to be cautious in making that assumption just because of the composition of the plumes,” the researcher said.
Moving forward, scientists hope to draw more definitive conclusions about the potential presence of life on Enceladus with future missions designed to sample the plumes with a specially designed sensor package. Some more aggressive proposals even suggest sending a robot that can drill through the icy shell and directly sample the ocean waters underneath.
“Understanding how to differentiate between ocean-derived organics and molecules formed by radiation interacting with the surface and the tiger stripes will be highly challenging,” the statement concluded. “More data from future missions will be required, such as a proposed Enceladus mission that is currently under consideration as part of the Voyage 2050 recommendations for the European Space Agency (ESA)’s science programme up until the middle of the century.”
The study “Water-Group Ion Irradiation Studies of Enceladus Surface Analogues” was presented earlier this month at the Joint Meeting of the Europlanet Science Congress and the American Astronomical Society’s Division for Planetary Science 2025 (EPSC-DPS2025).
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.