What are the chances of finding extraterrestrial life in our solar system? Professor Frank Postberg, planetary scientist at Freie Universität Berlin, has just published a study in Science Advances with a team of international researchers, in which they present new evidence that it is easier to determine the constituents of the ocean hidden under Enceladus's icy surface than previously assumed. Postberg was also part of a second study published on the same day, in which he and another planetary scientist from Freie Universität, Dr. Nozair Khawaja, contributed to research that reveals that certain microorganisms could actually tolerate the conditions in Enceladus's ocean better than was previously thought. These results increase the probability of finding evidence of life on Saturn's moon.
What Makes Enceladus so Attractive in the Search for Life in Space?
Enceladus is considered to be one of the most promising places to search for extraterrestrial life in our solar system. Researchers suspect that under the moon's icy crust there is a global ocean of liquid water and a rocky core further below. Due to cryovolcanic activity, gigantic plumes break through cracks in the crust at the moon's south pole, ejecting ice particles hundreds of kilometers into space.
NASA's Cassini spacecraft passed through these plumes multiple times to analyze its composition. Enceladus's ocean is the only extraterrestrial "body of water" from which scientists have been able to directly analyze samples. The samples revealed traces of various salts and organic compounds. Furthermore, previous analyses conducted by Cassini gave indications of hydrothermal processes on the seafloor and other conditions that are significant in supporting life.
Enceladus Ice Plumes Separate and Sort the Ocean's Components
Postberg's study, "Cassini CDA Observes Compositional Segregation of Enceladus' Ice Grains from Slow Freezing and Fragmentation of Oceanic Spray," includes surprising findings about what happens to the ocean water on its way into space. The international team of scientists working on the study used Cassini data, long-term laboratory experiments, and theoretical models to reconstruct the process.
Droplets form at the ocean's surface as bubbles filled with gas float up and pop. Water vapor then carries the droplets through cracks in the ice shell out into space. Until now, scientists believed that they froze instantaneously, however these new findings reveal that they freeze slowly. Due to this slow process, most components (including dissolved ones) separate from each other. Salts and organic materials are thus distributed at different locations inside each freezing droplet. Various types of previously dissolved salts also get segregated in the process; for example, sodium chloride (table salt) separates from sodium carbonate.
On their way up, the frozen droplets are accelerated to speeds of up to 1,000 km/h. If they smash into the walls of the icy cracks, they break into fragments only a few micrometers in size before they shoot into space. This results in the ice particles often consisting of just one highly concentrated, previously segregated, substance.
"Enceladus actually does a lot of the work for us in preparing samples for analysis that usually take a lot of effort in chemical labs on Earth," says Postberg, who led the study. "The oceanic constituents are separated from each other and simultaneously concentrated into individual ice particles."
Making It Easier to Find Signs of Life
When probing Enceladus's plumes, this mechanism is not just helpful in characterizing the ocean as a potential habitat for life, it is also particularly interesting in the search for biosignatures, i.e., measurable indications of life. If one of these ocean droplets contained components from alien microbes, they could be segregated from other components in the freezing process. After fragmentation, the microbial material would potentially only be contained in a small fraction of ice particles; however, in those ice particles it would be found in high concentration and in relatively pure form.
"That is great news in the search for life," says Postberg. "Future spacecrafts will have to analyze many individual ice particles in the plume. But if they come across one with microbial material in it, they could identify biosignatures in the particle relatively easy with already available technology."
This discovery could have important implications for future space missions to Enceladus, such as the ESA's L4 mission, which is currently in planning. The mission will be specifically looking for signs of life on Saturn's moon. Postberg's lab at Freie Universität Berlin has previously conducted laboratory studies that demonstrated the capacity for specialized instruments to detect microbial cellular material in individual particles from the ice plumes.
Could Life Really Exist on Enceladus?
A recent study is also providing new insights into this question. On the same day Postberg's article appeared in Science Advances, another article in the same journal was published by scientists at Ludwig-Maximilians-Universität München (LMU): "Enceladus-Like Geochemistry Fuels Methanogenesis under Extreme CO₂-Limitation." Postberg and another colleague from Freie Universität Berlin, Dr. Nozair Khawaja, contributed to this study. In it, scientists were able to reproduce the conditions of Enceladus's ocean in a laboratory. The ocean has a very low concentration of oxygen, a very high concentration of carbonate, and is very alkaline (with pH values of 10 or 11). After recreating these conditions, including its hydrothermal interaction with the rocky ocean floor, they introduced Methanothermococcus okinawensis into the contained environment. This microorganism is a methane-producing archaean that normally lives near deep-sea hydrothermal vents on Earth. They do not need oxygen, which is rare on Enceladus, to survive. Instead their metabolism requires only hydrogen and carbon dioxide.
The results were surprising: The organism failed to grow in an optimum laboratory medium at such a high pH, lacking dissolved carbon dioxide. By contrast, in the Enceladus simulant it continued to grow, producing methane using hydrogen generated by water-rock reactions. Under the simulated Enceladus conditions, the microorganisms were even able to adapt their metabolism to the low amounts of carbon dioxide. "This was really a surprise to us," Khawaja said. "This was an experiment for which we did not expect such a successful outcome."
Taken together, the two studies in Science Advances shed new light on the search for extraterrestrial life. "On Enceladus the specific geochemical conditions might allow one of the oldest known metabolic systems on Earth to work, even in very alkaline environments," Postberg says. "While that doesn't mean that there is life on Saturn's moon, our first study shows that – in the event that there is – future space missions might have a good chance of finding traces if they analyze individual ice grains from Enceladus's plume."
Freie Universität Researchers Investigating the Emergence of Life in Space
What are the prerequisites for planets and moons to provide suitable conditions for the formation and preservation of life? This is a central research topic for planetary scientists at Freie Universität Berlin. A new Collaborative Research Center funded by the German Research Foundation (DFG), CRC1759 "Habitability as a Fundamental Planetary Process," was launched in July 2026. The research center is led by Professor Lena Noack with Professor Frank Postberg as her deputy, both of whom are planetary scientists at Freie Universität Berlin. The research center will study the processes that could have enabled life to emerge in space in the first place, on Enceladus and other celestial bodies, both in our solar system and beyond.
