New research suggests that Enceladus’ subsurface ocean may trap signs of life in deep layers for thousands of years, making it unlikely that NASA’s planned plume samples will provide clear evidence of extraterrestrial organisms.
Warm oceans trapped below the icy surfaces of moons located outside the Sun’s habitable zone remain some of the best candidates for life in Earth’s solar system. Yet it now appears that even direct samples from Encedalus’ alien waters may be useless for identifying the presence of extraterrestrial life.
Focus On Enceladus For Extraterrestrial Life
The liquid oceans of Enceladus offer a unique feature that makes it a desirable destination in the search for life beyond Earth. However, drilling through deep ice at the edges of the solar system remains a major technical hurdle for examining these icy moons. Enceladus, however, continually vents its water into space through cracks in the moon’s frozen surface.
“Combined with the promise of Enceladus’ ocean as an abode for life, this has motivated NASA to prioritize a mission (the Enceladus Orbilander) to return to Enceladus, collecting samples of plume material and using this to figure out whether or not there is life within Enceladus,” lead author Flynn Ames explained to The Debrief about why the team focused on that particular moon.
Extraterrestrial Life May Be Well Hidden
The problem with NASA’s idea is a mismatch between where scientists expect to find life on Enceladus and where the water is venting from. The most favorable conditions for extraterrestrial life are at the ocean’s greatest depths, closer to the moon’s core.
However, Enceladus’ water plumes are ejected from 40 meters above the ocean floor. Any sign of biological life would have to make the chance journey to the edge of the moon’s liquid ocean, and then so happen to be perfectly positioned to be ejected with a well-placed plume.
Ames and the research team were skeptical of the chance such an event was likely to occur, so they set out to examine the possibilities.
“It has been previously suggested that particles could make their journey from ocean bottom-to-top (and then vented into space) within several months. This is incredibly fast,” Ames said. “We believed it was important to test whether this is possible given the ocean circulation patterns we might expect for Enceladus. By figuring out how long it takes for particles and chemical traces to get from the ocean bottom to ocean top, we could also provide planetary scientists with important context.”
“If the transport time is long, then it is possible that certain chemical traces and particulates could settle out, degrade, or transform before reaching the ocean top, impacting our ability to sample them,” Ames added. “Given it would be better to find this out before sending a mission to Enceladus, this motivated us to investigate the transport within Enceladus’ ocean, to determine whether this is something that observational scientists should consider.”
Examining Ocean Speeds On Enceladus
Since the crux of the team’s research was to investigate how an alien ocean behaves before sending a physical mission there, they had to rely on modeling instead of first-hand fieldwork. Ames and colleagues began with a commonly used model of Earth’s oceans and modified it step-by-step to reflect the conditions of Enceladus. This meant accounting for a smaller size, weaker gravity, deeper ocean, and other variables.
“By far the most important step was accounting for the kilometers-thick ice layer that covers Enceladus’ whole ocean,” Ames explained. “The cooling effect of that ice on the ocean, as well as patterns of ice melting and freezing, are critical components because they affect the density of the water. For the questions we wanted to answer, it was particularly important that we were representing these processes correctly.”
Without being on site, some information remained elusive, though. The saltiness of the water and the role of the tides in stirring the ocean were unknowns, causing the team to have to run many time-consuming iterations of the complex model.
Challenges Face The Search For Extraterrestrial Life
The team’s model identified that the moon’s ocean consists of many layers, impeding movement from the ocean floor to the surface. At each stop on the journey to the surface, chemicals, microbes, and other organic materials could break down before reaching their destination. As such, despite how teeming with life the bottom of Enceladus oceans may be, whatever rises to the surface may not accurately reflect that hidden reality.
“We’ve found that Enceladus’ ocean should behave like oil and water in a jar, with layers that resist vertical mixing,” Ames said. “These natural barriers could trap particles and chemical traces of life in the depths below for hundreds to hundreds of thousands of years. Previously, it was thought that these things could make their way efficiently to the ocean top within several months.”
The team’s modeling also uncovered other quirks in the moon’s ocean. For example, due to the expected lower salinity of Enceladus’ ocean than Earth’s, it may behave more like an enormous lake or pond than Earth’s oceans.
Adjusting To The New Outlook on Enceladus
Additional work remains to grasp the implications of these findings. One previous study demonstrated that some amino acids could degrade within 10,000 years. Theoretically, this could imply that evidence of life may be undetectable in plumes even when they eventually make their way out of the ocean. Future studies must answer the questions of what delays between reaching the ocean surfacing and ejecting look like and further understand how long amino acids and other signs of life may remain detectable.
“As the search for life continues, future space missions will need to be extra careful when sampling Enceladus’s surface waters,” Ames concluded.
The paper “Ocean Stratification Impedes Particulate Transport to the Plumes of Enceladus” appeared on February 6, 2025 in Communications Earth & Environment.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.